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Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern Jiangnan Orogen, South China
Accepted Manuscript Title: Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern Jiangnan Orogen, South China Author: Wei Wang Mei-Fu Zhou Dan-Ping Yan Liang Li John Malpas PII: DOI: Reference:
S0301-9268(13)00166-6 http://dx.doi.org/doi:10.1016/j.precamres.2013.05.013 PRECAM 3779
To appear in:
Precambrian Research
Received date: Revised date: Accepted date:
27-8-2012 17-4-2013 21-5-2013
Please cite this article as: Wang, W., Zhou, M.-F., Yan, D.-P., Li, L., Malpas, J., Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern Jiangnan Orogen, South China, Precambrian Research (2013), http://dx.doi.org/10.1016/j.precamres.2013.05.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights (for review)
Highlights: ► Combining U-Pb and Lu-Hf data of detrital zircons from the Neoproterozoic sedimentary rocks to constrain the tectonic evolution of the eastern Jiangnan Orogen.
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► The Jiangnan orogen lasted until ca. 830-815 Ma or even later.
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► The Shuangqiaoshan and Xikou Groups formed in a back-arc to retro-arc foreland basin at ca. 831~815 Ma and ca. 833~817 Ma, respectively.
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► There was no Grenville (ca. 1000-1300 Ma) juvenile crust in the eastern Yangtze Block.
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► The most important generation of juvenile crust occurred at ca. 980-810 Ma.
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*Manuscript Click here to view linked References
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Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern
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Jiangnan Orogen, South China
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Wei Wang1, Mei-Fu Zhou1,*, Dan-Ping Yan2, Liang Li3, John Malpas1
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10
an
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China
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2
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Geosciences, Beijing 100083, China
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3
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Academy of Sciences, Guiyang 550002, China
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State Key Lab of Geological Process and Mineral Resources, China University of
State Key Lab of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
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Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR,
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*
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E-mail: [email protected]
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Phone: +852 2857 8251
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Fax: +852 2517 6912
Corresponding author:
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Abstract: Precambrian sedimentary sequences in the eastern Jiangnan Orogen, South
27
China, include the Neoproterozoic Shuangqiaoshan and Xikou Groups and the
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overlying Nanhua Sequence. U-Pb ages of detrital zircons provide tight constraints on
29
the deposition of the Shuangqiaoshan and Xikou Groups at 831-815 Ma and 833-817
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Ma, respectively. Rocks from the lower parts of these strata contain dominantly
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Neoproterozoic detritus with a pronounced age peak at 830-850 Ma, interpreted to be
32
derived from a magmatic arc that has been mostly eroded. This magmatic arc was
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associated with sedimentation characterized by compositionally immature sediments
34
with dominant early-Neoproterozoic (~860-810 Ma) zircons that have variable εHf(t)
35
values of -21.5 to 14.8. The upper parts of these strata, uncomfortably underlain by
36
the
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pre-Neoproterozoic detritus, representing sediments accumulated in a retro-arc
38
foreland basin associated with the Jiangnan Orogen.
units,
are
molasse-type
assemblages
with
additional
input
of
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Combining four samples from the Nanhua Sequence, three major magmatic
40
activities at 2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma in the source areas are
41
identified. The older two events are characterized by reworking of pre-existing
42
continental crust. Grenville magmatism and juvenile crust were insignificant in the
43
eastern Jiangnan Orogen. Neoproterozoic zircons reflect generation of juvenile crust
44
at 980-860 Ma, involvement of both juvenile and recycled materials at 860-810 Ma
45
and reworking of pre-existing crust at 805-750 Ma, corresponding to island arc,
46
continental magmatic arc and post-collisional rifting stages in the eastern Jiangnan
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Orogen.
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Keywords: U-Pb ages, Lu-Hf isotopes, detrital zircons, Jiangnan Orogen, South
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China
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1. Introduction
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The Jiangnan Orogen in South China witnessed the amalgamation of the Yangtze
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and Cathaysia Blocks. Recent studies of sedimentary and igneous rocks have
55
demonstrated that the Jiangnan Orogen is a Neoproterozoic rather than
56
Mesoproterozoic tectonic unit, but the timing and evolution of this orogen are still
57
matters of debate (Wang et al., 2006, 2007, 2012b; Zheng et al., 2008; Li et al., 2009;
58
Zhao et al., 2011). The Jiangnan Orogen was thought to be part of the worldwide
59
Grenville Orogen, formed by the collision between the Yangtze and Cathaysia Blocks
60
(Li et al., 2007, 2009), followed by extensive rift-related magmatism at ca. 820 Ma
61
(Wu et al., 2006; Li et al., 2008c, 2009, 2010a; Zheng et al., 2008). On the other hand,
62
this orogeny is thought to have lasted until ca. 830 Ma or even later, followed by
63
post-extensional magmatism beginning at ca. 800 Ma (Li, 1999; Zhao and Cawood,
64
1999; Wang et al., 2006, 2011b, 2012b; Zhao et al., 2011; Zhang et al., 2012b).
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The eastern segment of the Jiangnan Orogen is crucial for the understanding of
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the orogenic cycle because it contains widespread sedimentary sequences, igneous
67
plutons and two major ophiolite belts, that witness the final amalgamation between
68
the Yangtze and Cathaysia Blocks (Li et al., 2009) (Fig.1). In past decades, numerous
69
studies examined the petrogenesis and tectonic affinity of igneous rocks (Wu et al.,
70
2006; Li et al., 2007, 2008b, 2009; Zheng et al., 2008; Zhang et al., 2012a), but
71
associated sedimentary sequences in the eastern Jiangnan Orogen are poorly
72
understood, due in part to unresolved stratigraphy, incomplete biostratigraphic data,
73
poor exposure and strong overprint by later deformation. These sedimentary
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sequences in the eastern Jiangnan Orogen include the Shuangqiaoshan Group in
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northern Jiangxi Province and the Xikou Group in southern Anhui Province (Fig. 1),
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which were interpreted to have formed in a back-arc basin associated with
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Mesoproterozoic NW-dipping (current coordinates) oceanic subduction beneath the
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Yangtze Block (Cheng and Wang, 2000; Huang et al., 2003). However, dating results
79
of the Shuangqiaoshan Group do not support this model and it has been proposed that
80
these sequences were deposited in a retroarc foreland basin, synchronous with the
81
amalgamation of the Yangtze and Cathaysia Blocks (Wang et al., 2008). More recent
82
studies suggest the Shuangqiaoshan Group likely formed at ca. 830 Ma (Gao et al.,
83
2008; Zhao et al., 2011), which is taken as the timing for the Jiangnan Orogeny (Zhao
84
et al., 2011). These sequences are also suggested to have formed in an early-phase of
85
rifting that post-dated the Jiangnan Orogen (Li et al., 2009) based on ca. 850 Ma
86
dolerite dykes (Li et al., 2008b) and bimodal volcanic rocks (Li et al., 2010a).
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Due to the strong later deformation of these sedimentary strata and intensive
88
reworking and erosion of the pre-existing igneous provenance (Wu et al., 2006; Zheng
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et al., 2008), one possible way to examine the timing and evolution of orogenic cycles
90
is to unearth the information contained by detrital zircons (Cawood and Nemchin,
91
2001; Liu et al., 2011; Wang et al., 2011c). Detrital zircon age spectra may contain
92
information about various sources linked to eustatic, depositional and tectonic change
93
(Wang et al., 2010b, 2012a), and thus can provide insight into the basin-orogen
94
coupling (Horton et al., 2010; Myrow et al., 2010). Hf isotopes of zircons can be used
95
for understanding juvenile or reworked zircon-hosting magma (Griffin et al., 2004;
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Xia et al., 2006; Zheng et al., 2006b, 2007; Zhu et al., 2011; Liu et al., 2012; Wang et
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al., 2012a), thought to be one of the most discriminating features among plume, rift
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and arc-related magmatism (Zheng et al., 2008).
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In this paper, we present the first integrated study of U-Pb ages and Hf isotopic
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compositions of detrital zircons from the major Neoproterozoic sedimentary strata in
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the eastern Jiangnan Orogen. This new dataset allows us to refine the depositional age
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of the hosting strata and to track provenance changes. The provenance characteristics
103
can help define the relationship between sedimentation and tectonism and potential
104
link to the configuration of the supercontinent Rodinia.
2. Geological background
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The South China Craton comprises the Yangtze and Cathaysia Blocks, with the
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Jiangnan Orogen being the southeastern part of the Yangtze Block. The Cathaysia
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Block has voluminous Phanerozoic igneous rocks with rarely exposed Precambrian
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rocks (Yu et al., 2010). Metamorphic complexes in the eastern Cathaysia Block were
112
traditionally thought to be Paleo-Mesoproterozoic to Neoarchean basement (Li, 1997),
113
but recent studies suggest that these complexes formed in the Neoproterozoic or even
114
younger (Wan et al., 2007; Li et al., 2010c). A Paleoproterozoic orogen is inferred on
115
the basis of abundant Paleoproterozoic granites and metamorphic rocks in the eastern
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Cathaysia Block (Yu et al., 2009). Precambrian rocks in the Yangtze Block are
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sporadically exposed and include Archean Tonalite–Trondhjemite–Granodiorite (TTG)
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in the north (Qiu et al., 2000; Gao et al., 2011) and Paleoproterozoic strata in the west
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(Sun et al., 2009; Zhao et al., 2010b), whereas Neoproterozoic sedimentary sequences
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and igneous plutons are widespread (Zhou et al., 2002b; Li et al., 2003a, b; Wang et
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al., 2006, 2010b; Zhao and Zhou, 2007a; Zheng et al., 2008; Zhao et al., 2011). The
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sedimentary cover of the Yangtze Block consists mainly of folded Paleozoic and
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Lower Mesozoic strata formed in a shallow marine environment (Yan et al., 2003).
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Precambrian rocks in the eastern Jiangnan Orogen include the Mesoproterozoic
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Tianli schist (Li et al., 2007), early-Neoproterozoic Shuangxiwu volcanic-clastic
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sequences (Ye et al., 2007; Li et al., 2009), mid-Neoproterozoic sedimentary strata 4 Page 6 of 105
(Gao et al., 2008; Zhao et al., 2011), igneous plutons (Zhong et al., 2005; Wu et al.,
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2006; Li et al., 2008b, 2009, 2010b; Zheng et al., 2008), and ophiolitic complexes
129
(Bai et al., 1986; Zhou, 1989; Zhang et al., 2012a). Mid-Neoproterozoic sedimentary
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strata including the Shuangqiaoshan and Xikou Groups in the eastern Jiangnan
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Orogen are overlain unconformably by a post-orogenic extensional basin deposits as
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the Nanhua Sequence. Granitoid plutons intruding the sedimentary sequences are
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represented by the Jiuling pluton in NW Jiangxi (Li et al., 2003a; Zhong et al., 2005)
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and the Xucun, Shexian and Xiuning plutons in southern Anhui (Li et al., 2003a; Wu
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et al., 2006). The NE-SW trending ophiolite complexes are in tectonic contact with
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the Shuangqiaoshan and Xikou Groups (Bai et al., 1986).
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A stratigraphic framework of the sedimentary succession in northwestern Jiangxi and southern Anhui Provinces is outlined in Figures. 2 and 3.
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2.1. Shuangqiaoshan Group
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The Shuangqiaoshan Group consists of silty, volcanic clastic detritus that
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gradually coarsens upwards, and has partially preserved primary sedimentary
144
structures. Based on primary sedimentary structure and lithology, this strata is divided
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into the Hengyong, Jilin, Anlelin and Xiushui Formations (Fms) from the base
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upward (Fig. 4) (BGMRJX, 1996).
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The Hengyong Fm comprises of grey to reddish, feldspar-lithic sandstone,
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feldspar-quartz sandstone and siltstone. The sandstone consists dominantly of
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subangular to subrounded, lithic fragments, with lesser amounts of quartz and feldspar.
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Graded bedding, banded bedding, and scour and slump marks are well developed.
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The Jilin Fm is conformable with both its underlying and overlying strata and
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contains mostly purplish-red, silty slate, usually referred to as a red bed sequence. 5 Page 7 of 105
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Within the silty slate are interbeds of siltstone and sandstone (Fig. 5a). Cross-bedding,
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graded bedding and partial Bouma sequences are common. The Anlelin Fm is widespread in northern Jiangxi province and is composed of
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thick grey to charcoal grey flysch with some tuffaceous siltstone and slate. In addition
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to greywacke, there are fine-grained, tuffaceous beds, feldspar-, quartz-rich sandstone
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and tuffaceous lithic-quartz sandstone. Lithic components include andesite, siliceous
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rocks, granite, basalt and silty mudstone (Wu, 2007). Cross-bedding, parallel bedding,
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scour and slump marks, and partial Bouma sequences are well developed (Figs. 5b
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and c).
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The Xiushui Fm, overlying the Anlelin Fm, has a basal ca. 2.5 m thick layer of
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conglomerate (Fig. 5d). Conglomerate contains gravels of variable sizes that are
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parallel to the orientation of the sedimentary layer. In some cases, this conglomerate
165
layer is absent and the bottom of the Xiushui Fm is marked by a 40-m-thick layer of
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greyish-white, pebbly sandstone or quartz conglomerate. The upper part of the
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Xiushui Fm consists mainly of greyish-white, grey or green yellow, tuffaceous slate
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interbedded with tuff. Cross-bedding, parallel-bedding and partial Bouma sequences
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are also common in this unit.
171 172 173
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2.2. Xikou Group
Widely distributed in southern Anhui Province, the Xikou Group has experienced
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weak to strong deformation and low-greenschist facies metamorphism, whereas
175
graded and crossing bedding are perfectly preserved (BGMRAH, 1984). The Xikou
176
Group is divided into the Zhangqian, Banqiao, Mukeng and Niuwu Fms upwards (Fig.
177
4) (BGMRAH, 1984). The Zhentou Fm unconformably overlies the Niuwu Fm and is
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tentatively interpreted as the upper part of the Xikou Group in this study, because of
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its similarity with the Xiushui Fm of the Shuangqiaoshan Group. The Zhangqian Fm comprises green sericite-quartz schist, arenaceous to silty
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phyllite and sericite-chlorite-quartz schist. Original pelitic rocks have been
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metamorphosed to phyllite during regional metamorphism, resulting in well
183
developed phyllitic structure. Spotted or banded magnetite is common and interlayers
184
of basic volcanic rocks are also sporadically present.
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Dark to grey phyllite, phyllitic slate and feldspar quartz sandstone are the
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dominant rocks of the Banqiao Fm that overlies the Zhangqian Fm conformably.
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Rhythmic layering between sandstone and slate are commonly observed and lenticular
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sandstone is developed probably due to current lamination (Fig. 5e). Feldspar and
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quartz with a few lithic detritus are the dominant clastic fragments, which is hosted by
190
cemented fine-grained sericite and clay minerals.
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The Mukeng Fm is composed of thick grey to greyish-green silt- to arenaceous-
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siliciclastic rocks dominated by fine-grained siltstone and sericite-chlorite slate,
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whereas fine-grained sandstone occurs as interlayers in the slate. Graded and parallel
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bedding, are well preserved (Fig. 5f). Contorted bed with varying wavelength formed
195
by wave current and slump structure are observed (Fig. 5f), suggesting fast
196
sedimentation in a turbulent environment.
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The Niuwu Fm is typical of turbiditic deposition, consisting of thick layer of
198
greyish-green to greyish-purple litharenite and thin layer of medium-grained
199
sandstone. Gravel-bearing sandstone and coarse- to medium-grained sandstone form
200
well developed graded bedding (Fig. 5g), typical of turbidite. Features of shallow
201
water and storm flow deposits are observed in the upper part of the Niuwu Fm, where
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ashy black slate is interbedded with thick layers of sandstones.
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Unconformably underlain by the Niuwu Fm, the Zhentou Fm contains
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conglomerate, gravel-bearing sandstone and gravel-bearing silty slate from the base to
205
the top. Angular to subangular gravels of the stratigraphically basal conglomerate are
206
poorly-sorted with diameters ranging between 1 and 8cm and are dominated by
207
fragments of slate, silicolite, granite and quartz. Gravel-bearing sandstone and slate
208
from the upper Zhentou Fm contain gravels smaller and less than the conglomerate
209
and quartzite, volcanic rocks and siltstone are the dominant rock fragments.
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211 212
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2.3. Nanhua Sequence
The Nanhua Sequence is a set of glacial sedimentary rocks corresponding to the
214
Cryogenian System defined by the International Commission on Stratigraphy (Plumb,
215
1991). The Nanhua Sequence includes the lower Dongmen and Xiuning Fms and the
216
upper Nantuo and Leigongwu Fms. The Dongmen and Xiuning Fms, correlated with
217
the pre-glacial Liantuo Fm in the central Yangtze Block, are composed largely of a
218
clastic succession unconformably underlain by the Shuangqiaoshan and Xikou Groups,
219
respectively. The basal parts of these units consist of conglomerate and coarse
220
quartzose sandstone, formed in an alluvial fan or fluvial environment. The Nantuo and
221
Leigongwu Fms, are widespread in the entire Yangtze Block, are composed of
222
diamictite typical of tillite formed during the Neoproterozoic ―snowball Earth‖ event
223
(Zheng, 2003).
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224 225 226
3. Sampling and analytical methods
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Ten samples were selected across major stratigraphic units for zircon dating in
228
order to constrain depositional ages, provenance and tectonic setting of the
8 Page 10 of 105
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sedimentary basin. Zircon was separated using standard heavy-liquid and magnetic
230
separation from ca. 5 Kg samples. Zircon separates were mounted in epoxy and
231
polished. U-Pb isotope analysis of zircon was performed by LA-ICP-MS at the State Key
233
Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
234
Academy of Sciences, Guiyang. A GeoLasPro laser-ablation system (Lamda Physik,
235
Gottingen, Germany) and Agilent 7700x ICP-MS (Agilent Technologies, Tokyo,
236
Japan) were combined for the experiments. The 193 nm ArF excimer laser,
237
homogenized by a set of beam delivery systems, was focused on the zircon surface
238
with the fluence of 10J/cm2. The ablation protocol employed a spot diameter of 32 µm
239
at 5 Hz repetition rate for 45 seconds (equating to 225 pulses). Helium was applied as
240
a carrier gas to allow efficient transportation of aerosol to the ICP-MS. Zircon 91500
241
was used as the primary standard to correct elemental fractionation. Meanwhile,
242
zircon GJ-1 (Jackson et al., 2004) and Plešovice (PL, Sláma et al., 2008) were
243
analyzed as unknown samples for quality control. Trace element compositions of
244
zircon were external calibrated against NIST SRM 610 with
245
standard. Raw data reduction was performed off-line by ICPMSDataCal (Liu et al.,
246
2010) and the results were reported with 2σ errors. Reported uncertainties (2σ) of the
247
206
248
(2 SD%) of standard zircon 91500 during the analytical session and the within-run
249
precision of each analysis (2 SE%; standard error) (c.f. Gerdes and Zeh. 2006, 2009).
250
Common Pb correction was corrected using the MS Excel program ―ComPbcorr#
251
3.15”(Andersen 2002). Data were processed using the ISOPLOT program (Luding,
252
2003). The analytical results of standard and reference materials are presented in
253
Supplementary Table 1.The concordant ages of analyzed GJ-1 (601 ± 17 Ma, 2σ,
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232
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Zr as the secondary
Pb/238U ratio were propagated by quadratic addition of the external reproducibility
9 Page 11 of 105
254
MSWD=1.3) and PL (334.2 ± 7.5 Ma, 2σ, MSWD=2.9) are consistent with the
255
reported or recommended values (GJ-1: 599.8 ± 1.7 Ma, 2σ, Jackson et al., 2004; PL:
256
337.13 ± 0.37 Ma, 2σ, Sláma et al., 2008). Hf isotopic analysis of zircons were conducted using a Resonetics Resolution
258
M-50 193nm excimer laser ablation system, attached to a Nu Plasma HR
259
multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) at the
260
University of Hong Kong. Hf isotopes were obtained with a beam diameter of 55 μm,
261
pulse rate of 10 Hz and energy density of 15 J/cm2. Atomic masses 172 to 179 were
262
simultaneously measured in a static-collection mode. Isobaric interference of
263
with
264
Instrumental mass bias correction of Yb isotope ratios were normalized to 172Yb/173Yb
265
of 1.35274 (Chu et al., 2002) and Hf isotope ratios to 179Hf/177Hf of 0.7325 (Patchett
266
et al., 1981) using an exponential law. A relationship between Yb and Hf of βYb
267
=0.872βHf are obtained and used for the mass bias offset. Interference of
176
268
176
Lu isotope
269
and using a recommended
270
2001). Due to insignificant contribution of signal intensity of 176Lu on 176Hf (generally
271
<1%), the mass bias of Lu isotopes (βLu) can be assumed to be identical to βHf (c.f.
272
lizuka and Hirata, 2005). Quality control was made by measuring zircon standard
273
91500 and GJ-1 for the unknown samples during the analyses to evaluate the
274
reliability of the analytical data (Supplementary Table 2).
Hf was corrected against the
176
176
Yb
Yb/172Yb ratio of 0.5886 (Chu et al., 2002).
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Hf was corrected by measuring the intensity of the interference-free 176
175
Lu with
Lu/175Lu ratio of 0.02655 (Machado and Simonetti,
275 276 277
4. Analytical results
278
10 Page 12 of 105
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Results of U-Pb dating are present in Supplementary Table 3 and concordant
280
diagrams (Figs. 6 and 7). Detrital zircons with concordant U-Pb ages (with
281
concordance between 90-110%) were selected for in-situ Hf isotopic analyses and the
282
results are given in Supplementary Table 4.
4.1.The Shuangqiaoshan Group
286
4.1.1. The Jilin Fm
cr
284 285
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283
Sample WW236, a reddish medium-grain sandstone from the Jilin Fm,
288
contains a predominant population of Neoproterozoic zircon grains with two major
289
age peaks at ca. 826 and ca. 850 Ma and three sub-peaks at ca. 870, 895 and 950 Ma
290
(Fig. 8). Pre-Neoproterozoic zircon grains are rare, with ages grouping at 1.15-1.26
291
Ga, 1.76-1.76 Ga and 1.87-2.22 Ga. One Archean zircon grain has a 207Pb/206Pb age of
292
2.59 Ga. Generally, all zircon grains have oscillatory zoning but are variably rounded
293
(Fig. 6a).
an
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Neoproterozoic zircon grains have highly variable εHf(t) values (-16.8 to 14.8) and
295
two stage hafnium model age (TDM2) (781-2758 Ma) (Fig. 9). Two Mesoproterozoic
296
zircon grains have identical ages but different εHf(t) values (3.3 and 10.8) and TDM2
297
ages (1.84 and 1.38 Ga). Five Paleoproterozoic zircon grains have variable εHf(t) values
298
(-8.1 to 7.2) and TDM2 ages (2.19-2.95 Ga).
299 300
4.1.2. The Anlelin Fm
301
Sample WW176 is a combination of chips from a series of thick layers of
302
fine-medium grained siltstones in the middle Anlelin Fm. Neoproterozoic (795-978
303
Ma) euhedral and oscillatory-zoned (Fig. 6b) grains are the dominant population and
304
have two major age peaks at ca. 818 Ma and ca. 843 Ma (Fig. 8). Nine 11 Page 13 of 105
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Pb/206Pb ages scattering from1.14 Ga to 2.46 Ga.
305
Pre-Neoproterozoic zircons have
306
These zircon grains are generally subhedral to rounded with partly preserved
307
oscillatory zoning (Fig. 6b). Mid-Neoproterozoic (795-850 Ma) zircon grains have positive εHf(t) values (1.2 to
309
15.1) and TDM2 ages ranging continuously from 739 to 1653 Ma (Fig. 9). In contrast,
310
Early-Neoproterozoic (851-978 Ma) zircon grains have highly variable εHf(t) values
311
(-17.7 to 14.7) and TDM2 ages (742-2836 Ma). Two Mesoproterozoic (1.14 and 1.35
312
Ga) zircon grains have identical
313
the other Mesoproterozoic grain (1.52 Ga) has a low 176Hf/177Hf ratio of 0.281980.
Hf/177Hf ratios (0.282232 and 0.282216), whereas
us
176
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308
315
an
314
4.1.3. The Xiushui Fm
Sample WW247, a coarse sandstone from the Xiushui Fm, contains predominant
317
Neoproterozoic grains, with five age peaks at ca. 815, 825-835, ca. 869, ca. 900 and
318
ca. 930 Ma (Fig. 8). All Neoproterozoic grains are euhedral and have well preserved
319
oscillatory zoning. Pre-Neoproterozoic zircon grains have ages scattering from 1.01 to
320
2.68 Ga. All these zircon grains are subhedral to rounded and show partially
321
oscillatory zoning or uniform internal structure (Fig. 6c).
322
Neoproterozoic (811-935 Ma) zircon grains have variable εHf(t) values (-16.0 to 13.7)
323
and TDM2 (742-2727 Ma) (Fig. 9). Eight Mesoproterozoic (1.01-1.49 Ga) zircon grains
324
have a wide range of εHf(t) values (-9.7 to 6.9) and TDM2 (1.42-2.47 Ga). Zircon grains
325
with ages between 1.57 and 1.63 Ga have a wide range of εHf(t) values (1.0-13.8) and
326
TDM2 (1.43-2.26 Ga). Paleoproterozoic to later Archean zircon grains have negative
327
εHf(t) values (-16.1 to -2.7) and old TDM2 (2.77-3.53 Ga).
Ac ce pt e
d
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316
328 329 330
4.2. The Xikou Group
12 Page 14 of 105
331
4.2.1. The Banqiao Fm Zircon grains from a grey phyllitic siltstone WN1004 are fairly small (<100 μm),
333
mostly euhedral and show oscillatory zoning with rare preexisting cores and
334
overgrowth rims (Fig. 7a). These detrital zircon grains are predominantly
335
Neoproterozoic and have ages ranging from 831 to 990 Ma with four age peaks at ca.
336
833, 860, 884 and 932 Ma (Fig. 8). There are also a few Meso- to Paleoproterozoic
337
zircon grains with ages scattering from 1.21 to 2.46 Ga.
cr
ip t
332
Nearly all Neoproterozoic zircon grains have positive εHf(t) values (1.2-14.0),
339
except for two zircon grains with negative εHf(t) values (-4.1 and -6.3) (Fig. 10). Three
340
Mesoproterozoic (1.21 to 1.53 Ga) zircon grainshave similar εHf(t) values (-5.0 to -2.3)
341
and TDM2 (2.32-2.45 Ga). All Paleoproterozoic zircon grains, except for the 1.81 Ga
342
zircon grain (εHf(t)=7.9), have negative εHf(t) values (-8.6 to -1.9) and TDM2 (2.59-3.16
343
Ga).
344
346
4.2.2. The Mukeng Fm
Ac ce pt e
345
d
M
an
us
338
Sample WN1012, a greyish-green phyllitic tuffaceous sandstone from the
347
Mukeng Fm, contains dominantly Neoproterozoic (798-988 Ma) zircon grains, with
348
three peaks at ca. 830, 860-870 and 913 Ma (Fig. 8). Pre-Neoproterozoic grains have
349
a wide range of ages between 1.18 and 2.70 Ga. Neoproterozoic grains are generally
350
euhedral with well developed concentric oscillatory zoning (Fig. 7b).
351
Neoproterozoic zircon grains from sample WN1012 have variable εHf(t) values
352
(-9.0 to 14.0) and TDM2 ( 862-2401 Ma). Pre-Neoproterozoic zircon grains have
353
evolved and scattered Hf isotopic compositions, with εHf(t) values from -3.8 to 7.5 and
354
TDM2 from 1.82 to 3.10 Ga (Fig. 10).
355
13 Page 15 of 105
356
4.2.3. The Niuwu Fm Sample WN1025, a grey tuffaceous sandstone from the Niuwu Fm, contains
358
zircon grains mostly with Neoproterozoic ages (805 to 965 Ma). Four of the six
359
Pre-Neoproterozoic grains cluster between 1.95 and 2.08 Ga and the other two have
360
ages of 2.42 and 2.58 Ga. Neoproterozoic grains have uniform internal structure with
361
typical concentric oscillatory zoning (Fig. 7c).
ip t
357
The Neoproterozoic zircon grains have variable εHf(t) values (-17.2 to 14.2) and
363
TDM2 (842-2809 Ma) (Fig. 10). The Paleoproterozoic to late Archean zircon grains
364
have relatively constant εHf(t) values from -9.2 to -0.6 and TDM2 from 2.71 to 3.30 Ga.
us
cr
362
366
an
365
4.2.4. The Zhentou Fm
Sample WN1086 from the Zhentou Fm contains nearly half (48%) of
368
Neoproterozoic (mostly between 801 and 860 Ma) zircon grains. Pre-Neoproterozoic
369
zircon grains cluster at groups of 1.64-1.75 Ga, 1.98-2.01 Ga and 2.44-2.58 Ga (Fig.
370
8).
d
Ac ce pt e
371
M
367
Neoproterozoic (798-965 Ma) zircon grains have a wide range of εHf(t) values
372
from -21.5 to 10.6 and TDM2 from 1.06 to 3.04 Ga (Fig. 10). Six late to
373
mid-Paleoproterozoic zircon grains (1.64-2.14 Ga) have εHf(t) values (-12.8 to -5.1)
374
and TDM2 (2.85-3.27 Ga). Zircon grains with ages between 2.33 and 2.76 Ga have a
375
wide range of εHf(t) values of-7.6 to 10.7 and TDM2 of 2.43-3.47 Ga.
376 377
4.3. The Nanhua Sequence
378 379
4.3.1. The Dongmen Fm
14 Page 16 of 105
Two coarse-grained sandstones (WW153 and WW197) from the Dongmen Fm
381
contain zircons with similar detrital age distribution dominated by two major age
382
groups at 1.80 to 2.10 Ga and 2.30 to 2.50 Ga and one sub-group of 800 to 900 Ma
383
(Fig. 8). Neoproterozoic grains are oscillatory-zoned and euhedral. Paleoproterozoic
384
zircon grains are euhedral to rounded and partly oscillatory-zoned (Figs. 6d and e).
ip t
380
Most Neoproterozoic zircon grains have sub-chondritic εHf(t) values scattered
386
between -19.2 and 7.4 (Fig. 9). Nearly all Pre-Neoproterozoic zircon grains have εHf(t)
387
values falling between the evolved Hf isotopic composition defined by the Hf
388
evolution trend of juvenile material derived from a depleted mantle reservoir at ca.
389
2.90 and 3.60 Ga (Fig. 9).
an
us
cr
385
391
4.3.2. The Xiuning Fm
M
390
Detrital zircon grains of sample WN1031 from the upper part of the Xiuning Fm
393
are mostly later Archean to mid-Paleoproterozoic in age, including 2.38-2.52 Ga and
394
1.95-2.07 Ga populations, with a small number of grains clustering at 2.24-2.33 Ga
395
(Fig. 8). Neoproterozoic zircon grains range in age from 750 to 874 Ma with no
396
early-Neoproterozoic detritus (900-1000 Ma).
Ac ce pt e
397
d
392
Neoproterozoic zircon grains have highly scattered Hf isotopic compositions (Fig.
398
10) with a wide range of εHf(t) values (-21.9 to 6.3) and TDM2 (1.31-3.05 Ga). Late- to
399
mid-Paleoproterozoic (~1.9-2.1 Ga) zircon grains have εHf(t) values between -13.1 and
400
-6.3 and TDM2 between 2.99 Ga and 3.42 Ga. 2.24-2.61 Ga zircon grains have
401
scattered εHf(t) values (-18.0 to 5.1) and TDM2 (2.65-3.89 Ga).
402 403 404
5. Discussion
405
5.1. Constraints on the timing of deposition 15 Page 17 of 105
406 407
5.1.1. The Shuangqiaoshan Group The Shuangqiaoshan Group was traditionally thought to be Mesoproterozoic in
409
age (1400-1000 Ma) (Huang et al., 2003; Wu, 2007), whereas a Neoproterozoic
410
depositional age has been widely inferred recently (870-820 Ma) (Gao et al., 2008;
411
Wang et al., 2008; Zhao et al., 2011). Combined with previously published data, new
412
age data in this study can provide tighter constraints on the age of the Shuangqiaoshan
413
Group. All Neoproterozoic zircons have oscillatory-zoning and euhedral shape
414
without metamorphic rim and fractures (Fig. 6). The Shuangqiaoshan Group
415
underwent only low greenschist-facies metamorphism and all Neoproterozoic zircons
416
have high Th/U ratios (generally >0.5), indicating detrital zircons are pristine and can
417
constrain the maximum depositional age of the sediments as they represent the ages of
418
source rocks (Fedo et al., 2003). The initial deposition of the Shuangqiaoshan Group
419
is constrained by a SHRIMP zircon U-Pb age of 831±5 Ma for a thin-bedded
420
bentonite in the middle part of the Henyong Fm, lowermost Shuangqiaoshan Group
421
(Gao et al., 2008). The youngest detrital zircons from the Jilin Fm have a weighted
422
mean age of 826 ± 3 Ma (2σ, MSWD=1.18), placing the maximum deposition age for
423
the Jilin Fm at ca. 828 Ma. A maximum age of 829 ± 5 Ma, bracketed by an
424
inter-bedded bentonite in the Anlelin Fm (Gao et al., 2008), indicates immediate
425
deposition of the Anlelin Fm after the Jilin Fm. One sample from the upper part of the
426
Anlelin Fm contains the youngest zircons with a weighted mean age of 818 ± 3 Ma
427
(2σ, MSWD=1.12), indicating a depositional age of ca. 818 Ma or younger. The
428
Xiushui Fm contains detrital zircons as young as 800 Ma and the youngest zircons
429
yield a weighted mean age of 815 ± 5 Ma (2σ, MSWD=0.32), consistent with the
Ac ce pt e
d
M
an
us
cr
ip t
408
16 Page 18 of 105
430
minimum depositional age of 819 ± 9 Ma bracketed by the Jiuling granitic intrusion
431
(Li et al., 2003a).
432 433
5.1.2. The Xikou Group The Xikou Group is intruded by ca. 824 Ma granitic plutons (Li et al., 2003a; Wu
435
et al., 2006). The youngest zircons of sample WN1004 from the Banqiao Fm have a
436
weighted mean age of 833 ± 8 Ma (2σ, MSWD=0.04), bracketing the initial
437
depositional age to the mid-Neoproterozoic. The youngest zircon group of sample
438
WN1012 give a weighted mean age of 830 ± 4 Ma (2σ, MSWD=0.45), constraining
439
the maximum deposition age of the Mukeng Fm at ca. 830 Ma. Sample WN1025 from
440
the uppermost Niuwu Fm have the youngest zircons with a weighted mean age of 827
441
± 5 Ma (2σ, MSWD=0.58), indicating the Niuwu Fm formed at ca. 827 Ma or
442
younger. There are only two single-grains with younger ages of 805 and 808 Ma, but
443
these are inconsistent with inferred ages from field relationship. Because of the
444
similar lithological assemblage and sedimentary environment, as well as being
445
separated from underlying strata by a similar regional unconformity (Ma et al., 1999;
446
Zhang et al., 1999), the Zhentou Fm can be correlated with the Xiushui Fm and is
447
regarded as the upper part of the Xikou Group. Apart from two exceptionally young
448
(789 and 801 Ma) zircons, the youngest zircons have a weighted mean age of 817 ± 4
449
Ma (2σ, MSWD=0.33), providing a maximum constraint on the deposition of the
450
Zhentou Fm. Therefore, the Xikou Group likely formed at 833-817 Ma.
Ac ce pt e
d
M
an
us
cr
ip t
434
451 452
5.2. Age groups and source terrains
453
17 Page 19 of 105
Among 888 zircon grains analyzed, 692 analyses are considered to be significant
455
in terms of concordance and have meaningful U-Pb ages. There are four principal age
456
groups (Fig. 11. Table 1): (1) Neoproterozoic zircons with ages between 750 and 980
457
Ma; (2) Early-Mesoproterozoic to Late-Paleoproterozoic zircons (1.50-1.80 Ga); (3)
458
Mid-Paleoproterozoic zircons defining a maximum frequency group at 1.80-2.10 Ga;
459
and (4) Early-Paleoproterozoic to Late-Archean zircons (2.35-2.75 Ga).
ip t
454
5.2.1. Neoproterozoic (750 -980 Ma) zircons
us
461
cr
460
All Shuangqiaoshan and Xikou samples have dominantly Neoproterozoic zircons
463
in spite of slightly diverse maximum age frequency. The early-Neoproterozoic
464
(980-860 Ma) detritus may be sourced from the ca. 970 Ma adakitic granite within the
465
northeastern Jiangxi ophiolite (Li and Li, 2003; Gao et al., 2009), the 930-890 Ma
466
volcanic rocks of the Shuangxiwu Group (Chen et al., 2009a; Li et al., 2009), ca. 910
467
Ma granitoid plutons intruding the Shuangxiwu Group (Ye et al., 2007) or ca. 880 Ma
468
obduction-type granite within the NE Jiangxi ophiolite (Li et al., 2008a). 860-820 Ma
469
detritus makes up one of the most important age populations. These zircons have
470
morphology and internal structure of igneous origin and the age spectrum is similar to
471
that recorded by a series of igneous events in the eastern Jiangnan Orogen.
472
Sporadically exposed igneous rocks, the ca. 848 Ma Gangbian alkaline complex (Li et
473
al., 2010b), ca. 849 Ma Shenwu dolerite (Li et al., 2008b) and ca. 850 Ma
474
Zhenzhushan volcanic rocks (Li et al., 2010a) may have provided the relevant detritus.
475
However, the abundance of detrital zircons in this study and inherited zircons within
476
this age range observed from younger granites and volcanic rocks (Wu et al., 2006;
477
Zheng et al., 2008), demonstrate the wider spread of sources that were largely
Ac ce pt e
d
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an
462
18 Page 20 of 105
478
reworked by later processes (Wu et al., 2006; Zheng et al., 2008) or eroded into
479
associated basins.
480 481
5.2.2. Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) zircons Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) material is an
483
important part of the Pre-Neoproterozoic detritus in the analyzed samples but does not
484
match any proximal source in the eastern Jiangnan Orogen (Fig. 11). The 1.5-1.7 Ga
485
Dahongshan Group (Greentree and Li, 2008) and the Dongchuan Group (Zhao et al.,
486
2010b; Wang et al., 2011a) in the western Yangtze Block may be the distal source
487
of the 1.50-1.80 Ga detritus. Nevertheless, the cumulative age histogram constructed
488
from these published data shows that the dominant ages from the western Yangtze
489
Block are ca. 150 million younger than those of the detrital zircons in this study (Fig.
490
11).
493
cr
us
an
M
d
492
5.2.3. Mid-Paleoproterozoic (1.80-2.10 Ga) zircons
Ac ce pt e
491
ip t
482
There are only a few zircon grains with ages of 1.82-1.90 Ga. This age spectrum
494
is similar to the ages of the 1.86-1.89 Ga granitic and metamorphic rocks in the
495
eastern Cathaysia Block (Yu et al., 2009, 2011), but the Cathaysia Block is
496
questionable as the source because of the paucity of such detritus. The
497
mid-Paleoproterozoic age spectrum (1.95-2.08 Ga) is similar to the ages of major
498
metamorphic events recorded by ca. 1.97 Ga metapelite in the Kongling terrane
499
(Zhang et al., 2006a) and ca. 2.00 Ga granulite in the Dabie orogenic belt (Sun et al.,
500
2008; Wu et al., 2008). However, typical core-rim internal structure and low Th/U
501
ratios of most of the metamorphic zircons in both terranes are entirely different from
502
the igneous characteristics of the detrital zircons in this study. In addition, the
19 Page 21 of 105
granulites contain abundant 2.70-2.90 Ga inherited igneous zircons (Sun et al., 2008;
504
Wu et al., 2008), which are absent in the Neoproterozoic sediments, demonstrating the
505
poor connection between these sources and the basin. The ultimate sources for these
506
grains can be the Tianli schist and/or nowadays unexposed crustal fragments, because
507
both sources contain a prominent mid-Paleoproterozoic age population (Fig. 11)
508
(Zheng et al., 2006a; Li et al., 2007).
ip t
503
5.2.4. Early-Paleoproterozoic to Late-Archean (2.35-2.75 Ga ) zircons
us
510
cr
509
A significant early-Paleoproterozoic (2.37-2.50 Ga) age peak is present, whereas
512
tectonothermal activities at 2.30-2.50 Ga are not known in the Yangtze Block. Similar
513
to Archean detritus, the ultimate sources for the early-Paleoproterozoic materials were
514
likely the Tianli schist and unexposed basement (Fig. 11).
M
an
511
The Archean (2.51-2.76 Ga) zircons are significantly younger than the 2.9-3.3 Ga
516
Kongling TTG of the Yangtze Block but similar to the age-frequency peak at
517
2.51-2.70 Ga of the Mesoproterozoic Tianli schist of the eastern Yangtze Block (Li et
518
al., 2007) (Fig. 11). Thus the Tianli schist may have likely provided the recycled
519
Archean material to the Neoproterozoic sediments. In addition, abundant 2.50-2.60
520
Ga xenocrystic zircons in lamproite are used to suggest a widespread Archean
521
basement of the Yangtze Block (Zheng et al., 2006a), reflecting this nowadays
522
unexposed Archean basement was available to supply detritus to the Neoproterozoic
523
sedimentary basin in the eastern Jiangnan Orogen during Neoproterozoic.
Ac ce pt e
d
515
524 525
5.2.5. Temporal and spatial variations in provenance
526
To examine the statistical relationship between the zircon age populations of
527
various samples, the Kolmogorov-Smirnov (K-S) test (Massey Jr, 1951) was applied
20 Page 22 of 105
using the Excel macro developed by the Arizona LaserChron Center. The K-S test
529
suggests a strong correlation among samples WW176, WW236, WN1012 and
530
WN1015 (Fig. 12 and Table 2), all of which have a relatively uniform zircon
531
provenance dominated by Neoproterozoic detritus with ages ranging from 810 to 860
532
Ma. Sample WN1004 seems to be less correlated with other samples (Table 2), which
533
is mainly due to the variable amounts of relative contribution of similarly old detritus
534
(Fig. 12). Apart from the prominent 810-860 Ma zircons, samples from the Xikou
535
Group also contain significant addition of 860-980 Ma materials, roughly consistent
536
with the present geographic framework of the eastern Jiangnan Orogen considering
537
that the 860-980 Ma materials were largely derived from volcanic rocks of the
538
Shuangxiwu Group. Sample WW247 from the Xiushui Fm has a detrital zircon
539
pattern similar to sample WN1086 from the Zhentou Fm (Fig. 12), both of which have
540
dominant Neoproterozoic detritus with several equal age peaks between ca. 800 and
541
900 Ma (Fig. 8) accompanied by significantly increased Pre-Neoproterozoic zircons,
542
indicating that the Xiushui and Zhentou Fms formed in a more open setting with a
543
broad source region than other formations of the Shuangqiaoshan and Xikou Groups.
cr
us
an
M
d
Ac ce pt e
544
ip t
528
The Nanhua Sequence is inferred to have accumulated in a passive margin setting
545
where the sedimentary detritus was mainly sourced from the interior part of the
546
Yangtze Block (Jiang et al., 2003), as reflected by the significant contribution from
547
cratonic components with Paleoproterozoic ages clustering at 1.90-2.10 Ga and
548
2.40-2.50 Ga.
549 550
5.3. Magmatic and crustal evolution
551
21 Page 23 of 105
552
U-Pb ages of detrital zircons reveal three major episodes of magmatic activity at
553
2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma with some minor magmatic events at
554
2.70-2.50 Ga, 1.90-1.50 Ga and 800-750 Ma.
555
5.3.1. Reworking of pre-existing crust in the late Archean to Mesoproterozoic
ip t
556
Most late Archean to early Paleoproterozoic (~2.70-2.30 Ga) zircons have
558
sub-chondritic εHf(t) values (-20.4 to -0.2) and old TDM2 ( 2.97-4.20 Ga), suggesting
559
this period of magmatism was characterized by reworking of a common pre-existing
560
continental crust. One 2.46 Ga zircon from WW153 has the oldest TDM2 age of 4.20
561
Ga, indicating the generation of continental crust as old as 4.20 Ga in the source
562
terrain. Six zircons with ages between 2.49 Ga and 2.61 Ga have εHf(t) values of (4.6 to
563
10.7) near to the depleted mantle (DM) reservoir, reflecting minor addition of juvenile
564
continental crust at this period.
M
an
us
cr
557
Most Mid-Paleoproterozoic (1.90-2.10 Ga) zircons have TDM2 ages (2.80-3.30 Ga)
566
similar to the 2.70-2.30 Ga zircons discussed above (Figs. 9 and 10), suggesting that
567
both periods of magmatism involved reworking of comparably evolved but
568
age-restricted source regions. One zircon grain has a TDM2 age of 1.94 Ga identical to
569
its U-Pb age of 1.92 Ga, and high εHf(t) value (9.9), indicating minor addition of
570
juvenile crust at this period.
Ac ce pt e
571
d
565
The majority of late Paleoproterozoic zircons with negative εHf(t) values ( -16.1 to
572
-1.0) and old TDM2 ages ( 2.51-3.42 Ga) suggest recycling origin of the
573
zircon-saturated magma. Two zircons with ages of 1.62 and 1.81 Ga have positive
574
εHf(t) values (4.3 and 7.9) and TDM2 ages (1.98 and 2.05 Ga), again supporting the
575
possibility of minor addition of juvenile materials between 1.90 and 2.10 Ga.
22 Page 24 of 105
Early Mesoproterozoic zircons (1.40-1.60 Ga) with scattered εHf(t) values (-18.1 to
577
13.8) and TDM2 ages (1.43-3.41 Ga), with the majority at 2.15-2.37 Ga) suggest
578
recycling of variable amounts of pre-existing continental crust. Nearly all late
579
Mesoproterozoic (1.00-1.30 Ga) zircons have εHf(t) values (-9.7 to 6.9) significantly
580
lower than the depleted mantle reservoir (Figs. 9 and 10), implying reworking of older
581
crust with insignificant addition of juvenile crust during this period.
5.3.2. Early-Neoproterozoic addition of juvenile crust
us
583
cr
582
ip t
576
The dominantly early Neoproterozoic (750-980 Ma) zircon detritus has
585
significant implications. Chondritic to near DM Hf isotopic compositions (εHf(t) values
586
mostly from 0 to 16.4) (Figs. 9 and 10) reveal formation of juvenile material at
587
860-980 Ma. A few 860-980 Ma zircons with negative εHf(t) values (-17.0 to -2.0) and
588
old TDM2 ages (1.91-2.81 Ga) suggest involvement of reworked older crust. The most
589
predominant detrital zircons between 810-860 Ma have a wide range of εHf(t) values
590
(-21.5 to 15.8) and TDM2 ages (739-3041 Ma) (Figs. 9 and 10), demonstrating
591
derivation of magmas from both depleted mantle reservoir and older continental curst.
592
Variable εHf(t) values and TDM2 ages imply variable degrees of mixing between
593
juvenile magmas and ancient crust, possibly due to the assimilation during magma
594
ascent. Addition of juvenile crustal materials likely became insignificant after ca. 805
595
Ma (Figs 9 and 10) as most 750-805 Ma detrital zircons have sub-chondritic Hf
596
isotopic compositions, e.g. low εHf
597
(1.85-3.05 Ga).
Ac ce pt e
d
M
an
584
(t)
values (-21.9 to -2.5) and old TDM2 ages
598 599
5.4. Implications for the tectonic evolution of the eastern Jiangnan Orogen
600
23 Page 25 of 105
601
5.4.1. Tectonic setting of the basin The obtained age spectra with predominant Neoproterozoic zircons and
603
statistically insignificant older continental-derived zircons in all Shuangqiaoshan
604
(except WW247 from the Xiushui Fm) and Xikou samples (except WN1086 from the
605
Zhentou Fm) are typical of sediments accumulated in basins associated with a
606
magmatic arc (DeGraaff-Surpless et al., 2002; Goodge et al., 2004) but are
607
inconsistent with continental rift or passive margin sedimentation, which would be
608
expected to have the majority of detritus derived from exhumed older continental
609
crust (Goodge et al., 2002, 2004). The nearly syn-magmatic sedimentation and
610
euhedral igneous zircons suggest a nearby source within the eastern Jiangnan Orogen
611
for the Neoproterozoic detritus and reflect fast erosion and deposition of newly
612
formed igneous rocks. The Cathaysia Block could be a possible source if it was
613
connected with the Yangtze Block during the sedimentation of the Shuangqiaoshan
614
and Xikou Groups. However, detritus derived from the Cathaysia Block would be
615
expected to contain Grenville (extending from 1300 to 950 Ma) materials (Wang et al.,
616
2010a and reference therein), which are scarce in the studied samples (Fig. 11),
617
suggesting the Cathaysia Block was separated from the Yangtze Block and could not
618
provide detritus to the Shuangqiaoshan and Xikou Groups. Additionally, Hf isotopic
619
compositions of the early Neoproterozoic (~810-860 Ma) zircons reveal variable
620
degrees of assimilation of pre-existing older crust to the juvenile magma, the mixing
621
process of which is typical of granitoid rocks in modern-day magmatic arc settings
622
(Tatsumi and Kogiso, 2003). Chemical compositions of the siliciclastic rocks from the
623
Shuangqiaoshan and Xikou Groups have features similar to sedimentary rocks
624
accumulated at active continental margins (Huang et al., 2003; Zhang et al., 2010),
625
consistent with the magmatic arc setting suggested by the detrital zircons. Sandstone
Ac ce pt e
d
M
an
us
cr
ip t
602
24 Page 26 of 105
from both the Shuangqiaoshan and Xikou Groups are compositionally immature with
627
dominantly poorly-sorted volcanic lithic and feldspar detritus and minor detrital
628
quartz (Ma et al., 2001; Huang et al., 2003), suggesting sedimentary detritus derived
629
exclusively from volcanic sources in a magmatic arc setting (Dickinson, 1970). The
630
Xiushui Fm in northwestern Jiangxi and the Zhentou Fm in southern Anhui contain
631
thick layers of conglomerate, pebbly sandstone and coarse sandstone at their bases
632
(Fig. 5), representing syn-orogenic molasse formed in a retro-arc foreland basin at
633
817-815 Ma. Samples WW247 from the Xiushui Fm and WN1086 from the Zhentou
634
Fm have additional input of Pre-Neoproterozoic detritus (Fig. 8), likely derived from
635
the uplifted older basement complexes.
an
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626
637
5.4.2. An integrated tectonic model
M
636
Our new dataset together with published data allow us to propose a modified
639
model for the tectonic evolution of the eastern Jiangnan Orogen (Fig. 13). A
640
NW-dipping oceanic subduction zone along what is the present-day eastern margin of
641
the Yangtze Block is possible on the basis of the 930-890 Ma arc volcanic rocks in the
642
Shuangxiwu Group (Li et al., 2009) and the presence of 930-890 Ma detrital zircons
643
with chondritic to DM-like Hf isotopic compositions (Figs. 9 and 10). Arc-continent
644
collision probably took place at 880-860 Ma as bracketed by the emplacement of 880
645
± 19 Ma obduction-type granites (Li et al., 2008a) and the 858 ± 11 Ma Huaiyu
646
ophiolite (Shu et al., 2006). A back-arc basin was initialed above the continental crust
647
as marked by the 848-824 Ma supra-subduction zone ophiolite in southern Anhui (Li
648
et al., 1997; Ding et al., 2008; Zhang et al., 2012a). Volcanic rocks in this period were
649
largely eroded and transported to the back-arc and retroarc foreland basins due to
650
subsequent orogenic uplift. Abundant 860-810 detrital zircons have Hf isotopic
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25 Page 27 of 105
compositions, indicating mixture between juvenile crust and continental basement
652
(Figs. 9 and 10) and providing support for the existence of an extensive magmatic arc
653
during this period. The basin began to form at ca. 830 Ma and was filled with a set of
654
volcanic-terrigenous arenopelitic flysch sequence with some well-preserved primary
655
sedimentary structures, such as cross- and graded-bedding and scoured based
656
sequences (Fig. 5) (Wu, 2007; Zhang et al., 2010). Greywacke of the flysch sequence
657
contains poorly-sorted and subangular fractions of lithic fragments and less feldspar
658
and quartz (Wu, 2007). Along with basin evolution, the sedimentary strata contained
659
additional interlayered calc-alkaline felsic-intermediate volcanic lava of arc-affinity
660
that strongly supports a magmatic arc setting (Zhang et al., 2010). The Niuwu and
661
Anlelin Fms are characterized by repeated sedimentary cycles of pebbly sandstone
662
and shale (Fig. 5), typical of flysch formed in a back-arc basin. Basin closure was
663
marked by the 828-819 Ma syn-collisional cordierite-bearing peraluminous granitoids
664
(CPG) (Li et al., 2003a; Zhong et al., 2005; Wang et al., 2006) and subsequent
665
syn-orogenic uplift which led to basin restriction and the formation of a regional
666
unconformity. As a result, a retro-arc foreland basin was formed, in which the Xiushui
667
and Zhentou Fms were deposited with detritus from both remnant magmatic arc and
668
uplifted basement. Subsequently, the emplacement of extensive 805-760 Ma bimodal
669
volcanic sequences (Wang et al., 2011b) and 780-770 Ma K-rich calc-alkaline
670
granitoids (KCG) (Zheng et al., 2008; Xue et al., 2010) in the eastern Jiangnan
671
Orogen record post-collisional orogenic rifting, which is marked by remelting of
672
pre-existing rocks as recorded by the sub-chondritic Hf isotopic compositions of most
673
805-750 Ma detrital zircons (Figs. 9 and 10).
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651
674 675
5.4.3. Possible reconstruction of the Yangtze Block in Rodinia
26 Page 28 of 105
It has long been debated if the Yangtze Block was in the central Rodinia, likewise
677
whether or not the Jiangnan Orogen is part of a Grenville Orogen (Li et al., 1995,
678
2008d; Zhou et al., 2002, 2008; Yan et al., 2002; Zheng, 2004; Yu et al., 2008; Wang
679
and Zhou, 2012). However, the back-arc to retro-arc foreland setting for the 830-815
680
Ma Shuangqiaoshan and Xikou Groups does not support an intra-cratonic setting.
681
Neither coeval mantle plume rift system nor a Grenville Orogen recorded in
682
southeastern Australia and western Laurentia (Li et al., 2008d) exist in the eastern
683
Jiangnan Orogen. In addition, the facts that the Jiangnan Orogen is somewhat younger
684
than the Grenville Orogen and that there is insignificant Grenville magmatism and no
685
Grenville juvenile crust recorded by detrital zircons from the strata in the Jiangnan
686
Orogen suggest that this orogen cannot be correlated with the worldwide Grenville
687
Orogen and that the Yangtze Block was unlikely located between Australia–East
688
Antarctica and Laurentia as proposed by Li et al. (1995). However, source analysis
689
suggests interior rather than extraneous detritus supplied to the widespread 830-815
690
Ma sedimentary sequences of the Jiangnan Orogen (Wang et al., 2010a and this study),
691
suggesting that the Yangtze Block was likely located along the margin of Rodinia as
692
an individual continental block rather than in the centre of the supercontinent.
694 695 696 697 698 699 700
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693
ip t
676
6. Conclusions
(1). The previously thought Mesoproterozoic sedimentary sequences in the eastern Yangtze Block was deposited betwee833 and 815 Ma. (2). The 833-815 Ma sedimentary sequence represents a sedimentary cycle from a back-arc to retro-arc foreland basin.
27 Page 29 of 105
701 702
(3). The juxtaposition of the Yangtze and Cathaysia Blocks likely lasted to ca. 815 Ma or even later. (4). Three major episodes of magmatic activities at 2.50-2.35 Ga, 2.10-1.90 Ga
704
and 980-800 Ma are recognized in the source areas of the Neoproterozoic sedimentary
705
basin, whereas the Grenville (1.30-1.00 Ga) magmatism was insignificant.
ip t
703
(5). No Grenville juvenile crust in the eastern Yangtze Block is identified. The
707
most important generation of juvenile crust occurred at early Neoproterozoic
708
(~980-810 Ma) in combination with reworked older crust at 860-810 Ma.
us
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709
Acknowledgements
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This study was supported by the Research Grant Council of Hong Kong SAR,
713
China (HKU 707210P), National Natural Science Foundation of China (NSFC
714
41272212) and the oversea famous professor program (MS2011ZGDZ (BJ) 019). We
715
would like to thank Dr. Jianfeng Gao for his help with field trip and Prof. Liang Qi for
716
the LA-ICPMS work. Thanks go to Dr. Jean Wong and Dr. Hongyan Geng for help
717
with Lu-Hf analysis and Lily Chiu for CL imaging. Constructive reviewers from
718
Journal Editor Professor Randall Parrish and two anonymous reviewers have
719
substantially improved the performance, especially the presentation of U-Pb-Hf
720
isotopic results, of this manuscript and are kindly acknowledge.
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Ding, B.H., Shi, R.D., Zhi, X.C., Zheng, L., Cheng, L., 2008. Neoproterozoic ( ～850 Ma) subduction in the Jiangnan orogen: evidence from the SHRIMP U- Pb dating of the SSZ - type ophiolite in southern Anhui Province. ACTA PETROLOGICA ET MINERALOGICA 27, 375-388 (in Chinese with English Abstract). Fedo, C.M., Sircombe, K.N., Rainbird, R.H., 2003. Detrital zircon analysis of the sedimentary record. Zircon,. In: Hanchar, J.M., Hoskin, P.W.O. (eds.) Rev. Mineral.Geochemical Journal 53, 277-303. Gao, J., Klemd, R., Long, L., Xiong, X., Qian, Q., 2009. Adakitic signature formed by fractional crystallization: An interpretation for the Neo-Proterozoic meta-plagiogranites of the NE Jiangxi ophiolitic mélange belt, South China. Lithos 110, 277-293. Gao, L.Z., Yang, M.G., Ding , X.Z., Liu, Y.X., Liu, X., Ling, L.H., Zhang, C.H., 2008. SHRIMP U-Pb zircon dating of tuff in the Shuangqiaoshan and Heshangzhen groups in South China-constraints on the evolution of the Jiangnan 29 Page 31 of 105
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Wang, W., Zhou, M.-F., 2012. Sedimentary records of the Yangtze Block (South China) and their correlation with equivalent Neoproterozoic sequences on adjacent continents. Sedimentary Geology 265–266, 126-142. Wang, W., Zhou, M.-F., Yan, D.-P., Li, J.-W., 2012b. Depositional age, provenance, and tectonic setting of the Neoproterozoic Sibao Group, southeastern Yangtze Block, South China. Precambrian Research 192-195, 107-124. Wang, X.L., Shu, L.S., Xing, G.F., Zhou, J.C., Tang, M., Shu, X.J., Qi, L., Hu, Y.H., 2011b. Post-orogenic extension in the eastern part of the Jiangnan orogen: Evidence from ca 800-760 Ma volcanic rocks. Precambrian Research in press. Wang, X.L., Zhao, G.C., Zhou, J.C., Liu, Y., Hu, J., 2008. Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen. Gondwana Research 14, 355-367. Wang, X.L., Zhou, J.C., Griffin, W.L., Wang, R.C., Qiu, J.S., O’Reilly, S.Y., Xu, X., Liu, X.M., Zhang, G.L., 2007. Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: Dating the assembly of the Yangtze and Cathaysia Blocks. Precambrian Research 159, 117-131. Wang, X.L., Zhou, J.C., Qiu, J.S., Zhang, W.L., Liu, X.M., Zhang, G.L., 2006. LA-ICP-MS U-Pb zircon geochronology of the Neoproterozoic igneous rocks from Northern Guangxi, South China: Implications for tectonic evolution. Precambrian Research 145, 111-130. Wang, Y.J., Zhang, F.F., Fan, W.M., Zhang, G.W., Chen, S.Y., Cawood, P.A., Zhang, A.M., 2011c. Tectonic setting of the South China Block in the early Paleozoic: resolving intracontinental and ocean closure models from detrital zircon U-Pb geochronology. Tectonics 29. Wu, R.X., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Zhang, S.B., Liu, X.M., Wu, F.Y., 2006. Reworking of juvenile crust: Element and isotope evidence from Neoproterozoic granodiorite in South China. Precambrian Research 146, 179-212. Wu, X.H., 2007. Rediscuss of Shuangqiaoshan group. Resources survey & environment (in Chinese with English abstract) 28, 95-105. Wu, Y.B., Zheng, Y.F., Gao, S., Jiao, W.F., Liu, Y.S., 2008. Zircon U-Pb age and trace element evidence for Paleoproterozoic granulite-facies metamorphism and Archean crustal rocks in the Dabie Orogen. Lithos 101, 308-322. Xia, X.P., Sun, M., Zhao, G.C., Wu, F.Y., Xu, P., Zhang, J., Luo, Y., 2006. U-Pb and Hf isotopic study of detrital zircons from the Wulashan khondalites: Constraints on the evolution of the Ordos Terrane, Western Block of the North China Craton. Earth and Planetary Science Letters 241, 581-593. Xue, H.M., Ma, F., Song, Y.Q., Xie, Y.P., 2010. Geochronology and geochemisty of the Neoproterozoic granitoid association from eastern segment of the Jiangnan orogen, China: Constraints on the timing and process of amalgamation between the Yangtze and Cathaysia blocks. Acta Petrologica Sinica 26, 3215-3244. (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Malpas, J., 2002. Where was South China located in the reconstruction of Rodinia. Earth Sci. Frontiers 9, 249-256 (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Wang, X.W., Malpas, J., 2003. Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China). Tectonophysics 361, 239-254.
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Ye, M.F., Li, X.H., Li, W.X., Liu, Y., Li, Z.X., 2007. SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc along the southeastern margin of the Yangtze Block. Gondwana Research 12, 144-156. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhang, M., Wang, R.C., Jiang, S.Y., Shu, L.S., 2008. Where was South China in the Rodinia supercontinent?:: Evidence from U-Pb geochronology and Hf isotopes of detrital zircons. Precambrian Research 164, 1-15. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhou, M.F., Zhang, M., Shu, L.S., 2010. Components and episodic growth of Precambrian crust in the Cathaysia Block, South China: Evidence from U-Pb ages and Hf isotopes of zircons in Neoproterozoic sediments. Precambrian Research 181, 97-114. Yu, J.H., O'Reilly, Y.S., Wang, L.J., Griffin, W.L., Jiang, S.Y., Wang, R.C., Xu, X.S., 2007. Finding of ancient materials in Cathaysia and implication for the formation of Precambrian crust. Chinese Science Bulletin 52, 11-18. Yu, J.H., O’Reilly, S.Y., Zhou, M.F., Griffin, W.L., Wang, L.J., 2011. U–Pb geochronology and Hf–Nd isotopic geochemistry of the Badu Complex, Southeastern China: Implications for the Precambrian crustal evolution and paleogeography of the Cathaysia Block. Precambrian Research. doi:10.1016/j.precamres.2011.07.014. Yu, J.H., Wang, L.J., O'Reilly, S.Y., Griffin, W.L., Zhang, M., Li, C.Z., Shu, L.S., 2009. A Paleoproterozoic orogeny recorded in a long-lived cratonic remnant (Wuyishan terrane), eastern Cathaysia Block, China. Precambrian Research 174, 347-363. Zhang, S.B., Wu, R.X., Zheng, Y.F., 2012a. Neoproterozoic continental accretion in South China: geochemical evidence from the Fuchuan ophiolite in the Jiangnan orogen. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.010 Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006a. Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China. Precambrian Research 151, 265-288. Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006b. Zircon U-Pb age and Hf isotope evidence for 3.8 Ga crustal remnant and episodic reworking of Archean crust in South China. Earth and Planetary Science Letters 252, 56-71. Zhang, X.H., Zhang, Z.J., Guo, J.Q., Xiong, Q.H., 1999. Stratigraphy and sedimentary sequences of the upper part of the Proterozoic Shuangqiaoshan Group in Xiushui-Wuning area, Jiangxi. Journal of Stratigraphy 23, 71-77. (in Chinese with English Abstract). Zhang, Y.J., Zhou, X.H., Liao, S.B., Zhang, X.D., Wu, B., Wang, C.Z., Yu, M.G., 2010. Neoproterozoic crustal composition and orogenic process of the Zhanggongshan area, Anhui-Jiangxi. Acta Geological Sinia 84, 1401-1427. (in Chinese with English Abstract). Zhang, Y.Z., Wang, Y.J., Fan, W.M., Zhang, A.M., Ma, L.Y., 2012b. Geochronological and geochemical constraints on the metasomatised source for the Neoproterozoic (∼825 Ma) high-Mg volcanic rocks from the Cangshuipu area (Hunan Province) along the Jiangnan Domain and their tectonic implications. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.003
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Zhao, G.C., Cawood, P., 1999. Tectonothermal evolution of the Mayuan Assemblage in the Cathaysia Block; implications for Neoproterozoic collision-related assembly of the South China Craton. American Journal of Science 299, 309-339. Zhao, J.-H., Zhou, M.-F., 2008. Neoproterozoic adakitic plutons in the northern margin of the Yangtze Block, China: Partial melting of a thickened lower crust and implications for secular crustal evolution. Lithos 104, 231-248. Zhao, J.-H., Zhou, M.-F., Zheng, J.-P., Fang, S.-M., 2010a. Neoproterozoic crustal growth and reworking of the Northwestern Yangtze Block: Constraints from the Xixiang dioritic intrusion, South China. Lithos 120, 439-452. Zhao, J.H., Zhou, M.F., 2007a. Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): Implications for subduction-related metasomatism in the upper mantle. Precambrian Research 152, 27-47. Zhao, J.H., Zhou, M.F., 2007b. Neoproterozoic adakitic plutons and arc magmatism along the western margin of the Yangtze Block, South China. The Journal of Geology 115, 675-689. Zhao, J.H., Zhou, M.F., Yan, D.P., Zheng, J.P., Li, J.W., 2011. Reappraisal of the ages of Neoproterozoic strata in South China: no connection with the Grenvillian orogeny. Geology 39, 299-302. Zhao, X.F., Zhou, M.F., Li, J.W., Sun, M., Gao, J.F., Sun, W.H., Yang, J.H., 2010b. Late Paleoproterozoic to early Mesoproterozoic Dongchuan Group in Yunnan, SW China: Implications for tectonic evolution of the Yangtze Block. Precambrian Research 182, 57-69 Zheng, J.P., Griffin, W.L., O’, Reilly, S.Y., 2006a. Widespread Archean basement beneath the Yangtze craton. Geology 34, 417-420. Zheng, Y.-F., Zhao, Z.-F., Wu, Y.-B., Zhang, S.-B., Liu, X., Wu, F.-Y., 2006b. Zircon U-Pb age, Hf and O isotope constraints on protolith origin of ultrahigh-pressure eclogite and gneiss in the Dabie orogen. Chemical Geology 231, 135-158. Zheng, Y.F., 2003. Neoproterozoic magmatic activity and global change. Chinese Science Bulletin 48, 1639-1656. Zheng, Y.F., 2004. Position of South China in configuration of Neoprotero-zoic supercontinent. Chinese Science Bulletin 49, 751-753. Zheng, Y.F., Wu, R.X., Wu, Y.B., Zhang, S.B., Yuan, H., Wu, F.Y., 2008. Rift melting of juvenile arc-derived crust: Geochemical evidence from Neoproterozoic volcanic and granitic rocks in the Jiangnan Orogen, South China. Precambrian Research 163, 351-383. Zheng, Y.F., Zhang, S.B., Zhao, Z.F., Wu, Y.B., Li, X.H., Li, Z.X., Wu, F.Y., 2007. Contrasting zircon Hf and O isotopes in the two episodes of Neoproterozoic granitoids in South China: Implications for growth and reworking of continental crust. Lithos 96, 127-150. Zhong, Y.F., Ma, C.Q., She, Z.B., Lin, G.C., Xu, H.J., Wang, R.J., Yang, K.G., Liu, Q., 2005. SHRIMP U-Pb Zircon Geochronology of the Jiuling Granitic Complex Batholith in Jiangxi Province. Earth Science-Journal of China University of Geosciences 30, 685-691. (in Chinese with English abstract). Zhou, G.Q., 1989. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high temperature-high pressure metamorphic rocks. Journal of Southeast Asian Earth Sciences 3, 237-247.
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Zhou, J.C., Wang, X.L., Qiu, J.S., 2008. Is the Jiangnan Orogenic Belt a Grenvillian Orogenic Belt: some problems about the Precambrian Geology of South China. Geological Journal of China Universities 14, 64-72. (in Chinese with English Abstract). Zhou, M.F., Kennedy, A.K., Sun, M., Malpas, J., Lesher, C.M., 2002a. Neoproterozoic arc-related mafic intrusions along the northern margin of South China: Implications for the accretion of Rodinia. The Journal of Geology 110, 611-618. Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006a. The Yanbian Terrane (Southern Sichuan Province, SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze Block. Precambrian Research 144, 19-38. Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y.Q., Ding, J., 2002b. SHRIMP zircon geochronological and geochemical evidence for Neoproterozoic arc-related magmatism along the western margin of the Yangtze Block, South China. Earth and Planetary Science Letters 196, 51-67. Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A., 2006b. Subduction-related origin of the 750 Ma Xuelongbao adakitic complex (Sichuan Province, China): Implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth and Planetary Science Letters 248, 286-300. Zhu, X.Y., Chen, F., Li, S.Q., Yang, Y.Z., Nie, H., Siebel, W., Zhai, M.G., 2011. Crustal evolution of the North Qinling terrain of the Qinling Orogen, China: Evidence from detrital zircon U-Pb ages and Hf isotopic composition. Gondwana Research 20, 194-204.
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Figure captions.
1152
Fig.1. Distribution of Precambrian units in the eastern segment of the Jiangnan orogen
1153
(modified after (Ma et al., 2002; Wang et al., 2011b). Inserted map on the top
1154 1155 1156
left showing location of the Jiangnan orogen in the South China Craton. Blue dash line shows the boundary between provinces. 1-ca.970-880 Ma northern Jiangxi ophiolitic complex (Li and Li, 2003; Li et al., 2008a); 2-ca. 930-890
1157
Ma Shuangxiwu volcanic rocks (Li et al., 2009); 3-ca. 910-900 Ma Pingshui
1158
plagiogranite (Ye et al., 2007; Chen et al., 2009b); 4- ca. 848 Ma Gangbian
1159
alkaline complex (Li et al., 2010b); 5- ca. 850 Ma Zhenzhushan volcanic rocks
1160
(Li et al., 2010a)
1161
37 Page 39 of 105
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Fig. 2. Sketch map showing the distribution of the Shuangqiaoshan Group and Nanhua sequence in the northwestern Jiangxi Province.
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Fig. 3. Sketch map showing the distribution of the Xikou Group as well as other
1166
Neoproterozoic units in the southern Anhui Province. Faults in this figure
1167
refers to legend in Fig. 2.
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Fig. 4. Stratigraphy of the major Neoproterozoic sedimentary units in the eastern
1170
Yangtze Block. The Zhentou Fm is tentatively considered as the upper part of
1171
the Xikou Group, considering its similarity with the Xiushui Fm in the upper
1172
part of the Shuangqiaoshan Group. The columns are not strictly to scale. Stars
1173
and italic numbers represent sample location relative to stratigraphic column
1174
and sample numbers. Bold italic numbers represent the reported ages of
1175
volcanic tuffs; see text for details and discussion.
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Fig. 5. Structures of marine sediments investigated during this study: (a) Parallel
1178
bedding and rhythmic layers between reddish siltstone and sandstone in the
1179 1180 1181 1182
Jilin Formation; (b) partial Bouma sequences in the Anlelin Fm; (c) Graded and cross bedding in the Anlelin Fm; (d) boundary between the Anlelin and Xiushui Fms. The sandstone interlayers in the silty slate are lenticular which may be result of wave current in the Banqiao Formation; (e) lenticular and
1183
cross bedding developed between grey siltstone and slate; (f) Wavy contoured
1184
bed with different wavelength and slump structure in the Mukeng Fm; (g)
1185
grading bedding developed in the Niuwu Fm; (h) coarse quartz sandstone from
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the Xiuning Fm.
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1187 1188
Fig. 6. Concordia diagrams showing results of U-Pb dating of detrital zircon grains
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from the Shuangqiaoshan Group and Dongmen Fm. Inserted diagrams show
1190
representative CL images and concordant ages (for ages<1.0 Ga,
1191
ages are presented and for ages>1.0 Ga,
1192
individual analyzed grains.
Pb/238U
Pb/206Pb ages are presented) of
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206
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Fig. 7. Concordia diagrams showing results of U-Pb dating of detrital zircon grains
1195
from the Xikou Group and Xiuning Formation. Inserted diagrams show
1196
representative CL images and concordant ages (for ages<1.0 Ga,
1197
ages are presented and for ages>1.0 Ga,
1198
individual analyzed grains.
Pb/238U
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206
207
Pb/206Pb ages are presented) of
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Fig. 8. Relative probability versus age diagrams. The reds curves show the frequency
1201
of individual zircon populations (for details see text). Some samples are
1203 1204
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plotted at two scales to highlight the distribution of Neoproterozoic ages. Samples are presented in stratigraphic order.
1205
Fig. 9. Hf isotopic compositions of detrital zircons from Shuangqiaoshan Group and
1206
Dongmen Fm. (a) εHf(t) values versus U-Pb ages; (b) Histograms of U-Pb ages.
1207
DM : delepted mantle ; CHUR : chondritic uniform reservoir ; 3.2 Ga crust
1208
means materials were derived from delepted mantle at 3.2 Ga and evolved
1209
with average continental crust 176Lu/177Hf of 0.015.
1210
39 Page 41 of 105
1211
Fig. 10. Hf isotopic compositions of detrital zircons from Xikou Group and Xiuning
1212
Fm. (a) εHf(t) values versus U-Pb ages; (b) Histograms of
1213
meaning of DM, CHUR and 3.2 Ga crust is explained in caption of Fig. 9.
U-Pb ages. The
1214
Fig. 11. Probability plots of detrital zircons from Neoproterozoic sedimentary units in
1216
the eastern Yangtze Block and their potential sources. The number of y-axis
1217
represents the number of analyses. Data sources for Pre-Neoproterozoic units:
1218
the Kongling complex, (Qiu et al., 2000; Zhang et al., 2006a, b; Gao et al.,
1219
2011); the Tianli schist, (Li et al., 2007); Xenocrystic zircons from lamproite,
1220
(Zheng et al., 2006a); the western Yangtze Block, (Greentree et al., 2006;
1221
Greentree and Li, 2008; Zhao et al., 2010b; Wang et al., 2011a); the Cathaysia
1222
Block, (Li, 1997; Wan et al., 2007; Li et al., 2010c; Yu et al., 2011). Data
1223
sources for Neoproterozoic unit: the southeastern Yangtze Block, (Li and Li,
1224
2003; Li et al., 2003b, 2008b, 2009, 2010b; Wang et al., 2006; Wu et al., 2006;
1225
Zheng et al., 2008); the western Yangtze Block, (Zhou et al., 2002b, 2006a; Li
1227 1228 1229 1230 1231
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et al., 2003b; Zhao and Zhou, 2007a, b); the northern Yangtze Block, (Zhou et al., 2002a, 2006b; Zhao and Zhou, 2008; Zhao et al., 2010a), the Cathaysia Block, (Wan et al., 2007; Li et al., 2010c; Shu et al., 2011).
Fig. 12. Cumulative probability plots of the zircon age data for Neoproterozoic siliciclastic sequences of the eastern Yangtze Block.
1232 1233 1234
Fig. 13. Sequential tectonic evolution of the eastern Jiangnan orogen. See text for discussion.
40 Page 42 of 105
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Graphical Abstract (for review)
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*Marked Manuscript Click here to view linked References
1
Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern
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Jiangnan Orogen, South China
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Wei Wang1, Mei-Fu Zhou1,*, Dan-Ping Yan2, Liang Li3, John Malpas1
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1
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China
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2
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Geosciences, Beijing 100083, China
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3
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Academy of Sciences, Guiyang 550002, China
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Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR,
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State Key Lab of Geological Process and Mineral Resources, China University of
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State Key Lab of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
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*
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E-mail: [email protected]
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Phone: +852 2857 8251
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Fax: +852 2517 6912
Corresponding author:
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Abstract: Precambrian sedimentary sequences in the eastern Jiangnan Orogen, South
27
China, include the Neoproterozoic Shuangqiaoshan and Xikou Groups and the
28
overlying Nanhua SystemSequence. U-Pb ages of detrital zircons provide tight
29
constraints on the deposition of the Shuangqiaoshan and Xikou Groups at 831-815 Ma
30
and 833-817 Ma, respectively. Rocks from the lower parts of these strata contain
31
dominantly Neoproterozoic detritus with a pronounced age peak at 830-850 Ma,
32
interpreted to be derived from a magmatic arc that has been mostly eroded. This
33
magmatic arc was associated with sedimentation characterized by compositionally
34
immature sediments with dominant early-Neoproterozoic (~860-810 Ma) zircons that
35
have variable εHf(t) values of -21.5 to 1514.8. The upper parts of these strata,
36
uncomfortably underlain by the low units, are molasse-type assemblages with
37
additional input of pre-Neoproterozoic detritus, representing sediments accumulated
38
in a retro-arc foreland basin associated with the Jiangnan Orogen.
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Combining four samples from the Nanhua SystemSequence, three major
40
magmatic activities at 2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma in the source areas
41
are identified. The older two events are characterized by reworking of pre-existing
42
continental crust. Grenville magmatism and juvenile crust were insignificant in the
43
eastern Jiangnan Orogen. Neoproterozoic zircons reflect generation of juvenile crust
44
at 980-860 Ma, involvement of both juvenile and recycled materials at 860-810 Ma
45
and reworking of pre-existing crust at 805-750 Ma, corresponding to island arc,
46
continental magmatic arc and post-collisional rifting stages in the eastern Jiangnan
47
Orogen.
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Keywords: U-Pb ages, Lu-Hf isotopes, detrital zircons, Jiangnan Orogen, South
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China
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1. Introduction
52
The Jiangnan Orogen in South China witnessed the amalgamation of the Yangtze
54
and Cathaysia Blocks. Recent studies of sedimentary and igneous rocks have
55
demonstrated that the Jiangnan Orogen is a Neoproterozoic rather than
56
Mesoproterozoic tectonic unit, but the timing and evolution of this orogen are still
57
matters of debate (Wang et al., 2006, 2007, 2012b; Zheng et al., 2008; Li et al., 2009;
58
Zhao et al., 2011). The Jiangnan Orogen was thought to be part of the worldwide
59
Grenville Orogen, formed by the collision between the Yangtze and Cathaysia Blocks
60
(Li et al., 2007, 2009), followed by extensive rift-related magmatism at ca. 820 Ma
61
(Wu et al., 2006; Li et al., 2008c, 2009, 2010a; Zheng et al., 2008). On the other hand,
62
this orogeny is thought to have lasted until ca. 830 Ma or even later, followed by
63
post-extensional magmatism beginning at ca. 800 Ma (Li, 1999; Zhao and Cawood,
64
1999; Wang et al., 2006, 2011b, 2012b; Zhao et al., 2011; Zhang et al., 2012b).
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The eastern segment of the Jiangnan Orogen is crucial for the understanding of
66
the orogenic cycle because it contains widespread sedimentary sequences, igneous
67
plutons and two major ophiolite belts, that witness the final amalgamation between
68
the Yangtze and Cathaysia Blocks (Li et al., 2009) (Fig.1). In past decades, numerous
69
studies examined the petrogenesis and tectonic affinity of igneous rocks (Wu et al.,
70
2006; Li et al., 2007, 2008b, 2009; Zheng et al., 2008; Zhang et al., 2012a), but
71
associated sedimentary sequences in the eastern Jiangnan Orogen are poorly
72
understood, due in part to unresolved stratigraphy, incomplete biostratigraphic data,
73
poor exposure and strong overprint by later deformation. These sedimentary
74
sequences in the eastern Jiangnan Orogen include the Shuangqiaoshan Group in
75
northern Jiangxi Province and the Xikou Group in southern Anhui Province (Fig. 1),
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Page 46 of 105
which were interpreted to have formed in a back-arc basin associated with
77
Mesoproterozoic NW-dipping (current coordinates) oceanic subduction beneath the
78
Yangtze Block (Cheng and Wang, 2000; Huang et al., 2003). However, dating results
79
of the Shuangqiaoshan Group do not support this model and it has been proposed that
80
these sequences were deposited in a retroarc foreland basin, synchronous with the
81
amalgamation of the Yangtze and Cathaysia Blocks (Wang et al., 2008). More recent
82
studies suggest the Shuangqiaoshan Group likely formed at ca. 830 Ma (Gao et al.,
83
2008; Zhao et al., 2011), which is taken as the timing for the Jiangnan Orogeny (Zhao
84
et al., 2011). These sequences are also suggested to have formed in an early-phase of
85
rifting that post-dated the Jiangnan Orogen (Li et al., 2009) based on ca. 850 Ma
86
dolerite dykes (Li et al., 2008b) and bimodal volcanic rocks (Li et al., 2010a).
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Due to the strong later deformation of these sedimentary strata and intensive
88
reworking and erosion of the pre-existing igneous provenance (Wu et al., 2006; Zheng
89
et al., 2008), one possible way to examine the timing and evolution of orogenic cycles
90
is to unearth the information contained by detrital zircons (Cawood and Nemchin,
91
2001; Liu et al., 2011; Wang et al., 2011c). Detrital zircon age spectra may contain
92
information about various sources linked to eustatic, depositional and tectonic change
93
(Wang et al., 2010b, 2012a), and thus can provide insight into the basin-orogen
94
coupling (Horton et al., 2010; Myrow et al., 2010). Hf isotopes of zircons can be used
95
for understanding juvenile or reworked zircon-hosting magma (Griffin et al., 2004;
96
Xia et al., 2006; Zheng et al., 2006b, 2007; Zhu et al., 2011; Liu et al., 2012; Wang et
97
al., 2012a), thought to be one of the most discriminating features among plume, rift
98
and arc-related magmatism (Zheng et al., 2008).
Ac ce pt e
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99
In this paper, we present the first integrated study of U-Pb ages and Hf isotopic
100
compositions of detrital zircons from the major Neoproterozoic sedimentary strata in
3
Page 47 of 105
101
the eastern Jiangnan Orogen. This new dataset allows us to refine the depositional age
102
of the hosting strata and to track provenance changes. The provenance characteristics
103
can help define the relationship between sedimentation and tectonism and potential
104
link to the configuration of the supercontinent Rodinia.
2. Geological background
cr
106 107
ip t
105
The South China Craton comprises the Yangtze and Cathaysia Blocks, with the
109
Jiangnan Orogen being the southeastern part of the Yangtze Block. The Cathaysia
110
Block has voluminous Phanerozoic igneous rocks with rarely exposed Precambrian
111
rocks (Yu et al., 2010). Metamorphic complexes in the eastern Cathaysia Block were
112
traditionally thought to be Paleo-Mesoproterozoic to Neoarchean basement (Li, 1997),
113
but recent studies suggest that these complexes formed in the Neoproterozoic or even
114
younger (Wan et al., 2007; Li et al., 2010c). A Paleoproterozoic orogen is inferred on
115
the basis of abundant Paleoproterozoic granites and metamorphic rocks in the eastern
116
Cathaysia Block (Yu et al., 2009). Precambrian rocks in the Yangtze Block are
117
sporadically exposed and include Archean Tonalite–Trondhjemite–Granodiorite (TTG)
118
in the north (Qiu et al., 2000; Gao et al., 2011) and Paleoproterozoic strata in the west
119
(Sun et al., 2009; Zhao et al., 2010b), whereas Neoproterozoic sedimentary sequences
120
and igneous plutons are widespread (Zhou et al., 2002b; Li et al., 2003a, b; Wang et
121
al., 2006, 2010b; Zhao and Zhou, 2007a; Zheng et al., 2008; Zhao et al., 2011). The
122
sedimentary cover of the Yangtze Block consists mainly of folded Paleozoic and
123
Lower Mesozoic strata formed in a shallow marine environment (Yan et al., 2003).
Ac ce pt e
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108
124
Precambrian rocks in the eastern Jiangnan Orogen include the Mesoproterozoic
125
Tianli schist (Li et al., 2007), early-Neoproterozoic Shuangxiwu volcanic-clastic
126
sequences (Ye et al., 2007; Li et al., 2009), mid-Neoproterozoic sedimentary strata 4
Page 48 of 105
(Gao et al., 2008; Zhao et al., 2011), igneous plutons (Zhong et al., 2005; Wu et al.,
128
2006; Li et al., 2008b, 2009, 2010b; Zheng et al., 2008), and ophiolitic complexes
129
(Bai et al., 1986; Zhou, 1989; Zhang et al., 2012a). Mid-Neoproterozoic sedimentary
130
strata including the Shuangqiaoshan and Xikou Groups in the eastern Jiangnan
131
Orogen are overlain unconformably by a post-orogenic extensional basin deposits as
132
the Nanhua SystemSequence. Granitoid plutons intruding the sedimentary sequences
133
are represented by the Jiuling pluton in NW Jiangxi (Li et al., 2003a; Zhong et al.,
134
2005) and the Xucun, Shexian and Xiuning plutons in southern Anhui (Li et al., 2003a;
135
Wu et al., 2006). The NE-SW trending ophiolite complexes are in tectonic contact
136
with the Shuangqiaoshan and Xikou Groups (Bai et al., 1986).
138
cr
and southern Anhui Provinces is outlined in Figures. 2 and 3.
M
139
2.1. Shuangqiaoshan Group
d
140 141
us
A stratigraphic framework of the sedimentary succession in northwestern Jiangxi
an
137
ip t
127
The Shuangqiaoshan Group consists of silty, volcanic clastic detritus that
143
gradually coarsens upwards, and has partially preserved primary sedimentary
144
structures. Based on primary sedimentary structure and lithology, this strata is divided
145
into the Hengyong, Jilin, Anlelin and Xiushui Formations (Fms) from the base
146
upward (Fig. 4) (BGMRJX, 1996).
Ac ce pt e
142
147
The Hengyong Fm comprises of grey to reddish, feldspar-lithic sandstone,
148
feldspar-quartz sandstone and siltstone. The sandstone consists dominantly of
149
subangular to subrounded, lithic fragments, with lesser amounts of quartz and feldspar.
150
Graded bedding, banded bedding, and scour and slump marks are well developed.
151
The Jilin Fm is conformable with both its underlying and overlying strata and
152
contains mostly purplish-red, silty slate, usually referred to as a red bed sequence. 5
Page 49 of 105
153
Within the silty slate are interbeds of siltstone and sandstone (Fig. 5a). Cross-bedding,
154
graded bedding and partial Bouma sequences are common. The Anlelin Fm is widespread in northern Jiangxi province and is composed of
156
thick grey to charcoal grey flysch with some tuffaceous siltstone and slate. In addition
157
to greywacke, there are fine-grained, tuffaceous beds, feldspar-, quartz-rich sandstone
158
and tuffaceous lithic-quartz sandstone. Lithic components include andesite, siliceous
159
rocks, granite, basalt and silty mudstone (Wu, 2007). Cross-bedding, parallel bedding,
160
scour and slump marks, and partial Bouma sequences are well developed (Figs. 5b
161
and c).
us
cr
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155
The Xiushui Fm, overlying the Anlelin Fm, has a basal ca. 2.5 m thick layer of
163
conglomerate (Fig. 5d). Conglomerate contains gravels of variable sizes that are
164
parallel to the orientation of the sedimentary layer. In some cases, this conglomerate
165
layer is absent and the bottom of the Xiushui Fm is marked by a 40-m-thick layer of
166
greyish-white, pebbly sandstone or quartz conglomerate. The upper part of the
167
Xiushui Fm consists mainly of greyish-white, grey or green yellow, tuffaceous slate
168
interbedded with tuff. Cross-bedding, parallel-bedding and partial Bouma sequences
169
are also common in this unit.
171 172
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170
an
162
2.2. Xikou Group
173
Widely distributed in southern Anhui Province, the Xikou Group has experienced
174
weak to strong deformation and low-greenschist facies metamorphism, whereas
175
graded and crossing bedding are perfectly preserved (BGMRAH, 1984). The Xikou
176
Group is divided into the Zhangqian, Banqiao, Mukeng and Niuwu Fms upwards (Fig.
177
4) (BGMRAH, 1984). The Zhentou Fm unconformably overlies the Niuwu Fm and is
6
Page 50 of 105
178
tentatively interpreted as the upper part of the Xikou Group in this study, because of
179
its similarity with the Xiushui Fm of the Shuangqiaoshan Group. The Zhangqian Fm comprises green sericite-quartz schist, arenaceousous to silty
181
phyllite and sericite-chlorite-quartz schist. Original pelitic rocks have been
182
metamorphosed to phyllite during regional metamorphism, resulting in well
183
developed phyllitic structure. Spotted or banded magnetite is common and interlayers
184
of basic volcanic rocks are also sporadically present.
cr
ip t
180
Dark to grey phyllite, phyllitic slate and feldspar quartz sandstone are the
186
dominant rocks of the Banqiao Fm that overlies the Zhangqian Fm conformably.
187
Rhythmic layering between sandstone and slate are commonly observed and lenticular
188
sandstone is developed probably due to current lamination (Fig. 5e). Feldspar and
189
quartz with a few lithic detritus are the dominant clastic fragments, which is hosted by
190
cemented fine-grained sericite and clay minerals.
M
an
us
185
The Mukeng Fm is composed of thick grey to greyish-green silt- to arenaceous-
192
siliciclastic rocks dominated by fine-grained siltstone and sericite-chlorite slate,
193
whereas fine-grained sandstone occuroccurs as interlayers in the slate. Graded and
194
parallel bedding, are well preserved (Fig. 5f). Contorted bed with varying wavelength
195
formed by waveing current and slump structure are observed (Fig. 5f), suggesting fast
196
sedimentation in a turbulent environment.
Ac ce pt e
d
191
197
The Niuwu Fm is typical of turbiditic deposition, consisting of thick layer of
198
greyish-green to greyish-purple litharenite and thin layer of medium-grained
199
sandstone. Gravel-bearing sandstone and coarse- to medium-grained sandstone form
200
well developed graded bedding (Fig. 5g), typical of turbidite. Features of shallow
201
water and storm flow deposits are observed in the upper part of the Niuwu Fm, where
202
ashy black slate is interbedded with thick layers of sandstones.
7
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Unconformably underlain by the Niuwu Fm, the Zhentou Fm contains
204
conglomerate, gravel-bearing sandstone and gravel-bearing silty slate from the base to
205
the top. Angular to subangular gravels of the stratigraphically basal conglomerate are
206
poorly-sorted with diameters ranging between 1 and 8cm and are dominated by
207
fragments of slate, silicolite, granite and quartz. Gravel-bearing sandstone and slate
208
from the upper Zhentou Fm contain gravels smaller and less than the conglomerate
209
and quartzite, volcanic rocks and siltstone are the dominant rock fragments.
211 212
cr
us
210
ip t
203
2.3. Nanhua SystemSequence
The Nanhua SequenceSystem is a set of glacial sedimentary rocks corresponding
214
to the Cryogenian System defined by the International Commission on Stratigraphy
215
(Plumb, 1991). The Nanhua SequenceSystem includes the lower Dongmen and
216
Xiuning Fms and the upper Nantuo and Leigongwu Fms. The Dongmen and Xiuning
217
Fms, correlated with the pre-glacial Liantuo Fm in the central Yangtze Block, are
218
composed largely of a clastic succession unconformably underlain by the
219
Shuangqiaoshan and Xikou Groups, respectively. The basal parts of these units
220
consist of conglomerate and coarse quartzose sandstone, formed in an alluvial fan or
221
fluvial environment. The Nantuo and Leigongwu Fms, are widespread in the entire
222
Yangtze Block, are composed of diamictite typical of tillite formed during the
223
Neoproterozoic ―snowball Earth‖ event (Zheng, 2003).
225 226
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224
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an
213
3. Sampling and analytical methods
227
Ten samples were selected across major stratigraphic units for zircon dating in
228
order to constrain depositional ages, provenance and tectonic setting of the
8
Page 52 of 105
229
sedimentary basin. Zircon was separated using standard heavy-liquid and magnetic
230
separation from ca. 5 Kg samples. Zircon separates were mounted in epoxy and
231
polished. U-Pb isotope analysis of zircon was performed by LA-ICP-MS at the State Key
233
Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
234
Academy of Sciences, Guiyang. A GeoLasPro laser-ablation system (Lamda Physik,
235
Gottingen, Germany) and Agilent 7700x ICP-MS (Agilent Technologies, Tokyo,
236
Japan) were combined for the experiments. The 193 nm ArF excimer laser,
237
homogenized by a set of beam delivery systems, was focused on the zircon surface
238
with the fluence of 10J/cm2. The ablation protocol employed a spot diameter of 32 µm
239
at 5 Hz repetition rate for 45 seconds (equating to 225 pulses). Helium was applied as
240
a carrier gas to allow efficient transportation of aerosol to the ICP-MS. Zircon 91500
241
was used as the primaryexternal standard to correct elemental fractionation.
242
Meanwhile, zircon GJ-1 (Jackson et al., 2004) and Plešovice (PL, Sláma et al., 2008)
243
were analyzed as unknown samples for quality control. Trace element compositions of
244
zircon were external calibrated against NIST SRM 610 with
245
secondary standard. Raw data reduction was performed off-line by ICPMSDataCal
246
(Liu et al., 2010) and the results were reported with 12σ errors. Reported uncertainties
247
(2σ) of the
248
reproducibility (2 SD%) of standard zircon 91500 during the analytical session and
249
the within-run precision of each analysis (2 SE%; standard error) (c.f. Gerdes and Zeh.
Formatted: Font color: Blue
250
2006, 2009). Common Pb correction was corrected using the MS Excel program
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251
―ComPbcorr# 3.15”(Andersen 2002). Data were processed using the ISOPLOT
252
program (Luding, 2003). The analytical results of standard and reference materials are
253
presented in Supplementary Table 1.The weighted mean 206Pb/238Uconcordant ages of
91
Zr as the internal
Ac ce pt e
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232
206
Pb/238U ratio were propagated by quadratic addition of the external
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Page 53 of 105
254
analyzed GJ-1 (598.0601 ± 3.517 Ma, 2σ, MSWD=1.3n=24) and PL (338334.25 ±
255
27.5 Ma, 2σ, n=22MSWD=2.9) are consistent with the reported or recommended
256
values (GJ-1: 599.8 ± 1.7 Ma, 2σ, Jackson et al., 2004; PL: 337.13 ± 0.37 Ma, 2σ,
257
Sláma et al., 2008). Hf isotopic analysis of zircons were conducted using a Resonetics Resolution
259
M-50 193nm excimer laser ablation system, attached to a Nu Plasma HR
260
multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) at the
261
University of Hong Kong. Hf isotopes were obtained with a beam diameter of 55 μm,
262
pulse rate of 10 Hz and energy density of 15 J/cm2. Atomic masses 172 to 179 were
263
simultaneously measured in a static-collection mode. Isobaric interference of 176
172
176
Yb
with
265
Instrumental mass bias correction of Yb isotope ratios were normalized to 172Yb/173Yb
266
of 1.35274 (Chu et al., 2002) and Hf isotope ratios to 179Hf/177Hf of 0.7325 (Patchett
267
et al., 1981) using an exponential law. A relationship between . Yb and Hf of βYb
268
=0.872βHf are obtained and used for the mass bias offset. Interference of
269
176
270
and using a recommended
271
2001). Due to insignificant contribution of signal intensity of 176Lu on 176Hf (generally
272
<1%), the mass bias of Lu isotopes (βLu) can be assumed to be identical to βHf (c.f.
273
lizuka and Hirata, 2005). External calibrationQuality control was made by measuring
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274
zircon standard 91500 and GJ-1 for the unknown samples during the analyses to
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275
evaluate the reliability of the analytical data, which yielded weighted mean
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276
176
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277
100), respectively (Supplementary Table 2).
an
Yb/ Yb ratio of 0.5886 (Chu et al., 2002).
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264
d
M
Hf was corrected against the
176
us
cr
ip t
258
Ac ce pt e
Hf was corrected by measuring the intensity of the interference-free 176
175
176
Lu with
Lu isotope
Lu/175Lu ratio of 0.02655 (Machado and Simonetti,
Hf/177Hf ratio of 0.282305 ± 3 for 91500 (n = 134) and 0.282019 ± 5 for GJ-1 (n =
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278
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279 280
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4. Analytical results
281
U-Pb isotope rResults of U-Pb dating aredetrital zircon grains appear present in
283
Supplementary Table 3 and concordant plots diagrams (Figs. 6 and 7). Detrital zircons
284
with concordant U-Pb ages (with concordance between 90-110%) were selected for
285
in-situ Hf isotopic analyses and the results are given in Supplementary Table 4.
cr
ip t
282
4.1.The Shuangqiaoshan Group
289
4.1.1. The Jilin Fm
an
287 288
us
286
Sample WW236, a reddish medium-grain sandstone from the Jilin Fm,
291
contains a predominant population of Neoproterozoic zircon grains with two major
292
age peaks at ca. 830 826 and ca. 850 Ma and three sub-peaks at ca. 870, 890 895 and
293
950 Ma (Fig. 8). These Neoproterozoic zircon grains are commonly oscillatory-zoned
294
(Fig. 6a). Pre-Neoproterozoic zircon grains are rare, with ages grouping at 1.15-1.26
295
Ga, 1.76-1.76 Ga and 1.87-2.22 Ga. One Archean zircon grain has a 207Pb/206Pb age of
296
2.59 Ga. Pre-NeoproterozoicGenerally, all zircon grains also have oscillatory zoning
297
but are variably rounded (Fig. 6a).
Ac ce pt e
d
M
290
298
Neoproterozoic zircon grains have highly variable εHf(t) values (-16.8 to 14.8) and
299
two stage hafnium model age (TDM2 ) ages (781-2758 Ma) (Fig. 9). Two
300
Mesoproterozoic zircon grains have identical ages but different εHf(t) values (3.3 and
301
10.8) and TDM2 ages (1.84 and 1.38 Ga). Five Paleoproterozoic zircon grains have
302
variable εHf(t) values (-8.1 to 7.2) and TDM2 ages (2.19-2.95 Ga).
303 304
4.1.2. The Anlelin Fm 11
Page 55 of 105
Sample WW176 is a combination of chips from a series of thick layers of
306
fine-medium grained siltstones in the middle Anlelin Fm. Neoproterozoic (795-978
307
Ma) euhedral and oscillatory-zoned (Fig. 6b) grains are the dominant population and
308
have two major age peaks at ca. 818 Ma and ca. 843 Ma (Fig. 8). Nine
309
Pre-Neoproterozoic
fromThree
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310
Mesoproterozoic grains have ages of 1.14 Ga to , 1.35 and 1.52 Ga. Six
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311
Paleoproterozoic zircon grains have age groups at 1.71-1.73 Ga, 2.03-2.17 Ga and
312
2.46 Ga. These zircon grains are generally subhedral to rounded with uniform internal
313
structure showing partly preserved oscillatory zoning (Fig. 6b).
have
207
Pb/206Pb
ages
scattering
us
cr
zircons
ip t
305
Mid-Neoproterozoic (795-850 Ma) zircon grains have positive εHf(t) values (1.2 to
315
15.1) and TDM2 ages ranging continuously from 739 to 1653 Ma (Fig. 9). In contrast,
316
Early-Neoproterozoic (851-978 Ma) zircon grains have highly variable εHf(t) values
317
(-17.7 to 16.214.7) and TDM2 ages (742-2836 Ma). Two Mesoproterozoic (1.14 and
318
1.35 Ga) zircon grains have identical
319
whereas the other Mesoproterozoic grain (1.52 Ga) has a low
320
0.281980. Two Paleoproterozoic (1.71 and 1.72 Ga) zircon grains have different εHf(t)
321
values (-5.0 and 1.3). The other three Paleoproterozoic zircons have negative εHf(t)
322
values (-2.0 to -8.3).
324
M
Hf/177Hf ratios (0.282232 and 0.282216), 176
Hf/177Hf ratio of
d
176
Ac ce pt e
323
an
314
4.1.3. The Xiushui Fm
325
Sample WW247, a coarse sandstone from the Xiushui Fm, contains predominant
326
Neoproterozoic grains, with five age peaks at ca. 815, 825-835, ca. 869, ca. 900 and
327
ca. 930 Ma (Fig. 8). All Neoproterozoic grains are euhedral and have well preserved
328
oscillatory zoning. Pre-Neoproterozoic zircon grains have ages scattering from 1.01 to
329
2.02 Ga with only one Archean age of 2.68 Ga. All these zircon grains are subhedral
12
Page 56 of 105
330
to rounded and show partially oscillatory zoning or uniform internal structure (Fig.
331
6c). Except for two grains with unreasonably high εHf(t) values (34.6 and 69.3),
333
Neoproterozoic (811-935 Ma) zircon grains have variable εHf(t) values (-16.0 to
334
16.413.7) and TDM2 (742-2727 Ma) (Fig. 9). Eight Four late-Mesoproterozoic
335
(1.01-1.101.49 Ga) zircon grains have a wide range of εHf(t) values (-9.7 to 6.9) and
336
TDM2 (1.42-2.47 Ga), whereas four early-Mesoproterozoic (1.26-1.49 Ga) zircon
337
grains have a narrow range of εHf(t) values (-4.2 to -0.3) and TDM2 (2.24-2.30 Ga).
338
Zircon grains with ages between 1.57 and 1.63 Ga have a wide range of εHf(t) values
339
(1.0-13.8) and TDM2 (1.43-2.26 Ga). Paleoproterozoic to later Archean zircon grains
340
have negative εHf(t) values (-16.1 to -2.7) and old TDM2 (2.77-3.53 Ga).
an
us
cr
ip t
332
342 343
4.2. The Xikou Group
344
4.2.1. The Banqiao Fm
M
341
Zircon grains from a grey phyllitic siltstone WN1004 are fairly small (<100 μm),
346
mostly euhedral and show oscillatory zoning with rare preexisting cores and
347
overgrowth rims (Fig. 7a). These detrital zircon grains are predominantly
348
Neoproterozoic and have ages ranging from 831 to 990 Ma with four age peaks at ca.
349
833, 860, 885 884 and 930 932 Ma (Fig. 8). There are also a few Meso- to
350
Paleoproterozoic zircon grains with ages scatteringed from 1.21 to 2.46 Ga.
Ac ce pt e
d
345
351
Nearly all Neoproterozoic zircon grains have positive εHf(t) values (1.2-14.0) and a
352
wide range of TDM2 (937-1664 Ma), except for two zircon grains with negative εHf(t)
353
values (-4.1 and -6.3) (Fig. 10). Three Mesoproterozoic (1.21 to 1.53 Ga) zircon
354
grains with U-Pb ages from 1.21 to 1.53 Ga have similar εHf(t) values (-5.0 to -2.3) and
355
TDM2 (2.32-2.45 Ga), whereas the 1.59 Ga zircon grain has low εHf(t) value (-18.1) and 13
Page 57 of 105
356
old TDM2 (3.41 Ga). All Paleoproterozoic zircon grains, except for the 1.81 Ga zircon
357
grain that has a positive( εHf(t) =value of 7.9), have negative εHf(t) values (-8.6 to -1.9)
358
and TDM2 (2.59-3.16 Ga).
359
361
4.2.2. The Mukeng Fm Sample WN1012, a
ip t
360
greyish-green phyllitic tuffaceous sandstone from the
Mukeng Fm, contains dominantly Neoproterozoic (798-988 Ma) zircon grains, with
363
three peaks at ca. 832830, 860-870 and 910 913 Ma (Fig. 8). Pre-Neoproterozoic
364
grains have a wide range of ages between 1.18 and 2.70 Ga. Neoproterozoic grains are
365
generally euhedral with well developed concentric oscillatory zoning (Fig. 7b).
us
cr
362
Neoproterozoic zircon grains from sample WN1012 have variable εHf(t) values
367
(-9.0 to 14.0) and TDM2 ( 862-2401 Ma). Pre-Neoproterozoic zircon grains have
368
evolved and scattered Hf isotopic compositions, with εHf(t) values from -3.8 to 7.5 and
369
TDM2 from 1.82 to 3.10 Ga (Fig. 10).
M
an
366
4.2.3. The Niuwu Fm
Ac ce pt e
371
d
370
372
Sample WN1025, a grey tuffaceous sandstone from the Niuwu Fm, contains
373
zircon grains mostly with Neoproterozoic ages ranging from (805 to 965 Ma). Four of
374
the six Pre-Neoproterozoic grains cluster between 1.95 and 2.08 Ga and the other two
375
have ages of 2.42 and 2.58 Ga. Neoproterozoic grains have uniform internal structure
376
with typical concentric oscillatory zoning (Fig. 7c).
377
The Neoproterozoic zircon grains have variable εHf(t) values (-17.2 to 14.2) and
378
TDM2 (842-2809 Ma) (Fig. 10). The Paleoproterozoic to late Archean zircon grains
379
have relatively constant εHf(t) values from -9.2 to -0.6 and TDM2 from 2.71 to 3.30 Ga.
380
14
Page 58 of 105
381
4.2.4. The Zhentou Fm Sample WN1086 from the Zhentou Fm contains nearly half (48%) of
383
Neoproterozoic (mostly between 801 and 860 Ma) zircon grains. Pre-Neoproterozoic
384
zircon grains cluster at groups of 1.64-1.75 Ga, 1.98-2.01 Ga and 2.44-2.58 Ga (Fig.
385
8).
ip t
382
Neoproterozoic (798-965 Ma) zircon grains have a wide range of εHf(t) values
387
from -21.5 to 10.6 and TDM2 from 1.06 to 3.04 Ga (Fig. 10). Six late to
388
mid-Paleoproterozoic zircon grains (1.64-2.14 Ga) have εHf(t) values (-12.8 to -5.1)
389
and TDM2 (2.85-3.27 Ga). Zircon grains with ages between 2.33 and 2.76 Ga have a
390
wide range of εHf(t) values of-7.6 to 10.7 and TDM2 of 2.43-3.47 Ga.
an
391 392
4.3. The Nanhua SystemSequence
Formatted: Line spacing: Double
M
393 394
us
cr
386
4.3.1. The Dongmen Fm
Two coarse-grained sandstones (WW153 and WW197) from the Dongmen Fm
396
contain zircons with similar detrital age distribution dominated by two major age
397
groups at 1.80 to 2.10 Ga and 2.30 to 2.50 Ga and one sub-group of 800 to 900 Ma
398
(Fig. 8). Neoproterozoic grains are oscillatory-zoned and euhedral., whereas
399
Paleoproterozoic zircon grains are euhedral to rounded zircon grains are and partly
400
oscillatory-zoned (Figs. 6d and e).
Ac ce pt e
d
395
401
In general, mMost Neoproterozoic zircon grains from the Dongmen Fm have
402
sub-chondritic εHf(t) values scattered between -19.2 and 7.4 (Fig. 9). Nearly all
403
Pre-Neoproterozoic zircon grains have εHf(t) values falling between the evolved Hf
404
isotopic composition defined by the Hf evolution trend of juvenile material derived
405
from a depleted mantle reservoir at ca. 2.90 and 3.60 Ga (Fig. 9).
15
Page 59 of 105
406 407
4.3.2. The Xiuning Fm Detrital zircon grains of sample WN1031 from the upper part of the Xiuning Fm
409
are mostly later Archean to mid-Paleoproterozoic in age, including 2.38-2.52 Ga and
410
1.95-2.07 Ga populations, with a small number of grains clustering at 2.24-2.33 Ga
411
(Fig. 8). Neoproterozoic zircon grains range in age from 750 to 874 Ma with no
412
early-Neoproterozoic detritus (900-1000 Ma).
cr
ip t
408
Neoproterozoic zircon grains from the Xiuning Fm have highly scattered Hf
414
isotopic compositions (Fig. 10) with a wide range of εHf(t) values (-21.9 to 6.3) and
415
TDM2 (1.31-3.05 Ga). Late- to mid-Paleoproterozoic (~1.9-2.1 Ga) zircon grains have
416
εHf(t) values between -13.1 and -6.3 and TDM2 between 2.99 Ga and 3.42 Ga. 2.24-2.61
417
Ga zircon grains have scattered εHf(t) values (-18.0 to 5.1) and TDM2 (2.65-3.89 Ga).
an
us
413
M
418
5. Discussion
421 422
5.1. Constraints on the timing of deposition
423
5.1.1. The Shuangqiaoshan Group
Ac ce pt e
d
419 420
424
The Shuangqiaoshan Group was traditionally thought to be Mesoproterozoic in
425
age (1400-1000 Ma) (Huang et al., 2003; Wu, 2007), whereas a Neoproterozoic
426
depositional age has been widely inferred recently (870-820 Ma) (Gao et al., 2008;
427
Wang et al., 2008; Zhao et al., 2011). Combined with previously published data, new
428
age data in this study can provide tighter constraints on the age of the Shuangqiaoshan
429
Group. All Neoproterozoic zircons have oscillatory-zoning and euhedral shape
430
without metamorphic rim and fractures (Fig. 6). The Shuangqiaoshan Group
431
underwent only low greenschist-facies metamorphism and all Neoproterozoic zircons
16
Page 60 of 105
have high Th/U ratios (generally >0.5), indicating detrital zircons were not
433
modifiedare pristine and can constrain the maximum depositional age of the
434
sediments as they represent the ages of source rocks (Fedo et al., 2003). The initial
435
deposition of the Shuangqiaoshan Group can beis constrained by a SHRIMP zircon
436
U-Pb age of 831±5 Ma for a thin-bedded bentonite in the middle part of the Henyong
437
Fm, lowermost Shuangqiaoshan Group (Gao et al., 2008). The youngest detrital
438
zircons from the Jilin Fm have a weighted mean age of 828 826 ± 3 Ma (2σ,
439
MSWD=2.71.18), placing the maximum deposition age for the Jilin Fm at ca. 828 Ma.
440
A maximum age of 829 ± 5 Ma, bracketed by an inter-bedded bentonite in the Anlelin
441
Fm (Gao et al., 2008), indicates immediate deposition of the Anlelin Fm after the Jilin
442
Fm. One sample from the upper part of the Anlelin Fm contains the youngest zircons
443
with a weighted mean age of 818 ± 4 3 Ma (2σ, MSWD=0.141.12), indicating a
444
depositional age of ca. 818 Ma or younger. The Xiushui Fm contains detrital zircons
445
as young as 800 Ma and the youngest zircons yield a weighted mean age of 815 ± 2 5
446
Ma (2σ, MSWD=1.20.32), consistent with the minimum depositional age of 819 ± 9
447
Ma bracketed by the Jiuling granitic intrusion (Li et al., 2003a).
449
cr
us
an
M
d
Ac ce pt e
448
ip t
432
5.1.2. The Xikou Group
450
The Xikou Group is intruded by ca. 824 Ma granitic plutons (Li et al., 2003a; Wu
451
et al., 2006). The youngest zircons of sample WN1004 from the Banqiao Fm have a
452
weighted mean age of 833 ± 5 8 Ma (2σ, MSWD=0.0724), bracketing the initial
453
depositional age to the mid-Neoproterozoic. The youngest zircon group of sample
454
WN1012 give a weighted mean age of 830 ± 3 4 Ma (2σ, MSWD=1.180.45),
455
constraining the maximum deposition age of the Mukeng Fm at ca. 830 Ma. Sample
456
WN1025 from the uppermost Niuwu Fm have the youngest zircons with a weighted
17
Page 61 of 105
mean age of 827 ± 53 Ma (2σ, MSWD=0.58), indicating the Niuwu Fm formed at ca.
458
827 Ma or younger. There are only two single-grains with younger ages of 805 and
459
808 Ma, but these are inconsistent with inferred ages from field relationship. Because
460
of the similar lithological assemblage and sedimentary environment, as well as being
461
separated from underlying strata by a similar regional uncomformityunconformity
462
(Ma et al., 1999; Zhang et al., 1999), the Zhentou Fm can be correlated with the
463
Xiushui Fm and is regarded as the upper part of the Xikou Group. Apart from two
464
exceptionally young (789 and 801 Ma) zircons, the youngest zircons have a weighted
465
mean age of 817 ± 3 4 Ma (2σ, MSWD=0.7633), providing a maximum constraint on
466
the deposition of the Zhentou Fm. Therefore, the Xikou Group likely formed at
467
833-817 Ma.
an
us
cr
ip t
457
468
5.2. Age groups and source terrains
M
469 470
Among 888 zircon grains analyzed, 692 analyses are considered to be significant
472
in terms of concordance and have meaningful U-Pb ages. There are four principal age
473
groups (Fig. 11. Table 1): (1) Neoproterozoic zircons with ages between 750 and 980
474
Ma; (2) Early-Mesoproterozoic to Late-Paleoproterozoic zircons (1.50-1.80 Ga); (3)
475
Mid-Paleoproterozoic zircons defining a maximum frequency group at 1.80-2.10 Ga;
476
and (4) Early-Paleoproterozoic to Late-Archean zircons (2.35-2.75 Ga).
478
Ac ce pt e
477
d
471
Formatted: Line spacing: Double
5.2.1. Neoproterozoic (750 -980 Ma) zircons
479
All Shuangqiaoshan and Xikou samples have dominantly Neoproterozoic zircons
480
in spite of slightly diverse maximum age frequency. The early-Neoproterozoic
481
(980-860 Ma) detritus may be sourced from the ca. 970 Ma adakitic granite within the
18
Page 62 of 105
northeastern Jiangxi ophiolite (Li and Li, 2003; Gao et al., 2009), the 930-890 Ma
483
volcanic rocks of the Shuangxiwu Group (Chen et al., 2009a; Li et al., 2009), ca. 910
484
Ma granitoid plutons intruding the Shuangxiwu Group (Ye et al., 2007) or ca. 880 Ma
485
obduction-type granite within the NE Jiangxi ophiolite (Li et al., 2008a). 860-820 Ma
486
detritus makes up one of the most important age populations. These zircons have
487
morphology and internal structure of igneous origin and the age spectrum is similar to
488
that recorded by a series of igneous events in the eastern Jiangnan Orogen.
489
Sporadically exposed igneous rocks, the ca. 848 Ma Gangbian alkaline complex (Li et
490
al., 2010b), ca. 849 Ma Shenwu dolerite (Li et al., 2008b) and ca. 850 Ma
491
Zhenzhushan volcanic rocks (Li et al., 2010a) may have provided the relevant detritus.
492
However, the abundance of detrital zircons in this study and inherited zircons within
493
this age range observed from younger granites and volcanic rocks (Wu et al., 2006;
494
Zheng et al., 2008), demonstrate the wider spread of sources that were largely
495
reworked by later processes (Wu et al., 2006; Zheng et al., 2008) or eroded into
496
associated basins.
498
cr
us
an
M
d Ac ce pt e
497
ip t
482
5.2.2. Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) zircons
499
Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) material is an
500
important part of the Pre-Neoproterozoic detritus in the analyzed samples but does not
501
match any proximal source in the eastern Jiangnan Orogen (Fig. 11). Although tThe
502
1.5-1.7 Ga Dahongshan Group (Greentree and Li, 2008) and the Dongchuan Group
503
(Zhao et al., 2010b; Wang et al., 2011a) in the western Yangtze Block likely
504
deposited at 1.5-1.7 Ga, may be the distal source of the 1.50-1.80 Ga detritus.
505
Nevertheless, the cumulative age histogram constructed from these published data
19
Page 63 of 105
506
shows that the dominant ages from the western Yangtze Block are ca. 150 million
507
younger than those of the detrital zircons in this study (Fig. 11).
508 509
5.2.3. Mid-Paleoproterozoic (1.80-2.10 Ga) zircons There are only a few zircon grains with ages of 1.82-1.90 Ga. This age spectrum
511
is similar to the ages of the 1.86-1.89 Ga granitic and metamorphic rocks in the
512
eastern Cathaysia Block (Yu et al., 2009, 2011), but the Cathaysia Block is
513
questionable as the source because of the paucity of such detritus. The
514
mid-Paleoproterozoic age spectrum (1.95-2.08 Ga) is similar to the ages of major
515
metamorphic events recorded by ca. 1.97 Ga metapelite in the Kongling terrane
516
(Zhang et al., 2006a) and ca. 2.00 Ga granulite in the Dabie orogenic belt (Sun et al.,
517
2008; Wu et al., 2008). However, typical core-rim internal structure and low Th/U
518
ratios of most of the metamorphic zircons in both terranes are entirely different from
519
the igneous characteristics of the detrital zircons in this study. In addition, the
520
granulites contain abundant 2.70-2.90 Ga inherited igneous zircons (Sun et al., 2008;
521
Wu et al., 2008), which are absent in the Neoproterozoic sediments, demonstrating the
522
poor connection between these sources and the basin. The ultimate sources for these
523
grains can be the Tianli schist and/or nowadays unexposed crustal fragments, because
524
both sources contain a prominent mid-Paleoproterozoic age population (Fig. 11)
525
(Zheng et al., 2006a; Li et al., 2007).
527
cr
us
an
M
d
Ac ce pt e
526
ip t
510
5.2.4. Early-Paleoproterozoic to Late-Archean (2.35-2.75 Ga ) zircons
528
A significant early-Paleoproterozoic (2.37-2.50 Ga) age peak is present, whereas
529
tectonothermal activities at 2.30-2.50 Ga are not known in the Yangtze Block. Similar
20
Page 64 of 105
530
to Archean detritus, the ultimate sources for the early-Paleoproterozoic materials were
531
likely the Tianli schist and unexposed basement (Fig. 11). The Archean (2.51-2.76 Ga) zircons are significantly younger than the 2.9-3.3 Ga
533
Kongling TTG of the Yangtze Block but similar to the age-frequency peak at
534
2.51-2.70 Ga of the Mesoproterozoic Tianli schist of the eastern Yangtze Block (Li et
535
al., 2007) (Fig. 11). Thus the Tianli schist may have likely provided the recycled
536
Archean material to the Neoproterozoic sediments. In addition, abundant 2.50-2.60
537
Ga xenocrystic zircons in lamproite are used to suggest a widespread Archean
538
basement of the Yangtze Block (Zheng et al., 2006a), reflecting this nowadays
539
unexposed Archean basement was available to supply detritus to the Neoproterozoic
540
sedimentary basin in the eastern Jiangnan Orogen during Neoproterozoic.
541
5.2.5. Temporal and spatial variations in provenance
M
542
an
us
cr
ip t
532
To examine the statistical relationship between the zircon age populations of
544
various samples, the Kolmogorov-Smirnov (K-S) test (Massey Jr, 1951) was applied
545
using the Excel macro developed by the Arizona LaserChron Center. The K-S test
546
suggests a strong correlation among samples WW176, WW236, WN1012 and
547
WN1015 (Fig. 12 and Table 2), all of which have a relatively uniform zircon
548
provenance dominated by Neoproterozoic detritus with ages ranging from 810 to 860
549
Ma. Sample WN1004 seems to be less correlated with other samples (Table 2), which
550
is mainly due to the variable amounts of relative contribution of similarly old detritus
551
(Fig. 12). Apart from the prominent 810-860 Ma zircons, samples from the Xikou
552
Group also contain significant addition of 860-980 Ma materials, roughly consistent
553
with the present geographic framework of the eastern Jiangnan Orogen considering
554
that the 860-980 Ma materials were largely derived from volcanic rocks of the
Ac ce pt e
d
543
21
Page 65 of 105
Shuangxiwu Group. Sample WW247 from the Xiushui Fm has a detrital zircon
556
pattern similar to sample WN1086 from the Zhentou Fm (Fig. 12), both of which have
557
dominant Neoproterozoic detritus with several equal age peaks between ca. 800 and
558
900 Ma (Fig. 8) accompanied by significantly increased Pre-Neoproterozoic zircons,
559
indicating that the Xiushui and Zhentou Fms formed in a more open setting with a
560
broad source region than other formations of the Shuangqiaoshan and Xikou Groups.
ip t
555
The Nanhua System Sequence is inferred to have accumulated in a passive
562
margin setting where the sedimentary detritus was mainly sourced from the interior
563
part of the Yangtze Block (Jiang et al., 2003), as reflected by the significant
564
contribution from cratonic components with Paleoproterozoic ages clustering at
565
1.90-2.10 Ga and 2.40-2.50 Ga.
an
us
cr
561
566
5.3. Magmatic and crustal evolution
M
567 568
U-Pb ages of detrital zircons reveal three major episodes of magmatic activity at
570
2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma with some minor magmatic events at
571
2.70-2.50 Ga, 1.90-1.50 Ga and 800-750 Ma.
573
Ac ce pt e
572
d
569
5.3.1. Reworking of pre-existing crust in the late Archean to Mesoproterozoic
574
Most late Archean to early Paleoproterozoic (~2.70-2.30 Ga) zircons have
575
sub-chondritic εHf(t) values (-20.4 to -0.2) and old TDM2 ( 2.97-4.20 Ga), suggesting
576
this period of magmatism was characterized by reworking of a common pre-existing
577
continental crust. One 2.46 Ga igneous zircon from WW153 has the oldest TDM2 age
578
of 4.20 Ga, indicating the generation of continental crust as old as 4.20 Ga in the
579
source terrain. Thirteen Six zircons with ages between 2.29 49 Ga and 2.69 61 Ga
22
Page 66 of 105
580
have εHf(t) values of (0.54.6 to 10.7) near to the depleted mantle (DM) reservoir,
581
reflecting minor addition of juvenile continental crust at this period. Most Mid-Paleoproterozoic (1.90-2.10 Ga) zircons have TDM2 ages (2.80-3.30 Ga)
583
similar to the 2.70-2.30 Ga zircons discussed above (Figs. 9 and 10), suggesting that
584
both periods of magmatism involved reworking of comparably evolved but
585
age-restricted source regions. One zircon grain has a TDM2 age of 1.94 Ga identical to
586
its U-Pb age of 1.92 Ga, and high εHf(t) value (9.9), indicating possibly minor addition
587
of juvenile crust at this period.
cr
ip t
582
The majority of late Paleoproterozoic zircons with negative εHf(t) values ( -16.1 to
589
-1.0) and old TDM2 ages ( 2.51-3.42 Ga) suggest recycling origin of the
590
zircon-saturated magma. Two zircons with ages of 1.62 and 1.81 Ga have positive
591
εHf(t) values (4.3 and 7.9) and TDM2 ages (1.98 and 2.05 Ga), again supporting the
592
possibility of minor addition of juvenile materials between 1.90 and 2.10 Ga.
M
an
us
588
Early Mesoproterozoic zircons (1.40-1.60 Ga) with scattered εHf(t) values (-18.1 to
594
13.8) and TDM2 ages (1.43-3.41 Ga), with the majority at 2.15-2.37 Ga) suggest
595
recycling of variable amounts of pre-existing continental crust. Nearly all late
596
Mesoproterozoic (1.00-1.30 Ga) zircons have εHf(t) values (-9.7 to 6.9) significantly
597
lower than the depleted mantle reservoir (Figs. 9 and 10), implying reworking of older
598
crust with insignificant addition of juvenile crust during this period.
600
Ac ce pt e
599
d
593
5.3.2. Early-Neoproterozoic addition of juvenile crust
601
The dominantly early Neoproterozoic (750-980 Ma) zircon detritus has
602
significant implications. Chondritic to near DM Hf isotopic compositions (εHf(t) values
603
mostly from 0 to 16.4) (Figs. 9 and 10) reveal formationaddition of juvenile material
604
at 860-980 Ma. A few 860-980 Ma zircons with negative εHf(t) values (-17.0 to -2.0)
23
Page 67 of 105
and old TDM2 ages (1.91-2.81 Ga) suggest involvement of reworked older crust. The
606
most important predominant detrital zircons between 810-860 Ma have a wide range
607
of εHf(t) values (-21.5 to 15.8) and TDM2 ages (739-3041 Ma) (Figs. 9 and 10),
608
demonstrating derivation of magmas from both depleted mantle reservoir and older
609
continental curst. Variable εHf(t) values and TDM2 ages imply variable degrees of
610
mixing between juvenile magmas and ancient crust, possibly due to the assimilation
611
during magma ascent. Addition of juvenile crustal materials likely became
612
insignificant after ca. 805 Ma (Figs 9 and 10) and as most 750-805 Ma detrital zircons
613
have sub-chondritic Hf isotopic compositions, e.g. low εHf (t) values (-21.9 to -2.5) and
614
old TDM2 ages (1.85-3.05 Ga).
an
us
cr
ip t
605
615 616
5.4. Implications for the tectonic evolution of the eastern Jiangnan Orogen
618
M
617
Formatted: Line spacing: Double
5.4.1. Tectonic setting of the basin
The obtained age spectra with predominantThe dominant Neoproterozoic
620
zircons and statistically insignificant older continental-derived zircons in all
621
Shuangqiaoshan (except WW247 from the Xiushui Fm) and Xikou samples (except
622
WN1086 from the Zhentou Fm) are typical of sediments accumulated in basins
623
associated with a magmatic arc (DeGraaff-Surpless et al., 2002; Goodge et al., 2004)
624
but are inconsistent with continental rift or passive margin sedimentation, which
625
would be expected to have the majority of detritus derived from exhumed older
626
continental crust (Goodge et al., 2002, 2004). The nearly syn-magmatic sedimentation
627
and relatively euhedral igneous zircons suggest a nearby source within the eastern
628
Jiangnan Orogen for the Neoproterozoic detritus and reflect fast erosion and
629
deposition of newly formed igneous rocks. etritus derived from the Cathaysia Block
Ac ce pt e
d
619
24
Page 68 of 105
would be expected to contain Grenville (extending from 1300 to 950 Ma) materials
631
(Wang et al., 2010a and reference therein) (Fig. 11). Such Grenville materials do not
632
appear to be present in the Shuangqiaoshan and Xikou Groups, The Cathaysia Block
633
could be a possible source if it was connected with the Yangtze Block during the
634
sedimentation of the Shuangqiaoshan and Xikou Groups. However, detritus derived
635
from the Cathaysia Block would be expected to contain Grenville (extending from
636
1300 to 950 Ma) materials (Wang et al., 2010a and reference therein), which are
Formatted: Font: Not Italic, Font color: Auto
637
scarce in the studied samples (Fig. 11), suggesting the Cathaysia Block was separated
Formatted: Font: Not Italic, Font color: Auto
638
from the Yangtze Block and could not provide detritus to the Shuangqiaoshan and
639
Xikou Groups. Although the Cathaysia Block could likely provide 1000-800 Ma
640
detritus (Li et al., 2005; Yu et al., 2007; Shu et al., 2011) to the nearby eastern
641
Yangtze Block if both were juxtaposed, detritus derived from the Cathaysia Block
642
would be expected to contain Grenville (extending from 1300 to 950 Ma) materials
643
(Wang et al., 2010a and reference therein) (Fig. 11). Such Grenville materials do not
644
appear to be present in the Shuangqiaoshan and Xikou Groups, suggesting the
645
Cathaysia and Yangtze Blocks were not sutured during the deposition of these strata.
646
Additionally, Hf isotopic compositions of the early Neoproterozoic (~810-860 Ma)
647
zircons reveal variable degrees of assimilation of pre-existing older crust to the
648
juvenile magma, the mixing process of which is typical of granitoid rocks in
649
modern-day magmatic arc settings (Tatsumi and Kogiso, 2003). Chemical
650
compositions of the siliciclastic rocks from the Shuangqiaoshan and Xikou Groups
651
have features similar to sedimentary rocks accumulated inat active continental
652
margins (Huang et al., 2003; Zhang et al., 2010), consistent with the magmatic arc
653
setting bracketedsuggested by the detrital zircons. Sandstone from both the
654
Shuangqiaoshan and Xikou Groups are compositionally immature with dominantly
Ac ce pt e
d
M
an
us
cr
ip t
630
25
Page 69 of 105
poorly-sorted volcanic lithic and feldspar detritus and minor detrital quartz (Ma et al.,
656
2001; Huang et al., 2003), suggesting sedimentary detritus derived exclusively from
657
volcanic sources in a magmatic arc setting (Dickinson, 1970). The Xiushui Fm in
658
northwestern Jiangxi and the Zhentou Fm in southern Anhui contain thick layers of
659
conglomerate, pebbly sandstone and coarse sandstone at their bases (Fig. 5),
660
representing syn-orogenic molasse formed in a retro-arc foreland basin at 817-815 Ma.
661
Samples WW247 from the Xiushui Fm and WN1086 from the Zhentou Fm have
662
additional input of Pre-Neoproterozoic detritus (Fig. 8), likely derived from the
663
uplifted older basement complexes.
us
cr
ip t
655
664
5.4.2. An integrated tectonic model
an
665
Our new dataset together with published data allow us to propose a modified
667
model for the tectonic evolution of the eastern Jiangnan Orogen (Fig. 13). A
668
NW-dipping oceanic subduction zone along what is the present-day eastern margin of
669
the Yangtze Block is possible on the basis of the 930-890 Ma arc volcanic rocks in the
670
Shuangxiwu Group (Li et al., 2009) and the presence of 930-890 Ma detrital zircons
671
with chondritic to DM-like Hf isotopic compositions (Figs. 9 and 10). Arc-continent
672
collision probably took place at 880-860 Ma as bracketed by the emplacement of 880
673
± 19 Ma obduction-type granites (Li et al., 2008a) and the 858 ± 11 Ma Huaiyu
674
ophiolite (Shu et al., 2006). A back-arc basin was initialed above the continental crust
675
as marked by the 848-824 Ma supra-subduction zone ophiolite in southern Anhui (Li
676
et al., 1997; Ding et al., 2008; Zhang et al., 2012a). Volcanic rocks in this period were
677
largely eroded and transported to the back-arc and retroarc foreland basins due to
678
subsequent orogenic uplift. Abundant 860-810 detrital zircons have Hf isotopic
679
compositions, indicating mixture between juvenile crust and continental basement
Ac ce pt e
d
M
666
26
Page 70 of 105
(Figs. 9 and 10) and revealing providing support for the existence of an extensive
681
magmatic arc during this period. The basin began to form at ca. 830 Ma and was filled
682
with a set of volcanic-terrigenous arenopelitic flysch sequence with some
683
well-preserved primary sedimentary structures, such as cross- and graded-bedding and
684
scoured based sequences (Fig. 5), indicative of a quiet and low-energy depositional
685
environment (Wu, 2007; Zhang et al., 2010). Greywacke of the flysch sequence
686
contains poorly-sorted and subangular fractions of lithic fragments and less feldspar
687
and quartz (Wu, 2007). Along with basin evolution, the sedimentary strata contained
688
additional interlayered calc-alkaline felsic-intermediate volcanic lava of arc-affinity
689
that strongly supports a magmatic arc setting (Zhang et al., 2010). The Niuwu and
690
Anlelin Fms are characterized by repeated sedimentary cycles of pebbly sandstone
691
and shale (Fig. 5), typical of flysch formed in a back-arc basin. Basin closure was
692
marked by the 828-819 Ma syn-collisional cordierite-bearing peraluminous granitoids
693
(CPG) (Li et al., 2003a; Zhong et al., 2005; Wang et al., 2006) and subsequent
694
syn-orogenic uplift which led to basin restriction and the formation of a regional
695
unconformity. As a result, a retro-arc foreland basin was formed, in which the Xiushui
696
and Zhentou Fms were deposited with detritus from both remnant magmatic arc and
697
uplifted basement. Subsequently, the emplacement of extensive 805-760 Ma bimodal
698
volcanic sequences (Wang et al., 2011b) and 780-770 Ma K-rich calc-alkaline
699
granitoids (KCG) (Zheng et al., 2008; Xue et al., 2010) in the eastern Jiangnan
700
Orogen record post-collisional orogenic rifting, which is marked by remelting of
701
pre-existing rocks as recorded by the sub-chondritic Hf isotopic compositions of most
702
805-750 Ma detrital zircons (Figs. 9 and 10).
Ac ce pt e
d
M
an
us
cr
ip t
680
703 704
5.4.3. Possible reconstruction of the Yangtze Block in Rodinia
27
Page 71 of 105
It has long been debated if the Yangtze Block was in the central Rodinia, likewise
706
whether or not the Jiangnan Orogen is part of a Grenville Orogen (Li et al., 1995,
707
2008d; Zhou et al., 2002, 2008; Yan et al., 2002; Zheng, 2004; Yu et al., 2008; Wang
708
and Zhou, 2012). However, the back-arc to retro-arc foreland setting for the 830-815
709
Ma Shuangqiaoshan and Xikou Groups does not support an intra-cratonic setting.
710
Neither coeval mantle plume rift system nor a Grenville Orogen recorded in
711
southeastern Australia and western Laurentia (Li et al., 2008d) exist in the eastern
712
Jiangnan Orogen. In addition, the facts that the Jiangnan Orogen is somewhat younger
713
than the Grenville Orogen and that there is insignificant Grenville magmatism and no
714
Grenville juvenile crust recorded by detrital zircons from the strata in the Jiangnan
715
Orogen suggest that this orogen cannot be correlated with the worldwide Grenville
716
Orogen and that the Yangtze Block was unlikely located between Australia–East
717
Antarctica and Laurentia as proposed by Li et al. (1995). However, source analysis
718
suggests interior rather than extraneous detritus supplied to the widespread 830-815
719
Ma sedimentary sequences of the Jiangnan Orogen (Wang et al., 2010a and this study),
720
suggesting that the Yangtze Block was likely located along the margin of Rodinia as
721
an individual continental block rather than in the centre of the supercontinent.
723 724 725 726 727 728 729
cr
us
an
M
d
Ac ce pt e
722
ip t
705
6. Conclusions
Principal conclusions of this study are as follows: (1). The previously thought Mesoproterozoic sedimentary sequences in the
eastern Yangtze Block actually formedwas deposited betwee at 833 and -815 Ma. (2). The 833-815 Ma sedimentary sequence represents a sedimentary cycle from a back-arc to retro-arc foreland basin.
28
Page 72 of 105
730 731
(3). and tThe juxtaposition of the Yangtze and Cathaysia Blocks likely lasted to ca. 815 Ma or even later. (34). Three major episodes of magmatic activities at 2.50-2.35 Ga, 2.10-1.90 Ga
733
and 980-800 Ma are recognized in the source areas of the Neoproterozoic sedimentary
734
basin, whereas the Grenville (1.30-1.00 Ga) magmatism was insignificant.
ip t
732
(45). No Grenville juvenile crust in the eastern Yangtze Block is identified. The
736
most important generation of juvenile crust occurred at early Neoproterozoic
737
(~980-810 Ma) in combination with reworked older crust at 860-810 Ma.
continent rather than in the centre of the supercontinent Rodinia.
740
Acknowledgements
M
741 742
us
(5). The Yangtze Block was likely located along the margin as an individual
an
739
cr
735
738
This study was supported by the Research Grant Council of Hong Kong SAR,
744
China (HKU 707210P), National Natural Science Foundation of China (NSFC
745
41272212) and the oversea famous professor program (MS2011ZGDZ (BJ) 019). We
746
would like to thank Dr. Jianfeng Gao for his help with field trip and Prof. Liang Qi for
747
the LA-ICPMS work. Thanks go to Dr. Jean Wong and Dr. Hongyan Geng for help
748
with Lu-Hf analysis and Lily Chiu for CL imaging. Constructive reviewers from
749
Journal Editor Professor Randall Parrish and two anonymous reviewers have
750
substantially improved the performance, especially the presentation of U-Pb-Hf
751
isotopic results, of this manuscript and are kindly acknowledge.
Ac ce pt e
d
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752
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753 754
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Wang, W., Wang, F., Chen, F., Zhu, X., Xiao, P., Siebel, W., 2010b. Detrital Zircon
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Ages and Hf‐Nd Isotopic Composition of Neoproterozoic Sedimentary Rocks in the Yangtze Block: Constraints on the Deposition Age and Provenance. The Journal of Geology 118, 79-94. Wang, W., Zhou, M.-F., 2012. Sedimentary records of the Yangtze Block (South China) and their correlation with equivalent Neoproterozoic sequences on adjacent continents. Sedimentary Geology 265–266, 126-142. Wang, W., Zhou, M.-F., Yan, D.-P., Li, J.-W., 2012b. Depositional age, provenance, and tectonic setting of the Neoproterozoic Sibao Group, southeastern Yangtze Block, South China. Precambrian Research 192-195, 107-124. Wang, X.L., Shu, L.S., Xing, G.F., Zhou, J.C., Tang, M., Shu, X.J., Qi, L., Hu, Y.H., 2011b. Post-orogenic extension in the eastern part of the Jiangnan orogen: Evidence from ca 800-760 Ma volcanic rocks. Precambrian Research in press. Wang, X.L., Zhao, G.C., Zhou, J.C., Liu, Y., Hu, J., 2008. Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen. Gondwana Research 14, 355-367. Wang, X.L., Zhou, J.C., Griffin, W.L., Wang, R.C., Qiu, J.S., O’Reilly, S.Y., Xu, X., Liu, X.M., Zhang, G.L., 2007. Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: Dating the assembly of the Yangtze and Cathaysia Blocks. Precambrian Research 159, 117-131. Wang, X.L., Zhou, J.C., Qiu, J.S., Zhang, W.L., Liu, X.M., Zhang, G.L., 2006. LA-ICP-MS U-Pb zircon geochronology of the Neoproterozoic igneous rocks from Northern Guangxi, South China: Implications for tectonic evolution. Precambrian Research 145, 111-130. Wang, Y.J., Zhang, F.F., Fan, W.M., Zhang, G.W., Chen, S.Y., Cawood, P.A., Zhang, A.M., 2011c. Tectonic setting of the South China Block in the early Paleozoic: resolving intracontinental and ocean closure models from detrital zircon U-Pb geochronology. Tectonics 29. Wu, R.X., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Zhang, S.B., Liu, X.M., Wu, F.Y., 2006. Reworking of juvenile crust: Element and isotope evidence from Neoproterozoic granodiorite in South China. Precambrian Research 146, 179-212. Wu, X.H., 2007. Rediscuss of Shuangqiaoshan group. Resources survey & environment (in Chinese with English abstract) 28, 95-105. Wu, Y.B., Zheng, Y.F., Gao, S., Jiao, W.F., Liu, Y.S., 2008. Zircon U-Pb age and trace element evidence for Paleoproterozoic granulite-facies metamorphism and Archean crustal rocks in the Dabie Orogen. Lithos 101, 308-322. Xia, X.P., Sun, M., Zhao, G.C., Wu, F.Y., Xu, P., Zhang, J., Luo, Y., 2006. U-Pb and Hf isotopic study of detrital zircons from the Wulashan khondalites: Constraints on the evolution of the Ordos Terrane, Western Block of the North China Craton. Earth and Planetary Science Letters 241, 581-593. Xue, H.M., Ma, F., Song, Y.Q., Xie, Y.P., 2010. Geochronology and geochemisty of the Neoproterozoic granitoid association from eastern segment of the Jiangnan orogen, China: Constraints on the timing and process of amalgamation between the Yangtze and Cathaysia blocks. Acta Petrologica Sinica 26, 3215-3244. (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Malpas, J., 2002. Where was South China located in the reconstruction of Rodinia. Earth Sci. Frontiers 9, 249-256 (in Chinese with English abstract).
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1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053
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Yan, D.P., Zhou, M.F., Song, H.L., Wang, X.W., Malpas, J., 2003. Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China). Tectonophysics 361, 239-254. Ye, M.F., Li, X.H., Li, W.X., Liu, Y., Li, Z.X., 2007. SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc along the southeastern margin of the Yangtze Block. Gondwana Research 12, 144-156. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhang, M., Wang, R.C., Jiang, S.Y., Shu, L.S., 2008. Where was South China in the Rodinia supercontinent?:: Evidence from U-Pb geochronology and Hf isotopes of detrital zircons. Precambrian Research 164, 1-15. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhou, M.F., Zhang, M., Shu, L.S., 2010. Components and episodic growth of Precambrian crust in the Cathaysia Block, South China: Evidence from U-Pb ages and Hf isotopes of zircons in Neoproterozoic sediments. Precambrian Research 181, 97-114. Yu, J.H., O'Reilly, Y.S., Wang, L.J., Griffin, W.L., Jiang, S.Y., Wang, R.C., Xu, X.S., 2007. Finding of ancient materials in Cathaysia and implication for the formation of Precambrian crust. Chinese Science Bulletin 52, 11-18. Yu, J.H., O’Reilly, S.Y., Zhou, M.F., Griffin, W.L., Wang, L.J., 2011. U–Pb geochronology and Hf–Nd isotopic geochemistry of the Badu Complex, Southeastern China: Implications for the Precambrian crustal evolution and paleogeography of the Cathaysia Block. Precambrian Research. doi:10.1016/j.precamres.2011.07.014. Yu, J.H., Wang, L.J., O'Reilly, S.Y., Griffin, W.L., Zhang, M., Li, C.Z., Shu, L.S., 2009. A Paleoproterozoic orogeny recorded in a long-lived cratonic remnant (Wuyishan terrane), eastern Cathaysia Block, China. Precambrian Research 174, 347-363. Zhang, S.B., Wu, R.X., Zheng, Y.F., 2012a. Neoproterozoic continental accretion in South China: geochemical evidence from the Fuchuan ophiolite in the Jiangnan orogen. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.010 Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006a. Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China. Precambrian Research 151, 265-288. Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006b. Zircon U-Pb age and Hf isotope evidence for 3.8 Ga crustal remnant and episodic reworking of Archean crust in South China. Earth and Planetary Science Letters 252, 56-71. Zhang, X.H., Zhang, Z.J., Guo, J.Q., Xiong, Q.H., 1999. Stratigraphy and sedimentary sequences of the upper part of the Proterozoic Shuangqiaoshan Group in Xiushui-Wuning area, Jiangxi. Journal of Stratigraphy 23, 71-77. (in Chinese with English Abstract). Zhang, Y.J., Zhou, X.H., Liao, S.B., Zhang, X.D., Wu, B., Wang, C.Z., Yu, M.G., 2010. Neoproterozoic crustal composition and orogenic process of the Zhanggongshan area, Anhui-Jiangxi. Acta Geological Sinia 84, 1401-1427. (in Chinese with English Abstract). Zhang, Y.Z., Wang, Y.J., Fan, W.M., Zhang, A.M., Ma, L.Y., 2012b. Geochronological and geochemical constraints on the metasomatised source for the Neoproterozoic (∼825 Ma) high-Mg volcanic rocks from the Cangshuipu area (Hunan Province) along the Jiangnan Domain and their
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tectonic implications. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.003 Zhao, G.C., Cawood, P., 1999. Tectonothermal evolution of the Mayuan Assemblage in the Cathaysia Block; implications for Neoproterozoic collision-related assembly of the South China Craton. American Journal of Science 299, 309-339. Zhao, J.-H., Zhou, M.-F., 2008. Neoproterozoic adakitic plutons in the northern margin of the Yangtze Block, China: Partial melting of a thickened lower crust and implications for secular crustal evolution. Lithos 104, 231-248. Zhao, J.-H., Zhou, M.-F., Zheng, J.-P., Fang, S.-M., 2010a. Neoproterozoic crustal growth and reworking of the Northwestern Yangtze Block: Constraints from the Xixiang dioritic intrusion, South China. Lithos 120, 439-452. Zhao, J.H., Zhou, M.F., 2007a. Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): Implications for subduction-related metasomatism in the upper mantle. Precambrian Research 152, 27-47. Zhao, J.H., Zhou, M.F., 2007b. Neoproterozoic adakitic plutons and arc magmatism along the western margin of the Yangtze Block, South China. The Journal of Geology 115, 675-689. Zhao, J.H., Zhou, M.F., Yan, D.P., Zheng, J.P., Li, J.W., 2011. Reappraisal of the ages of Neoproterozoic strata in South China: no connection with the Grenvillian orogeny. Geology 39, 299-302. Zhao, X.F., Zhou, M.F., Li, J.W., Sun, M., Gao, J.F., Sun, W.H., Yang, J.H., 2010b. Late Paleoproterozoic to early Mesoproterozoic Dongchuan Group in Yunnan, SW China: Implications for tectonic evolution of the Yangtze Block. Precambrian Research 182, 57-69 Zheng, J.P., Griffin, W.L., O’, Reilly, S.Y., 2006a. Widespread Archean basement beneath the Yangtze craton. Geology 34, 417-420. Zheng, Y.-F., Zhao, Z.-F., Wu, Y.-B., Zhang, S.-B., Liu, X., Wu, F.-Y., 2006b. Zircon U-Pb age, Hf and O isotope constraints on protolith origin of ultrahigh-pressure eclogite and gneiss in the Dabie orogen. Chemical Geology 231, 135-158. Zheng, Y.F., 2003. Neoproterozoic magmatic activity and global change. Chinese Science Bulletin 48, 1639-1656. Zheng, Y.F., 2004. Position of South China in configuration of Neoprotero-zoic supercontinent. Chinese Science Bulletin 49, 751-753. Zheng, Y.F., Wu, R.X., Wu, Y.B., Zhang, S.B., Yuan, H., Wu, F.Y., 2008. Rift melting of juvenile arc-derived crust: Geochemical evidence from Neoproterozoic volcanic and granitic rocks in the Jiangnan Orogen, South China. Precambrian Research 163, 351-383. Zheng, Y.F., Zhang, S.B., Zhao, Z.F., Wu, Y.B., Li, X.H., Li, Z.X., Wu, F.Y., 2007. Contrasting zircon Hf and O isotopes in the two episodes of Neoproterozoic granitoids in South China: Implications for growth and reworking of continental crust. Lithos 96, 127-150. Zhong, Y.F., Ma, C.Q., She, Z.B., Lin, G.C., Xu, H.J., Wang, R.J., Yang, K.G., Liu, Q., 2005. SHRIMP U-Pb Zircon Geochronology of the Jiuling Granitic Complex Batholith in Jiangxi Province. Earth Science-Journal of China University of Geosciences 30, 685-691. (in Chinese with English abstract). Zhou, G.Q., 1989. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high
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temperature-high pressure metamorphic rocks. Journal of Southeast Asian Earth Sciences 3, 237-247. Zhou, J.C., Wang, X.L., Qiu, J.S., 2008. Is the Jiangnan Orogenic Belt a Grenvillian Orogenic Belt: some problems about the Precambrian Geology of South China. Geological Journal of China Universities 14, 64-72. (in Chinese with English Abstract). Zhou, M.F., Kennedy, A.K., Sun, M., Malpas, J., Lesher, C.M., 2002a. Neoproterozoic arc-related mafic intrusions along the northern margin of South China: Implications for the accretion of Rodinia. The Journal of Geology 110, 611-618. Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006a. The Yanbian Terrane (Southern Sichuan Province, SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze Block. Precambrian Research 144, 19-38. Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y.Q., Ding, J., 2002b. SHRIMP zircon geochronological and geochemical evidence for Neoproterozoic arc-related magmatism along the western margin of the Yangtze Block, South China. Earth and Planetary Science Letters 196, 51-67. Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A., 2006b. Subduction-related origin of the 750 Ma Xuelongbao adakitic complex (Sichuan Province, China): Implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth and Planetary Science Letters 248, 286-300. Zhu, X.Y., Chen, F., Li, S.Q., Yang, Y.Z., Nie, H., Siebel, W., Zhai, M.G., 2011. Crustal evolution of the North Qinling terrain of the Qinling Orogen, China: Evidence from detrital zircon U-Pb ages and Hf isotopic composition. Gondwana Research 20, 194-204.
1182
d
1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181
Figure captions.
1184
Fig.1. Distribution of Precambrian units in the eastern segment of the Jiangnan orogen
1185
(modified after (Ma et al., 2002; Wang et al., 2011b). Inserted map on the top
1190
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1183
1191
plagiogranite (Ye et al., 2007; Chen et al., 2009b); 4- ca. 848 Ma Gangbian
1186 1187 1188 1189
left showing location of the Jiangnan orogen in the South China Craton. Blue dash line shows the boundary between provinces. AH: Anhui province; JX: Jiangxi province; ZJ: Zhejiang province. 1-ca.970-880 Ma northern Jiangxi ophiolitic complex (Li and Li, 2003; Li et al., 2008a); 2-ca. 930-890 Ma Shuangxiwu volcanic rocks (Li et al., 2009); 3-ca. 910-900 Ma Pingshui
38
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1192
alkaline complex (Li et al., 2010b); 5- ca. 850 Ma Zhenzhushan volcanic rocks
1193
(Li et al., 2010a)
1194
1196
Fig. 2. Sketch map showing the distribution of the Shuangqiaoshan Group and Nanhua system sequence in the northwestern Jiangxi Province.
1197
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1195
Fig. 3. Sketch map showing the distribution of the Xikou Group as well as other
1199
Neoproterozoic units in the southern Anhui Province. Faults in this figure
1200
refers to legend in Fig. 2.
us
cr
1198
1201
Fig. 4. Stratigraphy of the major Neoproterozoic sedimentary units in the eastern
1203
Yangtze Block. The Zhentou Fm is tentatively considered as the upper part of
1204
the Xikou Group, considering its similarity with the Xiushui Fm in the upper
1205
part of the Shuangqiaoshan Group. The columns are not strictly to scale. Stars
1206
and italic numbers represent sample location relative to stratigraphic column
1207
and sample numbers. Bold italic numbers represent the reported ages of
1209
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1208
an
1202
volcanic tuffs; see text for details and discussion.
1210
Fig. 5. Out crop features of represented sedimentary units.Structures of marine
1211
sediments investigated during this study: (a) Parallel bedding and rhythmic
1212 1213 1214
layers between reddish siltstone and sandstone in the Jilin Formation; (b) partial Bouma sequences in the Anlelin Fm; (c) Grading Graded and cross bedding in the Anlelin Fm; (d) boundary between the Anlelin and Xiushui
1215
Fms. The sandstone interlayers in the silty slate are lenticular which may be
1216
result of wave current
in the Banqiao Formation; (e) lenticular and cross
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1217
bedding developed between grey siltstone and slate; (f) Wavy contoured bed
1218
with different wavelength and slump structure in the Mukeng Fm; (g) grading
1219
bedding developed in the Niuwu Fm; (h) coarse quartz sandstone from the
1220
Xiuning Fm.
ip t
1221
Fig. 6. Concordia diagrams showing results of U-Pb dating of plots of detrital zircon
1223
grains from the Shuangqiaoshan Group and Dongmen Fm. Inserted diagrams
1224
show representative CL images and weighted meanconcordant ages (for
1225
ages<1.0 Ga,
1226
ages are presented) of the youngestindividual analyzed grains.
Pb/238U ages are presented and for ages>1.0 Ga,
207
Pb/206Pb
an
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206
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1222
1227
Fig. 7. Concordia diagrams showing results of U-Pb dating Concordia plots of detrital
1229
zircon grains from the Xikou Group and Xiuning Formation. Inserted
1230
diagrams show representative CL images and concordant ages (for ages<1.0
1231
Ga,
1232
presented) of individual analyzed grains.weighted mean ages of the youngest
1234
Formatted: Font: Not Italic, Superscript Formatted: Font: Not Italic, Superscript
Pb/238U ages are presented and for ages>1.0 Ga,
207
Pb/206Pb ages are
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1233
Formatted: Font: Not Italic, Superscript
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1228
Formatted: Font: Not Italic, Superscript
grains.
1235
Fig. 8. Relative probability versus age diagramsDetrital zircons age histograms. The
Formatted: Font: Not Italic
1236
reds curves show the frequency of individual zircon populations (for details
Formatted: Font: Not Italic
see text). Each Some samples isare plotted at two scales to highlight the
Formatted: Font: (Default) Times New Roman, 12 pt, Not Italic, Font color: Auto, Pattern: Clear
1237 1238 1239
distribution of Neoproterozoic ages. Samples are presented in stratigraphic order.
1240
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1241
Fig. 9. Hf isotopic compositions of detrital zircons from Shuangqiaoshan Group and
1242
Dongmen Fm. (a) εHf(t) values versus U-Pb ages; (b) TDM2 Histograms ofversus
1243
U-Pb ages. DM : delepted mantle ; CHUR : chondritic uniform reservoir ; 3.2
1244
Ga crust means materials were derived from delepted mantle at 3.2 Ga and
1245
evolved with average continental crust 176Lu/177Hf of 0.015.
ip t
Formatted: Font: Not Italic, Superscript Formatted: Font: Not Italic, Superscript
1246
Fig. 10. Hf isotopic compositions of detrital zircons from Xikou Group and Xiuning
1248
Fm. (a) εHf(t) values versus U-Pb ages; (b) Histograms of TDM2 versus U-Pb
1249
ages. The meaning of DM, CHUR and 3.2 Ga crust is explained in caption of
1250
Fig. 9.
an
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1247
1251
Fig. 11. Probability plots of detrital zircons from Neoproterozoic sedimentary units in
1253
the eastern Yangtze Block and their potential sources. The number of y-axis
1254
represents the number of analyses. Data sources for Pre-Neoproterozoic units:
1255
the Kongling complex, (Qiu et al., 2000; Zhang et al., 2006a, b; Gao et al.,
1256
2011); the Tianli schist, (Li et al., 2007); Xenocrystic zircons from lamproite,
1258 1259 1260 1261 1262 1263
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1257
M
1252
(Zheng et al., 2006a); the western Yangtze Block, (Greentree et al., 2006; Greentree and Li, 2008; Zhao et al., 2010b; Wang et al., 2011a); the Cathaysia Block, (Li, 1997; Wan et al., 2007; Li et al., 2010c; Yu et al., 2011). Data sources for Neoproterozoic unit: the southeastern Yangtze Block, (Li and Li, 2003; Li et al., 2003b, 2008b, 2009, 2010b; Wang et al., 2006; Wu et al., 2006; Zheng et al., 2008); the western Yangtze Block, (Zhou et al., 2002b, 2006a; Li et al., 2003b; Zhao and Zhou, 2007a, b); the northern Yangtze Block, (Zhou et
1264
al., 2002a, 2006b; Zhao and Zhou, 2008; Zhao et al., 2010a), the Cathaysia
1265
Block, (Wan et al., 2007; Li et al., 2010c; Shu et al., 2011).
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1266 1267 1268
Fig. 12. Cumulative probability plots of the zircon age data for Neoproterozoic siliciclastic sequences of the eastern Yangtze Block.
1269
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discussion.
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1271
Fig. 13. Sequential tectonic evolution of the eastern Jiangnan orogen. See text for
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Southern Anhui
us
The Xikou Group WN1004 WN1012
>2500 Ma
1021±31(3,0.16) 1392±32(2,0.11)
833±8(4,0.04) 860±4(17,0.35) 884±3(27,1.12) 906±6(9,0.19) 932±6(8,0.59)
1551±72(4,3.4)
WN1025
WN1086
The Nanhua Sequence WN1031 751±8(3,0.007) 777±7(6,0.99) 804±6(7,0.49)
817±4(12,0.33) 830±4(26,0.45) 827±5(10,0.28) 846±3(28,0.75) 840±3(22,0.61) 854±11(3,0.1) 860±4(19,0.67) 862±6(6,0.06) 870±5(9,0.03) 884±(12,1.13) 884±8(12,0.11) 886±14(2,0.06) 913±8(5,0.06） 906±16(1) 960±11(3,0.34) 932-965(3)
1419±35(2,0.004) 1567±33(2,0.007)
1457-1514Ma(2)
1720±26(3,0.24)1620±26(3,0.04) 1658±23(5,0.36) 1764±28(2,0.014) 1741±29(3,0.11) 1785±22(5,0.56）1803±28(3,0.62) 2083±87(5,31) 1945±110(4,8.2)1993±12(33,0.8) 2027±19(21,3.5)2058±156(1) 2015±42(1) 2040±76(4,3.7) 1991±27(4,0.07) 2369-2449(2) 2397±22(23,3.1）2366±17(13,2.1) 2379±44(1) 2461±38(1) 2445±13(8,0.31)2495±40(1) 2487±42(1) 2424±42(1) 2479±26(9,2.1) 2594±50(1) 2545±35(4,0.83) 2566±38(1) 2576±38(1) 2582±33(3,0.51) 2683±34(1) 2727±36(1) 2694±48(1) 2702-2759(2)
pt
~16002500
1253±38(3,1.8) 1139-1517(3)
ce
~10001600
ed
M
an
Table 1. Age groups for analyzed detrital zircons from the eastern Jiangnan Orogen Age Northwestern Jiangxi groups The Shuangqiaoshan Group The Nanhua Sequence WW236 WW176 WW247 WW153 WW197 ~750753±8(2,0.06) 1000 792±9(5,0.53) 801±5(7,0.54) 818±6(6,0.06) 815±5(9,0.32) 817±9(3,0.17) 823±8(4,0.08) 826±3(34,1.18) 830±5(8,0.42) 850±4(23,0.32) 843±3(24,1.12) 844±8(3,0.07) 865±7(7,0.41) 872±5(13,0.27) 869±6(6,0.83) 879±7(4,0.45) 895±10(3,0.23) 897±9(3,0.62) 898±6(6,1.04) 895±9(3,0.47) 946±22(5,2.3) 950±21(5,2.3) 931±6(6,0.32)
ip t
Table 1
1999±12(25,1.4) 2319±34(9,4.1） 2462±19(12,1.8) 2611±46(1)
Ac
Note: Weighted mean ages of each group of ages according to the age peaks shown in Figure 8. Only concordant ages (90%
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Table 2
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Table 2. K-S P-values using error in the CDF WW236 WW176 WW247 WN10-02 WN10-12 WN10-25 WN10-86 WN10-31 WW153 WW197 WW236 0.998 0.000 0.000 0.026 0.157 0.001 0.000 0.000 0.000 WW176 0.998 0.011 0.000 0.118 0.633 0.011 0.000 0.000 0.000 WW247 0.000 0.011 0.032 0.095 0.000 0.079 0.000 0.000 0.000 WN10-02 0.000 0.000 0.032 0.006 0.000 0.000 0.000 0.000 0.000 WN10-12 0.026 0.118 0.095 0.006 0.097 0.012 0.000 0.000 0.000 WN10-25 0.157 0.633 0.000 0.000 0.097 0.001 0.000 0.000 0.000 WN10-86 0.001 0.011 0.079 0.000 0.012 0.001 0.000 0.000 0.000 WN10-31 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.312 0.299 WW153 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.312 0.597 WW197 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.299 0.597 K-S: Kolmogorov-Smirnov test (Massey Jr, 1951); P values: the probability, if the test statistic really were distributed as it would be under the null hypothesis, of observing a test statistic the one actually observed; CDF: Cumulative Distribution Function.
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Figure 2 Click here to download high resolution image
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S0301-9268(13)00166-6 http://dx.doi.org/doi:10.1016/j.precamres.2013.05.013 PRECAM 3779
To appear in:
Precambrian Research
Received date: Revised date: Accepted date:
27-8-2012 17-4-2013 21-5-2013
Please cite this article as: Wang, W., Zhou, M.-F., Yan, D.-P., Li, L., Malpas, J., Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern Jiangnan Orogen, South China, Precambrian Research (2013), http://dx.doi.org/10.1016/j.precamres.2013.05.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights (for review)
Highlights: ► Combining U-Pb and Lu-Hf data of detrital zircons from the Neoproterozoic sedimentary rocks to constrain the tectonic evolution of the eastern Jiangnan Orogen.
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► The Jiangnan orogen lasted until ca. 830-815 Ma or even later.
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► The Shuangqiaoshan and Xikou Groups formed in a back-arc to retro-arc foreland basin at ca. 831~815 Ma and ca. 833~817 Ma, respectively.
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► There was no Grenville (ca. 1000-1300 Ma) juvenile crust in the eastern Yangtze Block.
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► The most important generation of juvenile crust occurred at ca. 980-810 Ma.
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*Manuscript Click here to view linked References
1
Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern
2
Jiangnan Orogen, South China
3 4
6
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Wei Wang1, Mei-Fu Zhou1,*, Dan-Ping Yan2, Liang Li3, John Malpas1
us
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5
10
an
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1
13
China
14
2
15
Geosciences, Beijing 100083, China
16
3
17
Academy of Sciences, Guiyang 550002, China
19 20
M
d
State Key Lab of Geological Process and Mineral Resources, China University of
State Key Lab of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
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Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR,
21
*
22
E-mail: [email protected]
23
Phone: +852 2857 8251
24
Fax: +852 2517 6912
Corresponding author:
25
Page 2 of 105
Abstract: Precambrian sedimentary sequences in the eastern Jiangnan Orogen, South
27
China, include the Neoproterozoic Shuangqiaoshan and Xikou Groups and the
28
overlying Nanhua Sequence. U-Pb ages of detrital zircons provide tight constraints on
29
the deposition of the Shuangqiaoshan and Xikou Groups at 831-815 Ma and 833-817
30
Ma, respectively. Rocks from the lower parts of these strata contain dominantly
31
Neoproterozoic detritus with a pronounced age peak at 830-850 Ma, interpreted to be
32
derived from a magmatic arc that has been mostly eroded. This magmatic arc was
33
associated with sedimentation characterized by compositionally immature sediments
34
with dominant early-Neoproterozoic (~860-810 Ma) zircons that have variable εHf(t)
35
values of -21.5 to 14.8. The upper parts of these strata, uncomfortably underlain by
36
the
37
pre-Neoproterozoic detritus, representing sediments accumulated in a retro-arc
38
foreland basin associated with the Jiangnan Orogen.
units,
are
molasse-type
assemblages
with
additional
input
of
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low
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Combining four samples from the Nanhua Sequence, three major magmatic
40
activities at 2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma in the source areas are
41
identified. The older two events are characterized by reworking of pre-existing
42
continental crust. Grenville magmatism and juvenile crust were insignificant in the
43
eastern Jiangnan Orogen. Neoproterozoic zircons reflect generation of juvenile crust
44
at 980-860 Ma, involvement of both juvenile and recycled materials at 860-810 Ma
45
and reworking of pre-existing crust at 805-750 Ma, corresponding to island arc,
46
continental magmatic arc and post-collisional rifting stages in the eastern Jiangnan
47
Orogen.
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48 49
Keywords: U-Pb ages, Lu-Hf isotopes, detrital zircons, Jiangnan Orogen, South
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China
1 Page 3 of 105
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1. Introduction
52
The Jiangnan Orogen in South China witnessed the amalgamation of the Yangtze
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and Cathaysia Blocks. Recent studies of sedimentary and igneous rocks have
55
demonstrated that the Jiangnan Orogen is a Neoproterozoic rather than
56
Mesoproterozoic tectonic unit, but the timing and evolution of this orogen are still
57
matters of debate (Wang et al., 2006, 2007, 2012b; Zheng et al., 2008; Li et al., 2009;
58
Zhao et al., 2011). The Jiangnan Orogen was thought to be part of the worldwide
59
Grenville Orogen, formed by the collision between the Yangtze and Cathaysia Blocks
60
(Li et al., 2007, 2009), followed by extensive rift-related magmatism at ca. 820 Ma
61
(Wu et al., 2006; Li et al., 2008c, 2009, 2010a; Zheng et al., 2008). On the other hand,
62
this orogeny is thought to have lasted until ca. 830 Ma or even later, followed by
63
post-extensional magmatism beginning at ca. 800 Ma (Li, 1999; Zhao and Cawood,
64
1999; Wang et al., 2006, 2011b, 2012b; Zhao et al., 2011; Zhang et al., 2012b).
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The eastern segment of the Jiangnan Orogen is crucial for the understanding of
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the orogenic cycle because it contains widespread sedimentary sequences, igneous
67
plutons and two major ophiolite belts, that witness the final amalgamation between
68
the Yangtze and Cathaysia Blocks (Li et al., 2009) (Fig.1). In past decades, numerous
69
studies examined the petrogenesis and tectonic affinity of igneous rocks (Wu et al.,
70
2006; Li et al., 2007, 2008b, 2009; Zheng et al., 2008; Zhang et al., 2012a), but
71
associated sedimentary sequences in the eastern Jiangnan Orogen are poorly
72
understood, due in part to unresolved stratigraphy, incomplete biostratigraphic data,
73
poor exposure and strong overprint by later deformation. These sedimentary
74
sequences in the eastern Jiangnan Orogen include the Shuangqiaoshan Group in
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northern Jiangxi Province and the Xikou Group in southern Anhui Province (Fig. 1),
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which were interpreted to have formed in a back-arc basin associated with
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Mesoproterozoic NW-dipping (current coordinates) oceanic subduction beneath the
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Yangtze Block (Cheng and Wang, 2000; Huang et al., 2003). However, dating results
79
of the Shuangqiaoshan Group do not support this model and it has been proposed that
80
these sequences were deposited in a retroarc foreland basin, synchronous with the
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amalgamation of the Yangtze and Cathaysia Blocks (Wang et al., 2008). More recent
82
studies suggest the Shuangqiaoshan Group likely formed at ca. 830 Ma (Gao et al.,
83
2008; Zhao et al., 2011), which is taken as the timing for the Jiangnan Orogeny (Zhao
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et al., 2011). These sequences are also suggested to have formed in an early-phase of
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rifting that post-dated the Jiangnan Orogen (Li et al., 2009) based on ca. 850 Ma
86
dolerite dykes (Li et al., 2008b) and bimodal volcanic rocks (Li et al., 2010a).
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Due to the strong later deformation of these sedimentary strata and intensive
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reworking and erosion of the pre-existing igneous provenance (Wu et al., 2006; Zheng
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et al., 2008), one possible way to examine the timing and evolution of orogenic cycles
90
is to unearth the information contained by detrital zircons (Cawood and Nemchin,
91
2001; Liu et al., 2011; Wang et al., 2011c). Detrital zircon age spectra may contain
92
information about various sources linked to eustatic, depositional and tectonic change
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(Wang et al., 2010b, 2012a), and thus can provide insight into the basin-orogen
94
coupling (Horton et al., 2010; Myrow et al., 2010). Hf isotopes of zircons can be used
95
for understanding juvenile or reworked zircon-hosting magma (Griffin et al., 2004;
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Xia et al., 2006; Zheng et al., 2006b, 2007; Zhu et al., 2011; Liu et al., 2012; Wang et
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al., 2012a), thought to be one of the most discriminating features among plume, rift
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and arc-related magmatism (Zheng et al., 2008).
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In this paper, we present the first integrated study of U-Pb ages and Hf isotopic
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compositions of detrital zircons from the major Neoproterozoic sedimentary strata in
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the eastern Jiangnan Orogen. This new dataset allows us to refine the depositional age
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of the hosting strata and to track provenance changes. The provenance characteristics
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can help define the relationship between sedimentation and tectonism and potential
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link to the configuration of the supercontinent Rodinia.
2. Geological background
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The South China Craton comprises the Yangtze and Cathaysia Blocks, with the
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Jiangnan Orogen being the southeastern part of the Yangtze Block. The Cathaysia
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Block has voluminous Phanerozoic igneous rocks with rarely exposed Precambrian
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rocks (Yu et al., 2010). Metamorphic complexes in the eastern Cathaysia Block were
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traditionally thought to be Paleo-Mesoproterozoic to Neoarchean basement (Li, 1997),
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but recent studies suggest that these complexes formed in the Neoproterozoic or even
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younger (Wan et al., 2007; Li et al., 2010c). A Paleoproterozoic orogen is inferred on
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the basis of abundant Paleoproterozoic granites and metamorphic rocks in the eastern
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Cathaysia Block (Yu et al., 2009). Precambrian rocks in the Yangtze Block are
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sporadically exposed and include Archean Tonalite–Trondhjemite–Granodiorite (TTG)
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in the north (Qiu et al., 2000; Gao et al., 2011) and Paleoproterozoic strata in the west
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(Sun et al., 2009; Zhao et al., 2010b), whereas Neoproterozoic sedimentary sequences
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and igneous plutons are widespread (Zhou et al., 2002b; Li et al., 2003a, b; Wang et
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al., 2006, 2010b; Zhao and Zhou, 2007a; Zheng et al., 2008; Zhao et al., 2011). The
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sedimentary cover of the Yangtze Block consists mainly of folded Paleozoic and
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Lower Mesozoic strata formed in a shallow marine environment (Yan et al., 2003).
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Precambrian rocks in the eastern Jiangnan Orogen include the Mesoproterozoic
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Tianli schist (Li et al., 2007), early-Neoproterozoic Shuangxiwu volcanic-clastic
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sequences (Ye et al., 2007; Li et al., 2009), mid-Neoproterozoic sedimentary strata 4 Page 6 of 105
(Gao et al., 2008; Zhao et al., 2011), igneous plutons (Zhong et al., 2005; Wu et al.,
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2006; Li et al., 2008b, 2009, 2010b; Zheng et al., 2008), and ophiolitic complexes
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(Bai et al., 1986; Zhou, 1989; Zhang et al., 2012a). Mid-Neoproterozoic sedimentary
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strata including the Shuangqiaoshan and Xikou Groups in the eastern Jiangnan
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Orogen are overlain unconformably by a post-orogenic extensional basin deposits as
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the Nanhua Sequence. Granitoid plutons intruding the sedimentary sequences are
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represented by the Jiuling pluton in NW Jiangxi (Li et al., 2003a; Zhong et al., 2005)
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and the Xucun, Shexian and Xiuning plutons in southern Anhui (Li et al., 2003a; Wu
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et al., 2006). The NE-SW trending ophiolite complexes are in tectonic contact with
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the Shuangqiaoshan and Xikou Groups (Bai et al., 1986).
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A stratigraphic framework of the sedimentary succession in northwestern Jiangxi and southern Anhui Provinces is outlined in Figures. 2 and 3.
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2.1. Shuangqiaoshan Group
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The Shuangqiaoshan Group consists of silty, volcanic clastic detritus that
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gradually coarsens upwards, and has partially preserved primary sedimentary
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structures. Based on primary sedimentary structure and lithology, this strata is divided
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into the Hengyong, Jilin, Anlelin and Xiushui Formations (Fms) from the base
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upward (Fig. 4) (BGMRJX, 1996).
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The Hengyong Fm comprises of grey to reddish, feldspar-lithic sandstone,
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feldspar-quartz sandstone and siltstone. The sandstone consists dominantly of
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subangular to subrounded, lithic fragments, with lesser amounts of quartz and feldspar.
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Graded bedding, banded bedding, and scour and slump marks are well developed.
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The Jilin Fm is conformable with both its underlying and overlying strata and
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contains mostly purplish-red, silty slate, usually referred to as a red bed sequence. 5 Page 7 of 105
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Within the silty slate are interbeds of siltstone and sandstone (Fig. 5a). Cross-bedding,
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graded bedding and partial Bouma sequences are common. The Anlelin Fm is widespread in northern Jiangxi province and is composed of
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thick grey to charcoal grey flysch with some tuffaceous siltstone and slate. In addition
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to greywacke, there are fine-grained, tuffaceous beds, feldspar-, quartz-rich sandstone
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and tuffaceous lithic-quartz sandstone. Lithic components include andesite, siliceous
159
rocks, granite, basalt and silty mudstone (Wu, 2007). Cross-bedding, parallel bedding,
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scour and slump marks, and partial Bouma sequences are well developed (Figs. 5b
161
and c).
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The Xiushui Fm, overlying the Anlelin Fm, has a basal ca. 2.5 m thick layer of
163
conglomerate (Fig. 5d). Conglomerate contains gravels of variable sizes that are
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parallel to the orientation of the sedimentary layer. In some cases, this conglomerate
165
layer is absent and the bottom of the Xiushui Fm is marked by a 40-m-thick layer of
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greyish-white, pebbly sandstone or quartz conglomerate. The upper part of the
167
Xiushui Fm consists mainly of greyish-white, grey or green yellow, tuffaceous slate
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interbedded with tuff. Cross-bedding, parallel-bedding and partial Bouma sequences
169
are also common in this unit.
171 172 173
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2.2. Xikou Group
Widely distributed in southern Anhui Province, the Xikou Group has experienced
174
weak to strong deformation and low-greenschist facies metamorphism, whereas
175
graded and crossing bedding are perfectly preserved (BGMRAH, 1984). The Xikou
176
Group is divided into the Zhangqian, Banqiao, Mukeng and Niuwu Fms upwards (Fig.
177
4) (BGMRAH, 1984). The Zhentou Fm unconformably overlies the Niuwu Fm and is
6 Page 8 of 105
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tentatively interpreted as the upper part of the Xikou Group in this study, because of
179
its similarity with the Xiushui Fm of the Shuangqiaoshan Group. The Zhangqian Fm comprises green sericite-quartz schist, arenaceous to silty
181
phyllite and sericite-chlorite-quartz schist. Original pelitic rocks have been
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metamorphosed to phyllite during regional metamorphism, resulting in well
183
developed phyllitic structure. Spotted or banded magnetite is common and interlayers
184
of basic volcanic rocks are also sporadically present.
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Dark to grey phyllite, phyllitic slate and feldspar quartz sandstone are the
186
dominant rocks of the Banqiao Fm that overlies the Zhangqian Fm conformably.
187
Rhythmic layering between sandstone and slate are commonly observed and lenticular
188
sandstone is developed probably due to current lamination (Fig. 5e). Feldspar and
189
quartz with a few lithic detritus are the dominant clastic fragments, which is hosted by
190
cemented fine-grained sericite and clay minerals.
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The Mukeng Fm is composed of thick grey to greyish-green silt- to arenaceous-
192
siliciclastic rocks dominated by fine-grained siltstone and sericite-chlorite slate,
193
whereas fine-grained sandstone occurs as interlayers in the slate. Graded and parallel
194
bedding, are well preserved (Fig. 5f). Contorted bed with varying wavelength formed
195
by wave current and slump structure are observed (Fig. 5f), suggesting fast
196
sedimentation in a turbulent environment.
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The Niuwu Fm is typical of turbiditic deposition, consisting of thick layer of
198
greyish-green to greyish-purple litharenite and thin layer of medium-grained
199
sandstone. Gravel-bearing sandstone and coarse- to medium-grained sandstone form
200
well developed graded bedding (Fig. 5g), typical of turbidite. Features of shallow
201
water and storm flow deposits are observed in the upper part of the Niuwu Fm, where
202
ashy black slate is interbedded with thick layers of sandstones.
7 Page 9 of 105
Unconformably underlain by the Niuwu Fm, the Zhentou Fm contains
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conglomerate, gravel-bearing sandstone and gravel-bearing silty slate from the base to
205
the top. Angular to subangular gravels of the stratigraphically basal conglomerate are
206
poorly-sorted with diameters ranging between 1 and 8cm and are dominated by
207
fragments of slate, silicolite, granite and quartz. Gravel-bearing sandstone and slate
208
from the upper Zhentou Fm contain gravels smaller and less than the conglomerate
209
and quartzite, volcanic rocks and siltstone are the dominant rock fragments.
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211 212
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2.3. Nanhua Sequence
The Nanhua Sequence is a set of glacial sedimentary rocks corresponding to the
214
Cryogenian System defined by the International Commission on Stratigraphy (Plumb,
215
1991). The Nanhua Sequence includes the lower Dongmen and Xiuning Fms and the
216
upper Nantuo and Leigongwu Fms. The Dongmen and Xiuning Fms, correlated with
217
the pre-glacial Liantuo Fm in the central Yangtze Block, are composed largely of a
218
clastic succession unconformably underlain by the Shuangqiaoshan and Xikou Groups,
219
respectively. The basal parts of these units consist of conglomerate and coarse
220
quartzose sandstone, formed in an alluvial fan or fluvial environment. The Nantuo and
221
Leigongwu Fms, are widespread in the entire Yangtze Block, are composed of
222
diamictite typical of tillite formed during the Neoproterozoic ―snowball Earth‖ event
223
(Zheng, 2003).
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224 225 226
3. Sampling and analytical methods
227
Ten samples were selected across major stratigraphic units for zircon dating in
228
order to constrain depositional ages, provenance and tectonic setting of the
8 Page 10 of 105
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sedimentary basin. Zircon was separated using standard heavy-liquid and magnetic
230
separation from ca. 5 Kg samples. Zircon separates were mounted in epoxy and
231
polished. U-Pb isotope analysis of zircon was performed by LA-ICP-MS at the State Key
233
Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
234
Academy of Sciences, Guiyang. A GeoLasPro laser-ablation system (Lamda Physik,
235
Gottingen, Germany) and Agilent 7700x ICP-MS (Agilent Technologies, Tokyo,
236
Japan) were combined for the experiments. The 193 nm ArF excimer laser,
237
homogenized by a set of beam delivery systems, was focused on the zircon surface
238
with the fluence of 10J/cm2. The ablation protocol employed a spot diameter of 32 µm
239
at 5 Hz repetition rate for 45 seconds (equating to 225 pulses). Helium was applied as
240
a carrier gas to allow efficient transportation of aerosol to the ICP-MS. Zircon 91500
241
was used as the primary standard to correct elemental fractionation. Meanwhile,
242
zircon GJ-1 (Jackson et al., 2004) and Plešovice (PL, Sláma et al., 2008) were
243
analyzed as unknown samples for quality control. Trace element compositions of
244
zircon were external calibrated against NIST SRM 610 with
245
standard. Raw data reduction was performed off-line by ICPMSDataCal (Liu et al.,
246
2010) and the results were reported with 2σ errors. Reported uncertainties (2σ) of the
247
206
248
(2 SD%) of standard zircon 91500 during the analytical session and the within-run
249
precision of each analysis (2 SE%; standard error) (c.f. Gerdes and Zeh. 2006, 2009).
250
Common Pb correction was corrected using the MS Excel program ―ComPbcorr#
251
3.15”(Andersen 2002). Data were processed using the ISOPLOT program (Luding,
252
2003). The analytical results of standard and reference materials are presented in
253
Supplementary Table 1.The concordant ages of analyzed GJ-1 (601 ± 17 Ma, 2σ,
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232
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Zr as the secondary
Pb/238U ratio were propagated by quadratic addition of the external reproducibility
9 Page 11 of 105
254
MSWD=1.3) and PL (334.2 ± 7.5 Ma, 2σ, MSWD=2.9) are consistent with the
255
reported or recommended values (GJ-1: 599.8 ± 1.7 Ma, 2σ, Jackson et al., 2004; PL:
256
337.13 ± 0.37 Ma, 2σ, Sláma et al., 2008). Hf isotopic analysis of zircons were conducted using a Resonetics Resolution
258
M-50 193nm excimer laser ablation system, attached to a Nu Plasma HR
259
multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) at the
260
University of Hong Kong. Hf isotopes were obtained with a beam diameter of 55 μm,
261
pulse rate of 10 Hz and energy density of 15 J/cm2. Atomic masses 172 to 179 were
262
simultaneously measured in a static-collection mode. Isobaric interference of
263
with
264
Instrumental mass bias correction of Yb isotope ratios were normalized to 172Yb/173Yb
265
of 1.35274 (Chu et al., 2002) and Hf isotope ratios to 179Hf/177Hf of 0.7325 (Patchett
266
et al., 1981) using an exponential law. A relationship between Yb and Hf of βYb
267
=0.872βHf are obtained and used for the mass bias offset. Interference of
176
268
176
Lu isotope
269
and using a recommended
270
2001). Due to insignificant contribution of signal intensity of 176Lu on 176Hf (generally
271
<1%), the mass bias of Lu isotopes (βLu) can be assumed to be identical to βHf (c.f.
272
lizuka and Hirata, 2005). Quality control was made by measuring zircon standard
273
91500 and GJ-1 for the unknown samples during the analyses to evaluate the
274
reliability of the analytical data (Supplementary Table 2).
Hf was corrected against the
176
176
Yb
Yb/172Yb ratio of 0.5886 (Chu et al., 2002).
d
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257
Ac ce pt e
Hf was corrected by measuring the intensity of the interference-free 176
175
Lu with
Lu/175Lu ratio of 0.02655 (Machado and Simonetti,
275 276 277
4. Analytical results
278
10 Page 12 of 105
279
Results of U-Pb dating are present in Supplementary Table 3 and concordant
280
diagrams (Figs. 6 and 7). Detrital zircons with concordant U-Pb ages (with
281
concordance between 90-110%) were selected for in-situ Hf isotopic analyses and the
282
results are given in Supplementary Table 4.
4.1.The Shuangqiaoshan Group
286
4.1.1. The Jilin Fm
cr
284 285
ip t
283
Sample WW236, a reddish medium-grain sandstone from the Jilin Fm,
288
contains a predominant population of Neoproterozoic zircon grains with two major
289
age peaks at ca. 826 and ca. 850 Ma and three sub-peaks at ca. 870, 895 and 950 Ma
290
(Fig. 8). Pre-Neoproterozoic zircon grains are rare, with ages grouping at 1.15-1.26
291
Ga, 1.76-1.76 Ga and 1.87-2.22 Ga. One Archean zircon grain has a 207Pb/206Pb age of
292
2.59 Ga. Generally, all zircon grains have oscillatory zoning but are variably rounded
293
(Fig. 6a).
an
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Neoproterozoic zircon grains have highly variable εHf(t) values (-16.8 to 14.8) and
295
two stage hafnium model age (TDM2) (781-2758 Ma) (Fig. 9). Two Mesoproterozoic
296
zircon grains have identical ages but different εHf(t) values (3.3 and 10.8) and TDM2
297
ages (1.84 and 1.38 Ga). Five Paleoproterozoic zircon grains have variable εHf(t) values
298
(-8.1 to 7.2) and TDM2 ages (2.19-2.95 Ga).
299 300
4.1.2. The Anlelin Fm
301
Sample WW176 is a combination of chips from a series of thick layers of
302
fine-medium grained siltstones in the middle Anlelin Fm. Neoproterozoic (795-978
303
Ma) euhedral and oscillatory-zoned (Fig. 6b) grains are the dominant population and
304
have two major age peaks at ca. 818 Ma and ca. 843 Ma (Fig. 8). Nine 11 Page 13 of 105
207
Pb/206Pb ages scattering from1.14 Ga to 2.46 Ga.
305
Pre-Neoproterozoic zircons have
306
These zircon grains are generally subhedral to rounded with partly preserved
307
oscillatory zoning (Fig. 6b). Mid-Neoproterozoic (795-850 Ma) zircon grains have positive εHf(t) values (1.2 to
309
15.1) and TDM2 ages ranging continuously from 739 to 1653 Ma (Fig. 9). In contrast,
310
Early-Neoproterozoic (851-978 Ma) zircon grains have highly variable εHf(t) values
311
(-17.7 to 14.7) and TDM2 ages (742-2836 Ma). Two Mesoproterozoic (1.14 and 1.35
312
Ga) zircon grains have identical
313
the other Mesoproterozoic grain (1.52 Ga) has a low 176Hf/177Hf ratio of 0.281980.
Hf/177Hf ratios (0.282232 and 0.282216), whereas
us
176
cr
ip t
308
315
an
314
4.1.3. The Xiushui Fm
Sample WW247, a coarse sandstone from the Xiushui Fm, contains predominant
317
Neoproterozoic grains, with five age peaks at ca. 815, 825-835, ca. 869, ca. 900 and
318
ca. 930 Ma (Fig. 8). All Neoproterozoic grains are euhedral and have well preserved
319
oscillatory zoning. Pre-Neoproterozoic zircon grains have ages scattering from 1.01 to
320
2.68 Ga. All these zircon grains are subhedral to rounded and show partially
321
oscillatory zoning or uniform internal structure (Fig. 6c).
322
Neoproterozoic (811-935 Ma) zircon grains have variable εHf(t) values (-16.0 to 13.7)
323
and TDM2 (742-2727 Ma) (Fig. 9). Eight Mesoproterozoic (1.01-1.49 Ga) zircon grains
324
have a wide range of εHf(t) values (-9.7 to 6.9) and TDM2 (1.42-2.47 Ga). Zircon grains
325
with ages between 1.57 and 1.63 Ga have a wide range of εHf(t) values (1.0-13.8) and
326
TDM2 (1.43-2.26 Ga). Paleoproterozoic to later Archean zircon grains have negative
327
εHf(t) values (-16.1 to -2.7) and old TDM2 (2.77-3.53 Ga).
Ac ce pt e
d
M
316
328 329 330
4.2. The Xikou Group
12 Page 14 of 105
331
4.2.1. The Banqiao Fm Zircon grains from a grey phyllitic siltstone WN1004 are fairly small (<100 μm),
333
mostly euhedral and show oscillatory zoning with rare preexisting cores and
334
overgrowth rims (Fig. 7a). These detrital zircon grains are predominantly
335
Neoproterozoic and have ages ranging from 831 to 990 Ma with four age peaks at ca.
336
833, 860, 884 and 932 Ma (Fig. 8). There are also a few Meso- to Paleoproterozoic
337
zircon grains with ages scattering from 1.21 to 2.46 Ga.
cr
ip t
332
Nearly all Neoproterozoic zircon grains have positive εHf(t) values (1.2-14.0),
339
except for two zircon grains with negative εHf(t) values (-4.1 and -6.3) (Fig. 10). Three
340
Mesoproterozoic (1.21 to 1.53 Ga) zircon grainshave similar εHf(t) values (-5.0 to -2.3)
341
and TDM2 (2.32-2.45 Ga). All Paleoproterozoic zircon grains, except for the 1.81 Ga
342
zircon grain (εHf(t)=7.9), have negative εHf(t) values (-8.6 to -1.9) and TDM2 (2.59-3.16
343
Ga).
344
346
4.2.2. The Mukeng Fm
Ac ce pt e
345
d
M
an
us
338
Sample WN1012, a greyish-green phyllitic tuffaceous sandstone from the
347
Mukeng Fm, contains dominantly Neoproterozoic (798-988 Ma) zircon grains, with
348
three peaks at ca. 830, 860-870 and 913 Ma (Fig. 8). Pre-Neoproterozoic grains have
349
a wide range of ages between 1.18 and 2.70 Ga. Neoproterozoic grains are generally
350
euhedral with well developed concentric oscillatory zoning (Fig. 7b).
351
Neoproterozoic zircon grains from sample WN1012 have variable εHf(t) values
352
(-9.0 to 14.0) and TDM2 ( 862-2401 Ma). Pre-Neoproterozoic zircon grains have
353
evolved and scattered Hf isotopic compositions, with εHf(t) values from -3.8 to 7.5 and
354
TDM2 from 1.82 to 3.10 Ga (Fig. 10).
355
13 Page 15 of 105
356
4.2.3. The Niuwu Fm Sample WN1025, a grey tuffaceous sandstone from the Niuwu Fm, contains
358
zircon grains mostly with Neoproterozoic ages (805 to 965 Ma). Four of the six
359
Pre-Neoproterozoic grains cluster between 1.95 and 2.08 Ga and the other two have
360
ages of 2.42 and 2.58 Ga. Neoproterozoic grains have uniform internal structure with
361
typical concentric oscillatory zoning (Fig. 7c).
ip t
357
The Neoproterozoic zircon grains have variable εHf(t) values (-17.2 to 14.2) and
363
TDM2 (842-2809 Ma) (Fig. 10). The Paleoproterozoic to late Archean zircon grains
364
have relatively constant εHf(t) values from -9.2 to -0.6 and TDM2 from 2.71 to 3.30 Ga.
us
cr
362
366
an
365
4.2.4. The Zhentou Fm
Sample WN1086 from the Zhentou Fm contains nearly half (48%) of
368
Neoproterozoic (mostly between 801 and 860 Ma) zircon grains. Pre-Neoproterozoic
369
zircon grains cluster at groups of 1.64-1.75 Ga, 1.98-2.01 Ga and 2.44-2.58 Ga (Fig.
370
8).
d
Ac ce pt e
371
M
367
Neoproterozoic (798-965 Ma) zircon grains have a wide range of εHf(t) values
372
from -21.5 to 10.6 and TDM2 from 1.06 to 3.04 Ga (Fig. 10). Six late to
373
mid-Paleoproterozoic zircon grains (1.64-2.14 Ga) have εHf(t) values (-12.8 to -5.1)
374
and TDM2 (2.85-3.27 Ga). Zircon grains with ages between 2.33 and 2.76 Ga have a
375
wide range of εHf(t) values of-7.6 to 10.7 and TDM2 of 2.43-3.47 Ga.
376 377
4.3. The Nanhua Sequence
378 379
4.3.1. The Dongmen Fm
14 Page 16 of 105
Two coarse-grained sandstones (WW153 and WW197) from the Dongmen Fm
381
contain zircons with similar detrital age distribution dominated by two major age
382
groups at 1.80 to 2.10 Ga and 2.30 to 2.50 Ga and one sub-group of 800 to 900 Ma
383
(Fig. 8). Neoproterozoic grains are oscillatory-zoned and euhedral. Paleoproterozoic
384
zircon grains are euhedral to rounded and partly oscillatory-zoned (Figs. 6d and e).
ip t
380
Most Neoproterozoic zircon grains have sub-chondritic εHf(t) values scattered
386
between -19.2 and 7.4 (Fig. 9). Nearly all Pre-Neoproterozoic zircon grains have εHf(t)
387
values falling between the evolved Hf isotopic composition defined by the Hf
388
evolution trend of juvenile material derived from a depleted mantle reservoir at ca.
389
2.90 and 3.60 Ga (Fig. 9).
an
us
cr
385
391
4.3.2. The Xiuning Fm
M
390
Detrital zircon grains of sample WN1031 from the upper part of the Xiuning Fm
393
are mostly later Archean to mid-Paleoproterozoic in age, including 2.38-2.52 Ga and
394
1.95-2.07 Ga populations, with a small number of grains clustering at 2.24-2.33 Ga
395
(Fig. 8). Neoproterozoic zircon grains range in age from 750 to 874 Ma with no
396
early-Neoproterozoic detritus (900-1000 Ma).
Ac ce pt e
397
d
392
Neoproterozoic zircon grains have highly scattered Hf isotopic compositions (Fig.
398
10) with a wide range of εHf(t) values (-21.9 to 6.3) and TDM2 (1.31-3.05 Ga). Late- to
399
mid-Paleoproterozoic (~1.9-2.1 Ga) zircon grains have εHf(t) values between -13.1 and
400
-6.3 and TDM2 between 2.99 Ga and 3.42 Ga. 2.24-2.61 Ga zircon grains have
401
scattered εHf(t) values (-18.0 to 5.1) and TDM2 (2.65-3.89 Ga).
402 403 404
5. Discussion
405
5.1. Constraints on the timing of deposition 15 Page 17 of 105
406 407
5.1.1. The Shuangqiaoshan Group The Shuangqiaoshan Group was traditionally thought to be Mesoproterozoic in
409
age (1400-1000 Ma) (Huang et al., 2003; Wu, 2007), whereas a Neoproterozoic
410
depositional age has been widely inferred recently (870-820 Ma) (Gao et al., 2008;
411
Wang et al., 2008; Zhao et al., 2011). Combined with previously published data, new
412
age data in this study can provide tighter constraints on the age of the Shuangqiaoshan
413
Group. All Neoproterozoic zircons have oscillatory-zoning and euhedral shape
414
without metamorphic rim and fractures (Fig. 6). The Shuangqiaoshan Group
415
underwent only low greenschist-facies metamorphism and all Neoproterozoic zircons
416
have high Th/U ratios (generally >0.5), indicating detrital zircons are pristine and can
417
constrain the maximum depositional age of the sediments as they represent the ages of
418
source rocks (Fedo et al., 2003). The initial deposition of the Shuangqiaoshan Group
419
is constrained by a SHRIMP zircon U-Pb age of 831±5 Ma for a thin-bedded
420
bentonite in the middle part of the Henyong Fm, lowermost Shuangqiaoshan Group
421
(Gao et al., 2008). The youngest detrital zircons from the Jilin Fm have a weighted
422
mean age of 826 ± 3 Ma (2σ, MSWD=1.18), placing the maximum deposition age for
423
the Jilin Fm at ca. 828 Ma. A maximum age of 829 ± 5 Ma, bracketed by an
424
inter-bedded bentonite in the Anlelin Fm (Gao et al., 2008), indicates immediate
425
deposition of the Anlelin Fm after the Jilin Fm. One sample from the upper part of the
426
Anlelin Fm contains the youngest zircons with a weighted mean age of 818 ± 3 Ma
427
(2σ, MSWD=1.12), indicating a depositional age of ca. 818 Ma or younger. The
428
Xiushui Fm contains detrital zircons as young as 800 Ma and the youngest zircons
429
yield a weighted mean age of 815 ± 5 Ma (2σ, MSWD=0.32), consistent with the
Ac ce pt e
d
M
an
us
cr
ip t
408
16 Page 18 of 105
430
minimum depositional age of 819 ± 9 Ma bracketed by the Jiuling granitic intrusion
431
(Li et al., 2003a).
432 433
5.1.2. The Xikou Group The Xikou Group is intruded by ca. 824 Ma granitic plutons (Li et al., 2003a; Wu
435
et al., 2006). The youngest zircons of sample WN1004 from the Banqiao Fm have a
436
weighted mean age of 833 ± 8 Ma (2σ, MSWD=0.04), bracketing the initial
437
depositional age to the mid-Neoproterozoic. The youngest zircon group of sample
438
WN1012 give a weighted mean age of 830 ± 4 Ma (2σ, MSWD=0.45), constraining
439
the maximum deposition age of the Mukeng Fm at ca. 830 Ma. Sample WN1025 from
440
the uppermost Niuwu Fm have the youngest zircons with a weighted mean age of 827
441
± 5 Ma (2σ, MSWD=0.58), indicating the Niuwu Fm formed at ca. 827 Ma or
442
younger. There are only two single-grains with younger ages of 805 and 808 Ma, but
443
these are inconsistent with inferred ages from field relationship. Because of the
444
similar lithological assemblage and sedimentary environment, as well as being
445
separated from underlying strata by a similar regional unconformity (Ma et al., 1999;
446
Zhang et al., 1999), the Zhentou Fm can be correlated with the Xiushui Fm and is
447
regarded as the upper part of the Xikou Group. Apart from two exceptionally young
448
(789 and 801 Ma) zircons, the youngest zircons have a weighted mean age of 817 ± 4
449
Ma (2σ, MSWD=0.33), providing a maximum constraint on the deposition of the
450
Zhentou Fm. Therefore, the Xikou Group likely formed at 833-817 Ma.
Ac ce pt e
d
M
an
us
cr
ip t
434
451 452
5.2. Age groups and source terrains
453
17 Page 19 of 105
Among 888 zircon grains analyzed, 692 analyses are considered to be significant
455
in terms of concordance and have meaningful U-Pb ages. There are four principal age
456
groups (Fig. 11. Table 1): (1) Neoproterozoic zircons with ages between 750 and 980
457
Ma; (2) Early-Mesoproterozoic to Late-Paleoproterozoic zircons (1.50-1.80 Ga); (3)
458
Mid-Paleoproterozoic zircons defining a maximum frequency group at 1.80-2.10 Ga;
459
and (4) Early-Paleoproterozoic to Late-Archean zircons (2.35-2.75 Ga).
ip t
454
5.2.1. Neoproterozoic (750 -980 Ma) zircons
us
461
cr
460
All Shuangqiaoshan and Xikou samples have dominantly Neoproterozoic zircons
463
in spite of slightly diverse maximum age frequency. The early-Neoproterozoic
464
(980-860 Ma) detritus may be sourced from the ca. 970 Ma adakitic granite within the
465
northeastern Jiangxi ophiolite (Li and Li, 2003; Gao et al., 2009), the 930-890 Ma
466
volcanic rocks of the Shuangxiwu Group (Chen et al., 2009a; Li et al., 2009), ca. 910
467
Ma granitoid plutons intruding the Shuangxiwu Group (Ye et al., 2007) or ca. 880 Ma
468
obduction-type granite within the NE Jiangxi ophiolite (Li et al., 2008a). 860-820 Ma
469
detritus makes up one of the most important age populations. These zircons have
470
morphology and internal structure of igneous origin and the age spectrum is similar to
471
that recorded by a series of igneous events in the eastern Jiangnan Orogen.
472
Sporadically exposed igneous rocks, the ca. 848 Ma Gangbian alkaline complex (Li et
473
al., 2010b), ca. 849 Ma Shenwu dolerite (Li et al., 2008b) and ca. 850 Ma
474
Zhenzhushan volcanic rocks (Li et al., 2010a) may have provided the relevant detritus.
475
However, the abundance of detrital zircons in this study and inherited zircons within
476
this age range observed from younger granites and volcanic rocks (Wu et al., 2006;
477
Zheng et al., 2008), demonstrate the wider spread of sources that were largely
Ac ce pt e
d
M
an
462
18 Page 20 of 105
478
reworked by later processes (Wu et al., 2006; Zheng et al., 2008) or eroded into
479
associated basins.
480 481
5.2.2. Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) zircons Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) material is an
483
important part of the Pre-Neoproterozoic detritus in the analyzed samples but does not
484
match any proximal source in the eastern Jiangnan Orogen (Fig. 11). The 1.5-1.7 Ga
485
Dahongshan Group (Greentree and Li, 2008) and the Dongchuan Group (Zhao et al.,
486
2010b; Wang et al., 2011a) in the western Yangtze Block may be the distal source
487
of the 1.50-1.80 Ga detritus. Nevertheless, the cumulative age histogram constructed
488
from these published data shows that the dominant ages from the western Yangtze
489
Block are ca. 150 million younger than those of the detrital zircons in this study (Fig.
490
11).
493
cr
us
an
M
d
492
5.2.3. Mid-Paleoproterozoic (1.80-2.10 Ga) zircons
Ac ce pt e
491
ip t
482
There are only a few zircon grains with ages of 1.82-1.90 Ga. This age spectrum
494
is similar to the ages of the 1.86-1.89 Ga granitic and metamorphic rocks in the
495
eastern Cathaysia Block (Yu et al., 2009, 2011), but the Cathaysia Block is
496
questionable as the source because of the paucity of such detritus. The
497
mid-Paleoproterozoic age spectrum (1.95-2.08 Ga) is similar to the ages of major
498
metamorphic events recorded by ca. 1.97 Ga metapelite in the Kongling terrane
499
(Zhang et al., 2006a) and ca. 2.00 Ga granulite in the Dabie orogenic belt (Sun et al.,
500
2008; Wu et al., 2008). However, typical core-rim internal structure and low Th/U
501
ratios of most of the metamorphic zircons in both terranes are entirely different from
502
the igneous characteristics of the detrital zircons in this study. In addition, the
19 Page 21 of 105
granulites contain abundant 2.70-2.90 Ga inherited igneous zircons (Sun et al., 2008;
504
Wu et al., 2008), which are absent in the Neoproterozoic sediments, demonstrating the
505
poor connection between these sources and the basin. The ultimate sources for these
506
grains can be the Tianli schist and/or nowadays unexposed crustal fragments, because
507
both sources contain a prominent mid-Paleoproterozoic age population (Fig. 11)
508
(Zheng et al., 2006a; Li et al., 2007).
ip t
503
5.2.4. Early-Paleoproterozoic to Late-Archean (2.35-2.75 Ga ) zircons
us
510
cr
509
A significant early-Paleoproterozoic (2.37-2.50 Ga) age peak is present, whereas
512
tectonothermal activities at 2.30-2.50 Ga are not known in the Yangtze Block. Similar
513
to Archean detritus, the ultimate sources for the early-Paleoproterozoic materials were
514
likely the Tianli schist and unexposed basement (Fig. 11).
M
an
511
The Archean (2.51-2.76 Ga) zircons are significantly younger than the 2.9-3.3 Ga
516
Kongling TTG of the Yangtze Block but similar to the age-frequency peak at
517
2.51-2.70 Ga of the Mesoproterozoic Tianli schist of the eastern Yangtze Block (Li et
518
al., 2007) (Fig. 11). Thus the Tianli schist may have likely provided the recycled
519
Archean material to the Neoproterozoic sediments. In addition, abundant 2.50-2.60
520
Ga xenocrystic zircons in lamproite are used to suggest a widespread Archean
521
basement of the Yangtze Block (Zheng et al., 2006a), reflecting this nowadays
522
unexposed Archean basement was available to supply detritus to the Neoproterozoic
523
sedimentary basin in the eastern Jiangnan Orogen during Neoproterozoic.
Ac ce pt e
d
515
524 525
5.2.5. Temporal and spatial variations in provenance
526
To examine the statistical relationship between the zircon age populations of
527
various samples, the Kolmogorov-Smirnov (K-S) test (Massey Jr, 1951) was applied
20 Page 22 of 105
using the Excel macro developed by the Arizona LaserChron Center. The K-S test
529
suggests a strong correlation among samples WW176, WW236, WN1012 and
530
WN1015 (Fig. 12 and Table 2), all of which have a relatively uniform zircon
531
provenance dominated by Neoproterozoic detritus with ages ranging from 810 to 860
532
Ma. Sample WN1004 seems to be less correlated with other samples (Table 2), which
533
is mainly due to the variable amounts of relative contribution of similarly old detritus
534
(Fig. 12). Apart from the prominent 810-860 Ma zircons, samples from the Xikou
535
Group also contain significant addition of 860-980 Ma materials, roughly consistent
536
with the present geographic framework of the eastern Jiangnan Orogen considering
537
that the 860-980 Ma materials were largely derived from volcanic rocks of the
538
Shuangxiwu Group. Sample WW247 from the Xiushui Fm has a detrital zircon
539
pattern similar to sample WN1086 from the Zhentou Fm (Fig. 12), both of which have
540
dominant Neoproterozoic detritus with several equal age peaks between ca. 800 and
541
900 Ma (Fig. 8) accompanied by significantly increased Pre-Neoproterozoic zircons,
542
indicating that the Xiushui and Zhentou Fms formed in a more open setting with a
543
broad source region than other formations of the Shuangqiaoshan and Xikou Groups.
cr
us
an
M
d
Ac ce pt e
544
ip t
528
The Nanhua Sequence is inferred to have accumulated in a passive margin setting
545
where the sedimentary detritus was mainly sourced from the interior part of the
546
Yangtze Block (Jiang et al., 2003), as reflected by the significant contribution from
547
cratonic components with Paleoproterozoic ages clustering at 1.90-2.10 Ga and
548
2.40-2.50 Ga.
549 550
5.3. Magmatic and crustal evolution
551
21 Page 23 of 105
552
U-Pb ages of detrital zircons reveal three major episodes of magmatic activity at
553
2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma with some minor magmatic events at
554
2.70-2.50 Ga, 1.90-1.50 Ga and 800-750 Ma.
555
5.3.1. Reworking of pre-existing crust in the late Archean to Mesoproterozoic
ip t
556
Most late Archean to early Paleoproterozoic (~2.70-2.30 Ga) zircons have
558
sub-chondritic εHf(t) values (-20.4 to -0.2) and old TDM2 ( 2.97-4.20 Ga), suggesting
559
this period of magmatism was characterized by reworking of a common pre-existing
560
continental crust. One 2.46 Ga zircon from WW153 has the oldest TDM2 age of 4.20
561
Ga, indicating the generation of continental crust as old as 4.20 Ga in the source
562
terrain. Six zircons with ages between 2.49 Ga and 2.61 Ga have εHf(t) values of (4.6 to
563
10.7) near to the depleted mantle (DM) reservoir, reflecting minor addition of juvenile
564
continental crust at this period.
M
an
us
cr
557
Most Mid-Paleoproterozoic (1.90-2.10 Ga) zircons have TDM2 ages (2.80-3.30 Ga)
566
similar to the 2.70-2.30 Ga zircons discussed above (Figs. 9 and 10), suggesting that
567
both periods of magmatism involved reworking of comparably evolved but
568
age-restricted source regions. One zircon grain has a TDM2 age of 1.94 Ga identical to
569
its U-Pb age of 1.92 Ga, and high εHf(t) value (9.9), indicating minor addition of
570
juvenile crust at this period.
Ac ce pt e
571
d
565
The majority of late Paleoproterozoic zircons with negative εHf(t) values ( -16.1 to
572
-1.0) and old TDM2 ages ( 2.51-3.42 Ga) suggest recycling origin of the
573
zircon-saturated magma. Two zircons with ages of 1.62 and 1.81 Ga have positive
574
εHf(t) values (4.3 and 7.9) and TDM2 ages (1.98 and 2.05 Ga), again supporting the
575
possibility of minor addition of juvenile materials between 1.90 and 2.10 Ga.
22 Page 24 of 105
Early Mesoproterozoic zircons (1.40-1.60 Ga) with scattered εHf(t) values (-18.1 to
577
13.8) and TDM2 ages (1.43-3.41 Ga), with the majority at 2.15-2.37 Ga) suggest
578
recycling of variable amounts of pre-existing continental crust. Nearly all late
579
Mesoproterozoic (1.00-1.30 Ga) zircons have εHf(t) values (-9.7 to 6.9) significantly
580
lower than the depleted mantle reservoir (Figs. 9 and 10), implying reworking of older
581
crust with insignificant addition of juvenile crust during this period.
5.3.2. Early-Neoproterozoic addition of juvenile crust
us
583
cr
582
ip t
576
The dominantly early Neoproterozoic (750-980 Ma) zircon detritus has
585
significant implications. Chondritic to near DM Hf isotopic compositions (εHf(t) values
586
mostly from 0 to 16.4) (Figs. 9 and 10) reveal formation of juvenile material at
587
860-980 Ma. A few 860-980 Ma zircons with negative εHf(t) values (-17.0 to -2.0) and
588
old TDM2 ages (1.91-2.81 Ga) suggest involvement of reworked older crust. The most
589
predominant detrital zircons between 810-860 Ma have a wide range of εHf(t) values
590
(-21.5 to 15.8) and TDM2 ages (739-3041 Ma) (Figs. 9 and 10), demonstrating
591
derivation of magmas from both depleted mantle reservoir and older continental curst.
592
Variable εHf(t) values and TDM2 ages imply variable degrees of mixing between
593
juvenile magmas and ancient crust, possibly due to the assimilation during magma
594
ascent. Addition of juvenile crustal materials likely became insignificant after ca. 805
595
Ma (Figs 9 and 10) as most 750-805 Ma detrital zircons have sub-chondritic Hf
596
isotopic compositions, e.g. low εHf
597
(1.85-3.05 Ga).
Ac ce pt e
d
M
an
584
(t)
values (-21.9 to -2.5) and old TDM2 ages
598 599
5.4. Implications for the tectonic evolution of the eastern Jiangnan Orogen
600
23 Page 25 of 105
601
5.4.1. Tectonic setting of the basin The obtained age spectra with predominant Neoproterozoic zircons and
603
statistically insignificant older continental-derived zircons in all Shuangqiaoshan
604
(except WW247 from the Xiushui Fm) and Xikou samples (except WN1086 from the
605
Zhentou Fm) are typical of sediments accumulated in basins associated with a
606
magmatic arc (DeGraaff-Surpless et al., 2002; Goodge et al., 2004) but are
607
inconsistent with continental rift or passive margin sedimentation, which would be
608
expected to have the majority of detritus derived from exhumed older continental
609
crust (Goodge et al., 2002, 2004). The nearly syn-magmatic sedimentation and
610
euhedral igneous zircons suggest a nearby source within the eastern Jiangnan Orogen
611
for the Neoproterozoic detritus and reflect fast erosion and deposition of newly
612
formed igneous rocks. The Cathaysia Block could be a possible source if it was
613
connected with the Yangtze Block during the sedimentation of the Shuangqiaoshan
614
and Xikou Groups. However, detritus derived from the Cathaysia Block would be
615
expected to contain Grenville (extending from 1300 to 950 Ma) materials (Wang et al.,
616
2010a and reference therein), which are scarce in the studied samples (Fig. 11),
617
suggesting the Cathaysia Block was separated from the Yangtze Block and could not
618
provide detritus to the Shuangqiaoshan and Xikou Groups. Additionally, Hf isotopic
619
compositions of the early Neoproterozoic (~810-860 Ma) zircons reveal variable
620
degrees of assimilation of pre-existing older crust to the juvenile magma, the mixing
621
process of which is typical of granitoid rocks in modern-day magmatic arc settings
622
(Tatsumi and Kogiso, 2003). Chemical compositions of the siliciclastic rocks from the
623
Shuangqiaoshan and Xikou Groups have features similar to sedimentary rocks
624
accumulated at active continental margins (Huang et al., 2003; Zhang et al., 2010),
625
consistent with the magmatic arc setting suggested by the detrital zircons. Sandstone
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24 Page 26 of 105
from both the Shuangqiaoshan and Xikou Groups are compositionally immature with
627
dominantly poorly-sorted volcanic lithic and feldspar detritus and minor detrital
628
quartz (Ma et al., 2001; Huang et al., 2003), suggesting sedimentary detritus derived
629
exclusively from volcanic sources in a magmatic arc setting (Dickinson, 1970). The
630
Xiushui Fm in northwestern Jiangxi and the Zhentou Fm in southern Anhui contain
631
thick layers of conglomerate, pebbly sandstone and coarse sandstone at their bases
632
(Fig. 5), representing syn-orogenic molasse formed in a retro-arc foreland basin at
633
817-815 Ma. Samples WW247 from the Xiushui Fm and WN1086 from the Zhentou
634
Fm have additional input of Pre-Neoproterozoic detritus (Fig. 8), likely derived from
635
the uplifted older basement complexes.
an
us
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626
637
5.4.2. An integrated tectonic model
M
636
Our new dataset together with published data allow us to propose a modified
639
model for the tectonic evolution of the eastern Jiangnan Orogen (Fig. 13). A
640
NW-dipping oceanic subduction zone along what is the present-day eastern margin of
641
the Yangtze Block is possible on the basis of the 930-890 Ma arc volcanic rocks in the
642
Shuangxiwu Group (Li et al., 2009) and the presence of 930-890 Ma detrital zircons
643
with chondritic to DM-like Hf isotopic compositions (Figs. 9 and 10). Arc-continent
644
collision probably took place at 880-860 Ma as bracketed by the emplacement of 880
645
± 19 Ma obduction-type granites (Li et al., 2008a) and the 858 ± 11 Ma Huaiyu
646
ophiolite (Shu et al., 2006). A back-arc basin was initialed above the continental crust
647
as marked by the 848-824 Ma supra-subduction zone ophiolite in southern Anhui (Li
648
et al., 1997; Ding et al., 2008; Zhang et al., 2012a). Volcanic rocks in this period were
649
largely eroded and transported to the back-arc and retroarc foreland basins due to
650
subsequent orogenic uplift. Abundant 860-810 detrital zircons have Hf isotopic
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25 Page 27 of 105
compositions, indicating mixture between juvenile crust and continental basement
652
(Figs. 9 and 10) and providing support for the existence of an extensive magmatic arc
653
during this period. The basin began to form at ca. 830 Ma and was filled with a set of
654
volcanic-terrigenous arenopelitic flysch sequence with some well-preserved primary
655
sedimentary structures, such as cross- and graded-bedding and scoured based
656
sequences (Fig. 5) (Wu, 2007; Zhang et al., 2010). Greywacke of the flysch sequence
657
contains poorly-sorted and subangular fractions of lithic fragments and less feldspar
658
and quartz (Wu, 2007). Along with basin evolution, the sedimentary strata contained
659
additional interlayered calc-alkaline felsic-intermediate volcanic lava of arc-affinity
660
that strongly supports a magmatic arc setting (Zhang et al., 2010). The Niuwu and
661
Anlelin Fms are characterized by repeated sedimentary cycles of pebbly sandstone
662
and shale (Fig. 5), typical of flysch formed in a back-arc basin. Basin closure was
663
marked by the 828-819 Ma syn-collisional cordierite-bearing peraluminous granitoids
664
(CPG) (Li et al., 2003a; Zhong et al., 2005; Wang et al., 2006) and subsequent
665
syn-orogenic uplift which led to basin restriction and the formation of a regional
666
unconformity. As a result, a retro-arc foreland basin was formed, in which the Xiushui
667
and Zhentou Fms were deposited with detritus from both remnant magmatic arc and
668
uplifted basement. Subsequently, the emplacement of extensive 805-760 Ma bimodal
669
volcanic sequences (Wang et al., 2011b) and 780-770 Ma K-rich calc-alkaline
670
granitoids (KCG) (Zheng et al., 2008; Xue et al., 2010) in the eastern Jiangnan
671
Orogen record post-collisional orogenic rifting, which is marked by remelting of
672
pre-existing rocks as recorded by the sub-chondritic Hf isotopic compositions of most
673
805-750 Ma detrital zircons (Figs. 9 and 10).
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651
674 675
5.4.3. Possible reconstruction of the Yangtze Block in Rodinia
26 Page 28 of 105
It has long been debated if the Yangtze Block was in the central Rodinia, likewise
677
whether or not the Jiangnan Orogen is part of a Grenville Orogen (Li et al., 1995,
678
2008d; Zhou et al., 2002, 2008; Yan et al., 2002; Zheng, 2004; Yu et al., 2008; Wang
679
and Zhou, 2012). However, the back-arc to retro-arc foreland setting for the 830-815
680
Ma Shuangqiaoshan and Xikou Groups does not support an intra-cratonic setting.
681
Neither coeval mantle plume rift system nor a Grenville Orogen recorded in
682
southeastern Australia and western Laurentia (Li et al., 2008d) exist in the eastern
683
Jiangnan Orogen. In addition, the facts that the Jiangnan Orogen is somewhat younger
684
than the Grenville Orogen and that there is insignificant Grenville magmatism and no
685
Grenville juvenile crust recorded by detrital zircons from the strata in the Jiangnan
686
Orogen suggest that this orogen cannot be correlated with the worldwide Grenville
687
Orogen and that the Yangtze Block was unlikely located between Australia–East
688
Antarctica and Laurentia as proposed by Li et al. (1995). However, source analysis
689
suggests interior rather than extraneous detritus supplied to the widespread 830-815
690
Ma sedimentary sequences of the Jiangnan Orogen (Wang et al., 2010a and this study),
691
suggesting that the Yangtze Block was likely located along the margin of Rodinia as
692
an individual continental block rather than in the centre of the supercontinent.
694 695 696 697 698 699 700
cr
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693
ip t
676
6. Conclusions
(1). The previously thought Mesoproterozoic sedimentary sequences in the eastern Yangtze Block was deposited betwee833 and 815 Ma. (2). The 833-815 Ma sedimentary sequence represents a sedimentary cycle from a back-arc to retro-arc foreland basin.
27 Page 29 of 105
701 702
(3). The juxtaposition of the Yangtze and Cathaysia Blocks likely lasted to ca. 815 Ma or even later. (4). Three major episodes of magmatic activities at 2.50-2.35 Ga, 2.10-1.90 Ga
704
and 980-800 Ma are recognized in the source areas of the Neoproterozoic sedimentary
705
basin, whereas the Grenville (1.30-1.00 Ga) magmatism was insignificant.
ip t
703
(5). No Grenville juvenile crust in the eastern Yangtze Block is identified. The
707
most important generation of juvenile crust occurred at early Neoproterozoic
708
(~980-810 Ma) in combination with reworked older crust at 860-810 Ma.
us
cr
706
709
Acknowledgements
an
710 711
This study was supported by the Research Grant Council of Hong Kong SAR,
713
China (HKU 707210P), National Natural Science Foundation of China (NSFC
714
41272212) and the oversea famous professor program (MS2011ZGDZ (BJ) 019). We
715
would like to thank Dr. Jianfeng Gao for his help with field trip and Prof. Liang Qi for
716
the LA-ICPMS work. Thanks go to Dr. Jean Wong and Dr. Hongyan Geng for help
717
with Lu-Hf analysis and Lily Chiu for CL imaging. Constructive reviewers from
718
Journal Editor Professor Randall Parrish and two anonymous reviewers have
719
substantially improved the performance, especially the presentation of U-Pb-Hf
720
isotopic results, of this manuscript and are kindly acknowledge.
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Ding, B.H., Shi, R.D., Zhi, X.C., Zheng, L., Cheng, L., 2008. Neoproterozoic ( ～850 Ma) subduction in the Jiangnan orogen: evidence from the SHRIMP U- Pb dating of the SSZ - type ophiolite in southern Anhui Province. ACTA PETROLOGICA ET MINERALOGICA 27, 375-388 (in Chinese with English Abstract). Fedo, C.M., Sircombe, K.N., Rainbird, R.H., 2003. Detrital zircon analysis of the sedimentary record. Zircon,. In: Hanchar, J.M., Hoskin, P.W.O. (eds.) Rev. Mineral.Geochemical Journal 53, 277-303. Gao, J., Klemd, R., Long, L., Xiong, X., Qian, Q., 2009. Adakitic signature formed by fractional crystallization: An interpretation for the Neo-Proterozoic meta-plagiogranites of the NE Jiangxi ophiolitic mélange belt, South China. Lithos 110, 277-293. Gao, L.Z., Yang, M.G., Ding , X.Z., Liu, Y.X., Liu, X., Ling, L.H., Zhang, C.H., 2008. SHRIMP U-Pb zircon dating of tuff in the Shuangqiaoshan and Heshangzhen groups in South China-constraints on the evolution of the Jiangnan 29 Page 31 of 105
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Sun, M., Chen, N., Zhao, G., Wilde, S.A., Ye, K., Guo, J., Chen, Y., Yuan, C., 2008. U-Pb Zircon and Sm-Nd isotopic study of the huangtuling granulite, dabie-sulu belt, China: Implication for the paleoproterozoic tectonic history of the yangtze craton. American Journal of Science 308, 469. Sun, W.H., Zhou, M.F., Gao, J.F., Yang, Y.H., Zhao, X.F., Zhao, J.H., 2009. Detrital zircon U-Pb geochronological and Lu-Hf isotopic constraints on the Precambrian magmatic and crustal evolution of the western Yangtze Block, SW China. Precambrian Research 172, 99-126. Tatsumi, Y., Kogiso, T., 2003. The subduction factory: its role in the evolution of the Earth’s crust and mantle. Geological Society, London, Special Publications 219, 55-80. Wan, Y., Liu, D., Xu, M., Zhuang, J., Song, B., Shi, Y., Du, L., 2007. SHRIMP U-Pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in Northwestern Fujian, Cathaysia block, China: Tectonic implications and the need to redefine lithostratigraphic units. Gondwana Research 12, 166-183. Wang, L.J., Griffin, W.L., Yu, J.H., O'Reilly, S.Y., 2010a. Precambrian crustal evolution of the Yangtze Block tracked by detrital zircons from Neoproterozoic sedimentary rocks. Precambrian Research 177, 131-144. Wang, L.J., Yu, J.H., Griffin, W.L., O’Reilly, S.Y., 2011a. Early crustal evolution in the western Yangtze Block: Evidence from U–Pb and Lu–Hf isotopes on detrital zircons from sedimentary rocks. Precambrian Research. in press, doi:10.1016/j.precamres.2011.08.001. Wang, W., Chen, F.K., Hu, R., Chu, Y., Yang, Y.Z., 2012a. Provenance and tectonic setting of Neoproterozoic sedimentary sequences in the South China Block: evidence from detrital zircon ages and Hf–Nd isotopes. International Journal of Earth Sciences. 101, 1723-1744 Wang, W., Wang, F., Chen, F., Zhu, X., Xiao, P., Siebel, W., 2010b. Detrital Zircon
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Wang, W., Zhou, M.-F., 2012. Sedimentary records of the Yangtze Block (South China) and their correlation with equivalent Neoproterozoic sequences on adjacent continents. Sedimentary Geology 265–266, 126-142. Wang, W., Zhou, M.-F., Yan, D.-P., Li, J.-W., 2012b. Depositional age, provenance, and tectonic setting of the Neoproterozoic Sibao Group, southeastern Yangtze Block, South China. Precambrian Research 192-195, 107-124. Wang, X.L., Shu, L.S., Xing, G.F., Zhou, J.C., Tang, M., Shu, X.J., Qi, L., Hu, Y.H., 2011b. Post-orogenic extension in the eastern part of the Jiangnan orogen: Evidence from ca 800-760 Ma volcanic rocks. Precambrian Research in press. Wang, X.L., Zhao, G.C., Zhou, J.C., Liu, Y., Hu, J., 2008. Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen. Gondwana Research 14, 355-367. Wang, X.L., Zhou, J.C., Griffin, W.L., Wang, R.C., Qiu, J.S., O’Reilly, S.Y., Xu, X., Liu, X.M., Zhang, G.L., 2007. Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: Dating the assembly of the Yangtze and Cathaysia Blocks. Precambrian Research 159, 117-131. Wang, X.L., Zhou, J.C., Qiu, J.S., Zhang, W.L., Liu, X.M., Zhang, G.L., 2006. LA-ICP-MS U-Pb zircon geochronology of the Neoproterozoic igneous rocks from Northern Guangxi, South China: Implications for tectonic evolution. Precambrian Research 145, 111-130. Wang, Y.J., Zhang, F.F., Fan, W.M., Zhang, G.W., Chen, S.Y., Cawood, P.A., Zhang, A.M., 2011c. Tectonic setting of the South China Block in the early Paleozoic: resolving intracontinental and ocean closure models from detrital zircon U-Pb geochronology. Tectonics 29. Wu, R.X., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Zhang, S.B., Liu, X.M., Wu, F.Y., 2006. Reworking of juvenile crust: Element and isotope evidence from Neoproterozoic granodiorite in South China. Precambrian Research 146, 179-212. Wu, X.H., 2007. Rediscuss of Shuangqiaoshan group. Resources survey & environment (in Chinese with English abstract) 28, 95-105. Wu, Y.B., Zheng, Y.F., Gao, S., Jiao, W.F., Liu, Y.S., 2008. Zircon U-Pb age and trace element evidence for Paleoproterozoic granulite-facies metamorphism and Archean crustal rocks in the Dabie Orogen. Lithos 101, 308-322. Xia, X.P., Sun, M., Zhao, G.C., Wu, F.Y., Xu, P., Zhang, J., Luo, Y., 2006. U-Pb and Hf isotopic study of detrital zircons from the Wulashan khondalites: Constraints on the evolution of the Ordos Terrane, Western Block of the North China Craton. Earth and Planetary Science Letters 241, 581-593. Xue, H.M., Ma, F., Song, Y.Q., Xie, Y.P., 2010. Geochronology and geochemisty of the Neoproterozoic granitoid association from eastern segment of the Jiangnan orogen, China: Constraints on the timing and process of amalgamation between the Yangtze and Cathaysia blocks. Acta Petrologica Sinica 26, 3215-3244. (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Malpas, J., 2002. Where was South China located in the reconstruction of Rodinia. Earth Sci. Frontiers 9, 249-256 (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Wang, X.W., Malpas, J., 2003. Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China). Tectonophysics 361, 239-254.
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Ye, M.F., Li, X.H., Li, W.X., Liu, Y., Li, Z.X., 2007. SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc along the southeastern margin of the Yangtze Block. Gondwana Research 12, 144-156. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhang, M., Wang, R.C., Jiang, S.Y., Shu, L.S., 2008. Where was South China in the Rodinia supercontinent?:: Evidence from U-Pb geochronology and Hf isotopes of detrital zircons. Precambrian Research 164, 1-15. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhou, M.F., Zhang, M., Shu, L.S., 2010. Components and episodic growth of Precambrian crust in the Cathaysia Block, South China: Evidence from U-Pb ages and Hf isotopes of zircons in Neoproterozoic sediments. Precambrian Research 181, 97-114. Yu, J.H., O'Reilly, Y.S., Wang, L.J., Griffin, W.L., Jiang, S.Y., Wang, R.C., Xu, X.S., 2007. Finding of ancient materials in Cathaysia and implication for the formation of Precambrian crust. Chinese Science Bulletin 52, 11-18. Yu, J.H., O’Reilly, S.Y., Zhou, M.F., Griffin, W.L., Wang, L.J., 2011. U–Pb geochronology and Hf–Nd isotopic geochemistry of the Badu Complex, Southeastern China: Implications for the Precambrian crustal evolution and paleogeography of the Cathaysia Block. Precambrian Research. doi:10.1016/j.precamres.2011.07.014. Yu, J.H., Wang, L.J., O'Reilly, S.Y., Griffin, W.L., Zhang, M., Li, C.Z., Shu, L.S., 2009. A Paleoproterozoic orogeny recorded in a long-lived cratonic remnant (Wuyishan terrane), eastern Cathaysia Block, China. Precambrian Research 174, 347-363. Zhang, S.B., Wu, R.X., Zheng, Y.F., 2012a. Neoproterozoic continental accretion in South China: geochemical evidence from the Fuchuan ophiolite in the Jiangnan orogen. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.010 Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006a. Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China. Precambrian Research 151, 265-288. Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006b. Zircon U-Pb age and Hf isotope evidence for 3.8 Ga crustal remnant and episodic reworking of Archean crust in South China. Earth and Planetary Science Letters 252, 56-71. Zhang, X.H., Zhang, Z.J., Guo, J.Q., Xiong, Q.H., 1999. Stratigraphy and sedimentary sequences of the upper part of the Proterozoic Shuangqiaoshan Group in Xiushui-Wuning area, Jiangxi. Journal of Stratigraphy 23, 71-77. (in Chinese with English Abstract). Zhang, Y.J., Zhou, X.H., Liao, S.B., Zhang, X.D., Wu, B., Wang, C.Z., Yu, M.G., 2010. Neoproterozoic crustal composition and orogenic process of the Zhanggongshan area, Anhui-Jiangxi. Acta Geological Sinia 84, 1401-1427. (in Chinese with English Abstract). Zhang, Y.Z., Wang, Y.J., Fan, W.M., Zhang, A.M., Ma, L.Y., 2012b. Geochronological and geochemical constraints on the metasomatised source for the Neoproterozoic (∼825 Ma) high-Mg volcanic rocks from the Cangshuipu area (Hunan Province) along the Jiangnan Domain and their tectonic implications. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.003
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Zhao, G.C., Cawood, P., 1999. Tectonothermal evolution of the Mayuan Assemblage in the Cathaysia Block; implications for Neoproterozoic collision-related assembly of the South China Craton. American Journal of Science 299, 309-339. Zhao, J.-H., Zhou, M.-F., 2008. Neoproterozoic adakitic plutons in the northern margin of the Yangtze Block, China: Partial melting of a thickened lower crust and implications for secular crustal evolution. Lithos 104, 231-248. Zhao, J.-H., Zhou, M.-F., Zheng, J.-P., Fang, S.-M., 2010a. Neoproterozoic crustal growth and reworking of the Northwestern Yangtze Block: Constraints from the Xixiang dioritic intrusion, South China. Lithos 120, 439-452. Zhao, J.H., Zhou, M.F., 2007a. Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): Implications for subduction-related metasomatism in the upper mantle. Precambrian Research 152, 27-47. Zhao, J.H., Zhou, M.F., 2007b. Neoproterozoic adakitic plutons and arc magmatism along the western margin of the Yangtze Block, South China. The Journal of Geology 115, 675-689. Zhao, J.H., Zhou, M.F., Yan, D.P., Zheng, J.P., Li, J.W., 2011. Reappraisal of the ages of Neoproterozoic strata in South China: no connection with the Grenvillian orogeny. Geology 39, 299-302. Zhao, X.F., Zhou, M.F., Li, J.W., Sun, M., Gao, J.F., Sun, W.H., Yang, J.H., 2010b. Late Paleoproterozoic to early Mesoproterozoic Dongchuan Group in Yunnan, SW China: Implications for tectonic evolution of the Yangtze Block. Precambrian Research 182, 57-69 Zheng, J.P., Griffin, W.L., O’, Reilly, S.Y., 2006a. Widespread Archean basement beneath the Yangtze craton. Geology 34, 417-420. Zheng, Y.-F., Zhao, Z.-F., Wu, Y.-B., Zhang, S.-B., Liu, X., Wu, F.-Y., 2006b. Zircon U-Pb age, Hf and O isotope constraints on protolith origin of ultrahigh-pressure eclogite and gneiss in the Dabie orogen. Chemical Geology 231, 135-158. Zheng, Y.F., 2003. Neoproterozoic magmatic activity and global change. Chinese Science Bulletin 48, 1639-1656. Zheng, Y.F., 2004. Position of South China in configuration of Neoprotero-zoic supercontinent. Chinese Science Bulletin 49, 751-753. Zheng, Y.F., Wu, R.X., Wu, Y.B., Zhang, S.B., Yuan, H., Wu, F.Y., 2008. Rift melting of juvenile arc-derived crust: Geochemical evidence from Neoproterozoic volcanic and granitic rocks in the Jiangnan Orogen, South China. Precambrian Research 163, 351-383. Zheng, Y.F., Zhang, S.B., Zhao, Z.F., Wu, Y.B., Li, X.H., Li, Z.X., Wu, F.Y., 2007. Contrasting zircon Hf and O isotopes in the two episodes of Neoproterozoic granitoids in South China: Implications for growth and reworking of continental crust. Lithos 96, 127-150. Zhong, Y.F., Ma, C.Q., She, Z.B., Lin, G.C., Xu, H.J., Wang, R.J., Yang, K.G., Liu, Q., 2005. SHRIMP U-Pb Zircon Geochronology of the Jiuling Granitic Complex Batholith in Jiangxi Province. Earth Science-Journal of China University of Geosciences 30, 685-691. (in Chinese with English abstract). Zhou, G.Q., 1989. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high temperature-high pressure metamorphic rocks. Journal of Southeast Asian Earth Sciences 3, 237-247.
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Zhou, J.C., Wang, X.L., Qiu, J.S., 2008. Is the Jiangnan Orogenic Belt a Grenvillian Orogenic Belt: some problems about the Precambrian Geology of South China. Geological Journal of China Universities 14, 64-72. (in Chinese with English Abstract). Zhou, M.F., Kennedy, A.K., Sun, M., Malpas, J., Lesher, C.M., 2002a. Neoproterozoic arc-related mafic intrusions along the northern margin of South China: Implications for the accretion of Rodinia. The Journal of Geology 110, 611-618. Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006a. The Yanbian Terrane (Southern Sichuan Province, SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze Block. Precambrian Research 144, 19-38. Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y.Q., Ding, J., 2002b. SHRIMP zircon geochronological and geochemical evidence for Neoproterozoic arc-related magmatism along the western margin of the Yangtze Block, South China. Earth and Planetary Science Letters 196, 51-67. Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A., 2006b. Subduction-related origin of the 750 Ma Xuelongbao adakitic complex (Sichuan Province, China): Implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth and Planetary Science Letters 248, 286-300. Zhu, X.Y., Chen, F., Li, S.Q., Yang, Y.Z., Nie, H., Siebel, W., Zhai, M.G., 2011. Crustal evolution of the North Qinling terrain of the Qinling Orogen, China: Evidence from detrital zircon U-Pb ages and Hf isotopic composition. Gondwana Research 20, 194-204.
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Figure captions.
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Fig.1. Distribution of Precambrian units in the eastern segment of the Jiangnan orogen
1153
(modified after (Ma et al., 2002; Wang et al., 2011b). Inserted map on the top
1154 1155 1156
left showing location of the Jiangnan orogen in the South China Craton. Blue dash line shows the boundary between provinces. 1-ca.970-880 Ma northern Jiangxi ophiolitic complex (Li and Li, 2003; Li et al., 2008a); 2-ca. 930-890
1157
Ma Shuangxiwu volcanic rocks (Li et al., 2009); 3-ca. 910-900 Ma Pingshui
1158
plagiogranite (Ye et al., 2007; Chen et al., 2009b); 4- ca. 848 Ma Gangbian
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alkaline complex (Li et al., 2010b); 5- ca. 850 Ma Zhenzhushan volcanic rocks
1160
(Li et al., 2010a)
1161
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Fig. 2. Sketch map showing the distribution of the Shuangqiaoshan Group and Nanhua sequence in the northwestern Jiangxi Province.
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Fig. 3. Sketch map showing the distribution of the Xikou Group as well as other
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Neoproterozoic units in the southern Anhui Province. Faults in this figure
1167
refers to legend in Fig. 2.
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Fig. 4. Stratigraphy of the major Neoproterozoic sedimentary units in the eastern
1170
Yangtze Block. The Zhentou Fm is tentatively considered as the upper part of
1171
the Xikou Group, considering its similarity with the Xiushui Fm in the upper
1172
part of the Shuangqiaoshan Group. The columns are not strictly to scale. Stars
1173
and italic numbers represent sample location relative to stratigraphic column
1174
and sample numbers. Bold italic numbers represent the reported ages of
1175
volcanic tuffs; see text for details and discussion.
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Fig. 5. Structures of marine sediments investigated during this study: (a) Parallel
1178
bedding and rhythmic layers between reddish siltstone and sandstone in the
1179 1180 1181 1182
Jilin Formation; (b) partial Bouma sequences in the Anlelin Fm; (c) Graded and cross bedding in the Anlelin Fm; (d) boundary between the Anlelin and Xiushui Fms. The sandstone interlayers in the silty slate are lenticular which may be result of wave current in the Banqiao Formation; (e) lenticular and
1183
cross bedding developed between grey siltstone and slate; (f) Wavy contoured
1184
bed with different wavelength and slump structure in the Mukeng Fm; (g)
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grading bedding developed in the Niuwu Fm; (h) coarse quartz sandstone from
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the Xiuning Fm.
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Fig. 6. Concordia diagrams showing results of U-Pb dating of detrital zircon grains
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from the Shuangqiaoshan Group and Dongmen Fm. Inserted diagrams show
1190
representative CL images and concordant ages (for ages<1.0 Ga,
1191
ages are presented and for ages>1.0 Ga,
1192
individual analyzed grains.
Pb/238U
Pb/206Pb ages are presented) of
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206
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Fig. 7. Concordia diagrams showing results of U-Pb dating of detrital zircon grains
1195
from the Xikou Group and Xiuning Formation. Inserted diagrams show
1196
representative CL images and concordant ages (for ages<1.0 Ga,
1197
ages are presented and for ages>1.0 Ga,
1198
individual analyzed grains.
Pb/238U
an
206
207
Pb/206Pb ages are presented) of
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Fig. 8. Relative probability versus age diagrams. The reds curves show the frequency
1201
of individual zircon populations (for details see text). Some samples are
1203 1204
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plotted at two scales to highlight the distribution of Neoproterozoic ages. Samples are presented in stratigraphic order.
1205
Fig. 9. Hf isotopic compositions of detrital zircons from Shuangqiaoshan Group and
1206
Dongmen Fm. (a) εHf(t) values versus U-Pb ages; (b) Histograms of U-Pb ages.
1207
DM : delepted mantle ; CHUR : chondritic uniform reservoir ; 3.2 Ga crust
1208
means materials were derived from delepted mantle at 3.2 Ga and evolved
1209
with average continental crust 176Lu/177Hf of 0.015.
1210
39 Page 41 of 105
1211
Fig. 10. Hf isotopic compositions of detrital zircons from Xikou Group and Xiuning
1212
Fm. (a) εHf(t) values versus U-Pb ages; (b) Histograms of
1213
meaning of DM, CHUR and 3.2 Ga crust is explained in caption of Fig. 9.
U-Pb ages. The
1214
Fig. 11. Probability plots of detrital zircons from Neoproterozoic sedimentary units in
1216
the eastern Yangtze Block and their potential sources. The number of y-axis
1217
represents the number of analyses. Data sources for Pre-Neoproterozoic units:
1218
the Kongling complex, (Qiu et al., 2000; Zhang et al., 2006a, b; Gao et al.,
1219
2011); the Tianli schist, (Li et al., 2007); Xenocrystic zircons from lamproite,
1220
(Zheng et al., 2006a); the western Yangtze Block, (Greentree et al., 2006;
1221
Greentree and Li, 2008; Zhao et al., 2010b; Wang et al., 2011a); the Cathaysia
1222
Block, (Li, 1997; Wan et al., 2007; Li et al., 2010c; Yu et al., 2011). Data
1223
sources for Neoproterozoic unit: the southeastern Yangtze Block, (Li and Li,
1224
2003; Li et al., 2003b, 2008b, 2009, 2010b; Wang et al., 2006; Wu et al., 2006;
1225
Zheng et al., 2008); the western Yangtze Block, (Zhou et al., 2002b, 2006a; Li
1227 1228 1229 1230 1231
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et al., 2003b; Zhao and Zhou, 2007a, b); the northern Yangtze Block, (Zhou et al., 2002a, 2006b; Zhao and Zhou, 2008; Zhao et al., 2010a), the Cathaysia Block, (Wan et al., 2007; Li et al., 2010c; Shu et al., 2011).
Fig. 12. Cumulative probability plots of the zircon age data for Neoproterozoic siliciclastic sequences of the eastern Yangtze Block.
1232 1233 1234
Fig. 13. Sequential tectonic evolution of the eastern Jiangnan orogen. See text for discussion.
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Graphical Abstract (for review)
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*Marked Manuscript Click here to view linked References
1
Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern
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Jiangnan Orogen, South China
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Wei Wang1, Mei-Fu Zhou1,*, Dan-Ping Yan2, Liang Li3, John Malpas1
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1
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China
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2
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Geosciences, Beijing 100083, China
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3
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Academy of Sciences, Guiyang 550002, China
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Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR,
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State Key Lab of Geological Process and Mineral Resources, China University of
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State Key Lab of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
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*
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E-mail: [email protected]
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Phone: +852 2857 8251
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Fax: +852 2517 6912
Corresponding author:
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Abstract: Precambrian sedimentary sequences in the eastern Jiangnan Orogen, South
27
China, include the Neoproterozoic Shuangqiaoshan and Xikou Groups and the
28
overlying Nanhua SystemSequence. U-Pb ages of detrital zircons provide tight
29
constraints on the deposition of the Shuangqiaoshan and Xikou Groups at 831-815 Ma
30
and 833-817 Ma, respectively. Rocks from the lower parts of these strata contain
31
dominantly Neoproterozoic detritus with a pronounced age peak at 830-850 Ma,
32
interpreted to be derived from a magmatic arc that has been mostly eroded. This
33
magmatic arc was associated with sedimentation characterized by compositionally
34
immature sediments with dominant early-Neoproterozoic (~860-810 Ma) zircons that
35
have variable εHf(t) values of -21.5 to 1514.8. The upper parts of these strata,
36
uncomfortably underlain by the low units, are molasse-type assemblages with
37
additional input of pre-Neoproterozoic detritus, representing sediments accumulated
38
in a retro-arc foreland basin associated with the Jiangnan Orogen.
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Combining four samples from the Nanhua SystemSequence, three major
40
magmatic activities at 2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma in the source areas
41
are identified. The older two events are characterized by reworking of pre-existing
42
continental crust. Grenville magmatism and juvenile crust were insignificant in the
43
eastern Jiangnan Orogen. Neoproterozoic zircons reflect generation of juvenile crust
44
at 980-860 Ma, involvement of both juvenile and recycled materials at 860-810 Ma
45
and reworking of pre-existing crust at 805-750 Ma, corresponding to island arc,
46
continental magmatic arc and post-collisional rifting stages in the eastern Jiangnan
47
Orogen.
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Keywords: U-Pb ages, Lu-Hf isotopes, detrital zircons, Jiangnan Orogen, South
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China
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1. Introduction
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The Jiangnan Orogen in South China witnessed the amalgamation of the Yangtze
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and Cathaysia Blocks. Recent studies of sedimentary and igneous rocks have
55
demonstrated that the Jiangnan Orogen is a Neoproterozoic rather than
56
Mesoproterozoic tectonic unit, but the timing and evolution of this orogen are still
57
matters of debate (Wang et al., 2006, 2007, 2012b; Zheng et al., 2008; Li et al., 2009;
58
Zhao et al., 2011). The Jiangnan Orogen was thought to be part of the worldwide
59
Grenville Orogen, formed by the collision between the Yangtze and Cathaysia Blocks
60
(Li et al., 2007, 2009), followed by extensive rift-related magmatism at ca. 820 Ma
61
(Wu et al., 2006; Li et al., 2008c, 2009, 2010a; Zheng et al., 2008). On the other hand,
62
this orogeny is thought to have lasted until ca. 830 Ma or even later, followed by
63
post-extensional magmatism beginning at ca. 800 Ma (Li, 1999; Zhao and Cawood,
64
1999; Wang et al., 2006, 2011b, 2012b; Zhao et al., 2011; Zhang et al., 2012b).
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The eastern segment of the Jiangnan Orogen is crucial for the understanding of
66
the orogenic cycle because it contains widespread sedimentary sequences, igneous
67
plutons and two major ophiolite belts, that witness the final amalgamation between
68
the Yangtze and Cathaysia Blocks (Li et al., 2009) (Fig.1). In past decades, numerous
69
studies examined the petrogenesis and tectonic affinity of igneous rocks (Wu et al.,
70
2006; Li et al., 2007, 2008b, 2009; Zheng et al., 2008; Zhang et al., 2012a), but
71
associated sedimentary sequences in the eastern Jiangnan Orogen are poorly
72
understood, due in part to unresolved stratigraphy, incomplete biostratigraphic data,
73
poor exposure and strong overprint by later deformation. These sedimentary
74
sequences in the eastern Jiangnan Orogen include the Shuangqiaoshan Group in
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northern Jiangxi Province and the Xikou Group in southern Anhui Province (Fig. 1),
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which were interpreted to have formed in a back-arc basin associated with
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Mesoproterozoic NW-dipping (current coordinates) oceanic subduction beneath the
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Yangtze Block (Cheng and Wang, 2000; Huang et al., 2003). However, dating results
79
of the Shuangqiaoshan Group do not support this model and it has been proposed that
80
these sequences were deposited in a retroarc foreland basin, synchronous with the
81
amalgamation of the Yangtze and Cathaysia Blocks (Wang et al., 2008). More recent
82
studies suggest the Shuangqiaoshan Group likely formed at ca. 830 Ma (Gao et al.,
83
2008; Zhao et al., 2011), which is taken as the timing for the Jiangnan Orogeny (Zhao
84
et al., 2011). These sequences are also suggested to have formed in an early-phase of
85
rifting that post-dated the Jiangnan Orogen (Li et al., 2009) based on ca. 850 Ma
86
dolerite dykes (Li et al., 2008b) and bimodal volcanic rocks (Li et al., 2010a).
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Due to the strong later deformation of these sedimentary strata and intensive
88
reworking and erosion of the pre-existing igneous provenance (Wu et al., 2006; Zheng
89
et al., 2008), one possible way to examine the timing and evolution of orogenic cycles
90
is to unearth the information contained by detrital zircons (Cawood and Nemchin,
91
2001; Liu et al., 2011; Wang et al., 2011c). Detrital zircon age spectra may contain
92
information about various sources linked to eustatic, depositional and tectonic change
93
(Wang et al., 2010b, 2012a), and thus can provide insight into the basin-orogen
94
coupling (Horton et al., 2010; Myrow et al., 2010). Hf isotopes of zircons can be used
95
for understanding juvenile or reworked zircon-hosting magma (Griffin et al., 2004;
96
Xia et al., 2006; Zheng et al., 2006b, 2007; Zhu et al., 2011; Liu et al., 2012; Wang et
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al., 2012a), thought to be one of the most discriminating features among plume, rift
98
and arc-related magmatism (Zheng et al., 2008).
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In this paper, we present the first integrated study of U-Pb ages and Hf isotopic
100
compositions of detrital zircons from the major Neoproterozoic sedimentary strata in
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the eastern Jiangnan Orogen. This new dataset allows us to refine the depositional age
102
of the hosting strata and to track provenance changes. The provenance characteristics
103
can help define the relationship between sedimentation and tectonism and potential
104
link to the configuration of the supercontinent Rodinia.
2. Geological background
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The South China Craton comprises the Yangtze and Cathaysia Blocks, with the
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Jiangnan Orogen being the southeastern part of the Yangtze Block. The Cathaysia
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Block has voluminous Phanerozoic igneous rocks with rarely exposed Precambrian
111
rocks (Yu et al., 2010). Metamorphic complexes in the eastern Cathaysia Block were
112
traditionally thought to be Paleo-Mesoproterozoic to Neoarchean basement (Li, 1997),
113
but recent studies suggest that these complexes formed in the Neoproterozoic or even
114
younger (Wan et al., 2007; Li et al., 2010c). A Paleoproterozoic orogen is inferred on
115
the basis of abundant Paleoproterozoic granites and metamorphic rocks in the eastern
116
Cathaysia Block (Yu et al., 2009). Precambrian rocks in the Yangtze Block are
117
sporadically exposed and include Archean Tonalite–Trondhjemite–Granodiorite (TTG)
118
in the north (Qiu et al., 2000; Gao et al., 2011) and Paleoproterozoic strata in the west
119
(Sun et al., 2009; Zhao et al., 2010b), whereas Neoproterozoic sedimentary sequences
120
and igneous plutons are widespread (Zhou et al., 2002b; Li et al., 2003a, b; Wang et
121
al., 2006, 2010b; Zhao and Zhou, 2007a; Zheng et al., 2008; Zhao et al., 2011). The
122
sedimentary cover of the Yangtze Block consists mainly of folded Paleozoic and
123
Lower Mesozoic strata formed in a shallow marine environment (Yan et al., 2003).
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Precambrian rocks in the eastern Jiangnan Orogen include the Mesoproterozoic
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Tianli schist (Li et al., 2007), early-Neoproterozoic Shuangxiwu volcanic-clastic
126
sequences (Ye et al., 2007; Li et al., 2009), mid-Neoproterozoic sedimentary strata 4
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(Gao et al., 2008; Zhao et al., 2011), igneous plutons (Zhong et al., 2005; Wu et al.,
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2006; Li et al., 2008b, 2009, 2010b; Zheng et al., 2008), and ophiolitic complexes
129
(Bai et al., 1986; Zhou, 1989; Zhang et al., 2012a). Mid-Neoproterozoic sedimentary
130
strata including the Shuangqiaoshan and Xikou Groups in the eastern Jiangnan
131
Orogen are overlain unconformably by a post-orogenic extensional basin deposits as
132
the Nanhua SystemSequence. Granitoid plutons intruding the sedimentary sequences
133
are represented by the Jiuling pluton in NW Jiangxi (Li et al., 2003a; Zhong et al.,
134
2005) and the Xucun, Shexian and Xiuning plutons in southern Anhui (Li et al., 2003a;
135
Wu et al., 2006). The NE-SW trending ophiolite complexes are in tectonic contact
136
with the Shuangqiaoshan and Xikou Groups (Bai et al., 1986).
138
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and southern Anhui Provinces is outlined in Figures. 2 and 3.
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2.1. Shuangqiaoshan Group
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A stratigraphic framework of the sedimentary succession in northwestern Jiangxi
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The Shuangqiaoshan Group consists of silty, volcanic clastic detritus that
143
gradually coarsens upwards, and has partially preserved primary sedimentary
144
structures. Based on primary sedimentary structure and lithology, this strata is divided
145
into the Hengyong, Jilin, Anlelin and Xiushui Formations (Fms) from the base
146
upward (Fig. 4) (BGMRJX, 1996).
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The Hengyong Fm comprises of grey to reddish, feldspar-lithic sandstone,
148
feldspar-quartz sandstone and siltstone. The sandstone consists dominantly of
149
subangular to subrounded, lithic fragments, with lesser amounts of quartz and feldspar.
150
Graded bedding, banded bedding, and scour and slump marks are well developed.
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The Jilin Fm is conformable with both its underlying and overlying strata and
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contains mostly purplish-red, silty slate, usually referred to as a red bed sequence. 5
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Within the silty slate are interbeds of siltstone and sandstone (Fig. 5a). Cross-bedding,
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graded bedding and partial Bouma sequences are common. The Anlelin Fm is widespread in northern Jiangxi province and is composed of
156
thick grey to charcoal grey flysch with some tuffaceous siltstone and slate. In addition
157
to greywacke, there are fine-grained, tuffaceous beds, feldspar-, quartz-rich sandstone
158
and tuffaceous lithic-quartz sandstone. Lithic components include andesite, siliceous
159
rocks, granite, basalt and silty mudstone (Wu, 2007). Cross-bedding, parallel bedding,
160
scour and slump marks, and partial Bouma sequences are well developed (Figs. 5b
161
and c).
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The Xiushui Fm, overlying the Anlelin Fm, has a basal ca. 2.5 m thick layer of
163
conglomerate (Fig. 5d). Conglomerate contains gravels of variable sizes that are
164
parallel to the orientation of the sedimentary layer. In some cases, this conglomerate
165
layer is absent and the bottom of the Xiushui Fm is marked by a 40-m-thick layer of
166
greyish-white, pebbly sandstone or quartz conglomerate. The upper part of the
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Xiushui Fm consists mainly of greyish-white, grey or green yellow, tuffaceous slate
168
interbedded with tuff. Cross-bedding, parallel-bedding and partial Bouma sequences
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are also common in this unit.
171 172
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2.2. Xikou Group
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Widely distributed in southern Anhui Province, the Xikou Group has experienced
174
weak to strong deformation and low-greenschist facies metamorphism, whereas
175
graded and crossing bedding are perfectly preserved (BGMRAH, 1984). The Xikou
176
Group is divided into the Zhangqian, Banqiao, Mukeng and Niuwu Fms upwards (Fig.
177
4) (BGMRAH, 1984). The Zhentou Fm unconformably overlies the Niuwu Fm and is
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tentatively interpreted as the upper part of the Xikou Group in this study, because of
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its similarity with the Xiushui Fm of the Shuangqiaoshan Group. The Zhangqian Fm comprises green sericite-quartz schist, arenaceousous to silty
181
phyllite and sericite-chlorite-quartz schist. Original pelitic rocks have been
182
metamorphosed to phyllite during regional metamorphism, resulting in well
183
developed phyllitic structure. Spotted or banded magnetite is common and interlayers
184
of basic volcanic rocks are also sporadically present.
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Dark to grey phyllite, phyllitic slate and feldspar quartz sandstone are the
186
dominant rocks of the Banqiao Fm that overlies the Zhangqian Fm conformably.
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Rhythmic layering between sandstone and slate are commonly observed and lenticular
188
sandstone is developed probably due to current lamination (Fig. 5e). Feldspar and
189
quartz with a few lithic detritus are the dominant clastic fragments, which is hosted by
190
cemented fine-grained sericite and clay minerals.
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The Mukeng Fm is composed of thick grey to greyish-green silt- to arenaceous-
192
siliciclastic rocks dominated by fine-grained siltstone and sericite-chlorite slate,
193
whereas fine-grained sandstone occuroccurs as interlayers in the slate. Graded and
194
parallel bedding, are well preserved (Fig. 5f). Contorted bed with varying wavelength
195
formed by waveing current and slump structure are observed (Fig. 5f), suggesting fast
196
sedimentation in a turbulent environment.
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The Niuwu Fm is typical of turbiditic deposition, consisting of thick layer of
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greyish-green to greyish-purple litharenite and thin layer of medium-grained
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sandstone. Gravel-bearing sandstone and coarse- to medium-grained sandstone form
200
well developed graded bedding (Fig. 5g), typical of turbidite. Features of shallow
201
water and storm flow deposits are observed in the upper part of the Niuwu Fm, where
202
ashy black slate is interbedded with thick layers of sandstones.
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Unconformably underlain by the Niuwu Fm, the Zhentou Fm contains
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conglomerate, gravel-bearing sandstone and gravel-bearing silty slate from the base to
205
the top. Angular to subangular gravels of the stratigraphically basal conglomerate are
206
poorly-sorted with diameters ranging between 1 and 8cm and are dominated by
207
fragments of slate, silicolite, granite and quartz. Gravel-bearing sandstone and slate
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from the upper Zhentou Fm contain gravels smaller and less than the conglomerate
209
and quartzite, volcanic rocks and siltstone are the dominant rock fragments.
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2.3. Nanhua SystemSequence
The Nanhua SequenceSystem is a set of glacial sedimentary rocks corresponding
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to the Cryogenian System defined by the International Commission on Stratigraphy
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(Plumb, 1991). The Nanhua SequenceSystem includes the lower Dongmen and
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Xiuning Fms and the upper Nantuo and Leigongwu Fms. The Dongmen and Xiuning
217
Fms, correlated with the pre-glacial Liantuo Fm in the central Yangtze Block, are
218
composed largely of a clastic succession unconformably underlain by the
219
Shuangqiaoshan and Xikou Groups, respectively. The basal parts of these units
220
consist of conglomerate and coarse quartzose sandstone, formed in an alluvial fan or
221
fluvial environment. The Nantuo and Leigongwu Fms, are widespread in the entire
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Yangtze Block, are composed of diamictite typical of tillite formed during the
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Neoproterozoic ―snowball Earth‖ event (Zheng, 2003).
225 226
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3. Sampling and analytical methods
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Ten samples were selected across major stratigraphic units for zircon dating in
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order to constrain depositional ages, provenance and tectonic setting of the
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sedimentary basin. Zircon was separated using standard heavy-liquid and magnetic
230
separation from ca. 5 Kg samples. Zircon separates were mounted in epoxy and
231
polished. U-Pb isotope analysis of zircon was performed by LA-ICP-MS at the State Key
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Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese
234
Academy of Sciences, Guiyang. A GeoLasPro laser-ablation system (Lamda Physik,
235
Gottingen, Germany) and Agilent 7700x ICP-MS (Agilent Technologies, Tokyo,
236
Japan) were combined for the experiments. The 193 nm ArF excimer laser,
237
homogenized by a set of beam delivery systems, was focused on the zircon surface
238
with the fluence of 10J/cm2. The ablation protocol employed a spot diameter of 32 µm
239
at 5 Hz repetition rate for 45 seconds (equating to 225 pulses). Helium was applied as
240
a carrier gas to allow efficient transportation of aerosol to the ICP-MS. Zircon 91500
241
was used as the primaryexternal standard to correct elemental fractionation.
242
Meanwhile, zircon GJ-1 (Jackson et al., 2004) and Plešovice (PL, Sláma et al., 2008)
243
were analyzed as unknown samples for quality control. Trace element compositions of
244
zircon were external calibrated against NIST SRM 610 with
245
secondary standard. Raw data reduction was performed off-line by ICPMSDataCal
246
(Liu et al., 2010) and the results were reported with 12σ errors. Reported uncertainties
247
(2σ) of the
248
reproducibility (2 SD%) of standard zircon 91500 during the analytical session and
249
the within-run precision of each analysis (2 SE%; standard error) (c.f. Gerdes and Zeh.
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2006, 2009). Common Pb correction was corrected using the MS Excel program
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―ComPbcorr# 3.15”(Andersen 2002). Data were processed using the ISOPLOT
252
program (Luding, 2003). The analytical results of standard and reference materials are
253
presented in Supplementary Table 1.The weighted mean 206Pb/238Uconcordant ages of
91
Zr as the internal
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206
Pb/238U ratio were propagated by quadratic addition of the external
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analyzed GJ-1 (598.0601 ± 3.517 Ma, 2σ, MSWD=1.3n=24) and PL (338334.25 ±
255
27.5 Ma, 2σ, n=22MSWD=2.9) are consistent with the reported or recommended
256
values (GJ-1: 599.8 ± 1.7 Ma, 2σ, Jackson et al., 2004; PL: 337.13 ± 0.37 Ma, 2σ,
257
Sláma et al., 2008). Hf isotopic analysis of zircons were conducted using a Resonetics Resolution
259
M-50 193nm excimer laser ablation system, attached to a Nu Plasma HR
260
multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) at the
261
University of Hong Kong. Hf isotopes were obtained with a beam diameter of 55 μm,
262
pulse rate of 10 Hz and energy density of 15 J/cm2. Atomic masses 172 to 179 were
263
simultaneously measured in a static-collection mode. Isobaric interference of 176
172
176
Yb
with
265
Instrumental mass bias correction of Yb isotope ratios were normalized to 172Yb/173Yb
266
of 1.35274 (Chu et al., 2002) and Hf isotope ratios to 179Hf/177Hf of 0.7325 (Patchett
267
et al., 1981) using an exponential law. A relationship between . Yb and Hf of βYb
268
=0.872βHf are obtained and used for the mass bias offset. Interference of
269
176
270
and using a recommended
271
2001). Due to insignificant contribution of signal intensity of 176Lu on 176Hf (generally
272
<1%), the mass bias of Lu isotopes (βLu) can be assumed to be identical to βHf (c.f.
273
lizuka and Hirata, 2005). External calibrationQuality control was made by measuring
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zircon standard 91500 and GJ-1 for the unknown samples during the analyses to
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evaluate the reliability of the analytical data, which yielded weighted mean
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176
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277
100), respectively (Supplementary Table 2).
an
Yb/ Yb ratio of 0.5886 (Chu et al., 2002).
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Hf was corrected against the
176
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Hf was corrected by measuring the intensity of the interference-free 176
175
176
Lu with
Lu isotope
Lu/175Lu ratio of 0.02655 (Machado and Simonetti,
Hf/177Hf ratio of 0.282305 ± 3 for 91500 (n = 134) and 0.282019 ± 5 for GJ-1 (n =
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4. Analytical results
281
U-Pb isotope rResults of U-Pb dating aredetrital zircon grains appear present in
283
Supplementary Table 3 and concordant plots diagrams (Figs. 6 and 7). Detrital zircons
284
with concordant U-Pb ages (with concordance between 90-110%) were selected for
285
in-situ Hf isotopic analyses and the results are given in Supplementary Table 4.
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4.1.The Shuangqiaoshan Group
289
4.1.1. The Jilin Fm
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287 288
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Sample WW236, a reddish medium-grain sandstone from the Jilin Fm,
291
contains a predominant population of Neoproterozoic zircon grains with two major
292
age peaks at ca. 830 826 and ca. 850 Ma and three sub-peaks at ca. 870, 890 895 and
293
950 Ma (Fig. 8). These Neoproterozoic zircon grains are commonly oscillatory-zoned
294
(Fig. 6a). Pre-Neoproterozoic zircon grains are rare, with ages grouping at 1.15-1.26
295
Ga, 1.76-1.76 Ga and 1.87-2.22 Ga. One Archean zircon grain has a 207Pb/206Pb age of
296
2.59 Ga. Pre-NeoproterozoicGenerally, all zircon grains also have oscillatory zoning
297
but are variably rounded (Fig. 6a).
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298
Neoproterozoic zircon grains have highly variable εHf(t) values (-16.8 to 14.8) and
299
two stage hafnium model age (TDM2 ) ages (781-2758 Ma) (Fig. 9). Two
300
Mesoproterozoic zircon grains have identical ages but different εHf(t) values (3.3 and
301
10.8) and TDM2 ages (1.84 and 1.38 Ga). Five Paleoproterozoic zircon grains have
302
variable εHf(t) values (-8.1 to 7.2) and TDM2 ages (2.19-2.95 Ga).
303 304
4.1.2. The Anlelin Fm 11
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Sample WW176 is a combination of chips from a series of thick layers of
306
fine-medium grained siltstones in the middle Anlelin Fm. Neoproterozoic (795-978
307
Ma) euhedral and oscillatory-zoned (Fig. 6b) grains are the dominant population and
308
have two major age peaks at ca. 818 Ma and ca. 843 Ma (Fig. 8). Nine
309
Pre-Neoproterozoic
fromThree
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Mesoproterozoic grains have ages of 1.14 Ga to , 1.35 and 1.52 Ga. Six
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Paleoproterozoic zircon grains have age groups at 1.71-1.73 Ga, 2.03-2.17 Ga and
312
2.46 Ga. These zircon grains are generally subhedral to rounded with uniform internal
313
structure showing partly preserved oscillatory zoning (Fig. 6b).
have
207
Pb/206Pb
ages
scattering
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Mid-Neoproterozoic (795-850 Ma) zircon grains have positive εHf(t) values (1.2 to
315
15.1) and TDM2 ages ranging continuously from 739 to 1653 Ma (Fig. 9). In contrast,
316
Early-Neoproterozoic (851-978 Ma) zircon grains have highly variable εHf(t) values
317
(-17.7 to 16.214.7) and TDM2 ages (742-2836 Ma). Two Mesoproterozoic (1.14 and
318
1.35 Ga) zircon grains have identical
319
whereas the other Mesoproterozoic grain (1.52 Ga) has a low
320
0.281980. Two Paleoproterozoic (1.71 and 1.72 Ga) zircon grains have different εHf(t)
321
values (-5.0 and 1.3). The other three Paleoproterozoic zircons have negative εHf(t)
322
values (-2.0 to -8.3).
324
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Hf/177Hf ratios (0.282232 and 0.282216), 176
Hf/177Hf ratio of
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4.1.3. The Xiushui Fm
325
Sample WW247, a coarse sandstone from the Xiushui Fm, contains predominant
326
Neoproterozoic grains, with five age peaks at ca. 815, 825-835, ca. 869, ca. 900 and
327
ca. 930 Ma (Fig. 8). All Neoproterozoic grains are euhedral and have well preserved
328
oscillatory zoning. Pre-Neoproterozoic zircon grains have ages scattering from 1.01 to
329
2.02 Ga with only one Archean age of 2.68 Ga. All these zircon grains are subhedral
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330
to rounded and show partially oscillatory zoning or uniform internal structure (Fig.
331
6c). Except for two grains with unreasonably high εHf(t) values (34.6 and 69.3),
333
Neoproterozoic (811-935 Ma) zircon grains have variable εHf(t) values (-16.0 to
334
16.413.7) and TDM2 (742-2727 Ma) (Fig. 9). Eight Four late-Mesoproterozoic
335
(1.01-1.101.49 Ga) zircon grains have a wide range of εHf(t) values (-9.7 to 6.9) and
336
TDM2 (1.42-2.47 Ga), whereas four early-Mesoproterozoic (1.26-1.49 Ga) zircon
337
grains have a narrow range of εHf(t) values (-4.2 to -0.3) and TDM2 (2.24-2.30 Ga).
338
Zircon grains with ages between 1.57 and 1.63 Ga have a wide range of εHf(t) values
339
(1.0-13.8) and TDM2 (1.43-2.26 Ga). Paleoproterozoic to later Archean zircon grains
340
have negative εHf(t) values (-16.1 to -2.7) and old TDM2 (2.77-3.53 Ga).
an
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342 343
4.2. The Xikou Group
344
4.2.1. The Banqiao Fm
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341
Zircon grains from a grey phyllitic siltstone WN1004 are fairly small (<100 μm),
346
mostly euhedral and show oscillatory zoning with rare preexisting cores and
347
overgrowth rims (Fig. 7a). These detrital zircon grains are predominantly
348
Neoproterozoic and have ages ranging from 831 to 990 Ma with four age peaks at ca.
349
833, 860, 885 884 and 930 932 Ma (Fig. 8). There are also a few Meso- to
350
Paleoproterozoic zircon grains with ages scatteringed from 1.21 to 2.46 Ga.
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351
Nearly all Neoproterozoic zircon grains have positive εHf(t) values (1.2-14.0) and a
352
wide range of TDM2 (937-1664 Ma), except for two zircon grains with negative εHf(t)
353
values (-4.1 and -6.3) (Fig. 10). Three Mesoproterozoic (1.21 to 1.53 Ga) zircon
354
grains with U-Pb ages from 1.21 to 1.53 Ga have similar εHf(t) values (-5.0 to -2.3) and
355
TDM2 (2.32-2.45 Ga), whereas the 1.59 Ga zircon grain has low εHf(t) value (-18.1) and 13
Page 57 of 105
356
old TDM2 (3.41 Ga). All Paleoproterozoic zircon grains, except for the 1.81 Ga zircon
357
grain that has a positive( εHf(t) =value of 7.9), have negative εHf(t) values (-8.6 to -1.9)
358
and TDM2 (2.59-3.16 Ga).
359
361
4.2.2. The Mukeng Fm Sample WN1012, a
ip t
360
greyish-green phyllitic tuffaceous sandstone from the
Mukeng Fm, contains dominantly Neoproterozoic (798-988 Ma) zircon grains, with
363
three peaks at ca. 832830, 860-870 and 910 913 Ma (Fig. 8). Pre-Neoproterozoic
364
grains have a wide range of ages between 1.18 and 2.70 Ga. Neoproterozoic grains are
365
generally euhedral with well developed concentric oscillatory zoning (Fig. 7b).
us
cr
362
Neoproterozoic zircon grains from sample WN1012 have variable εHf(t) values
367
(-9.0 to 14.0) and TDM2 ( 862-2401 Ma). Pre-Neoproterozoic zircon grains have
368
evolved and scattered Hf isotopic compositions, with εHf(t) values from -3.8 to 7.5 and
369
TDM2 from 1.82 to 3.10 Ga (Fig. 10).
M
an
366
4.2.3. The Niuwu Fm
Ac ce pt e
371
d
370
372
Sample WN1025, a grey tuffaceous sandstone from the Niuwu Fm, contains
373
zircon grains mostly with Neoproterozoic ages ranging from (805 to 965 Ma). Four of
374
the six Pre-Neoproterozoic grains cluster between 1.95 and 2.08 Ga and the other two
375
have ages of 2.42 and 2.58 Ga. Neoproterozoic grains have uniform internal structure
376
with typical concentric oscillatory zoning (Fig. 7c).
377
The Neoproterozoic zircon grains have variable εHf(t) values (-17.2 to 14.2) and
378
TDM2 (842-2809 Ma) (Fig. 10). The Paleoproterozoic to late Archean zircon grains
379
have relatively constant εHf(t) values from -9.2 to -0.6 and TDM2 from 2.71 to 3.30 Ga.
380
14
Page 58 of 105
381
4.2.4. The Zhentou Fm Sample WN1086 from the Zhentou Fm contains nearly half (48%) of
383
Neoproterozoic (mostly between 801 and 860 Ma) zircon grains. Pre-Neoproterozoic
384
zircon grains cluster at groups of 1.64-1.75 Ga, 1.98-2.01 Ga and 2.44-2.58 Ga (Fig.
385
8).
ip t
382
Neoproterozoic (798-965 Ma) zircon grains have a wide range of εHf(t) values
387
from -21.5 to 10.6 and TDM2 from 1.06 to 3.04 Ga (Fig. 10). Six late to
388
mid-Paleoproterozoic zircon grains (1.64-2.14 Ga) have εHf(t) values (-12.8 to -5.1)
389
and TDM2 (2.85-3.27 Ga). Zircon grains with ages between 2.33 and 2.76 Ga have a
390
wide range of εHf(t) values of-7.6 to 10.7 and TDM2 of 2.43-3.47 Ga.
an
391 392
4.3. The Nanhua SystemSequence
Formatted: Line spacing: Double
M
393 394
us
cr
386
4.3.1. The Dongmen Fm
Two coarse-grained sandstones (WW153 and WW197) from the Dongmen Fm
396
contain zircons with similar detrital age distribution dominated by two major age
397
groups at 1.80 to 2.10 Ga and 2.30 to 2.50 Ga and one sub-group of 800 to 900 Ma
398
(Fig. 8). Neoproterozoic grains are oscillatory-zoned and euhedral., whereas
399
Paleoproterozoic zircon grains are euhedral to rounded zircon grains are and partly
400
oscillatory-zoned (Figs. 6d and e).
Ac ce pt e
d
395
401
In general, mMost Neoproterozoic zircon grains from the Dongmen Fm have
402
sub-chondritic εHf(t) values scattered between -19.2 and 7.4 (Fig. 9). Nearly all
403
Pre-Neoproterozoic zircon grains have εHf(t) values falling between the evolved Hf
404
isotopic composition defined by the Hf evolution trend of juvenile material derived
405
from a depleted mantle reservoir at ca. 2.90 and 3.60 Ga (Fig. 9).
15
Page 59 of 105
406 407
4.3.2. The Xiuning Fm Detrital zircon grains of sample WN1031 from the upper part of the Xiuning Fm
409
are mostly later Archean to mid-Paleoproterozoic in age, including 2.38-2.52 Ga and
410
1.95-2.07 Ga populations, with a small number of grains clustering at 2.24-2.33 Ga
411
(Fig. 8). Neoproterozoic zircon grains range in age from 750 to 874 Ma with no
412
early-Neoproterozoic detritus (900-1000 Ma).
cr
ip t
408
Neoproterozoic zircon grains from the Xiuning Fm have highly scattered Hf
414
isotopic compositions (Fig. 10) with a wide range of εHf(t) values (-21.9 to 6.3) and
415
TDM2 (1.31-3.05 Ga). Late- to mid-Paleoproterozoic (~1.9-2.1 Ga) zircon grains have
416
εHf(t) values between -13.1 and -6.3 and TDM2 between 2.99 Ga and 3.42 Ga. 2.24-2.61
417
Ga zircon grains have scattered εHf(t) values (-18.0 to 5.1) and TDM2 (2.65-3.89 Ga).
an
us
413
M
418
5. Discussion
421 422
5.1. Constraints on the timing of deposition
423
5.1.1. The Shuangqiaoshan Group
Ac ce pt e
d
419 420
424
The Shuangqiaoshan Group was traditionally thought to be Mesoproterozoic in
425
age (1400-1000 Ma) (Huang et al., 2003; Wu, 2007), whereas a Neoproterozoic
426
depositional age has been widely inferred recently (870-820 Ma) (Gao et al., 2008;
427
Wang et al., 2008; Zhao et al., 2011). Combined with previously published data, new
428
age data in this study can provide tighter constraints on the age of the Shuangqiaoshan
429
Group. All Neoproterozoic zircons have oscillatory-zoning and euhedral shape
430
without metamorphic rim and fractures (Fig. 6). The Shuangqiaoshan Group
431
underwent only low greenschist-facies metamorphism and all Neoproterozoic zircons
16
Page 60 of 105
have high Th/U ratios (generally >0.5), indicating detrital zircons were not
433
modifiedare pristine and can constrain the maximum depositional age of the
434
sediments as they represent the ages of source rocks (Fedo et al., 2003). The initial
435
deposition of the Shuangqiaoshan Group can beis constrained by a SHRIMP zircon
436
U-Pb age of 831±5 Ma for a thin-bedded bentonite in the middle part of the Henyong
437
Fm, lowermost Shuangqiaoshan Group (Gao et al., 2008). The youngest detrital
438
zircons from the Jilin Fm have a weighted mean age of 828 826 ± 3 Ma (2σ,
439
MSWD=2.71.18), placing the maximum deposition age for the Jilin Fm at ca. 828 Ma.
440
A maximum age of 829 ± 5 Ma, bracketed by an inter-bedded bentonite in the Anlelin
441
Fm (Gao et al., 2008), indicates immediate deposition of the Anlelin Fm after the Jilin
442
Fm. One sample from the upper part of the Anlelin Fm contains the youngest zircons
443
with a weighted mean age of 818 ± 4 3 Ma (2σ, MSWD=0.141.12), indicating a
444
depositional age of ca. 818 Ma or younger. The Xiushui Fm contains detrital zircons
445
as young as 800 Ma and the youngest zircons yield a weighted mean age of 815 ± 2 5
446
Ma (2σ, MSWD=1.20.32), consistent with the minimum depositional age of 819 ± 9
447
Ma bracketed by the Jiuling granitic intrusion (Li et al., 2003a).
449
cr
us
an
M
d
Ac ce pt e
448
ip t
432
5.1.2. The Xikou Group
450
The Xikou Group is intruded by ca. 824 Ma granitic plutons (Li et al., 2003a; Wu
451
et al., 2006). The youngest zircons of sample WN1004 from the Banqiao Fm have a
452
weighted mean age of 833 ± 5 8 Ma (2σ, MSWD=0.0724), bracketing the initial
453
depositional age to the mid-Neoproterozoic. The youngest zircon group of sample
454
WN1012 give a weighted mean age of 830 ± 3 4 Ma (2σ, MSWD=1.180.45),
455
constraining the maximum deposition age of the Mukeng Fm at ca. 830 Ma. Sample
456
WN1025 from the uppermost Niuwu Fm have the youngest zircons with a weighted
17
Page 61 of 105
mean age of 827 ± 53 Ma (2σ, MSWD=0.58), indicating the Niuwu Fm formed at ca.
458
827 Ma or younger. There are only two single-grains with younger ages of 805 and
459
808 Ma, but these are inconsistent with inferred ages from field relationship. Because
460
of the similar lithological assemblage and sedimentary environment, as well as being
461
separated from underlying strata by a similar regional uncomformityunconformity
462
(Ma et al., 1999; Zhang et al., 1999), the Zhentou Fm can be correlated with the
463
Xiushui Fm and is regarded as the upper part of the Xikou Group. Apart from two
464
exceptionally young (789 and 801 Ma) zircons, the youngest zircons have a weighted
465
mean age of 817 ± 3 4 Ma (2σ, MSWD=0.7633), providing a maximum constraint on
466
the deposition of the Zhentou Fm. Therefore, the Xikou Group likely formed at
467
833-817 Ma.
an
us
cr
ip t
457
468
5.2. Age groups and source terrains
M
469 470
Among 888 zircon grains analyzed, 692 analyses are considered to be significant
472
in terms of concordance and have meaningful U-Pb ages. There are four principal age
473
groups (Fig. 11. Table 1): (1) Neoproterozoic zircons with ages between 750 and 980
474
Ma; (2) Early-Mesoproterozoic to Late-Paleoproterozoic zircons (1.50-1.80 Ga); (3)
475
Mid-Paleoproterozoic zircons defining a maximum frequency group at 1.80-2.10 Ga;
476
and (4) Early-Paleoproterozoic to Late-Archean zircons (2.35-2.75 Ga).
478
Ac ce pt e
477
d
471
Formatted: Line spacing: Double
5.2.1. Neoproterozoic (750 -980 Ma) zircons
479
All Shuangqiaoshan and Xikou samples have dominantly Neoproterozoic zircons
480
in spite of slightly diverse maximum age frequency. The early-Neoproterozoic
481
(980-860 Ma) detritus may be sourced from the ca. 970 Ma adakitic granite within the
18
Page 62 of 105
northeastern Jiangxi ophiolite (Li and Li, 2003; Gao et al., 2009), the 930-890 Ma
483
volcanic rocks of the Shuangxiwu Group (Chen et al., 2009a; Li et al., 2009), ca. 910
484
Ma granitoid plutons intruding the Shuangxiwu Group (Ye et al., 2007) or ca. 880 Ma
485
obduction-type granite within the NE Jiangxi ophiolite (Li et al., 2008a). 860-820 Ma
486
detritus makes up one of the most important age populations. These zircons have
487
morphology and internal structure of igneous origin and the age spectrum is similar to
488
that recorded by a series of igneous events in the eastern Jiangnan Orogen.
489
Sporadically exposed igneous rocks, the ca. 848 Ma Gangbian alkaline complex (Li et
490
al., 2010b), ca. 849 Ma Shenwu dolerite (Li et al., 2008b) and ca. 850 Ma
491
Zhenzhushan volcanic rocks (Li et al., 2010a) may have provided the relevant detritus.
492
However, the abundance of detrital zircons in this study and inherited zircons within
493
this age range observed from younger granites and volcanic rocks (Wu et al., 2006;
494
Zheng et al., 2008), demonstrate the wider spread of sources that were largely
495
reworked by later processes (Wu et al., 2006; Zheng et al., 2008) or eroded into
496
associated basins.
498
cr
us
an
M
d Ac ce pt e
497
ip t
482
5.2.2. Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) zircons
499
Early-Mesoproterozoic to Late-Paleoproterozoic (1.50-1.80 Ga) material is an
500
important part of the Pre-Neoproterozoic detritus in the analyzed samples but does not
501
match any proximal source in the eastern Jiangnan Orogen (Fig. 11). Although tThe
502
1.5-1.7 Ga Dahongshan Group (Greentree and Li, 2008) and the Dongchuan Group
503
(Zhao et al., 2010b; Wang et al., 2011a) in the western Yangtze Block likely
504
deposited at 1.5-1.7 Ga, may be the distal source of the 1.50-1.80 Ga detritus.
505
Nevertheless, the cumulative age histogram constructed from these published data
19
Page 63 of 105
506
shows that the dominant ages from the western Yangtze Block are ca. 150 million
507
younger than those of the detrital zircons in this study (Fig. 11).
508 509
5.2.3. Mid-Paleoproterozoic (1.80-2.10 Ga) zircons There are only a few zircon grains with ages of 1.82-1.90 Ga. This age spectrum
511
is similar to the ages of the 1.86-1.89 Ga granitic and metamorphic rocks in the
512
eastern Cathaysia Block (Yu et al., 2009, 2011), but the Cathaysia Block is
513
questionable as the source because of the paucity of such detritus. The
514
mid-Paleoproterozoic age spectrum (1.95-2.08 Ga) is similar to the ages of major
515
metamorphic events recorded by ca. 1.97 Ga metapelite in the Kongling terrane
516
(Zhang et al., 2006a) and ca. 2.00 Ga granulite in the Dabie orogenic belt (Sun et al.,
517
2008; Wu et al., 2008). However, typical core-rim internal structure and low Th/U
518
ratios of most of the metamorphic zircons in both terranes are entirely different from
519
the igneous characteristics of the detrital zircons in this study. In addition, the
520
granulites contain abundant 2.70-2.90 Ga inherited igneous zircons (Sun et al., 2008;
521
Wu et al., 2008), which are absent in the Neoproterozoic sediments, demonstrating the
522
poor connection between these sources and the basin. The ultimate sources for these
523
grains can be the Tianli schist and/or nowadays unexposed crustal fragments, because
524
both sources contain a prominent mid-Paleoproterozoic age population (Fig. 11)
525
(Zheng et al., 2006a; Li et al., 2007).
527
cr
us
an
M
d
Ac ce pt e
526
ip t
510
5.2.4. Early-Paleoproterozoic to Late-Archean (2.35-2.75 Ga ) zircons
528
A significant early-Paleoproterozoic (2.37-2.50 Ga) age peak is present, whereas
529
tectonothermal activities at 2.30-2.50 Ga are not known in the Yangtze Block. Similar
20
Page 64 of 105
530
to Archean detritus, the ultimate sources for the early-Paleoproterozoic materials were
531
likely the Tianli schist and unexposed basement (Fig. 11). The Archean (2.51-2.76 Ga) zircons are significantly younger than the 2.9-3.3 Ga
533
Kongling TTG of the Yangtze Block but similar to the age-frequency peak at
534
2.51-2.70 Ga of the Mesoproterozoic Tianli schist of the eastern Yangtze Block (Li et
535
al., 2007) (Fig. 11). Thus the Tianli schist may have likely provided the recycled
536
Archean material to the Neoproterozoic sediments. In addition, abundant 2.50-2.60
537
Ga xenocrystic zircons in lamproite are used to suggest a widespread Archean
538
basement of the Yangtze Block (Zheng et al., 2006a), reflecting this nowadays
539
unexposed Archean basement was available to supply detritus to the Neoproterozoic
540
sedimentary basin in the eastern Jiangnan Orogen during Neoproterozoic.
541
5.2.5. Temporal and spatial variations in provenance
M
542
an
us
cr
ip t
532
To examine the statistical relationship between the zircon age populations of
544
various samples, the Kolmogorov-Smirnov (K-S) test (Massey Jr, 1951) was applied
545
using the Excel macro developed by the Arizona LaserChron Center. The K-S test
546
suggests a strong correlation among samples WW176, WW236, WN1012 and
547
WN1015 (Fig. 12 and Table 2), all of which have a relatively uniform zircon
548
provenance dominated by Neoproterozoic detritus with ages ranging from 810 to 860
549
Ma. Sample WN1004 seems to be less correlated with other samples (Table 2), which
550
is mainly due to the variable amounts of relative contribution of similarly old detritus
551
(Fig. 12). Apart from the prominent 810-860 Ma zircons, samples from the Xikou
552
Group also contain significant addition of 860-980 Ma materials, roughly consistent
553
with the present geographic framework of the eastern Jiangnan Orogen considering
554
that the 860-980 Ma materials were largely derived from volcanic rocks of the
Ac ce pt e
d
543
21
Page 65 of 105
Shuangxiwu Group. Sample WW247 from the Xiushui Fm has a detrital zircon
556
pattern similar to sample WN1086 from the Zhentou Fm (Fig. 12), both of which have
557
dominant Neoproterozoic detritus with several equal age peaks between ca. 800 and
558
900 Ma (Fig. 8) accompanied by significantly increased Pre-Neoproterozoic zircons,
559
indicating that the Xiushui and Zhentou Fms formed in a more open setting with a
560
broad source region than other formations of the Shuangqiaoshan and Xikou Groups.
ip t
555
The Nanhua System Sequence is inferred to have accumulated in a passive
562
margin setting where the sedimentary detritus was mainly sourced from the interior
563
part of the Yangtze Block (Jiang et al., 2003), as reflected by the significant
564
contribution from cratonic components with Paleoproterozoic ages clustering at
565
1.90-2.10 Ga and 2.40-2.50 Ga.
an
us
cr
561
566
5.3. Magmatic and crustal evolution
M
567 568
U-Pb ages of detrital zircons reveal three major episodes of magmatic activity at
570
2.50-2.35 Ga, 2.10-1.90 Ga and 980-810 Ma with some minor magmatic events at
571
2.70-2.50 Ga, 1.90-1.50 Ga and 800-750 Ma.
573
Ac ce pt e
572
d
569
5.3.1. Reworking of pre-existing crust in the late Archean to Mesoproterozoic
574
Most late Archean to early Paleoproterozoic (~2.70-2.30 Ga) zircons have
575
sub-chondritic εHf(t) values (-20.4 to -0.2) and old TDM2 ( 2.97-4.20 Ga), suggesting
576
this period of magmatism was characterized by reworking of a common pre-existing
577
continental crust. One 2.46 Ga igneous zircon from WW153 has the oldest TDM2 age
578
of 4.20 Ga, indicating the generation of continental crust as old as 4.20 Ga in the
579
source terrain. Thirteen Six zircons with ages between 2.29 49 Ga and 2.69 61 Ga
22
Page 66 of 105
580
have εHf(t) values of (0.54.6 to 10.7) near to the depleted mantle (DM) reservoir,
581
reflecting minor addition of juvenile continental crust at this period. Most Mid-Paleoproterozoic (1.90-2.10 Ga) zircons have TDM2 ages (2.80-3.30 Ga)
583
similar to the 2.70-2.30 Ga zircons discussed above (Figs. 9 and 10), suggesting that
584
both periods of magmatism involved reworking of comparably evolved but
585
age-restricted source regions. One zircon grain has a TDM2 age of 1.94 Ga identical to
586
its U-Pb age of 1.92 Ga, and high εHf(t) value (9.9), indicating possibly minor addition
587
of juvenile crust at this period.
cr
ip t
582
The majority of late Paleoproterozoic zircons with negative εHf(t) values ( -16.1 to
589
-1.0) and old TDM2 ages ( 2.51-3.42 Ga) suggest recycling origin of the
590
zircon-saturated magma. Two zircons with ages of 1.62 and 1.81 Ga have positive
591
εHf(t) values (4.3 and 7.9) and TDM2 ages (1.98 and 2.05 Ga), again supporting the
592
possibility of minor addition of juvenile materials between 1.90 and 2.10 Ga.
M
an
us
588
Early Mesoproterozoic zircons (1.40-1.60 Ga) with scattered εHf(t) values (-18.1 to
594
13.8) and TDM2 ages (1.43-3.41 Ga), with the majority at 2.15-2.37 Ga) suggest
595
recycling of variable amounts of pre-existing continental crust. Nearly all late
596
Mesoproterozoic (1.00-1.30 Ga) zircons have εHf(t) values (-9.7 to 6.9) significantly
597
lower than the depleted mantle reservoir (Figs. 9 and 10), implying reworking of older
598
crust with insignificant addition of juvenile crust during this period.
600
Ac ce pt e
599
d
593
5.3.2. Early-Neoproterozoic addition of juvenile crust
601
The dominantly early Neoproterozoic (750-980 Ma) zircon detritus has
602
significant implications. Chondritic to near DM Hf isotopic compositions (εHf(t) values
603
mostly from 0 to 16.4) (Figs. 9 and 10) reveal formationaddition of juvenile material
604
at 860-980 Ma. A few 860-980 Ma zircons with negative εHf(t) values (-17.0 to -2.0)
23
Page 67 of 105
and old TDM2 ages (1.91-2.81 Ga) suggest involvement of reworked older crust. The
606
most important predominant detrital zircons between 810-860 Ma have a wide range
607
of εHf(t) values (-21.5 to 15.8) and TDM2 ages (739-3041 Ma) (Figs. 9 and 10),
608
demonstrating derivation of magmas from both depleted mantle reservoir and older
609
continental curst. Variable εHf(t) values and TDM2 ages imply variable degrees of
610
mixing between juvenile magmas and ancient crust, possibly due to the assimilation
611
during magma ascent. Addition of juvenile crustal materials likely became
612
insignificant after ca. 805 Ma (Figs 9 and 10) and as most 750-805 Ma detrital zircons
613
have sub-chondritic Hf isotopic compositions, e.g. low εHf (t) values (-21.9 to -2.5) and
614
old TDM2 ages (1.85-3.05 Ga).
an
us
cr
ip t
605
615 616
5.4. Implications for the tectonic evolution of the eastern Jiangnan Orogen
618
M
617
Formatted: Line spacing: Double
5.4.1. Tectonic setting of the basin
The obtained age spectra with predominantThe dominant Neoproterozoic
620
zircons and statistically insignificant older continental-derived zircons in all
621
Shuangqiaoshan (except WW247 from the Xiushui Fm) and Xikou samples (except
622
WN1086 from the Zhentou Fm) are typical of sediments accumulated in basins
623
associated with a magmatic arc (DeGraaff-Surpless et al., 2002; Goodge et al., 2004)
624
but are inconsistent with continental rift or passive margin sedimentation, which
625
would be expected to have the majority of detritus derived from exhumed older
626
continental crust (Goodge et al., 2002, 2004). The nearly syn-magmatic sedimentation
627
and relatively euhedral igneous zircons suggest a nearby source within the eastern
628
Jiangnan Orogen for the Neoproterozoic detritus and reflect fast erosion and
629
deposition of newly formed igneous rocks. etritus derived from the Cathaysia Block
Ac ce pt e
d
619
24
Page 68 of 105
would be expected to contain Grenville (extending from 1300 to 950 Ma) materials
631
(Wang et al., 2010a and reference therein) (Fig. 11). Such Grenville materials do not
632
appear to be present in the Shuangqiaoshan and Xikou Groups, The Cathaysia Block
633
could be a possible source if it was connected with the Yangtze Block during the
634
sedimentation of the Shuangqiaoshan and Xikou Groups. However, detritus derived
635
from the Cathaysia Block would be expected to contain Grenville (extending from
636
1300 to 950 Ma) materials (Wang et al., 2010a and reference therein), which are
Formatted: Font: Not Italic, Font color: Auto
637
scarce in the studied samples (Fig. 11), suggesting the Cathaysia Block was separated
Formatted: Font: Not Italic, Font color: Auto
638
from the Yangtze Block and could not provide detritus to the Shuangqiaoshan and
639
Xikou Groups. Although the Cathaysia Block could likely provide 1000-800 Ma
640
detritus (Li et al., 2005; Yu et al., 2007; Shu et al., 2011) to the nearby eastern
641
Yangtze Block if both were juxtaposed, detritus derived from the Cathaysia Block
642
would be expected to contain Grenville (extending from 1300 to 950 Ma) materials
643
(Wang et al., 2010a and reference therein) (Fig. 11). Such Grenville materials do not
644
appear to be present in the Shuangqiaoshan and Xikou Groups, suggesting the
645
Cathaysia and Yangtze Blocks were not sutured during the deposition of these strata.
646
Additionally, Hf isotopic compositions of the early Neoproterozoic (~810-860 Ma)
647
zircons reveal variable degrees of assimilation of pre-existing older crust to the
648
juvenile magma, the mixing process of which is typical of granitoid rocks in
649
modern-day magmatic arc settings (Tatsumi and Kogiso, 2003). Chemical
650
compositions of the siliciclastic rocks from the Shuangqiaoshan and Xikou Groups
651
have features similar to sedimentary rocks accumulated inat active continental
652
margins (Huang et al., 2003; Zhang et al., 2010), consistent with the magmatic arc
653
setting bracketedsuggested by the detrital zircons. Sandstone from both the
654
Shuangqiaoshan and Xikou Groups are compositionally immature with dominantly
Ac ce pt e
d
M
an
us
cr
ip t
630
25
Page 69 of 105
poorly-sorted volcanic lithic and feldspar detritus and minor detrital quartz (Ma et al.,
656
2001; Huang et al., 2003), suggesting sedimentary detritus derived exclusively from
657
volcanic sources in a magmatic arc setting (Dickinson, 1970). The Xiushui Fm in
658
northwestern Jiangxi and the Zhentou Fm in southern Anhui contain thick layers of
659
conglomerate, pebbly sandstone and coarse sandstone at their bases (Fig. 5),
660
representing syn-orogenic molasse formed in a retro-arc foreland basin at 817-815 Ma.
661
Samples WW247 from the Xiushui Fm and WN1086 from the Zhentou Fm have
662
additional input of Pre-Neoproterozoic detritus (Fig. 8), likely derived from the
663
uplifted older basement complexes.
us
cr
ip t
655
664
5.4.2. An integrated tectonic model
an
665
Our new dataset together with published data allow us to propose a modified
667
model for the tectonic evolution of the eastern Jiangnan Orogen (Fig. 13). A
668
NW-dipping oceanic subduction zone along what is the present-day eastern margin of
669
the Yangtze Block is possible on the basis of the 930-890 Ma arc volcanic rocks in the
670
Shuangxiwu Group (Li et al., 2009) and the presence of 930-890 Ma detrital zircons
671
with chondritic to DM-like Hf isotopic compositions (Figs. 9 and 10). Arc-continent
672
collision probably took place at 880-860 Ma as bracketed by the emplacement of 880
673
± 19 Ma obduction-type granites (Li et al., 2008a) and the 858 ± 11 Ma Huaiyu
674
ophiolite (Shu et al., 2006). A back-arc basin was initialed above the continental crust
675
as marked by the 848-824 Ma supra-subduction zone ophiolite in southern Anhui (Li
676
et al., 1997; Ding et al., 2008; Zhang et al., 2012a). Volcanic rocks in this period were
677
largely eroded and transported to the back-arc and retroarc foreland basins due to
678
subsequent orogenic uplift. Abundant 860-810 detrital zircons have Hf isotopic
679
compositions, indicating mixture between juvenile crust and continental basement
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26
Page 70 of 105
(Figs. 9 and 10) and revealing providing support for the existence of an extensive
681
magmatic arc during this period. The basin began to form at ca. 830 Ma and was filled
682
with a set of volcanic-terrigenous arenopelitic flysch sequence with some
683
well-preserved primary sedimentary structures, such as cross- and graded-bedding and
684
scoured based sequences (Fig. 5), indicative of a quiet and low-energy depositional
685
environment (Wu, 2007; Zhang et al., 2010). Greywacke of the flysch sequence
686
contains poorly-sorted and subangular fractions of lithic fragments and less feldspar
687
and quartz (Wu, 2007). Along with basin evolution, the sedimentary strata contained
688
additional interlayered calc-alkaline felsic-intermediate volcanic lava of arc-affinity
689
that strongly supports a magmatic arc setting (Zhang et al., 2010). The Niuwu and
690
Anlelin Fms are characterized by repeated sedimentary cycles of pebbly sandstone
691
and shale (Fig. 5), typical of flysch formed in a back-arc basin. Basin closure was
692
marked by the 828-819 Ma syn-collisional cordierite-bearing peraluminous granitoids
693
(CPG) (Li et al., 2003a; Zhong et al., 2005; Wang et al., 2006) and subsequent
694
syn-orogenic uplift which led to basin restriction and the formation of a regional
695
unconformity. As a result, a retro-arc foreland basin was formed, in which the Xiushui
696
and Zhentou Fms were deposited with detritus from both remnant magmatic arc and
697
uplifted basement. Subsequently, the emplacement of extensive 805-760 Ma bimodal
698
volcanic sequences (Wang et al., 2011b) and 780-770 Ma K-rich calc-alkaline
699
granitoids (KCG) (Zheng et al., 2008; Xue et al., 2010) in the eastern Jiangnan
700
Orogen record post-collisional orogenic rifting, which is marked by remelting of
701
pre-existing rocks as recorded by the sub-chondritic Hf isotopic compositions of most
702
805-750 Ma detrital zircons (Figs. 9 and 10).
Ac ce pt e
d
M
an
us
cr
ip t
680
703 704
5.4.3. Possible reconstruction of the Yangtze Block in Rodinia
27
Page 71 of 105
It has long been debated if the Yangtze Block was in the central Rodinia, likewise
706
whether or not the Jiangnan Orogen is part of a Grenville Orogen (Li et al., 1995,
707
2008d; Zhou et al., 2002, 2008; Yan et al., 2002; Zheng, 2004; Yu et al., 2008; Wang
708
and Zhou, 2012). However, the back-arc to retro-arc foreland setting for the 830-815
709
Ma Shuangqiaoshan and Xikou Groups does not support an intra-cratonic setting.
710
Neither coeval mantle plume rift system nor a Grenville Orogen recorded in
711
southeastern Australia and western Laurentia (Li et al., 2008d) exist in the eastern
712
Jiangnan Orogen. In addition, the facts that the Jiangnan Orogen is somewhat younger
713
than the Grenville Orogen and that there is insignificant Grenville magmatism and no
714
Grenville juvenile crust recorded by detrital zircons from the strata in the Jiangnan
715
Orogen suggest that this orogen cannot be correlated with the worldwide Grenville
716
Orogen and that the Yangtze Block was unlikely located between Australia–East
717
Antarctica and Laurentia as proposed by Li et al. (1995). However, source analysis
718
suggests interior rather than extraneous detritus supplied to the widespread 830-815
719
Ma sedimentary sequences of the Jiangnan Orogen (Wang et al., 2010a and this study),
720
suggesting that the Yangtze Block was likely located along the margin of Rodinia as
721
an individual continental block rather than in the centre of the supercontinent.
723 724 725 726 727 728 729
cr
us
an
M
d
Ac ce pt e
722
ip t
705
6. Conclusions
Principal conclusions of this study are as follows: (1). The previously thought Mesoproterozoic sedimentary sequences in the
eastern Yangtze Block actually formedwas deposited betwee at 833 and -815 Ma. (2). The 833-815 Ma sedimentary sequence represents a sedimentary cycle from a back-arc to retro-arc foreland basin.
28
Page 72 of 105
730 731
(3). and tThe juxtaposition of the Yangtze and Cathaysia Blocks likely lasted to ca. 815 Ma or even later. (34). Three major episodes of magmatic activities at 2.50-2.35 Ga, 2.10-1.90 Ga
733
and 980-800 Ma are recognized in the source areas of the Neoproterozoic sedimentary
734
basin, whereas the Grenville (1.30-1.00 Ga) magmatism was insignificant.
ip t
732
(45). No Grenville juvenile crust in the eastern Yangtze Block is identified. The
736
most important generation of juvenile crust occurred at early Neoproterozoic
737
(~980-810 Ma) in combination with reworked older crust at 860-810 Ma.
continent rather than in the centre of the supercontinent Rodinia.
740
Acknowledgements
M
741 742
us
(5). The Yangtze Block was likely located along the margin as an individual
an
739
cr
735
738
This study was supported by the Research Grant Council of Hong Kong SAR,
744
China (HKU 707210P), National Natural Science Foundation of China (NSFC
745
41272212) and the oversea famous professor program (MS2011ZGDZ (BJ) 019). We
746
would like to thank Dr. Jianfeng Gao for his help with field trip and Prof. Liang Qi for
747
the LA-ICPMS work. Thanks go to Dr. Jean Wong and Dr. Hongyan Geng for help
748
with Lu-Hf analysis and Lily Chiu for CL imaging. Constructive reviewers from
749
Journal Editor Professor Randall Parrish and two anonymous reviewers have
750
substantially improved the performance, especially the presentation of U-Pb-Hf
751
isotopic results, of this manuscript and are kindly acknowledge.
Ac ce pt e
d
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752
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753 754
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Plumb, K., 1991. New Precambrian time scale. Episodes 14, 139-140. Qiu, Y.M., Gao, S., McNaughton, N.J., Groves, D.I., Ling, W., 2000. First evidence of >3.2 Ga continental crust in the Yangtze craton of south China and its implications for Archean crustal evolution and Phanerozoic tectonics. Geology 28, 11-14. Shu, L., Faure, M., Jiang, S., Yang, Q., Wang, Y., 2006. SHRIMP zircon U-Pb age, litho-and biostratigraphic analyses of the Huaiyu Domain in South China. Episodes 29, 244-252. Shu, L.S., Faure, M., Yu, J.H., Jahn, B.M., 2011. Geochronological and geochemical features of the Cathaysia block (South China): New evidence for the Neoproterozoic breakup of Rodinia. Precambrian Research 187, 263-276. Sláma, J., Košler, J., Condon, D. J., Crowley, J. L., Gerdes, A., Hanchar, J. M., Horstwood, M. S. A., Morris, G. A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M. N., and Whitehouse, M. J. (2008) Plešovice zircon—A new natural reference material for U-Pb and Hf isotopic microanalysis. Chemical Geology 249(1-2): 1-35.
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Wang, W., Wang, F., Chen, F., Zhu, X., Xiao, P., Siebel, W., 2010b. Detrital Zircon
1005
Ages and Hf‐Nd Isotopic Composition of Neoproterozoic Sedimentary Rocks in the Yangtze Block: Constraints on the Deposition Age and Provenance. The Journal of Geology 118, 79-94. Wang, W., Zhou, M.-F., 2012. Sedimentary records of the Yangtze Block (South China) and their correlation with equivalent Neoproterozoic sequences on adjacent continents. Sedimentary Geology 265–266, 126-142. Wang, W., Zhou, M.-F., Yan, D.-P., Li, J.-W., 2012b. Depositional age, provenance, and tectonic setting of the Neoproterozoic Sibao Group, southeastern Yangtze Block, South China. Precambrian Research 192-195, 107-124. Wang, X.L., Shu, L.S., Xing, G.F., Zhou, J.C., Tang, M., Shu, X.J., Qi, L., Hu, Y.H., 2011b. Post-orogenic extension in the eastern part of the Jiangnan orogen: Evidence from ca 800-760 Ma volcanic rocks. Precambrian Research in press. Wang, X.L., Zhao, G.C., Zhou, J.C., Liu, Y., Hu, J., 2008. Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: Implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen. Gondwana Research 14, 355-367. Wang, X.L., Zhou, J.C., Griffin, W.L., Wang, R.C., Qiu, J.S., O’Reilly, S.Y., Xu, X., Liu, X.M., Zhang, G.L., 2007. Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: Dating the assembly of the Yangtze and Cathaysia Blocks. Precambrian Research 159, 117-131. Wang, X.L., Zhou, J.C., Qiu, J.S., Zhang, W.L., Liu, X.M., Zhang, G.L., 2006. LA-ICP-MS U-Pb zircon geochronology of the Neoproterozoic igneous rocks from Northern Guangxi, South China: Implications for tectonic evolution. Precambrian Research 145, 111-130. Wang, Y.J., Zhang, F.F., Fan, W.M., Zhang, G.W., Chen, S.Y., Cawood, P.A., Zhang, A.M., 2011c. Tectonic setting of the South China Block in the early Paleozoic: resolving intracontinental and ocean closure models from detrital zircon U-Pb geochronology. Tectonics 29. Wu, R.X., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Zhang, S.B., Liu, X.M., Wu, F.Y., 2006. Reworking of juvenile crust: Element and isotope evidence from Neoproterozoic granodiorite in South China. Precambrian Research 146, 179-212. Wu, X.H., 2007. Rediscuss of Shuangqiaoshan group. Resources survey & environment (in Chinese with English abstract) 28, 95-105. Wu, Y.B., Zheng, Y.F., Gao, S., Jiao, W.F., Liu, Y.S., 2008. Zircon U-Pb age and trace element evidence for Paleoproterozoic granulite-facies metamorphism and Archean crustal rocks in the Dabie Orogen. Lithos 101, 308-322. Xia, X.P., Sun, M., Zhao, G.C., Wu, F.Y., Xu, P., Zhang, J., Luo, Y., 2006. U-Pb and Hf isotopic study of detrital zircons from the Wulashan khondalites: Constraints on the evolution of the Ordos Terrane, Western Block of the North China Craton. Earth and Planetary Science Letters 241, 581-593. Xue, H.M., Ma, F., Song, Y.Q., Xie, Y.P., 2010. Geochronology and geochemisty of the Neoproterozoic granitoid association from eastern segment of the Jiangnan orogen, China: Constraints on the timing and process of amalgamation between the Yangtze and Cathaysia blocks. Acta Petrologica Sinica 26, 3215-3244. (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Malpas, J., 2002. Where was South China located in the reconstruction of Rodinia. Earth Sci. Frontiers 9, 249-256 (in Chinese with English abstract).
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1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053
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Yan, D.P., Zhou, M.F., Song, H.L., Wang, X.W., Malpas, J., 2003. Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China). Tectonophysics 361, 239-254. Ye, M.F., Li, X.H., Li, W.X., Liu, Y., Li, Z.X., 2007. SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc along the southeastern margin of the Yangtze Block. Gondwana Research 12, 144-156. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhang, M., Wang, R.C., Jiang, S.Y., Shu, L.S., 2008. Where was South China in the Rodinia supercontinent?:: Evidence from U-Pb geochronology and Hf isotopes of detrital zircons. Precambrian Research 164, 1-15. Yu, J.H., O'Reilly, S.Y., Wang, L.J., Griffin, W.L., Zhou, M.F., Zhang, M., Shu, L.S., 2010. Components and episodic growth of Precambrian crust in the Cathaysia Block, South China: Evidence from U-Pb ages and Hf isotopes of zircons in Neoproterozoic sediments. Precambrian Research 181, 97-114. Yu, J.H., O'Reilly, Y.S., Wang, L.J., Griffin, W.L., Jiang, S.Y., Wang, R.C., Xu, X.S., 2007. Finding of ancient materials in Cathaysia and implication for the formation of Precambrian crust. Chinese Science Bulletin 52, 11-18. Yu, J.H., O’Reilly, S.Y., Zhou, M.F., Griffin, W.L., Wang, L.J., 2011. U–Pb geochronology and Hf–Nd isotopic geochemistry of the Badu Complex, Southeastern China: Implications for the Precambrian crustal evolution and paleogeography of the Cathaysia Block. Precambrian Research. doi:10.1016/j.precamres.2011.07.014. Yu, J.H., Wang, L.J., O'Reilly, S.Y., Griffin, W.L., Zhang, M., Li, C.Z., Shu, L.S., 2009. A Paleoproterozoic orogeny recorded in a long-lived cratonic remnant (Wuyishan terrane), eastern Cathaysia Block, China. Precambrian Research 174, 347-363. Zhang, S.B., Wu, R.X., Zheng, Y.F., 2012a. Neoproterozoic continental accretion in South China: geochemical evidence from the Fuchuan ophiolite in the Jiangnan orogen. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.010 Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006a. Zircon U-Pb age and Hf-O isotope evidence for Paleoproterozoic metamorphic event in South China. Precambrian Research 151, 265-288. Zhang, S.B., Zheng, Y.F., Wu, Y.B., Zhao, Z.F., Gao, S., Wu, F.Y., 2006b. Zircon U-Pb age and Hf isotope evidence for 3.8 Ga crustal remnant and episodic reworking of Archean crust in South China. Earth and Planetary Science Letters 252, 56-71. Zhang, X.H., Zhang, Z.J., Guo, J.Q., Xiong, Q.H., 1999. Stratigraphy and sedimentary sequences of the upper part of the Proterozoic Shuangqiaoshan Group in Xiushui-Wuning area, Jiangxi. Journal of Stratigraphy 23, 71-77. (in Chinese with English Abstract). Zhang, Y.J., Zhou, X.H., Liao, S.B., Zhang, X.D., Wu, B., Wang, C.Z., Yu, M.G., 2010. Neoproterozoic crustal composition and orogenic process of the Zhanggongshan area, Anhui-Jiangxi. Acta Geological Sinia 84, 1401-1427. (in Chinese with English Abstract). Zhang, Y.Z., Wang, Y.J., Fan, W.M., Zhang, A.M., Ma, L.Y., 2012b. Geochronological and geochemical constraints on the metasomatised source for the Neoproterozoic (∼825 Ma) high-Mg volcanic rocks from the Cangshuipu area (Hunan Province) along the Jiangnan Domain and their
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1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103
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tectonic implications. Precambrian Research, in press, doi: 10.1016/j.precamres.2012.07.003 Zhao, G.C., Cawood, P., 1999. Tectonothermal evolution of the Mayuan Assemblage in the Cathaysia Block; implications for Neoproterozoic collision-related assembly of the South China Craton. American Journal of Science 299, 309-339. Zhao, J.-H., Zhou, M.-F., 2008. Neoproterozoic adakitic plutons in the northern margin of the Yangtze Block, China: Partial melting of a thickened lower crust and implications for secular crustal evolution. Lithos 104, 231-248. Zhao, J.-H., Zhou, M.-F., Zheng, J.-P., Fang, S.-M., 2010a. Neoproterozoic crustal growth and reworking of the Northwestern Yangtze Block: Constraints from the Xixiang dioritic intrusion, South China. Lithos 120, 439-452. Zhao, J.H., Zhou, M.F., 2007a. Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): Implications for subduction-related metasomatism in the upper mantle. Precambrian Research 152, 27-47. Zhao, J.H., Zhou, M.F., 2007b. Neoproterozoic adakitic plutons and arc magmatism along the western margin of the Yangtze Block, South China. The Journal of Geology 115, 675-689. Zhao, J.H., Zhou, M.F., Yan, D.P., Zheng, J.P., Li, J.W., 2011. Reappraisal of the ages of Neoproterozoic strata in South China: no connection with the Grenvillian orogeny. Geology 39, 299-302. Zhao, X.F., Zhou, M.F., Li, J.W., Sun, M., Gao, J.F., Sun, W.H., Yang, J.H., 2010b. Late Paleoproterozoic to early Mesoproterozoic Dongchuan Group in Yunnan, SW China: Implications for tectonic evolution of the Yangtze Block. Precambrian Research 182, 57-69 Zheng, J.P., Griffin, W.L., O’, Reilly, S.Y., 2006a. Widespread Archean basement beneath the Yangtze craton. Geology 34, 417-420. Zheng, Y.-F., Zhao, Z.-F., Wu, Y.-B., Zhang, S.-B., Liu, X., Wu, F.-Y., 2006b. Zircon U-Pb age, Hf and O isotope constraints on protolith origin of ultrahigh-pressure eclogite and gneiss in the Dabie orogen. Chemical Geology 231, 135-158. Zheng, Y.F., 2003. Neoproterozoic magmatic activity and global change. Chinese Science Bulletin 48, 1639-1656. Zheng, Y.F., 2004. Position of South China in configuration of Neoprotero-zoic supercontinent. Chinese Science Bulletin 49, 751-753. Zheng, Y.F., Wu, R.X., Wu, Y.B., Zhang, S.B., Yuan, H., Wu, F.Y., 2008. Rift melting of juvenile arc-derived crust: Geochemical evidence from Neoproterozoic volcanic and granitic rocks in the Jiangnan Orogen, South China. Precambrian Research 163, 351-383. Zheng, Y.F., Zhang, S.B., Zhao, Z.F., Wu, Y.B., Li, X.H., Li, Z.X., Wu, F.Y., 2007. Contrasting zircon Hf and O isotopes in the two episodes of Neoproterozoic granitoids in South China: Implications for growth and reworking of continental crust. Lithos 96, 127-150. Zhong, Y.F., Ma, C.Q., She, Z.B., Lin, G.C., Xu, H.J., Wang, R.J., Yang, K.G., Liu, Q., 2005. SHRIMP U-Pb Zircon Geochronology of the Jiuling Granitic Complex Batholith in Jiangxi Province. Earth Science-Journal of China University of Geosciences 30, 685-691. (in Chinese with English abstract). Zhou, G.Q., 1989. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high
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1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153
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temperature-high pressure metamorphic rocks. Journal of Southeast Asian Earth Sciences 3, 237-247. Zhou, J.C., Wang, X.L., Qiu, J.S., 2008. Is the Jiangnan Orogenic Belt a Grenvillian Orogenic Belt: some problems about the Precambrian Geology of South China. Geological Journal of China Universities 14, 64-72. (in Chinese with English Abstract). Zhou, M.F., Kennedy, A.K., Sun, M., Malpas, J., Lesher, C.M., 2002a. Neoproterozoic arc-related mafic intrusions along the northern margin of South China: Implications for the accretion of Rodinia. The Journal of Geology 110, 611-618. Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006a. The Yanbian Terrane (Southern Sichuan Province, SW China): A Neoproterozoic arc assemblage in the western margin of the Yangtze Block. Precambrian Research 144, 19-38. Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y.Q., Ding, J., 2002b. SHRIMP zircon geochronological and geochemical evidence for Neoproterozoic arc-related magmatism along the western margin of the Yangtze Block, South China. Earth and Planetary Science Letters 196, 51-67. Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A., 2006b. Subduction-related origin of the 750 Ma Xuelongbao adakitic complex (Sichuan Province, China): Implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth and Planetary Science Letters 248, 286-300. Zhu, X.Y., Chen, F., Li, S.Q., Yang, Y.Z., Nie, H., Siebel, W., Zhai, M.G., 2011. Crustal evolution of the North Qinling terrain of the Qinling Orogen, China: Evidence from detrital zircon U-Pb ages and Hf isotopic composition. Gondwana Research 20, 194-204.
1182
d
1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181
Figure captions.
1184
Fig.1. Distribution of Precambrian units in the eastern segment of the Jiangnan orogen
1185
(modified after (Ma et al., 2002; Wang et al., 2011b). Inserted map on the top
1190
Ac ce pt e
1183
1191
plagiogranite (Ye et al., 2007; Chen et al., 2009b); 4- ca. 848 Ma Gangbian
1186 1187 1188 1189
left showing location of the Jiangnan orogen in the South China Craton. Blue dash line shows the boundary between provinces. AH: Anhui province; JX: Jiangxi province; ZJ: Zhejiang province. 1-ca.970-880 Ma northern Jiangxi ophiolitic complex (Li and Li, 2003; Li et al., 2008a); 2-ca. 930-890 Ma Shuangxiwu volcanic rocks (Li et al., 2009); 3-ca. 910-900 Ma Pingshui
38
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1192
alkaline complex (Li et al., 2010b); 5- ca. 850 Ma Zhenzhushan volcanic rocks
1193
(Li et al., 2010a)
1194
1196
Fig. 2. Sketch map showing the distribution of the Shuangqiaoshan Group and Nanhua system sequence in the northwestern Jiangxi Province.
1197
ip t
1195
Fig. 3. Sketch map showing the distribution of the Xikou Group as well as other
1199
Neoproterozoic units in the southern Anhui Province. Faults in this figure
1200
refers to legend in Fig. 2.
us
cr
1198
1201
Fig. 4. Stratigraphy of the major Neoproterozoic sedimentary units in the eastern
1203
Yangtze Block. The Zhentou Fm is tentatively considered as the upper part of
1204
the Xikou Group, considering its similarity with the Xiushui Fm in the upper
1205
part of the Shuangqiaoshan Group. The columns are not strictly to scale. Stars
1206
and italic numbers represent sample location relative to stratigraphic column
1207
and sample numbers. Bold italic numbers represent the reported ages of
1209
M
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Ac ce pt e
1208
an
1202
volcanic tuffs; see text for details and discussion.
1210
Fig. 5. Out crop features of represented sedimentary units.Structures of marine
1211
sediments investigated during this study: (a) Parallel bedding and rhythmic
1212 1213 1214
layers between reddish siltstone and sandstone in the Jilin Formation; (b) partial Bouma sequences in the Anlelin Fm; (c) Grading Graded and cross bedding in the Anlelin Fm; (d) boundary between the Anlelin and Xiushui
1215
Fms. The sandstone interlayers in the silty slate are lenticular which may be
1216
result of wave current
in the Banqiao Formation; (e) lenticular and cross
39
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1217
bedding developed between grey siltstone and slate; (f) Wavy contoured bed
1218
with different wavelength and slump structure in the Mukeng Fm; (g) grading
1219
bedding developed in the Niuwu Fm; (h) coarse quartz sandstone from the
1220
Xiuning Fm.
ip t
1221
Fig. 6. Concordia diagrams showing results of U-Pb dating of plots of detrital zircon
1223
grains from the Shuangqiaoshan Group and Dongmen Fm. Inserted diagrams
1224
show representative CL images and weighted meanconcordant ages (for
1225
ages<1.0 Ga,
1226
ages are presented) of the youngestindividual analyzed grains.
Pb/238U ages are presented and for ages>1.0 Ga,
207
Pb/206Pb
an
us
206
cr
1222
1227
Fig. 7. Concordia diagrams showing results of U-Pb dating Concordia plots of detrital
1229
zircon grains from the Xikou Group and Xiuning Formation. Inserted
1230
diagrams show representative CL images and concordant ages (for ages<1.0
1231
Ga,
1232
presented) of individual analyzed grains.weighted mean ages of the youngest
1234
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Pb/238U ages are presented and for ages>1.0 Ga,
207
Pb/206Pb ages are
d
206
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1233
Formatted: Font: Not Italic, Superscript
M
1228
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grains.
1235
Fig. 8. Relative probability versus age diagramsDetrital zircons age histograms. The
Formatted: Font: Not Italic
1236
reds curves show the frequency of individual zircon populations (for details
Formatted: Font: Not Italic
see text). Each Some samples isare plotted at two scales to highlight the
Formatted: Font: (Default) Times New Roman, 12 pt, Not Italic, Font color: Auto, Pattern: Clear
1237 1238 1239
distribution of Neoproterozoic ages. Samples are presented in stratigraphic order.
1240
40
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1241
Fig. 9. Hf isotopic compositions of detrital zircons from Shuangqiaoshan Group and
1242
Dongmen Fm. (a) εHf(t) values versus U-Pb ages; (b) TDM2 Histograms ofversus
1243
U-Pb ages. DM : delepted mantle ; CHUR : chondritic uniform reservoir ; 3.2
1244
Ga crust means materials were derived from delepted mantle at 3.2 Ga and
1245
evolved with average continental crust 176Lu/177Hf of 0.015.
ip t
Formatted: Font: Not Italic, Superscript Formatted: Font: Not Italic, Superscript
1246
Fig. 10. Hf isotopic compositions of detrital zircons from Xikou Group and Xiuning
1248
Fm. (a) εHf(t) values versus U-Pb ages; (b) Histograms of TDM2 versus U-Pb
1249
ages. The meaning of DM, CHUR and 3.2 Ga crust is explained in caption of
1250
Fig. 9.
an
us
cr
1247
1251
Fig. 11. Probability plots of detrital zircons from Neoproterozoic sedimentary units in
1253
the eastern Yangtze Block and their potential sources. The number of y-axis
1254
represents the number of analyses. Data sources for Pre-Neoproterozoic units:
1255
the Kongling complex, (Qiu et al., 2000; Zhang et al., 2006a, b; Gao et al.,
1256
2011); the Tianli schist, (Li et al., 2007); Xenocrystic zircons from lamproite,
1258 1259 1260 1261 1262 1263
d
Ac ce pt e
1257
M
1252
(Zheng et al., 2006a); the western Yangtze Block, (Greentree et al., 2006; Greentree and Li, 2008; Zhao et al., 2010b; Wang et al., 2011a); the Cathaysia Block, (Li, 1997; Wan et al., 2007; Li et al., 2010c; Yu et al., 2011). Data sources for Neoproterozoic unit: the southeastern Yangtze Block, (Li and Li, 2003; Li et al., 2003b, 2008b, 2009, 2010b; Wang et al., 2006; Wu et al., 2006; Zheng et al., 2008); the western Yangtze Block, (Zhou et al., 2002b, 2006a; Li et al., 2003b; Zhao and Zhou, 2007a, b); the northern Yangtze Block, (Zhou et
1264
al., 2002a, 2006b; Zhao and Zhou, 2008; Zhao et al., 2010a), the Cathaysia
1265
Block, (Wan et al., 2007; Li et al., 2010c; Shu et al., 2011).
41
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1266 1267 1268
Fig. 12. Cumulative probability plots of the zircon age data for Neoproterozoic siliciclastic sequences of the eastern Yangtze Block.
1269
ip t
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discussion.
d
1271
Fig. 13. Sequential tectonic evolution of the eastern Jiangnan orogen. See text for
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1270
42
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cr
Southern Anhui
us
The Xikou Group WN1004 WN1012
>2500 Ma
1021±31(3,0.16) 1392±32(2,0.11)
833±8(4,0.04) 860±4(17,0.35) 884±3(27,1.12) 906±6(9,0.19) 932±6(8,0.59)
1551±72(4,3.4)
WN1025
WN1086
The Nanhua Sequence WN1031 751±8(3,0.007) 777±7(6,0.99) 804±6(7,0.49)
817±4(12,0.33) 830±4(26,0.45) 827±5(10,0.28) 846±3(28,0.75) 840±3(22,0.61) 854±11(3,0.1) 860±4(19,0.67) 862±6(6,0.06) 870±5(9,0.03) 884±(12,1.13) 884±8(12,0.11) 886±14(2,0.06) 913±8(5,0.06） 906±16(1) 960±11(3,0.34) 932-965(3)
1419±35(2,0.004) 1567±33(2,0.007)
1457-1514Ma(2)
1720±26(3,0.24)1620±26(3,0.04) 1658±23(5,0.36) 1764±28(2,0.014) 1741±29(3,0.11) 1785±22(5,0.56）1803±28(3,0.62) 2083±87(5,31) 1945±110(4,8.2)1993±12(33,0.8) 2027±19(21,3.5)2058±156(1) 2015±42(1) 2040±76(4,3.7) 1991±27(4,0.07) 2369-2449(2) 2397±22(23,3.1）2366±17(13,2.1) 2379±44(1) 2461±38(1) 2445±13(8,0.31)2495±40(1) 2487±42(1) 2424±42(1) 2479±26(9,2.1) 2594±50(1) 2545±35(4,0.83) 2566±38(1) 2576±38(1) 2582±33(3,0.51) 2683±34(1) 2727±36(1) 2694±48(1) 2702-2759(2)
pt
~16002500
1253±38(3,1.8) 1139-1517(3)
ce
~10001600
ed
M
an
Table 1. Age groups for analyzed detrital zircons from the eastern Jiangnan Orogen Age Northwestern Jiangxi groups The Shuangqiaoshan Group The Nanhua Sequence WW236 WW176 WW247 WW153 WW197 ~750753±8(2,0.06) 1000 792±9(5,0.53) 801±5(7,0.54) 818±6(6,0.06) 815±5(9,0.32) 817±9(3,0.17) 823±8(4,0.08) 826±3(34,1.18) 830±5(8,0.42) 850±4(23,0.32) 843±3(24,1.12) 844±8(3,0.07) 865±7(7,0.41) 872±5(13,0.27) 869±6(6,0.83) 879±7(4,0.45) 895±10(3,0.23) 897±9(3,0.62) 898±6(6,1.04) 895±9(3,0.47) 946±22(5,2.3) 950±21(5,2.3) 931±6(6,0.32)
ip t
Table 1
1999±12(25,1.4) 2319±34(9,4.1） 2462±19(12,1.8) 2611±46(1)
Ac
Note: Weighted mean ages of each group of ages according to the age peaks shown in Figure 8. Only concordant ages (90%
Page 87 of 105
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Table 2
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ce
pt
ed
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an
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Table 2. K-S P-values using error in the CDF WW236 WW176 WW247 WN10-02 WN10-12 WN10-25 WN10-86 WN10-31 WW153 WW197 WW236 0.998 0.000 0.000 0.026 0.157 0.001 0.000 0.000 0.000 WW176 0.998 0.011 0.000 0.118 0.633 0.011 0.000 0.000 0.000 WW247 0.000 0.011 0.032 0.095 0.000 0.079 0.000 0.000 0.000 WN10-02 0.000 0.000 0.032 0.006 0.000 0.000 0.000 0.000 0.000 WN10-12 0.026 0.118 0.095 0.006 0.097 0.012 0.000 0.000 0.000 WN10-25 0.157 0.633 0.000 0.000 0.097 0.001 0.000 0.000 0.000 WN10-86 0.001 0.011 0.079 0.000 0.012 0.001 0.000 0.000 0.000 WN10-31 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.312 0.299 WW153 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.312 0.597 WW197 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.299 0.597 K-S: Kolmogorov-Smirnov test (Massey Jr, 1951); P values: the probability, if the test statistic really were distributed as it would be under the null hypothesis, of observing a test statistic the one actually observed; CDF: Cumulative Distribution Function.
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Gravel-bearing sandstone
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Supplementary Table 1 Click here to download Supplementary material for on-line publication: Supplementary Table 1.xlsx
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Supplementary Table 2 Click here to download Supplementary material for on-line publication: Supplementary Table 2.xlsx
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Supplementary Table 3 Click here to download Supplementary material for on-line publication: Supplementary Table 3.xlsx
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Supplementary Table 4 Click here to download Supplementary material for on-line publication: Supplementary Table 4.xlsx
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