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Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent
Accepted Manuscript Title: Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent Author: Xiaozhuang Cui Xinsheng Jiang Jian Wang Xuance Wang Jiewen Zhuo Qi Deng Shiyong Liao Hao Wu Zhuofei Jiang Yanan Wei PII: DOI: Reference:
S0301-9268(15)00257-0 http://dx.doi.org/doi:10.1016/j.precamres.2015.07.017 PRECAM 4324
To appear in:
Precambrian Research
Received date: Revised date: Accepted date:
10-2-2015 22-7-2015 27-7-2015
Please cite this article as: Cui, X., Jiang, X., Wang, J., Wang, X., Zhuo, J., Deng, Q., Liao, S., Wu, H., Jiang, Z., Wei, Y.,Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent, Precambrian Research (2015), http://dx.doi.org/10.1016/j.precamres.2015.07.017 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.
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Highlights
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1. The Xide diabase dykes formed in a continental rift setting at ca. 800-810 Ma;
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2. Mid-Neoproterozoic continental rifting occurred in the western Yangtze Block;
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3. The South China Block played a key role in the assembly and breakup of Rodinia.
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Mid-Neoproterozoic diabase dykes from Xide in the western
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Yangtze Block, South China: New evidence for continental
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rifting related to the breakup of Rodinia supercontinent
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Xiaozhuang Cui a, b, *, Xinsheng Jiang a, b, **, Jian Wang a, b, Xuance Wang c,
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Jiewen Zhuo a, b, Qi Deng a, b, Shiyong Liao d, Hao Wu a, Zhuofei Jiang e, Yanan Wei e
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a
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b
Resources, Chengdu 610081 China c
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ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), Curtin University, GPO Box U1987, Perth, WA 6845, Australia
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Key Laboratory of Sedimentary Basin and Hydrocarbon Resource, Ministry of Land and
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Chengdu Center, China Geological Survey, Chengdu 610081, China
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Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
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e
School of Geosciences and Resources, China University of Geosciences, Beijing 100083,
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China
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Corresponding author:
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* Email: [email protected]. Tel: +86 28 83220166. (X.Z. Cui)
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** Email: [email protected]. Tel: +86 28 83231155. (X.S. Jiang)
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Abstract: The petrogenesis of widespread Mid-Neoproterozoic mafic dykes is crucial
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for the paleographic position of the South China Block (SCB) in Rodinia
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supercontinent and the mechanism of Rodinia breakup. Here, new detailed
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geochronological and geochemical data on the diabase dykes from Xide in the
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western Yangtze Block are presented. Zircon SHRIMP/LA-ICP-MS U-Pb dating
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shows that four diabase samples yield uniform crystallization age varying from 796 ±
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6 Ma to 809 ± 15 Ma, while one sample gives a slight older age of 824 ± 11 Ma that is
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overlapped with ca. 810 Ma within uncertainties. This suggests that the Xide diabase
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dykes emplaced at ca.800-810 Ma and were coeval with regional bimodal magmatism
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(e.g., the Suxiong bimodal volcanics). The Xide diabase dykes are characterized by
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low SiO2 contents, high Mg# values and Cr, Ni contents, relative enrichment of light
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rare-earth elements, and slight depletion of high field strength elements (e.g., Nb, Ta,
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Zr, and Hf) and nearly constant Zr/Hf, Nb/Ta and Nb/La ratios. Our analyses indicate
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that the diabase was mainly produced by interaction between lithospheric and
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asthenospheric mantle. Moreover, the diabase samples display geochemical
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characteristics affinity with typical intra-plate basalts. Together with the widespread
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coeval bimodal magmatic suite and sedimentary records in the Kangdian Rift, we
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proposed that the western Yangtze Block once experienced continental rifting during
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the Mid-Neoproterozoic, which also occurred in other Rodinia blocks, such as Tarim,
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Australia and North America. In addition, the Grenville-aged magmatism records
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throughout SCB with the widespread Mid-Neoproterozoic rift-related magmatism and
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sedimentation records imply that SCB probably played a key role in the assembly and
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breakup of Rodinia supercontinent.
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Keywords: Diabase dykes, Neoproterozoic, Continental rifting, Western Yangtze
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Block, South China, Rodinia supercontinent
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1. Introduction
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Assembly and breakup of supercontinents exert major influences on global
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tectonic framework, mantle dynamics, mineral systems, and surface geological
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features (e.g., Rogers and Santosh, 2003; Zhao et al., 2004; 2006; Santosh, 2010;
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Pirajno and Santosh, 2015). The Rodinia supercontinent, assembled between 1.3 and
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0.9 Ga and broken up between 850 and 740 Ma (Li et al., 2008a), has been topics of
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great interest in the last decades (e.g. Wingate et al., 1998; Li et al., 1999, 2003a,
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2008a; Li et al., 2002a, 2003b, 2010a; Ling et al., 2003; Wang and Li, 2003; Wang et
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al., 2007, 2008a, 2010a; Ernst et al., 2008; Jacobs et al., 2008; Wang et al., 2010b;
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Shu et al., 2011; Zhang et al., 2012a; Deng et al., 2013; McClellan and Gazel, 2014;
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Teixeira et al., 2014). Multiple episodic records of anorogenic magmatism during
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850-740 Ma are widespread on several blocks, including South China, Tarim, North
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America, India, Southern Africa, and Australia (Powell et al., 1994; Park et al., 1995;
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Wingate et al., 1998; Li et al., 1999, 2003a, 2008a; Preiss, 2000; Frimmel et al., 2001;
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Li et al., 2002a, 2003b, 2008c, 2010a; Ling et al., 2003; Wang et al., 2007, 2008a,
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2010a; Ernst et al., 2008; Xu et al., 2013; Zhang et al., 2013a; McClellan and Gazel,
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2014). These magmatic records provide important constraints on the process and
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mechanism of Rodinia breakup. The South China Block (SCB) is generally thought to have retained some of the
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best-preserved 850-720 Ma magmatism and sedimentary records (Li et al., 2003a,
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2008a; Li et al., 2002a, 2003b, 2008b,c; Ling et al., 2003; Wang and Li, 2003; Lin et
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al., 2007; Wang et al., 2009, 2011a, 2012a; Wang et al., 2010b; Shu et al., 2011; Zhao
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et al., 2011; Xia et al., 2012; Zhao and Cawood, 2012; Wang et al., 2012b) (Fig. 1).
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However, petrogenesis and tectonic interpretations of these widespread magmatic
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events are still highly debating, and two main, but conflicting, models have been
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proposed. One model suggests that these igneous rocks were produced within a
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intracontinental rift setting as a result of mantle plume activities, which finally caused
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the breakup of Rodinia (Li et al., 1999, 2003a, 2008a; Li et al., 2002a,c, 2003b,
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2010a,b; Ling et al., 2003; Lin et al., 2007; Zhu et al., 2006, 2007, 2008; Wang et al.,
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2007, 2008a, 2009; Wang et al., 2010b). The other model argues that most of these
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rocks formed under either an arc setting related to the steeply dipping subduction of
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the oceanic lithosphere eastward (present-day orientation) underneath the Yangtze
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Block (Yan et al., 2002; Zhou et al., 2002a,b, 2006a,b; Zhao and Zhou, 2007a,b; Dong
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et al., 2011, 2012; Zhao et al., 2008, 2011; Meng et al., 2014) or collision-related
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environments (Zhao and Cawood, 1999; Wang et al., 2004, 2006). A growing
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agreement is that these 850-720 Ma magmatism and sedimentary records in SCB were
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formed in an extensional setting; however, the remaining controversy is its dynamics.
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Mafic dykes can yield insights on the study of mechanism and processes of
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supercontinent breakup (e.g. Yang et al., 2011; Stepanova et al., 2014; Wang et al.,
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2014a). Neoproterozoic mafic dykes widespread in many Rodinia blocks have been
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well studied and demonstrated to record the information related to the breakup of
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Rodinia supercontinent (e.g., Park, 1995; Wingate et al., 1998; Li et al., 1999, 2003a,
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2008a; Li et al., 2002c, 2006a; Ernst et al., 2008; Pisarevsky et al., 2008). Abundant
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diabase dykes are widely distributed in the Xide region (Fig. 2), which intruded into
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the Mesoproterozoic Dengxiangying Group. However, their petrogenesis and tectonic
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implications have not been well studied by geochronological and geochemical data. In
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this contribution, we present detailed field, petrological, geochronological and
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geochemical studies on the Xide diabase dykes. These new data, in combination with
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available regional geological data, are crucial not only for constraining the
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Mid-Neoproterozoic continental rifting in the western Yangtze Block, but also for
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understanding the Neoproterozoic tectonic setting of SCB.
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2. Geological background and samples
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The SCB consists of the Yangtze Block to the northwest and the Cathaysia Block
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to the southeast (Fig. 1). It is separated from the North China Craton by the
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Qinling-Dabie-Sulu orogenic belt to the north, from the Songpan-Gantze terrane by
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the Longmenshan Fault Zone to the northwest, and from the Indochina Block by the
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Ailaoshan-Red River Fault to the southwest, and bounded by the continental slope of
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the Pacific Ocean to the southeast (Fig. 1). Although it is generally accepted that the
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Yangtze and Cathaysia blocks amalgamated during the Proterozoic Sibao orogeny
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(a.k.a the “Jiangnan” or “Jinning” orogeny), the timing of this orogeny is still
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controversial (e.g., Li et al., 1995, 2002b, 2007, 2008a; Zhao and Cawood, 1999;
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Wang et al., 2004, 2006, 2014b; Greentree et al., 2006; Ye et al., 2007; Zhang et al.,
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2012b; Yin et al., 2013; Zhang et al., 2013b; Zhao, 2014). Nonetheless, there are
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significant numbers of Grenvillian subduction- or collision-related magmatism
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records in the western (Mou et al., 2003; Greentree et al., 2006; Geng et al., 2007;
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Zhang et al., 2007; Yang et al., 2009; Wang et al., 2012c; Li et al., 2013; Zhang et al.,
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2013c) and northern Yangtze (Qiu et al., 2011, 2015; Wang et al., 2013a) and the
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Cathaysia blocks (Wang et al., 2008b; Shu et al., 2011; Zhang et al., 2012d; Cawood
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et al., 2013; Wang et al., 2013d, 2014c).
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Outcrops of Archean rocks are mainly distributed in the northern Yangtze Block,
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whereas Paleoproterozoic basement rocks occur sporadically in the western and
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northwestern Yangtze Block (Greentree et al., 2006; Zhao and Cawood, 2012; Chen et
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al., 2013; Wu et al., 2014a; Zhou et al., 2015). However, the Mid-Neoproterozoic
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(mainly 820-725 Ma) magmatism and sedimentary records, which were preserved as
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wedge-shaped rift successions (Wang and Li, 2003; Wang et al., 2015), are widely
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distributed within the three major rift basins in SCB: the roughly E-W trending
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Bikou-Hannan Rift along the northwestern Yangtze Block, the N-S trending Kangdian
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Rift near the present western Yangtze Block, and the major NE-SW trending Nanhua
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Rift to the southeast (Fig. 1) (Li et al., 1999, 2003a, 2008a; Wang and Li, 2003; Wang
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et al., 2008a, 2009, 2011a, 2012a; Cui et al., 2014; Wang et al., 2015). These
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successions consist of continental and marine siliciclastic and volcaniclastic rocks
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interbedded with bimodal volcanics and tuffs (Li et al., 2002a; Wang and Li, 2003;
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Wang et al., 2011a, 2012a; Jiang et al., 2012; Wang et al., 2015). In the Kangdian Rift,
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the wedge-shaped rift successions include the Suxiong, Kaijianqiao, Chengjiang,
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Luliang, and Niutoushan Formations (Wang and Li, 2003; Jiang et al., 2012; Zhuo et
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al., 2013, 2015; Cui et al., 2013, 2014). In the western Yangtze Block, the rift basement (pre-rift successions) is
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composed of the Paleoproterozoic and Mesoproterozoic strata. The Paleoproterozoic
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strata include the Dahongshan, Dongchuan and Hekou Groups, while the
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Mesoproterozoic strata include the Kunyang, Huili, Dengxiangying and Ebian Groups
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(Greentree et al., 2006; Geng et al., 2007, 2008; Chen et al., 2013; Li et al., 2013).
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Among them, the Dengxiangying Group is mainly distributed in the Xide County,
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western Sichuan Province, and covers an area of approximately 200 km2 (Fig. 2). The
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Dengxiangying Group is a sequence of meta-sedimentary and volcanic rocks
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including phyllite, slate, quartzite and marble interbedded with meta-dacite and has a
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total thickness of more than 8500 meters (BGMR, 1991, 1996). It underwent lower
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greenschist facies metamorphism and strong deformation. A meta-dacite sample from
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the Dengxiangying Group gave a SHRIMP zircon U-Pb age of 1017 ± 17 Ma (Geng
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et al., 2008), which is consistent with those ages of the Kunyang, Huili and Ebian
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Groups (Zhang et al., 2007; Geng et al., 2007, 2008; Li et al., 2013; Authors’
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unpublished data). The Dengxiangying Group is unconformably overlain by the
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Suxiong and Kaijianqiao Formations to the north, by the Sinian and younger strata to
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the east and south, and intruded by granites to the west (Fig. 2).
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The diabase dykes (with minor sills) in the Xide region intruded into the pre-rift
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meta-sedimentary and volcanic rocks (Dengxiangying Group), but did not penetrate
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the Neoproterozoic rift successions (Fig. 3a, b). Their intrusive contacts are very clear
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and thin baked zones or thermal recrystallization that can be observed near the
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boundary of the dykes. These diabase dykes are rarely subjected to deformation and
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metamorphism in contrast to their strongly deformed metamorphic wall-rocks. They
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are commonly several meters wide and tens of meters strike length. The weathered
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surface of these diabase dykes is yellowish-grey in color, while the fresh surface is
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grayish-black (Fig. 3a-c). Most diabase dykes have a dominant N-S trend that is
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sub-parallel to the Kangdian Rift and are oblique or nearly vertical. All the diabase
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samples, collected from the Xide region, display typical diabasic texture (Fig. 3d) and
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are massive structure (Fig. 3c). These diabase samples have similar mineral
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compositions of plagioclase (40-55%), pyroxene (20-30%), Fe-Ti oxides (5-15%),
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ordinary hornblende (5-10%), and olivine (5-10%) with minor opaque minerals such
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as apatite (Fig. 3d). In this study, a total of thirty diabase samples were collected, of
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which fourteen relatively fresh samples were chosen for whole-rock geochemical
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analyses and five samples were analyzed by zircon U-Pb dating.
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3. Analytical techniques
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3.1 Zircon U-Pb dating
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Zircons were separated from crushed rock using a combination of conventional
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heavy liquid and magnetic separation techniques. Individual zircon grains were
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handpicked under a binocular microscope and were mounted in an epoxy resin
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together with several grains of standard zircon TEMORA 1. Mounts were polished to
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expose zircon surfaces suitable for U-Pb dating using either SHRIMP or LA-ICP-MS
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methods. Prior to U-Pb analyses, the structures of the zircon grains were imaged by
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cathodoluminescence (CL) techniques with a HITACHI S-3000N electron microprobe
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(GATAN) at the Beijing SHRIMP Center, Chinese Academy of Geological Sciences
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(CAGS).
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Samples 12XD-D1, 12XD-D4 and 12XD-D9 were analyzed using the SHRIMP
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II ion microprobe at the Beijing SHRIMP Center, CAGS. The SHRIMP analytical
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procedures were similar to those described by Williams (1998). The intensity of the
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primary O2− ion beam was 3.5-5.0 nA with the spot size of 25-30 μm. Each analytical
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site was rastered for 2.5-3.0 min prior to analysis to remove surface common Pb. Five
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scans through the mass stations were made for each age determination of zircon.
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Reference zircon M257 (U = 840 ppm, Nasdala et al., 2008) were used for U
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elemental abundance calibration, whereas TEMORA 1 (206Pb/238U age = 417 Ma,
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Black et al., 2003) were used for calibration the U-Pb ages. Common lead corrections
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were applied using the measured
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using the SQUID and ISOPLOT programs (Ludwig, 2001, 2003). SHRIMP analytical
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data are presented with 1 errors in Table 1, and uncertainties for weighted mean ages
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in the text are quoted at the 95 % confidence level.
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Pb abundances. Data processing was carried out
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Samples 13XD-D12 and 13XD-D13 were analyzed using the LA-ICP-MS at the
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State Key Laboratory of Geological Processes and Mineral Resources, China
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University of Geosciences, Wuhan. Laser sampling was performed using a GeoLas
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2005 ArF excimer laser ablation system. The ablation was carried out by a pulsed
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(GeoLas) 193 nm ArF excimer (Lambda Physik, Göttingen, Germany) with laser
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power of 50 mJ/pulse energy at a repetition ratio of 8 Hz coupled to an Agilent 7500a
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quadrupole ICP-MS. Helium was used as a carrier gas to transport the ablated
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material from the laser ablation cell to the ICPMS. The diameter of the laser ablation
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crater was 32 μm. Zircon 91500 was used as external standard for U-Pb dating, and
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was analyzed twice every five analyses. NIST610 glass was used as an external
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standard to normalize the U, Th, and Pb concentrations of the unknowns. The detailed
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analytical procedures followed Liu et al. (2010). Off-line selection and integration of
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background and analyze signals, and time-drift correction and quantitative calibration
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for U-Pb dating were performed by ICPMSDataCal (Liu et al., 2010). Calculation of
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concordia plots and weighted mean ages were made using ISOPLOT, with
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uncertainties quoted at the 1σ and 95% confidence levels (Ludwig, 2003).
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3.2. Major and trace element analyses
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Based on petrographic examination, fifteen relatively fresh diabase samples were
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selected for geochemical analysis. The marginal parts of these samples were cut off,
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and then the remnant core part with a dimension of about 5×3×4 cm3 was powdered to
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agrain size of 200-mesh. The major elements were determined by X-ray fluorescence
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(XRF) at the National Research Center for Geoanalysis, CAGS, with an analytical
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uncertainties ranging from 1 to 3 %. The trace elements were determined as solute by
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Agilent 7500ce inductively coupled plasma mass spectrometry (ICP-MS) at the same
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laboratory. The analytical uncertainties were less than 5 % for elements occurring at
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concentrations > 10 ppm, less than 8 % for those at concentrations of < 10 ppm, and
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about 10 % for transition metals.
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4. Analytical results
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4.1. Geochronology Cathodoluminescence imaging (CL) of representative zircon grains are shown in
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Fig. 4. Results of SHRIMP and LA-ICP-MS zircon U-Pb dating are presented in
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Tables 1 and 2, respectively, and all of these analyses are plotted on Concordia
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diagrams (Figs. 5 and 6). Unless otherwise stated, in the figures and the following
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discussions, for the zircon grains with age older than 1.0 Ga, we use
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to represent their crystallisation ages, whereas for the younger grains, their
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crystallisation ages are determined by 206Pb/238U ages.
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4.1.1. 12XD-D1 (N28°27′50.07″, E102°21′30.23″)
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Pb/206Pb ages
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Zircon grains from sample 12XD-D1 are euhedral and transparent, up to 100-250
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μm long, and have length/width ratios of between 1:1 and 5:1. In CL images, most of
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zircon grains display slight to dark luminescence and homogeneous structure with or
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without straight and wide growth bands (Fig. 4a, c, e), which are similar to typical
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magmatic zircons. The rest grains are rounded and show relatively blurry oscillatory
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zoning, which are interpreted to be xenocrysts (Fig. 4b, d). Eight analyses were
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obtained from this sample (Table 1). These analyses give relatively low U and Th
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contents (U = 28-272 ppm and Th = 18-150 ppm), and variable Th/U ratios ranging
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from 0.46 to 1.39. Spots 02 and 06 give significantly older concordant
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ages of 2481 ± 15 Ma and 2525 ± 16 Ma, respectively. Spot 08 produces a younger
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age of 755 ± 8 Ma and is rejected in calculation due to its high common lead (1.5 wt%
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Pbc). The five remaining analyses produce a
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Pb/206Pb
Pb/238U weighted mean age of 809
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± 15 Ma (MSWD = 1.8), which is interpreted as the best estimate of the
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crystallization age of sample 12XD-D1.
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4.1.2. 12XD-D4 (N28°27′53.58″, E102°21′38.91″) Zircon grains from sample 12XD-D4 are euhedral, transparent and colorless.
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They are 80-250 μm long with length/width of about 1:1 to 5:1. Most grains show
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slight to dark luminescence and homogeneous structure without core-rim texture in
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CL images (Fig. 4f, g, j), while some have blurry oscillatory zoning (Fig. 4h, i),
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indicating that all of them should be magmatic zircon grains from mafic rocks. Nine
254
analyses give variable concentrations of U (64-302 ppm) and Th (41-362 ppm), with
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Th/U ratios of 0.25-3.44 (Table 1). Eight spots yield a relatively uniform range of
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concordant
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809 ± 8 Ma (MSWD = 1.04) (Fig. 5). This age is regarded as the crystallization age of
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sample 12XD-D4.
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4.1.3. 12XD-D9 (N28°27′59.23″, E102°21′58.05″)
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Pb/238U ages from 796 to 828 Ma, which give a weighted mean age of
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Zircon grains from sample 12XD-D9 are mostly colorless and range in size from
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100-150 × 50-120 μm with aspect ratios of about 1:1 to 3:1. They are mostly stubby to
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long prismatic in shape and euhedral. In CL images, most zircon grains show
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relatively clear oscillatory zoning and without core-rim texture (Fig. 4k, m, o), while
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some zircon grains display indistinct sector zoning or homogeneous structure (Fig. 4l,
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n). Eleven analyses on 11 zircon grains have 46-459 ppm U and 25-162 ppm Th with
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Th/U ratios of 0.22-0.75, indicating a magmatic origin. Spot 08 is rejected in the
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following calculation due to its high common lead (1.9 wt% 206Pbc). The ten analyses
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Pb/238U ages ranging from 793 to 843 Ma (Table 1).
yield scattered concordant
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They give a weighted mean age of 824 ± 11 Ma (MSWD = 2.9) (Fig. 5). Although this
270
age is slight older than the others, it is overlapped with ca. 810 Ma with considering
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the uncertainties.
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4.1.4. 13XD-D12 (N28°22′28.00″, E102°21′23.12″)
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Zircon grains from sample 13XD-D12 are mostly colorless euhedral prismatic
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crystal, about 100-200 μm long, and 50-70 μm wide with length/width ratios of
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2:1-4:1. Vast majority of these zircons show prismatic crystals, with regular edges and
276
without any core-rim textures. Their CL images display relative homogenous inner
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structure or indistinct wide oscillatory zoning (Fig. 4p, r, s, t), while a minority of
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zircons show wide oscillatory zoning (Fig. 4q). Ten analyses conducted on 10 zircons
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yield variable U and Th contents (U = 58-426 ppm, Th = 56-312 ppm, Th/U = 0.2-3.0)
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(Table 2). They obtain concordant and consistent
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827 Ma, which give a weighted mean age of 808 ± 8 Ma (MSWD = 0.74) (Fig. 6).
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This age is interpreted as the crystallization age of sample 13XD-D12.
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4.1.5 13XD-D13 (N28°28′06.12″, E102°22′10.06″)
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Pb/238U ages varying from 798 to
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Zircon grains from sample 13XD-D13 are mostly colorless, transparent and
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euhedral prismatic grains. The length of grains range from 100 to 200 μm and have
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aspect ratios of between 1:1 and 3:1. In CL images, zircon grains commonly show
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slight to dark luminescence and homogeneous structure without any core-rim texture,
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similar to those crystallized from mafic magma (Fig. 4u, w, x, y), whereas minority
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zircons display clear striped oscillatory zoning (Fig. 4 v). Fourteen analyses were
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290
carried out on 14 zircons from sample 13XD-D13 (Table 2). The results show large
291
range of U and Th concentrations (U = 21-506 ppm, Th = 45-529 ppm) with Th/U
292
ratios ranging from 0.2 to 2.6, indicating a magmatic origin. Two analyses (spots 01,
293
04) yield a weighted mean
294
twelve remaining analyses give relatively uniform and concordant
295
from 789 to 823 Ma, yielding a weighted mean age of 796 ± 6 Ma (MSWD = 0.57)
296
(Fig. 6). This age is interpreted to represent the crystallization age of sample
297
13XD-D13.
298
4.2. Geochemistry
ip t
Pb/238U age of 852 ± 34 Ma (MSWD = 0.01). The 206
Pb/238U ages
an
us
cr
206
Major and trace elements concentrations of the representative fourteen diabase
300
samples are presented in Table 3. In general, these samples displayed lager range of
301
SiO2, MgO, Al2O3, FeOt, and CaO contents. The diabase samples are characterized by
302
relatively high MgO contents and magnesium number (Mg#). It should be noticed that
303
diabase samples 12XD-03 and 12XD-08 have anomalously low SiO2 contents and
304
high LOI values that suggest intense alternation, and thus are rejected from the
305
following discussions. Due to possible migration of large ion lithophile elements
306
(LILE, e.g., K, Na, Rb, Sr, Ba, Cs, etc.) in the studied samples, only the immobile
307
elements, such as high field strength elements (HFSE) and rare earth elements (REE),
308
are employed in the rock classification and petrogenesis discussion (see discussion in
309
5.2). In the Nb/Y-Zr/TiO2 diagram, all the samples plot in the field of subalkaline
310
basalts (Fig. 7a). In the FeOT/MgO-TiO2 diagram, all the samples belong to the
311
tholeiitic series (Fig. 7b).
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299
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Page 15 of 69
312
Chondrite-normalized REE patterns for all the samples are shown in Fig. 8a. The Xide diabase samples have relatively high REE contents (ΣREE = 75.30-172.38 ppm).
314
Most of these samples are enriched in LREE (LREE = 52.38-146.64 ppm,
315
LREE/HREE = 2.29-5.70, LaN/SmN = 1.02-2.64, LaN/YbN = 1.52-5.81), and display
316
the smooth to right-inclined REE distribution patterns (Fig. 8a). It is worth noting that
317
sample 12XD-04 (LREE = 146.64 ppm, LREE/HREE = 5.70) and 13XD-10 (LREE =
318
52.38 ppm, LREE/HREE = 2.29) exhibit strongly and slightly enriched LREE
319
patterns, respectively. Still, all the analyzed samples can’t be distinguished by their
320
geochemical signatures of major and trace elements. On the whole, they all fall into
321
the field between normal mid-ocean ridge basalt (N-MORB) and OIB (Fig. 8a), and
322
are differentiated in LREE and HREE with enriched in LREE. These patterns quite
323
differ from those for the representative N-MORBs which are strongly depleted in
324
LREE. In the primitive mantle-normalized spidergrams (Fig. 8b), all the samples
325
exhibit clear enrichments in Th, La, and depletions in Nb, Ta without visible Ti
326
depletions. The trace element distribution patterns are comparable with OIBs, with the
327
exception of the depletion of Nb-Ta. More importantly, the high Nb-Ta abundance and
328
the absence of Zr-Hf negative anomalies are different from subduction-related
329
island-arc basalts (IABs).
330
5. Discussion
331
5.1. Age of the Xide diabase dykes and regional synchronous magmatism
Ac ce
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M
an
us
cr
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313
332
Although the Mid-Neoproterozoic mafic intrusions have been well documented
333
in the western Yangtze Block (Li et al., 2008a and references therein), few
16
Page 16 of 69
geochronological studies have been carried on the diabase dykes in the Xide region.
335
The diabase dykes, which intruded into the Dengxiangying Group, were previously
336
considered to form during the Sinian Period (the 1: 200,000 geological maps). In our
337
analyses, most of the analyzed zircon grains were attributed to mafic magmatic origin
338
during the diabase dyke emplacement according to CL images and Th/U ratios (Fig. 4,
339
Tables 1 and 2). Forty five of the 52 analyses give uniform and concordant ages, and
340
have a Gaussian-style distribution pattern on the probability plot. They yield a
341
weighted mean age of 810 ± 5 Ma (MSWD = 2.4, n = 45). Although the obtained age
342
of sample 12XD-D9 is slight older than the others, it is overlapped with ca. 810 Ma
343
within uncertainties. The other four samples give a coherent age span between 796
344
and 809 Ma, which can not be distinguished from each other within analytical errors.
345
Considering the ca. 800 and 725 Ma formation age of the overlain rift successions (Li
346
et al., 2002a; Zhuo et al., 2015), the emplacement age of the Xide diabase dykes can
347
be regarded as ca. 800-810 Ma.
cr
us
an
M
ed
pt
Various magmatism records that are broadly coeval with the Xide diabase dykes
Ac ce
348
ip t
334
349
in the western Yangtze Block as summarized in Table 4. The bimodal volcanics of the
350
Suxiong Formation were erupted at 803 ± 12 Ma (Li et al., 2002a), and is
351
synchronous with the 799 ± 8 Ma basalts of the Huangshuihe Group (Ren et al., 2013)
352
and 809 ± 9 Ma rhyolitic tuffs of the Yanjing Group (Geng et al., 2008). Mafic and
353
felsic intrusions are also widely distributed, including the Kangding granitoids with
354
ages ranging from 795 to 797 Ma (Zhou et al., 2002a), 796 ± 5 Ma picritic dykes (Li
355
et al., 2010a), 801 ± 7 Ma Xiatianba A-type granites (Wu et al., 2014b), 803 ± 15 Ma
17
Page 17 of 69
Xiacun granites (Guo et al., 2007), 806 ± 4 Ma Lengshuiqing gabbros (Zhou et al.,
357
2006b) and 808 ± 12 Ma Lengqi gabbros (Li et al., 2002c). In addition, the initiation
358
of mature rifting in the southern Kangdian Rift has been assumed at ca. 800 Ma,
359
constrained by zircon U-Pb ages between 798 ± 8 and 805 ± 14 Ma of felsic tuffs and
360
basalts from the lowermost part of the Chengjiang Formation and its equivalents
361
(Jiang et al., 2012; Zhuo et al., 2013, 2015; Cui et al., 2015). These magmatic rocks
362
constitute a typical bimodal magmatic association, suggesting their genetic link with a
363
continental rift environment. They yield a weighted mean
364
Ma (MSWD = 0.33, n = 17) (Fig. 9). This age is identical to ones obtained from our
365
diabase samples (Figs. 5 and 6). Thus, the Xide diabase dykes were part of the ca.
366
800-810 Ma bimodal magmatism in the western Yangtze Block. Furthermore,
367
although the major phase of mafic magmatic rocks in the western Yangtze was formed
368
at ca. 800-810 Ma, the mafic-ultramafic complex in the Yanbian area suggested that
369
the Mid-Neoproterozoic mafic magmatism initiated at ca. 825 Ma (Zhu et al., 2007).
370
5.2. Petrogenesis of the Xide diabase dykes
cr
us
Pb/238U age of 803 ± 3
pt
ed
M
an
206
Ac ce
371
ip t
356
The diabase samples used in this study experienced little metamorphism, but
372
they show various LOI values (Table 3), suggesting varying degrees of alteration.
373
Bivariate plots of Zr against selected trace elements can be used for evaluating the
374
motilities of such elements during alteration (e.g., Polat et al., 2002; Wang et al.,
375
2010a). As shown in Fig. 10, rare earth elements (REE, e.g., Nd, Yb), high field
376
strength elements (HFSE, e.g., Nb, Ta, Hf), and Y are all well correlated with Zr,
377
indicating that they were essentially immobile during alteration. In contrast, alkaline
18
Page 18 of 69
378
elements (e.g., Rb), alkaline earth elements (e.g., Sr), and transition metal elements do
379
not have co-vary with Zr, suggestive of variable degree of mobility. Therefore, only
380
the REE and HSFE are used for the discussions. Major and trace element distribution pattern has revealed the evolution of the
382
magma. The samples show pronounced negative Eu and Sr anomalies in trace element
383
distribution patterns (Fig. 8a), and suggest that fractionation crystallization of
384
plagioclase may have played an important role in these magma evolution. The Ni and
385
Cr decrease along with MgO, indicating fractional crystallization of olivine. Negative
386
correlations between CaO, CaO/Al2O3 and MgO do not support the fractionation of
387
clinopyroxene. The magma also underwent slight fractionation of apatite, which is
388
suggested by positive correlation between MgO and P2O5. Moreover, FeOT and TiO2
389
are generally negatively correlated with MgO in all the rocks, suggesting possible
390
Fe-Ti oxides fractionation crystallization.
ed
M
an
us
cr
ip t
381
Enriched LREE patterns and negative Nb and Ta anomalies of the samples show
392
that the Xide diabase dykes may have been subjected to crustal contamination.
393
However, the following lines of evidence showed that crustal contamination is
394
insignificant, if any, in the generation of these mafic dykes. The studied samples have
395
large range of major element compositions (SiO2 = 47.51 to 53.78 wt% and MgO =
396
6.02 to 12.72 wt%), but nearly constant Zr/Hf (37.3 to 47, with an average of 39.8)
397
and Nb/Ta (14.6 to 17.0, with an average of 15.3) ratios. Zr/Hf and Nb/Ta ratios are
398
insensitive to fractionation crystallization, but sensitive to crustal input due to contrast
399
values between asthenosphere mantle-derived melts and crustal materials (Weaver,
Ac ce
pt
391
19
Page 19 of 69
1991; Barth et al., 2000). Thus, if the major element variation was caused by crustal
401
contamination, considering the mass balance, the large range and crust-like Zr/Hf and
402
Nb/Ta ratios should be observed in the final magmas. However, the nearly constant
403
and OIB-like Nb/Ta and Zr/Hf ratios (OIB with Nb/Ta = 15.9 ± 0.6 and Zr/Hf = 36.3)
404
are inconsistent with the prediction of crustal contamination. It ruled out that the
405
possibility of intense crustal contamination. On the other hand, the analyzed samples
406
exhibit a large range of Nb/Th and Zr/Nb ratios but relatively constant Nb/La ratios
407
(Fig.11), also contradicting large input of crustal materials (Pearce, 2008; Zhang et al.,
408
2013b). Furthermore, the lack of country rock xenoliths in the dykes and the sharp
409
contact along dyke margins also suggest insignificant crustal contamination.
M
an
us
cr
ip t
400
The asthenosphere-lithosphere interaction plays a key role in producing
411
continental basalts (Turner and Hawkesworth, 1995; Wang et al., 2008a, 2009, 2014d).
412
The Nb/La ratio is effective to distinguish between asthenospheric mantle and
413
sub-continental lithospheric mantle (SCLM) contributions. The asthenospheric
414
mantle-derived melts are generally characterized by high Nb/La ratios, varying from
415
0.9 (N-MORB) to 1.3 (OIB and E-MORB) (Sun and McDonough, 1989). By contrast,
416
the SCLM-derived melts display low Nb/La ratios and similar to that of continental
417
crust (Wang et al., 2014d). The studied samples have large range in Nb/La ratios,
418
varying from 0.4 to 1.4. They can be further divided into two sub-types: high-Nb/La
419
types with Nb/La ratios ≥0.8, including 12DX-07 and 12DX-09 and low-Nb/La with
420
constant Nb/La ratios, varying from 0.4 to 0.6. Within them, the high-Nb/La sample
421
12DX-09 has highest Nb/La (1.4), Zr/Hf (43.8), and Nb/Ta (17.0) ratios, similar to
Ac ce
pt
ed
410
20
Page 20 of 69
OIB. The parental of this sample was mainly derived from asthenospheric mantle. The
423
other high-Nb/La sample 12DX-07 displays relatively low Nb/La (0.8), Nb/Ta (14.8),
424
and Zr/Hf (38.4). This source of this sample may record the asthenosphere-lithosphere
425
interaction. The low-Nb/La samples are characterized by nearly constant Nb/La ratios,
426
which are comparable to the typical SCLM-derived melts (lower to 0.3; Wang et al.,
427
2014d). Thus, the source of low-Nb/La types was most likely dominated by SCLM.
428
By contrast, most of the coeval Suxiong basalts display high Nb/La ratios (≥1.0),
429
suggesting their source was dominant by an OIB-like mantle (Li et al. 2002a).
430
5.3. Implications for continental rifting in the western Yangtze Block
an
us
cr
ip t
422
All the diabase samples display negative Nb-Ta anomalies in the primitive
432
mantle-normalized spidergrams (Fig. 8b), which are generally regarded as signatures
433
of arc related basalts (Pearce, 1982; Keppler, 1996). However, several lines of
434
geochemical evidence argue against an arc origin for the Xide diabase dykes. (1) The
435
contents of incompatible elements are relatively generally higher than those of IABs,
436
varying between the OIBs and IABs (Fig. 8b). (2) The Xide diabase dykes have
437
relatively high TiO2 (1.73-2.56 wt.%) and Ti/V ratios (> 45), different from arc related
438
basalts. (3) Most samples are characterized by high and various Th/U ranging from
439
6.06 to 45.00 with one exception of 0.67, in contrast to arc related basalts that are
440
generally low in Th/U (2.4 ± 0.8). (4) Contents of Ni (34.8-137 ppm; average = 73.4
441
ppm) and Cr (172-440 ppm; average = 317 ppm) are clearly higher than those of
442
typical island arc tholeiitic basalts (Ni = 25 ppm; Cr = 50 ppm) (Pearce, 1982; Wilson,
443
1989). (5) The Zr/Y ratios (3.72-7.51) are significantly higher than those of arc related
Ac ce
pt
ed
M
431
21
Page 21 of 69
basalts as they are plotted in the field of within plate basalts rather than the island arc
445
basalts in the Zr-TiO2 and Zr-Zr/Y diagrams (Fig. 12a,b). This is further supported by
446
the Ta/Hf-Th/Hf diagram proposed by Wang et al., (2001) (Fig.12c), as most of the
447
samples fall in the field of continental within plate basalts. Overall, the Xide diabase
448
dykes should be interpreted to generate in a continental rift environment. Furthermore,
449
the dominant N-S trend of the Xide diabase dykes is sub-parallel to the Kangdian Rift
450
(Fig. 2), which also coincides with this interpretation.
us
cr
ip t
444
As discussed above, there are widespread ca. 800-810 Ma bimodal magmatic
452
rocks in the western Yangtze Block, suggesting a possible continental rift environment
453
(Wilson, 1989; Xia et al., 2012). Based on geochemical and Nd isotopic data, Li et al.
454
(2002a) concluded that the Suxiong basalts were most likely derived from an OIB-like
455
mantle source, while the rhyolites were possibly generated by shallow dehydration
456
melting of hornblende-bearing granitoids, indicating that they should be formed in a
457
continental rift environment. Recently identified ca. 800 Ma high-MgO lavas, the
458
Tongde picrites, also suggested presence of a hot mantle plume beneath SCB (Li et al.,
459
2010a). The basalts of the Chengjiang Formation display lower SiO2, high K2O+Na2O
460
and TiO2 contents with Rittmann index (σ) > 3.3, similar to those alkaline basalts
461
generated in the continental rift (Zhu, 1990; Cui et al., 2015). Additionally, the
462
recently identified A-type Xiatianba granites have been demonstrated to be produced
463
within an intra-plate extension environment (Wu et al., 2014b).
Ac ce
pt
ed
M
an
451
464
Recent studies confirm that the sedimentary history of the Kangdian Rift in the
465
western Yangtze Block can be well correlated with the Nanhua Rift in the
22
Page 22 of 69
southeastern Yangtze Block (Wang and Li, 2003) and the Adelaide Rift in Australia
467
(Preiss, 2000). A SHRIMP zircon U-Pb age of tuffs from the lowermost part of the
468
Luliang Formation is 819±9 Ma, representing the initiation of the Kangdian rifting
469
(Zhuo et al., 2013). However, the rifting just produced narrow, deeply subsidence,
470
unidirectional N-S trending half-grabens before 800 Ma. Since 800 Ma, accompanied
471
with drastic bimodal magmatism, the rifting clearly widened the zone of continental
472
extension which made those mini half-grabens into a large united half-graben.
473
Accordingly, a large-scale transgressive overlap occurred (Zhuo et al., 2013; Cui et al.,
474
2014). Provenance analyses show that the clastic wedges were derived from the
475
western rift shoulder, which was mainly consisted of the Kunyang Group and its
476
equivalents, rather than synchronous andesitic volcanic rocks indicating the existence
477
of an Andean magmatic arc (Cui et al., 2014). More intriguingly, the latest proposed
478
tectonic model and filling pattern of the Kangdian Rift (Zhuo et al., 2013; Cui et al.,
479
2014) are comparable to those of the East Africa Rift, a typical continental rift
480
(Chorowicz, 2005).
cr
us
an
M
ed
pt
Ac ce
481
ip t
466
In summary, the Xide diabase dykes that underwent negligible crustal
482
contamination display geochemical characteristics of intra-plate basalts, instead of
483
arc-related basalts. Combined with the synchronous bimodal magmatism and
484
sedimentary history, it is suggested that the Mid-Neoproterozoic continental rifting
485
once occurred in the western Yangtze Block. The widespread Mid-Neoproterozoic
486
continental rifting and anorogenic magmatism are also preserved in other Rodinia
487
blocks, such as Tarim (e.g., Xu et al., 2013; Zhang et al., 2013a), Australia (e.g.,
23
Page 23 of 69
Powell et al., 1994; Wingate et al., 1998; Preiss, 2000; Li et al., 2006a; Wang et al.,
489
2010a), North America (e.g., Park et al., 1995; McClellan and Gazel, 2014) and
490
Southern Africa (e.g., Frimmel et a., 2001). All these observations indicate that the
491
Mid-Neoproterozoic continental rifting in the western Yangtze Block could be part of
492
a major global rifting event, which triggered the breakup of Rodinia supercontinent.
493
5.4. Reconsidering the proposed tectonic models of South China
cr
ip t
488
Aside from the plume-rift model proposed by Li and co-authors (Li et al., 1999,
495
2003a, 2008a; Li et al., 2002a, 2003b; Ling et al., 2003; Wang and Li, 2003; Wang et
496
al., 2007, 2008a, 2009, 2011a) and the slab-arc model proposed by Zhou and
497
co-authors (Yan et al., 2002; Zhou et al., 2002a,b, 2006a,b; Zhao and Zhou, 2007a,b;
498
Zhao et al., 2008, 2011), Zheng et al. (2007, 2008a,b) recently proposed the plate-rift
499
model. However, the plate-rift model was established merely on the basis of
500
Neoproterozoic felsic volcanic rocks and granites from the northeastern segment of
501
the Jiangnan Orogen. However, the felsic igneous rocks are not suitable to constrain
502
on tectonic setting due to their highly complex petrogenesis. At least, it still needs
503
further testing as to whether or not this model can be successfully applied to
504
understanding of the Neoproterozoic tectonic processes of the whole SCB.
an
M
ed
pt
Ac ce
505
us
494
The slab-arc model proposes that there was a long-lived (950-735 Ma) oceanic
506
subduction zone along the western-northern Yangtze Block and the rift basins in SCB
507
were attributed to back arc spreading (Yan et al., 2002; Zhou et al., 2002a,b, 2006a,b;
508
Zhao and Zhou, 2007a,b; Zhao et al., 2008, 2011; Dong et al., 2011, 2012; Wang and
509
Zhou, 2012). The slab-arc model overlooked some important observations of
24
Page 24 of 69
structural geology and metamorphism. For instance, the slab-arc model is inconsistent
511
with a general northward structural vergence of the Yanbian Group (Li et al., 2006b).
512
The first and second phases of metamorphism and deformation of the Tianli Schist
513
occurred respectively at 1.04-1.01 Ga and 0.97-0.94 Ga (Li et al., 2007), which are
514
broadly coincident with the ages of Northern Jiangxi Ophiolites (Chen et al., 1991)
515
and the Shuangxiwu magmatic arcs (Li et al., 2009). The petrographic observations
516
demonstrated ca. 820 Ma mafic rocks in the western Yangtze Block are dominated by
517
olivine-plagioclase-clinopyroxene (Li et al., 2006b). This suggests an anhydrous
518
parental magma for these mafic rocks, which is contracted with the predictions of the
519
slab-arc model.
M
an
us
cr
ip t
510
Recently, Chen et al. (2014) proposed that the ca. 1050 Ma Julin basalts might
521
formed in a passive continental margin, which is in accord with the subsequent
522
oceanic subduction since 950 Ma. However, as mentioned earlier, abundant
523
Grenville-aged subduction- or collision-related magmatism records are distributed
524
along the western-northern Yangtze Block. For example, the 1014 ± 8 Ma Yakou
525
granites display characteristics of those crust-derived collisional granites (Yang et al.,
526
2009); Andesitic tuffs from the Heishantou Formation give a SHRIMP U-Pb age of
527
1032 ± 9 Ma (Zhang et al., 2007), which further support the Kunyang Group was
528
deposited within a foreland basin associated with the collision events (Greentree et al.,
529
2006); In the northern Yangtze Block, the volcanic suites of the Shennongjia Group
530
yield zircon U-Pb ages between 1063 ± 16 and 1103 ± 8 Ma and have been interpreted
531
to be developed within subduction-related collision environments (Qiu et al., 2011,
Ac ce
pt
ed
520
25
Page 25 of 69
532
2015). These geologic records contradict the existence of a passive continental margin
533
along the western-northern Yangtze Block during 1100-960 Ma. Obviously, the interpretation of back-arc rift basins for the Neoproterozoic
535
tectonic setting of SCB remains open to question. The data present in this paper show
536
that the Xide diabase dykes emplaced at ca. 800-810 Ma and formed in a continental
537
rift setting. This suggests that a continental rift environment is relatively appropriate,
538
which is broadly in agreement with the plume-rift model. The following lines of
539
positive geological evidence also support this proposal.
us
cr
ip t
534
(1) The episodic bimodal magmatism were widespread throughout SCB, e.g., the
541
ca. 800 Ma bimodal magmatism suite recognized in this study, Shangshu and Puling
542
bimodal volcanic rocks (Li et al., 2008b; Wang et al., 2012b) and 780-760 Ma
543
Kangding mafic dykes and synchronous granites (Li et al., 2003a; Lin et al., 2007);
ed
M
an
540
(2) The Mid-Neoproterozoic (825-760 Ma) basaltic rocks in SCB have
545
continental intra-plate geochemical signatures and high mantle potential temperatures
546
(Li et al., 2008c; Wang et al., 2009), and some of them are most likely the remnants of
547
plume-related continental flood basalts (e.g., Wang et al., 2008a, Deng et al., 2013);
Ac ce
548
pt
544
(3) Many Mid-Neoproterozoic igneous rocks are characterized by exceptional
549
low-18O values, indicating intensive high-temperature water-rock interaction and
550
generation of the low-18O magmatism in rift tectonic zones (e.g., Zheng et al., 2008b;
551
Wang et a., 2011b; Liu and Zhang, 2013);
552
(4) In situ U-Pb, Hf and O isotopic analyses of detrital zircon grains from
553
sandstones across the Mid-Neoproterozoic unconformity in the Nanhua Basin, which
26
Page 26 of 69
554
was previously interpreted as orogenic origin, demonstrated that sediments across this
555
unconformity should be deposited within a continental rift setting (Yang et al., 2015); (5) The sedimentary overlap and filling process of the Neoproterozoic rift basins
557
in SCB are characterized by a deepening water trend and comparable with those
558
typical continental rifts (Wang and Li, 2003; Zhuo et al., 2013; Cui et al., 2014; Wang
559
et al., 2015).
cr
ip t
556
In short, SCB experienced continental rifting during 825-740 Ma, probably
561
linking with the breakup of Rodinia. Although the specific position of SCB in Rodinia
562
is not well constrained (e.g., Li et al., 1995, 1999, 2008a; Zhou et al., 2002a,b; Wang
563
et al., 2010a; Wang and Zhou, 2012; Cawood et al., 2013; Zhang et al., 2013d), we
564
proposed that SCB should play a key role in the assembly and breakup history of this
565
supercontinent.
566
6. Conclusions
569
an
M
ed
pt
568
Our geochronological and geochemical study on the Xide diabase dykes come into the following conclusions:
Ac ce
567
us
560
1. New SHRIMP and LA-ICP-MS zircon U-Pb dating results show that the
570
emplacement of the Xide diabase dykes occurred at ca. 800-810 Ma, coeval with the
571
widespread bimodal magmatism in the western Yangtze Block.
572
2. The Xide diabase dykes underwent insignificantly crustal contamination
573
during magma evolution and ascent, and were mainly derived from a sub-continental
574
lithospheric mantle.
575
3. The Xide diabase dykes formed in a continental rift setting, rather than
27
Page 27 of 69
576
arc-related or post-orogenic setting, indicating that the western Yangtze Block once
577
experienced the continental rifting during the Mid-Neoproterozoic.
579
4. SCB should play a significant role in the assembly and breakup history of Rodinia supercontinent.
ip t
578
580
Acknowledgments
cr
581
This research was supported by the National Natural Science Foundation of
583
China (41030315, 41402103, and 41202048), China Geological Survey project
584
(12120114067901 and 12120114005301), and the Australian Research Council (ARC)
585
Future Fellowship (FT140100826) for Xuan-Ce Wang. We thank Guoqing Xiong and
586
Junze Lu for their help with the field work. We thank Drs. Zhaochu Hu, Keqing Zong,
587
Mingzhu Ma, and Jianhui Liu for their assistance during zircon analysis and data
588
processing. Constructive comments and suggestions from Prof. Guochun Zhao and
589
two anonymous reviewers have helped to improve the manuscript substantially and
590
are gratefully acknowledged. This is TIGeR publication No. xx.
an
M
ed
pt
Ac ce
591
us
582
592
References
593
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936
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999
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1002
western margin of the Yangtze Block, South China. Earth and Planetary Science Letters 196,
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1005
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1006
the Accretion of Rodinia. Journal of Geology 110, 611-618.
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1008
750 Ma Xuelongbao adakitic complex (Sichuan Province, China): implications for the
1010
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1009
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1007
tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth and Planetary Science Letters 248, 286-300.
1011
Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006b. The Yanbian Terrane
1012
(Southern Sichuan Province, SW China): A Neoproterozoic arc assemblage in the western
1013
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1014
Zhu, C.Y., 1990. The sequences of filling and tectonic evolution of Qiaojia-Shiping basin, Yunnan
1015
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English abstract). Zhu, W.G., Zhong, H., Deng, H.L., Wilson, A.H., Liu, B.G., Li, C.Y., Qin, Y., 2006. SHRIMP
1018
zircon U-Pb age, geochemistry and Nd-Sr isotopes of the Gaojiacun mafic-ultramafic
1019
intrusive complex, SW China. Int. Geol. Rev. 48, 650-668.
1020
ip t
1017
Zhu, W.G., Zhong, H., Li, X.H., Liu, B.G., Deng, H.L., Qin, Y., 2007. Age, geochemistry and Sr-Nd-Pb
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Lengshuiqing
Cu-Ni
1022
mafic-ultramafic complex, SW China. Precambrian Research 155, 98-124.
sulfide-bearing
us
cr
1021
Zhu, W.G., Zhong, H., Li, X.H., Liu, B.G., Deng, H.L., He, D.F., Wu, K.W., Bai, Z.J., 2008.
1024
SHRIMP zircon U-Pb geochronology, elemental, and Nd isotopic geochemistry of the
1025
Neoproterozoic mafic dykes in the Yanbian area, SW China. Precambrian Research 164,
1026
66-85.
M
an
1023
Zhuo, J.W., Jiang, X.S., Wang, J., Cui, X.Z., Xiong, G.Q., Lu, J.Z., Liu, J.H., Ma, M.Z., 2013.
1028
Opening time and filling pattern of the Neoproterozoic Kangdian Rift Basin, western
1029
Yangtze Continent, South China. Science China: Earth Sciences 56, 1664-1676.
pt
ed
1027
Zhuo, J.W., Jiang, X.S., Wang, J., Cui, X.Z., Xiong, G.Q., Lu, J.Z., Liu, J.H., Ma, M.Z., 2015.
1031
SHRIMP U-Pb age of tuff from the Neoproterozoic Kaijianqiao Formation and its geological
1032 1033
Ac ce
1030
significance. Journal of Mineralogy and Petrology 35(1), 91-99 (in Chinese with English abstract).
1034
48
Page 48 of 69
Figure captions
1035
Fig.1. Schematic map of the Precambrian South China Block emphasizing the three
1036
Mid-Neoproterozoic rift basins (after Li et al., 2003a; Wang and Li, 2003; Wang et al.,
1037
2011). The inset is a tectonic sketch of China showing the three Precambrian blocks
1038
(after Zhao and Cawood, 2012).
ip t
1034
cr
1039
Fig.2. Geological map of the Xide region in the western Yangtze Block showing the
1041
sampling locations.
us
1040
an
1042
Fig.3. Field occurrence and petrography of the Xide diabase dyke swarms in the
1044
western Yangtze Block. (a)-(b) Field photos showing the Xide diabase dykes intruded
1045
host meta-sedimentary rocks of the Dengxiangying Group; (c) Outcrop photo showing
1046
fresh surface color and massive structure of the sampling diabase; (d) Representative
1047
photomicrograph of diabasic texture and mineral assemblages including Plagioclase
1048
(Pl), Pyroxene (Py) and Magnetite (Mt).
ed
pt
Ac ce
1049
M
1043
1050
Fig.4. Representative CL images with SHRIMP and LA-ICP-MS U-Pb spots and ages
1051
for analyzed zircons of diabase samples. Scale bar in each diagram is 50 μm long.
1052 1053
Fig.5. SHRIMP zircon U-Pb concordia diagrams for diabase samples 12XD-D1,
1054
12XD-D4 and 12XD-D9. The red and green line spots represent xenocryst and
1055
discordant ages, respectively.
49
Page 49 of 69
1056 1057
Fig.6. LA-ICP-MS zircon U-Pb concordia diagrams for diabase samples 13XD-D12
1058
and 13XD-D13. The red line spots represent xenocryst ages.
ip t
1059
Fig.7. Rock classification diagrams for the diabase samples. (a) Nb/Y-Zr/TiO2*0.0001
1061
diagram distinguishing subalkaline and alkaline basalts (Winchester and Floyd, 1977);
1062
(b) FeOT/MgO-TiO2 diagram distinguishing tholeiitic and calc-alkaline series
1063
(Miyashiro, 1974).
us
cr
1060
an
1064
Fig.8. Chondrite-normalized REE patterns (a) and primitive mantle-normalized spider
1066
diagrams (b) for the Xide diabase dykes. The data for chondrite, primitive mantle,
1067
enriched mid-ocean ridge basalt (E-MORB), normal mid-ocean ridge basalt
1068
(N-MORB) and ocean island basalt (OIB) are from Sun and McDonough (1989). The
1069
data for island arc basalts (IAB) are from George et al. (2003).
ed
pt
Ac ce
1070
M
1065
1071
Fig.9. Weighted average of zircon U-Pb ages for the ca. 800-810 Ma magmatic rocks
1072
in the western Yangtze Block. The age data are list in Table 4.
1073 1074
Fig.10. Bi-elemental plots of Nd, Yb, Y, Nb, Ta, Hf, Rb and Sr versus Zr to evaluate
1075
the mobility of these elements of the Xide diabase dykes during alteration.
1076 1077
Fig.11. Nb/La-Nb/Th (a) and Nb/La-Zr/Nb (b) diagrams showing the negligible
50
Page 50 of 69
1078
crustal contamination of the parental magma for the Xide diabase dykes.
1079
Fig.12. Tectonic discrimination diagrams for the Xide diabase dykes. (a) Zr-Zr/Y
1081
diagram (after Pearce and Norry, 1979); (b) Ti-Zr diagram (after Pearce, 1982); (c)
1082
Ta/Hf-Th/Hf diagram (after Wang et al., 2001). The data for the Suxiong basalts (gray
1083
shadow) are from Li et al. (2002a).
cr
ip t
1080
1085
us
1084
Table captions
an
1086
Table 1 Zircon U-Pb isotopic data obtained by SHRIMP for diabase samples
1088
12XD-D1, 12XD-D4 and 12XD-D9. The data are the mean values of five consequent
1089
scans for each analytical spot.
ed
1090
M
1087
Table 2 Zircon U-Pb isotopic data obtained by LA-ICP-MS for diabase samples
1092
13XD-D12 and 13XD-D13.
1094 1095
Ac ce
1093
pt
1091
Table 3 Major and trace element contents of diabase samples from the Xide region.
1096
Table 4 Summary of published zircon U-Pb ages for the ca. 800-810 Ma magmatic
1097
rocks in the western Yangtze Block.
1098
51
Page 51 of 69
1098
Figures
1099 1100
1102 1103 1104 1105 1106
Ac ce
pt
ed
M
an
us
cr
ip t
1101
Fig. 1
1107 1108 1109 1110 1111
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1112
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pt
ed
M
an
us
cr
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1113
1114 1115 1116
Fig. 2
1117 1118
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1119 1120
1124 1125 1126 1127 1128 1129 1130
pt
1123
Fig. 3
Ac ce
1122
ed
M
an
us
cr
ip t
1121
1131 1132 1133 1134 1135
54
Page 54 of 69
1136 1137
1140 1141 1142 1143
Ac ce
1139
pt
ed
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an
us
cr
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1138
Fig. 4
1144 1145 1146 1147 1148 1149 55
Page 55 of 69
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pt
ed
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cr
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1152 1153 1154
Fig. 5
1155 1156 56
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1161 1162 1163 1164 1165
pt
1160
Ac ce
1159
ed
M
an
us
cr
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1158
Fig. 6
1166 1167 1168 1169 1170 1171 57
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1176 1177 1178 1179 1180
pt
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Ac ce
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ed
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an
us
cr
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1173
Fig. 7
1181 1182 1183 1184 1185 1186 58
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1187 1188
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cr
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1189
1190
an
1191 1192
Fig. 8
M
1193
1197 1198 1199 1200 1201 1202 1203
pt
1196
Ac ce
1195
ed
1194
1204 1205 1206 1207 1208 1209 59
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1210 1211 1212
an
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1214 1215 1216
M
Fig. 9
1220 1221 1222 1223 1224 1225 1226
pt
1219
Ac ce
1218
ed
1217
1227 1228 1229 1230 1231 1232 60
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1234 1235 1236
Fig. 10 61
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1237 1238 1239
1242 1243 1244 1245 1246
Ac ce
1241
pt
ed
M
an
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1240
Fig. 11
1247 1248 1249 1250 1251 1252 62
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1258 1259
pt
1257
Fig. 12
Ac ce
1256
ed
M
an
us
cr
ip t
1255
63
Page 63 of 69
ip t Spot
Pbc/%
U/ppm
Th/ppm
Th/U
Pb*/
206
Pb/238U
207
Pb/206Pb
us
206 206
cr
Table 1
207
Pb*/206Pb*
207
Pb*/235U
206
Pb*/238U
ppm
Age/Ma
Age/Ma
±%
±%
±%
795±9
740±41
0.0639±1.9
1.16±2.3
0.131±1.2
2482±32
2481±15
0.1624±0.9
10.51±1.8
0.470±1.6
826±9
773±31
0.0650±1.5
1.22±1.9
0.137±1.2
0.41
137
150
1.13
15
12XD-D1-02
0.22
43
56
1.35
17
12XD-D1-03
0.35
159
70
0.46
19
12XD-D1-04
0.17
187
136
0.75
21
800±9
an
754±26
0.0644±1.2
1.17±1.7
0.132±1.2
12XD-D1-05
0.11
100
135
1.39
12
813±10
829±29
0.0667±1.4
1.24±1.9
0.134±1.3
12XD-D1-06
0.19
28
18
0.67
11
2418±35
2525±16
0.1667±1.0
10.46±2.0
0.455±1.7
12XD-D1-07
0.25
180
106
0.61
21
814±9
865±24
0.0679±1.2
1.26±1.6
0.135±1.2
12XD-D1-08
1.52
272
143
0.54
29
755±8
803±35
0.0659±1.6
1.13±2.0
0.124±1.1
12XD-D4-01
0.45
302
12XD-D4-02
0.26
148
12XD-D4-03
0.22
183
12XD-D4-04
0.13
150
12XD-D4-05
0.39
95
12XD-D4-06
0.00
124
12XD-D4-07
0.08
12XD-D4-08 12XD-D4-09
ep te
12XD-D4
M
12XD-D1-01
d
12XD-D1
0.52
27
637±10
810±41
0.0661±2.0
0.95±2.6
0.104±1.6
76
0.53
17
804±11
808±35
0.0661±1.7
1.21±2.2
0.133±1.5
102
0.57
21
796±11
827±43
0.0667±2.1
1.21±2.5
0.131±1.4
164
1.13
18
828±11
846±31
0.0673±1.5
1.27±2.1
0.137±1.5
315
3.44
11
803±12
746±51
0.0641±2.4
1.17±2.9
0.133±1.5
362
3.02
14
819±16
833±43
0.0669±2.0
1.25±2.9
0.136±2.0
64
136
2.20
7
825±13
672±104
0.0619±4.9
1.17±5.2
0.137±1.7
0.30
173
41
0.25
20
801±11
870±38
0.0680±1.8
1.24±2.3
0.132±1.4
0.12
96
275
2.94
11
808±13
796±38
0.0657±1.8
1.21±2.4
0.134±1.5
12XD-D9-01
0.15
367
130
0.37
43
825±9
844±18
0.0672±0.8
1.26±1.4
0.136±1.1
12XD-D9-02
0.07
206
91
0.46
24
820±9
840±21
0.0671±1.0
1.25±1.5
0.136±1.2
12XD-D9-03
0.18
92
43
0.48
11
838±10
806±36
0.0660±1.7
1.26±2.1
0.139±1.3
12XD-D9-04
0.10
459
96
0.22
53
810±8
808±14
0.0661±0.7
1.22±1.3
0.134±1.1
12XD-D9-05
0.29
158
113
0.74
19
831±9
751±46
0.0643±2.2
1.22±2.5
0.138±1.2
12XD-D9-06
0.28
247
137
0.57
29
834±9
869±40
0.0680±1.9
1.30±2.2
0.138±1.1
12XD-D9-07
0.14
291
64
0.23
34
826±9
811±20
0.0661±0.9
1.25±1.5
0.137±1.1
12XD-D9
Ac c
150
Page 64 of 69
ip t
1.99
46
25
0.55
5
814±12
602±138
0.0600±6.4
1.11±6.6
0.135±1.5
12XD-D9-09
0.12
198
145
0.75
23
831±9
836±23
0.0669±1.1
1.27±1.6
0.138±1.2
12XD-D9-10
0.58
365
146
0.40
41
793±8
816±29
0.0663±1.4
1.20±1.8
0.131±1.1
12XD-D9-11
0.12
370
162
0.45
44
843±9
794±18
0.0656±0.9
1.26±1.4
0.140±1.1
204
Pb. All errors are 1σ.
Ac c
ep te
d
M
an
Notes: The radiogenic lead Pb corrected for common Pb using
us
*
cr
12XD-D9-08
Page 65 of 69
ip t
Table 2 Th/ppm
U/ppm
Th/U
207
Pb/206Pb
±%
207
Pb/235U
±%
3.0
0.0661
6.6
1.2122
7.2
02
74
426
0.2
0.0680
4.0
1.2418
4.5
03
133
58
2.3
0.0642
8.3
1.2165
4.6
04
265
267
1.0
0.0695
4.3
1.2514
05
99
234
0.4
0.0667
3.7
1.2183
06
223
198
1.1
0.0684
3.1
1.2917
07
249
117
2.1
0.0658
5.7
1.1772
08
113
59
1.9
0.0669
6.5
09
56
317
0.2
0.0672
10
166
92
1.8
01
46
21
02
192
03 04
206
Pb/238U
2.0
809
139
806
40
802
15
0.1318
2.5
878
82
820
25
798
19
0.1363
2.6
746
181
808
26
824
20
±%
us
105
Pb/235U
0.1325
Pb/238U
an
312
207
1σ
206
13XD-D12 01
Pb/206Pb
cr
207
Spot
Age/Ma
Age/Ma
1σ
Age/Ma
1σ
0.1324
1.5
915
83
824
24
801
12
3.5
0.1327
1.5
828
76
809
20
803
11
3.2
0.1369
1.4
880
64
842
19
827
11
5.4
0.1321
1.9
800
119
790
30
800
14
1.2200
6.4
0.1328
1.7
835
136
810
36
804
13
3.1
1.2285
3.3
0.1324
1.4
843
65
814
18
801
11
0.0671
5.9
1.2569
3.4
0.1366
2.0
839
122
827
20
825
15
2.2
0.0716
11.1
1.3267
10.6
0.1411
2.7
976
227
857
61
851
22
168
1.1
0.0707
3.8
1.2979
4.1
0.1319
1.4
950
75
845
23
799
10
71
31
2.3
0.0687
8.1
1.2768
8.0
0.1337
2.0
900
164
835
45
809
16
45
23
1.9
0.0689
11.5
1.3591
11.4
0.1417
3.5
894
239
871
67
854
28
05
196
272
0.7
0.0701
3.8
1.2695
3.8
0.1306
1.1
931
78
832
22
791
8
06
195
86
2.3
0.0681
11.2
1.2787
10.5
0.1358
3.1
870
235
836
60
821
24
07
529
219
08
177
313
09
194
102
10
79
35
11
432
165
12
268
13 14
Ac c
d
ep te
13XD-D13
M
4.2
2.4
0.0688
4.3
1.2427
4.3
0.1315
1.8
892
95
820
24
797
14
0.6
0.0697
2.9
1.2615
3.2
0.1315
1.7
918
59
829
18
796
13
1.9
0.0655
7.7
1.1749
7.5
0.1306
1.9
791
162
789
41
791
14
2.3
0.0695
8.9
1.2908
8.7
0.1363
2.4
922
185
842
50
823
18
2.6
0.0686
5.1
1.2379
4.8
0.1312
1.4
887
100
818
27
795
11
506
0.5
0.0695
3.0
1.2601
3.1
0.1302
1.0
917
61
828
18
789
7
454
394
1.2
0.0669
2.7
1.2238
2.6
0.1325
1.1
833
56
812
15
802
9
57
300
0.2
0.0684
2.5
1.2402
2.5
0.1309
0.8
880
52
819
14
793
6
Page 66 of 69
ip t 12XD-01
12XD-02
12XD-03
12XD-04
12XD-05
12XD-06
12XD-07
Major (wt.%)
12XD-08
us
Sample
cr
Table 3
12XD-09
13XD-10
13XD-11
13XD-12
13XD-13
13XD-14
SiO2
47.51
48.19
41.64
51.94
49.65
49.57
50.30
34.80
50.04
53.78
48.44
48.96
49.93
47.82
Al2O3
15.17
14.86
14.78
15.66
15.5
15.47
16.87
20.04
18.67
15.74
17.05
17.24
15.97
15.13
Fe2O3
2.87
2.29
3.08
2.06
2.28
2.59
3.25
3.91
2.46
2.92
2.49
2.40
3.76
FeO
11.49
11.37
13.59
8.12
9.81
9.64
8.04
12.27
8.72
7.86
8.31
7.40
8.03
10.61
MgO
7.55
7.87
14.78
9.23
8.19
8.13
12.28
20.86
6.02
10.74
10.75
12.72
8.84
7.35
CaO
9.62
8.99
7.41
7.73
9.48
9.47
4.73
4.58
6.69
4.27
5.49
4.42
9.24
9.68
Na2O
2.23
2.58
1.10
1.73
2.03
2.06
0.92
0.21
1.18
0.97
0.99
0.96
2.09
2.50
K2O
0.83
0.88
0.40
1.33
0.68
0.73
1.70
0.57
2.28
1.57
3.15
2.85
1.15
0.51
MnO
0.23
0.21
0.21
0.18
0.18
0.19
0.07
0.11
0.19
0.07
0.15
0.16
0.20
0.24
TiO2
2.18
2.56
2.70
1.73
1.90
1.92
2.41
2.93
2.14
2.20
2.41
2.45
1.83
2.22
P2O5
0.19
0.34
0.37
0.25
0.26
0.28
0.37
0.40
0.20
0.35
0.35
0.34
0.24
0.19
TOTAL
99.87
100.14
100.06
100.05
100.09
100.02
100.04
100.01
100.01
99.99
99.92
100.01
0.92
1.81
5.15
Mg#
52.95
55.14
65.46
La
17.43
15.9
16.5
Ce
39.0
37.5
39.5
Pr
5.84
5.12
Nd
25.2
Sm
an
M
d
ep te
LOI
99.96
99.96
2.4
1.89
1.42
1.36
3.61
8.25
4.25
4.85
4.09
4.34
1.79
1.21
66.00
59.16
58.76
71.63
74.22
50.78
69.10
67.34
73.46
64.54
52.42
29.8
15.2
14.6
12.8
14.7
7.69
15.9
17.7
17.4
20.0
17.56
66.3
34.7
33.2
31.1
37.4
19.9
38.2
41.5
41.1
45.5
39.1
5.38
7.93
4.49
4.31
4.08
4.96
3.01
4.86
5.37
5.27
5.59
5.85
24.3
26.1
33.7
20.3
19.6
19.2
24.0
15.5
22.3
24.6
24.1
25.0
25.5
4.76
6.61
7.41
7.30
5.14
5.19
4.84
6.12
4.89
5.78
6.03
5.84
5.82
4.93
Eu
1.85
2.37
2.48
1.61
1.62
1.58
1.16
1.89
1.39
1.44
1.55
1.51
1.33
1.79
Gd
6.41
8.13
8.94
7.28
6.17
5.80
5.63
7.22
6.02
5.97
6.94
6.64
6.32
6.39
Ac c
Trace (ppm)
Tb
1.09
1.32
1.53
1.15
1.00
0.97
0.94
1.07
0.95
0.96
1.06
1.03
0.99
1.10
Dy
7.07
8.45
9.41
6.82
6.35
6.30
5.95
6.66
6.03
5.78
6.55
6.43
6.02
7.24
Ho
1.53
1.76
2.00
1.40
1.32
1.35
1.25
1.39
1.28
1.20
1.36
1.32
1.25
1.54
Er
4.78
5.55
6.13
4.30
4.08
4.01
3.78
4.28
3.93
3.47
4.16
4.02
3.74
4.77
Tm
0.64
0.69
0.81
0.57
0.56
0.54
0.50
0.55
0.53
0.46
0.56
0.53
0.51
0.66
Page 67 of 69
4.71
5.20
3.68
3.65
3.67
3.28
3.83
Lu
0.63
0.73
0.77
0.54
0.55
0.55
0.51
0.56
3.63
3.09
3.60
3.47
3.36
4.28
0.55
0.46
0.56
0.54
0.48
0.64
12XD-01
12XD-02
12XD-03
12XD-04
12XD-05
12XD-06
12XD-07
12XD-08
12XD-09
13XD-10
13XD-11
13XD-12
13XD-13
13XD-14
Sc
47.0
49.6
52.5
34.8
38.1
40.0
33.6
47.2
46.0
30.5
36.0
35.2
36.8
47.1
V
241
279
301
190
178
187
207
91.0
250
199
222
222
218
245
Cr
214
172
179
419
282
292
424
358
218
386
428
418
440
213
Co
53.5
48.7
45.5
44.2
45.0
48.1
38.0
38.2
55.6
32.8
47.8
46.1
49.2
50.7
Ni
44.4
39.5
34.8
126
72.6
75.8
83.4
88.0
50.1
76.3
80.8
79.2
137
39.3
148
144
253
134
102
105
121
192
362
114
116
119
83.0
129
22.6
22.9
22.8
19.5
20.5
21.0
20.5
21.3
21.5
19.1
20.6
20.4
20.0
23.1
Rb
39.2
32.2
13.6
51.2
22.2
24.8
64.4
25.1
104
62.7
145
149
45.4
19.2
Sr
166
152
58.0
130
178
173
45.7
9.78
141
60.6
64.3
65.6
160
169
Y
41.9
47.8
56.6
37.8
36.4
35.8
33.3
39.0
34.8
32.3
37.5
37.8
34.2
43.1
Zr
156
211
234
253
149
149
191
216
169
174
195
197
193
173
Nb
8.99
8.23
8.89
Cs
13.2
5.37
2.72
Ba
246
379
158
Hf
3.79
5.56
5.87
0.56
0.58
8.43
6.37
Th
3.52
1.72
U
0.13
Cu
19.4
ep te
0.58 8.04
10.8
8.66
8.52
9.94
11.8
10.88
9.22
10.1
10.3
8.53
9.04
15.5
7.82
9.71
8.02
1.99
14.0
9.33
17.7
17.9
11.4
6.01
419
331
345
1161
398
177
1000
1923
1935
414
193
6.42
3.99
3.95
4.97
5.49
3.86
4.63
5.05
4.90
5.01
3.68
0.72
0.56
0.54
0.67
0.75
0.64
0.62
0.69
0.67
0.57
0.77
25.4
33.8
20.1
21.5
16.4
13.0
21.7
30.4
29.5
18.0
12.9
1.88
10.1
2.16
2.11
3.42
3.84
5.06
3.15
3.53
3.43
6.06
4.50
0.24
0.31
0.88
0.32
0.32
0.46
5.70
0.17
0.44
0.48
0.44
0.50
0.10
29.9
14.9
32.3
28.5
35.6
6.34
3.16
2.59
11.4
4.11
5.32
24.5
24.0
Ac c
Ta Pb
d
Zn Ga
M
an
us
Table 3 (continued) Sample
ip t
4.20
cr
Yb
Page 68 of 69
ip t cr Location
Rock type
1
Kangding
Gneissic granites
2
Kangding
Gneissic granites
3
Kangding
Gneissic granites
SHRIMP U-Pb
4
Tongde
Picritic dykes
5
Songlinping
6
Changshiba
7
Xide
8
Xiatianba
9
Kaijianqiao
10
Zhonghe
13 14 15
SHRIMP U-Pb
795±11
Zhou et al., 2002a
SHRIMP U-Pb
796±13
Zhou et al., 2002a
797±10
Zhou et al., 2002a
SIMS U-Pb
796±5
Li et al., 2010a
Felsic tuffs
SHRIMP U-Pb
798±8
Jiang et al., 2012
Metabasalts
SHRIMP U-Pb
799±8
Ren et al., 2013
Diabases
LA-ICP-MS U-Pb
800-810
This study
A-type granites
LA-ICP-MS U-Pb
801±7
Wu et al., 2014b
Felsic tuffs
SHRIMP U-Pb
801±7
Zhuo et al., 2015
Felsic tuffs
SHRIMP U-Pb
803±9
Jiang et al., 2012
Suxiong
Rhyolites and Basalts
SHRIMP U-Pb
803±12
Li et al., 2002a
Xiacun
Granites
SHRIMP U-Pb
803±15
Guo et al., 2007
Luoci
Basalts
LA-ICP-MS U-Pb
804±3
Cui et al., 2015
Luliang
Felsic tuffs
SHRIMP U-Pb
805±14
Zhuo et al., 2013
Lengshuiqing
Gabbros
SHRIMP U-Pb
806±4
Zhou et al., 2006b
Lengqi
Gabbros
SHRIMP U-Pb
808±12
Li et al., 2002c
Yanjing
Rhyolitic tuffs
SHRIMP U-Pb
809±9
Geng et al., 2008
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16
Reference
17
d
ep te
12
Age (Ma)
an
No.
11
Dating method
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S0301-9268(15)00257-0 http://dx.doi.org/doi:10.1016/j.precamres.2015.07.017 PRECAM 4324
To appear in:
Precambrian Research
Received date: Revised date: Accepted date:
10-2-2015 22-7-2015 27-7-2015
Please cite this article as: Cui, X., Jiang, X., Wang, J., Wang, X., Zhuo, J., Deng, Q., Liao, S., Wu, H., Jiang, Z., Wei, Y.,Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent, Precambrian Research (2015), http://dx.doi.org/10.1016/j.precamres.2015.07.017 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.
1
Highlights
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1. The Xide diabase dykes formed in a continental rift setting at ca. 800-810 Ma;
3
2. Mid-Neoproterozoic continental rifting occurred in the western Yangtze Block;
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3. The South China Block played a key role in the assembly and breakup of Rodinia.
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Mid-Neoproterozoic diabase dykes from Xide in the western
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Yangtze Block, South China: New evidence for continental
9
rifting related to the breakup of Rodinia supercontinent
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cr
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Xiaozhuang Cui a, b, *, Xinsheng Jiang a, b, **, Jian Wang a, b, Xuance Wang c,
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Jiewen Zhuo a, b, Qi Deng a, b, Shiyong Liao d, Hao Wu a, Zhuofei Jiang e, Yanan Wei e
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a
15
b
Resources, Chengdu 610081 China c
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ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS), Curtin University, GPO Box U1987, Perth, WA 6845, Australia
pt
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Key Laboratory of Sedimentary Basin and Hydrocarbon Resource, Ministry of Land and
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Chengdu Center, China Geological Survey, Chengdu 610081, China
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14
an
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d
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
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e
School of Geosciences and Resources, China University of Geosciences, Beijing 100083,
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China
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Corresponding author:
24
* Email: [email protected]. Tel: +86 28 83220166. (X.Z. Cui)
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** Email: [email protected]. Tel: +86 28 83231155. (X.S. Jiang)
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2
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Abstract: The petrogenesis of widespread Mid-Neoproterozoic mafic dykes is crucial
27
for the paleographic position of the South China Block (SCB) in Rodinia
28
supercontinent and the mechanism of Rodinia breakup. Here, new detailed
29
geochronological and geochemical data on the diabase dykes from Xide in the
30
western Yangtze Block are presented. Zircon SHRIMP/LA-ICP-MS U-Pb dating
31
shows that four diabase samples yield uniform crystallization age varying from 796 ±
32
6 Ma to 809 ± 15 Ma, while one sample gives a slight older age of 824 ± 11 Ma that is
33
overlapped with ca. 810 Ma within uncertainties. This suggests that the Xide diabase
34
dykes emplaced at ca.800-810 Ma and were coeval with regional bimodal magmatism
35
(e.g., the Suxiong bimodal volcanics). The Xide diabase dykes are characterized by
36
low SiO2 contents, high Mg# values and Cr, Ni contents, relative enrichment of light
37
rare-earth elements, and slight depletion of high field strength elements (e.g., Nb, Ta,
38
Zr, and Hf) and nearly constant Zr/Hf, Nb/Ta and Nb/La ratios. Our analyses indicate
39
that the diabase was mainly produced by interaction between lithospheric and
40
asthenospheric mantle. Moreover, the diabase samples display geochemical
41
characteristics affinity with typical intra-plate basalts. Together with the widespread
42
coeval bimodal magmatic suite and sedimentary records in the Kangdian Rift, we
43
proposed that the western Yangtze Block once experienced continental rifting during
44
the Mid-Neoproterozoic, which also occurred in other Rodinia blocks, such as Tarim,
45
Australia and North America. In addition, the Grenville-aged magmatism records
46
throughout SCB with the widespread Mid-Neoproterozoic rift-related magmatism and
47
sedimentation records imply that SCB probably played a key role in the assembly and
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breakup of Rodinia supercontinent.
49
Keywords: Diabase dykes, Neoproterozoic, Continental rifting, Western Yangtze
51
Block, South China, Rodinia supercontinent
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1. Introduction
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Assembly and breakup of supercontinents exert major influences on global
55
tectonic framework, mantle dynamics, mineral systems, and surface geological
56
features (e.g., Rogers and Santosh, 2003; Zhao et al., 2004; 2006; Santosh, 2010;
57
Pirajno and Santosh, 2015). The Rodinia supercontinent, assembled between 1.3 and
58
0.9 Ga and broken up between 850 and 740 Ma (Li et al., 2008a), has been topics of
59
great interest in the last decades (e.g. Wingate et al., 1998; Li et al., 1999, 2003a,
60
2008a; Li et al., 2002a, 2003b, 2010a; Ling et al., 2003; Wang and Li, 2003; Wang et
61
al., 2007, 2008a, 2010a; Ernst et al., 2008; Jacobs et al., 2008; Wang et al., 2010b;
62
Shu et al., 2011; Zhang et al., 2012a; Deng et al., 2013; McClellan and Gazel, 2014;
63
Teixeira et al., 2014). Multiple episodic records of anorogenic magmatism during
64
850-740 Ma are widespread on several blocks, including South China, Tarim, North
65
America, India, Southern Africa, and Australia (Powell et al., 1994; Park et al., 1995;
66
Wingate et al., 1998; Li et al., 1999, 2003a, 2008a; Preiss, 2000; Frimmel et al., 2001;
67
Li et al., 2002a, 2003b, 2008c, 2010a; Ling et al., 2003; Wang et al., 2007, 2008a,
68
2010a; Ernst et al., 2008; Xu et al., 2013; Zhang et al., 2013a; McClellan and Gazel,
69
2014). These magmatic records provide important constraints on the process and
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mechanism of Rodinia breakup. The South China Block (SCB) is generally thought to have retained some of the
72
best-preserved 850-720 Ma magmatism and sedimentary records (Li et al., 2003a,
73
2008a; Li et al., 2002a, 2003b, 2008b,c; Ling et al., 2003; Wang and Li, 2003; Lin et
74
al., 2007; Wang et al., 2009, 2011a, 2012a; Wang et al., 2010b; Shu et al., 2011; Zhao
75
et al., 2011; Xia et al., 2012; Zhao and Cawood, 2012; Wang et al., 2012b) (Fig. 1).
76
However, petrogenesis and tectonic interpretations of these widespread magmatic
77
events are still highly debating, and two main, but conflicting, models have been
78
proposed. One model suggests that these igneous rocks were produced within a
79
intracontinental rift setting as a result of mantle plume activities, which finally caused
80
the breakup of Rodinia (Li et al., 1999, 2003a, 2008a; Li et al., 2002a,c, 2003b,
81
2010a,b; Ling et al., 2003; Lin et al., 2007; Zhu et al., 2006, 2007, 2008; Wang et al.,
82
2007, 2008a, 2009; Wang et al., 2010b). The other model argues that most of these
83
rocks formed under either an arc setting related to the steeply dipping subduction of
84
the oceanic lithosphere eastward (present-day orientation) underneath the Yangtze
85
Block (Yan et al., 2002; Zhou et al., 2002a,b, 2006a,b; Zhao and Zhou, 2007a,b; Dong
86
et al., 2011, 2012; Zhao et al., 2008, 2011; Meng et al., 2014) or collision-related
87
environments (Zhao and Cawood, 1999; Wang et al., 2004, 2006). A growing
88
agreement is that these 850-720 Ma magmatism and sedimentary records in SCB were
89
formed in an extensional setting; however, the remaining controversy is its dynamics.
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Mafic dykes can yield insights on the study of mechanism and processes of
91
supercontinent breakup (e.g. Yang et al., 2011; Stepanova et al., 2014; Wang et al.,
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2014a). Neoproterozoic mafic dykes widespread in many Rodinia blocks have been
93
well studied and demonstrated to record the information related to the breakup of
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Rodinia supercontinent (e.g., Park, 1995; Wingate et al., 1998; Li et al., 1999, 2003a,
95
2008a; Li et al., 2002c, 2006a; Ernst et al., 2008; Pisarevsky et al., 2008). Abundant
96
diabase dykes are widely distributed in the Xide region (Fig. 2), which intruded into
97
the Mesoproterozoic Dengxiangying Group. However, their petrogenesis and tectonic
98
implications have not been well studied by geochronological and geochemical data. In
99
this contribution, we present detailed field, petrological, geochronological and
100
geochemical studies on the Xide diabase dykes. These new data, in combination with
101
available regional geological data, are crucial not only for constraining the
102
Mid-Neoproterozoic continental rifting in the western Yangtze Block, but also for
103
understanding the Neoproterozoic tectonic setting of SCB.
104
2. Geological background and samples
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The SCB consists of the Yangtze Block to the northwest and the Cathaysia Block
106
to the southeast (Fig. 1). It is separated from the North China Craton by the
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Qinling-Dabie-Sulu orogenic belt to the north, from the Songpan-Gantze terrane by
108
the Longmenshan Fault Zone to the northwest, and from the Indochina Block by the
109
Ailaoshan-Red River Fault to the southwest, and bounded by the continental slope of
110
the Pacific Ocean to the southeast (Fig. 1). Although it is generally accepted that the
111
Yangtze and Cathaysia blocks amalgamated during the Proterozoic Sibao orogeny
112
(a.k.a the “Jiangnan” or “Jinning” orogeny), the timing of this orogeny is still
113
controversial (e.g., Li et al., 1995, 2002b, 2007, 2008a; Zhao and Cawood, 1999;
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Wang et al., 2004, 2006, 2014b; Greentree et al., 2006; Ye et al., 2007; Zhang et al.,
115
2012b; Yin et al., 2013; Zhang et al., 2013b; Zhao, 2014). Nonetheless, there are
116
significant numbers of Grenvillian subduction- or collision-related magmatism
117
records in the western (Mou et al., 2003; Greentree et al., 2006; Geng et al., 2007;
118
Zhang et al., 2007; Yang et al., 2009; Wang et al., 2012c; Li et al., 2013; Zhang et al.,
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2013c) and northern Yangtze (Qiu et al., 2011, 2015; Wang et al., 2013a) and the
120
Cathaysia blocks (Wang et al., 2008b; Shu et al., 2011; Zhang et al., 2012d; Cawood
121
et al., 2013; Wang et al., 2013d, 2014c).
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Outcrops of Archean rocks are mainly distributed in the northern Yangtze Block,
123
whereas Paleoproterozoic basement rocks occur sporadically in the western and
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northwestern Yangtze Block (Greentree et al., 2006; Zhao and Cawood, 2012; Chen et
125
al., 2013; Wu et al., 2014a; Zhou et al., 2015). However, the Mid-Neoproterozoic
126
(mainly 820-725 Ma) magmatism and sedimentary records, which were preserved as
127
wedge-shaped rift successions (Wang and Li, 2003; Wang et al., 2015), are widely
128
distributed within the three major rift basins in SCB: the roughly E-W trending
129
Bikou-Hannan Rift along the northwestern Yangtze Block, the N-S trending Kangdian
130
Rift near the present western Yangtze Block, and the major NE-SW trending Nanhua
131
Rift to the southeast (Fig. 1) (Li et al., 1999, 2003a, 2008a; Wang and Li, 2003; Wang
132
et al., 2008a, 2009, 2011a, 2012a; Cui et al., 2014; Wang et al., 2015). These
133
successions consist of continental and marine siliciclastic and volcaniclastic rocks
134
interbedded with bimodal volcanics and tuffs (Li et al., 2002a; Wang and Li, 2003;
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Wang et al., 2011a, 2012a; Jiang et al., 2012; Wang et al., 2015). In the Kangdian Rift,
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the wedge-shaped rift successions include the Suxiong, Kaijianqiao, Chengjiang,
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Luliang, and Niutoushan Formations (Wang and Li, 2003; Jiang et al., 2012; Zhuo et
138
al., 2013, 2015; Cui et al., 2013, 2014). In the western Yangtze Block, the rift basement (pre-rift successions) is
140
composed of the Paleoproterozoic and Mesoproterozoic strata. The Paleoproterozoic
141
strata include the Dahongshan, Dongchuan and Hekou Groups, while the
142
Mesoproterozoic strata include the Kunyang, Huili, Dengxiangying and Ebian Groups
143
(Greentree et al., 2006; Geng et al., 2007, 2008; Chen et al., 2013; Li et al., 2013).
144
Among them, the Dengxiangying Group is mainly distributed in the Xide County,
145
western Sichuan Province, and covers an area of approximately 200 km2 (Fig. 2). The
146
Dengxiangying Group is a sequence of meta-sedimentary and volcanic rocks
147
including phyllite, slate, quartzite and marble interbedded with meta-dacite and has a
148
total thickness of more than 8500 meters (BGMR, 1991, 1996). It underwent lower
149
greenschist facies metamorphism and strong deformation. A meta-dacite sample from
150
the Dengxiangying Group gave a SHRIMP zircon U-Pb age of 1017 ± 17 Ma (Geng
151
et al., 2008), which is consistent with those ages of the Kunyang, Huili and Ebian
152
Groups (Zhang et al., 2007; Geng et al., 2007, 2008; Li et al., 2013; Authors’
153
unpublished data). The Dengxiangying Group is unconformably overlain by the
154
Suxiong and Kaijianqiao Formations to the north, by the Sinian and younger strata to
155
the east and south, and intruded by granites to the west (Fig. 2).
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The diabase dykes (with minor sills) in the Xide region intruded into the pre-rift
157
meta-sedimentary and volcanic rocks (Dengxiangying Group), but did not penetrate
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the Neoproterozoic rift successions (Fig. 3a, b). Their intrusive contacts are very clear
159
and thin baked zones or thermal recrystallization that can be observed near the
160
boundary of the dykes. These diabase dykes are rarely subjected to deformation and
161
metamorphism in contrast to their strongly deformed metamorphic wall-rocks. They
162
are commonly several meters wide and tens of meters strike length. The weathered
163
surface of these diabase dykes is yellowish-grey in color, while the fresh surface is
164
grayish-black (Fig. 3a-c). Most diabase dykes have a dominant N-S trend that is
165
sub-parallel to the Kangdian Rift and are oblique or nearly vertical. All the diabase
166
samples, collected from the Xide region, display typical diabasic texture (Fig. 3d) and
167
are massive structure (Fig. 3c). These diabase samples have similar mineral
168
compositions of plagioclase (40-55%), pyroxene (20-30%), Fe-Ti oxides (5-15%),
169
ordinary hornblende (5-10%), and olivine (5-10%) with minor opaque minerals such
170
as apatite (Fig. 3d). In this study, a total of thirty diabase samples were collected, of
171
which fourteen relatively fresh samples were chosen for whole-rock geochemical
172
analyses and five samples were analyzed by zircon U-Pb dating.
173
3. Analytical techniques
174
3.1 Zircon U-Pb dating
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Zircons were separated from crushed rock using a combination of conventional
176
heavy liquid and magnetic separation techniques. Individual zircon grains were
177
handpicked under a binocular microscope and were mounted in an epoxy resin
178
together with several grains of standard zircon TEMORA 1. Mounts were polished to
179
expose zircon surfaces suitable for U-Pb dating using either SHRIMP or LA-ICP-MS
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methods. Prior to U-Pb analyses, the structures of the zircon grains were imaged by
181
cathodoluminescence (CL) techniques with a HITACHI S-3000N electron microprobe
182
(GATAN) at the Beijing SHRIMP Center, Chinese Academy of Geological Sciences
183
(CAGS).
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Samples 12XD-D1, 12XD-D4 and 12XD-D9 were analyzed using the SHRIMP
185
II ion microprobe at the Beijing SHRIMP Center, CAGS. The SHRIMP analytical
186
procedures were similar to those described by Williams (1998). The intensity of the
187
primary O2− ion beam was 3.5-5.0 nA with the spot size of 25-30 μm. Each analytical
188
site was rastered for 2.5-3.0 min prior to analysis to remove surface common Pb. Five
189
scans through the mass stations were made for each age determination of zircon.
190
Reference zircon M257 (U = 840 ppm, Nasdala et al., 2008) were used for U
191
elemental abundance calibration, whereas TEMORA 1 (206Pb/238U age = 417 Ma,
192
Black et al., 2003) were used for calibration the U-Pb ages. Common lead corrections
193
were applied using the measured
194
using the SQUID and ISOPLOT programs (Ludwig, 2001, 2003). SHRIMP analytical
195
data are presented with 1 errors in Table 1, and uncertainties for weighted mean ages
196
in the text are quoted at the 95 % confidence level.
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Pb abundances. Data processing was carried out
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Samples 13XD-D12 and 13XD-D13 were analyzed using the LA-ICP-MS at the
198
State Key Laboratory of Geological Processes and Mineral Resources, China
199
University of Geosciences, Wuhan. Laser sampling was performed using a GeoLas
200
2005 ArF excimer laser ablation system. The ablation was carried out by a pulsed
201
(GeoLas) 193 nm ArF excimer (Lambda Physik, Göttingen, Germany) with laser
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power of 50 mJ/pulse energy at a repetition ratio of 8 Hz coupled to an Agilent 7500a
203
quadrupole ICP-MS. Helium was used as a carrier gas to transport the ablated
204
material from the laser ablation cell to the ICPMS. The diameter of the laser ablation
205
crater was 32 μm. Zircon 91500 was used as external standard for U-Pb dating, and
206
was analyzed twice every five analyses. NIST610 glass was used as an external
207
standard to normalize the U, Th, and Pb concentrations of the unknowns. The detailed
208
analytical procedures followed Liu et al. (2010). Off-line selection and integration of
209
background and analyze signals, and time-drift correction and quantitative calibration
210
for U-Pb dating were performed by ICPMSDataCal (Liu et al., 2010). Calculation of
211
concordia plots and weighted mean ages were made using ISOPLOT, with
212
uncertainties quoted at the 1σ and 95% confidence levels (Ludwig, 2003).
213
3.2. Major and trace element analyses
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Based on petrographic examination, fifteen relatively fresh diabase samples were
215
selected for geochemical analysis. The marginal parts of these samples were cut off,
216
and then the remnant core part with a dimension of about 5×3×4 cm3 was powdered to
217
agrain size of 200-mesh. The major elements were determined by X-ray fluorescence
218
(XRF) at the National Research Center for Geoanalysis, CAGS, with an analytical
219
uncertainties ranging from 1 to 3 %. The trace elements were determined as solute by
220
Agilent 7500ce inductively coupled plasma mass spectrometry (ICP-MS) at the same
221
laboratory. The analytical uncertainties were less than 5 % for elements occurring at
222
concentrations > 10 ppm, less than 8 % for those at concentrations of < 10 ppm, and
223
about 10 % for transition metals.
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224
4. Analytical results
225
4.1. Geochronology Cathodoluminescence imaging (CL) of representative zircon grains are shown in
227
Fig. 4. Results of SHRIMP and LA-ICP-MS zircon U-Pb dating are presented in
228
Tables 1 and 2, respectively, and all of these analyses are plotted on Concordia
229
diagrams (Figs. 5 and 6). Unless otherwise stated, in the figures and the following
230
discussions, for the zircon grains with age older than 1.0 Ga, we use
231
to represent their crystallisation ages, whereas for the younger grains, their
232
crystallisation ages are determined by 206Pb/238U ages.
233
4.1.1. 12XD-D1 (N28°27′50.07″, E102°21′30.23″)
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Pb/206Pb ages
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Zircon grains from sample 12XD-D1 are euhedral and transparent, up to 100-250
235
μm long, and have length/width ratios of between 1:1 and 5:1. In CL images, most of
236
zircon grains display slight to dark luminescence and homogeneous structure with or
237
without straight and wide growth bands (Fig. 4a, c, e), which are similar to typical
238
magmatic zircons. The rest grains are rounded and show relatively blurry oscillatory
239
zoning, which are interpreted to be xenocrysts (Fig. 4b, d). Eight analyses were
240
obtained from this sample (Table 1). These analyses give relatively low U and Th
241
contents (U = 28-272 ppm and Th = 18-150 ppm), and variable Th/U ratios ranging
242
from 0.46 to 1.39. Spots 02 and 06 give significantly older concordant
243
ages of 2481 ± 15 Ma and 2525 ± 16 Ma, respectively. Spot 08 produces a younger
244
age of 755 ± 8 Ma and is rejected in calculation due to its high common lead (1.5 wt%
245
206
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Pbc). The five remaining analyses produce a
206
207
Pb/206Pb
Pb/238U weighted mean age of 809
12
Page 12 of 69
246
± 15 Ma (MSWD = 1.8), which is interpreted as the best estimate of the
247
crystallization age of sample 12XD-D1.
248
4.1.2. 12XD-D4 (N28°27′53.58″, E102°21′38.91″) Zircon grains from sample 12XD-D4 are euhedral, transparent and colorless.
250
They are 80-250 μm long with length/width of about 1:1 to 5:1. Most grains show
251
slight to dark luminescence and homogeneous structure without core-rim texture in
252
CL images (Fig. 4f, g, j), while some have blurry oscillatory zoning (Fig. 4h, i),
253
indicating that all of them should be magmatic zircon grains from mafic rocks. Nine
254
analyses give variable concentrations of U (64-302 ppm) and Th (41-362 ppm), with
255
Th/U ratios of 0.25-3.44 (Table 1). Eight spots yield a relatively uniform range of
256
concordant
257
809 ± 8 Ma (MSWD = 1.04) (Fig. 5). This age is regarded as the crystallization age of
258
sample 12XD-D4.
259
4.1.3. 12XD-D9 (N28°27′59.23″, E102°21′58.05″)
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Pb/238U ages from 796 to 828 Ma, which give a weighted mean age of
pt
206
Zircon grains from sample 12XD-D9 are mostly colorless and range in size from
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261
100-150 × 50-120 μm with aspect ratios of about 1:1 to 3:1. They are mostly stubby to
262
long prismatic in shape and euhedral. In CL images, most zircon grains show
263
relatively clear oscillatory zoning and without core-rim texture (Fig. 4k, m, o), while
264
some zircon grains display indistinct sector zoning or homogeneous structure (Fig. 4l,
265
n). Eleven analyses on 11 zircon grains have 46-459 ppm U and 25-162 ppm Th with
266
Th/U ratios of 0.22-0.75, indicating a magmatic origin. Spot 08 is rejected in the
267
following calculation due to its high common lead (1.9 wt% 206Pbc). The ten analyses
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Page 13 of 69
206
Pb/238U ages ranging from 793 to 843 Ma (Table 1).
yield scattered concordant
269
They give a weighted mean age of 824 ± 11 Ma (MSWD = 2.9) (Fig. 5). Although this
270
age is slight older than the others, it is overlapped with ca. 810 Ma with considering
271
the uncertainties.
272
4.1.4. 13XD-D12 (N28°22′28.00″, E102°21′23.12″)
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Zircon grains from sample 13XD-D12 are mostly colorless euhedral prismatic
274
crystal, about 100-200 μm long, and 50-70 μm wide with length/width ratios of
275
2:1-4:1. Vast majority of these zircons show prismatic crystals, with regular edges and
276
without any core-rim textures. Their CL images display relative homogenous inner
277
structure or indistinct wide oscillatory zoning (Fig. 4p, r, s, t), while a minority of
278
zircons show wide oscillatory zoning (Fig. 4q). Ten analyses conducted on 10 zircons
279
yield variable U and Th contents (U = 58-426 ppm, Th = 56-312 ppm, Th/U = 0.2-3.0)
280
(Table 2). They obtain concordant and consistent
281
827 Ma, which give a weighted mean age of 808 ± 8 Ma (MSWD = 0.74) (Fig. 6).
282
This age is interpreted as the crystallization age of sample 13XD-D12.
283
4.1.5 13XD-D13 (N28°28′06.12″, E102°22′10.06″)
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Pb/238U ages varying from 798 to
pt
206
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cr
273
Zircon grains from sample 13XD-D13 are mostly colorless, transparent and
285
euhedral prismatic grains. The length of grains range from 100 to 200 μm and have
286
aspect ratios of between 1:1 and 3:1. In CL images, zircon grains commonly show
287
slight to dark luminescence and homogeneous structure without any core-rim texture,
288
similar to those crystallized from mafic magma (Fig. 4u, w, x, y), whereas minority
289
zircons display clear striped oscillatory zoning (Fig. 4 v). Fourteen analyses were
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Page 14 of 69
290
carried out on 14 zircons from sample 13XD-D13 (Table 2). The results show large
291
range of U and Th concentrations (U = 21-506 ppm, Th = 45-529 ppm) with Th/U
292
ratios ranging from 0.2 to 2.6, indicating a magmatic origin. Two analyses (spots 01,
293
04) yield a weighted mean
294
twelve remaining analyses give relatively uniform and concordant
295
from 789 to 823 Ma, yielding a weighted mean age of 796 ± 6 Ma (MSWD = 0.57)
296
(Fig. 6). This age is interpreted to represent the crystallization age of sample
297
13XD-D13.
298
4.2. Geochemistry
ip t
Pb/238U age of 852 ± 34 Ma (MSWD = 0.01). The 206
Pb/238U ages
an
us
cr
206
Major and trace elements concentrations of the representative fourteen diabase
300
samples are presented in Table 3. In general, these samples displayed lager range of
301
SiO2, MgO, Al2O3, FeOt, and CaO contents. The diabase samples are characterized by
302
relatively high MgO contents and magnesium number (Mg#). It should be noticed that
303
diabase samples 12XD-03 and 12XD-08 have anomalously low SiO2 contents and
304
high LOI values that suggest intense alternation, and thus are rejected from the
305
following discussions. Due to possible migration of large ion lithophile elements
306
(LILE, e.g., K, Na, Rb, Sr, Ba, Cs, etc.) in the studied samples, only the immobile
307
elements, such as high field strength elements (HFSE) and rare earth elements (REE),
308
are employed in the rock classification and petrogenesis discussion (see discussion in
309
5.2). In the Nb/Y-Zr/TiO2 diagram, all the samples plot in the field of subalkaline
310
basalts (Fig. 7a). In the FeOT/MgO-TiO2 diagram, all the samples belong to the
311
tholeiitic series (Fig. 7b).
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Page 15 of 69
312
Chondrite-normalized REE patterns for all the samples are shown in Fig. 8a. The Xide diabase samples have relatively high REE contents (ΣREE = 75.30-172.38 ppm).
314
Most of these samples are enriched in LREE (LREE = 52.38-146.64 ppm,
315
LREE/HREE = 2.29-5.70, LaN/SmN = 1.02-2.64, LaN/YbN = 1.52-5.81), and display
316
the smooth to right-inclined REE distribution patterns (Fig. 8a). It is worth noting that
317
sample 12XD-04 (LREE = 146.64 ppm, LREE/HREE = 5.70) and 13XD-10 (LREE =
318
52.38 ppm, LREE/HREE = 2.29) exhibit strongly and slightly enriched LREE
319
patterns, respectively. Still, all the analyzed samples can’t be distinguished by their
320
geochemical signatures of major and trace elements. On the whole, they all fall into
321
the field between normal mid-ocean ridge basalt (N-MORB) and OIB (Fig. 8a), and
322
are differentiated in LREE and HREE with enriched in LREE. These patterns quite
323
differ from those for the representative N-MORBs which are strongly depleted in
324
LREE. In the primitive mantle-normalized spidergrams (Fig. 8b), all the samples
325
exhibit clear enrichments in Th, La, and depletions in Nb, Ta without visible Ti
326
depletions. The trace element distribution patterns are comparable with OIBs, with the
327
exception of the depletion of Nb-Ta. More importantly, the high Nb-Ta abundance and
328
the absence of Zr-Hf negative anomalies are different from subduction-related
329
island-arc basalts (IABs).
330
5. Discussion
331
5.1. Age of the Xide diabase dykes and regional synchronous magmatism
Ac ce
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M
an
us
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313
332
Although the Mid-Neoproterozoic mafic intrusions have been well documented
333
in the western Yangtze Block (Li et al., 2008a and references therein), few
16
Page 16 of 69
geochronological studies have been carried on the diabase dykes in the Xide region.
335
The diabase dykes, which intruded into the Dengxiangying Group, were previously
336
considered to form during the Sinian Period (the 1: 200,000 geological maps). In our
337
analyses, most of the analyzed zircon grains were attributed to mafic magmatic origin
338
during the diabase dyke emplacement according to CL images and Th/U ratios (Fig. 4,
339
Tables 1 and 2). Forty five of the 52 analyses give uniform and concordant ages, and
340
have a Gaussian-style distribution pattern on the probability plot. They yield a
341
weighted mean age of 810 ± 5 Ma (MSWD = 2.4, n = 45). Although the obtained age
342
of sample 12XD-D9 is slight older than the others, it is overlapped with ca. 810 Ma
343
within uncertainties. The other four samples give a coherent age span between 796
344
and 809 Ma, which can not be distinguished from each other within analytical errors.
345
Considering the ca. 800 and 725 Ma formation age of the overlain rift successions (Li
346
et al., 2002a; Zhuo et al., 2015), the emplacement age of the Xide diabase dykes can
347
be regarded as ca. 800-810 Ma.
cr
us
an
M
ed
pt
Various magmatism records that are broadly coeval with the Xide diabase dykes
Ac ce
348
ip t
334
349
in the western Yangtze Block as summarized in Table 4. The bimodal volcanics of the
350
Suxiong Formation were erupted at 803 ± 12 Ma (Li et al., 2002a), and is
351
synchronous with the 799 ± 8 Ma basalts of the Huangshuihe Group (Ren et al., 2013)
352
and 809 ± 9 Ma rhyolitic tuffs of the Yanjing Group (Geng et al., 2008). Mafic and
353
felsic intrusions are also widely distributed, including the Kangding granitoids with
354
ages ranging from 795 to 797 Ma (Zhou et al., 2002a), 796 ± 5 Ma picritic dykes (Li
355
et al., 2010a), 801 ± 7 Ma Xiatianba A-type granites (Wu et al., 2014b), 803 ± 15 Ma
17
Page 17 of 69
Xiacun granites (Guo et al., 2007), 806 ± 4 Ma Lengshuiqing gabbros (Zhou et al.,
357
2006b) and 808 ± 12 Ma Lengqi gabbros (Li et al., 2002c). In addition, the initiation
358
of mature rifting in the southern Kangdian Rift has been assumed at ca. 800 Ma,
359
constrained by zircon U-Pb ages between 798 ± 8 and 805 ± 14 Ma of felsic tuffs and
360
basalts from the lowermost part of the Chengjiang Formation and its equivalents
361
(Jiang et al., 2012; Zhuo et al., 2013, 2015; Cui et al., 2015). These magmatic rocks
362
constitute a typical bimodal magmatic association, suggesting their genetic link with a
363
continental rift environment. They yield a weighted mean
364
Ma (MSWD = 0.33, n = 17) (Fig. 9). This age is identical to ones obtained from our
365
diabase samples (Figs. 5 and 6). Thus, the Xide diabase dykes were part of the ca.
366
800-810 Ma bimodal magmatism in the western Yangtze Block. Furthermore,
367
although the major phase of mafic magmatic rocks in the western Yangtze was formed
368
at ca. 800-810 Ma, the mafic-ultramafic complex in the Yanbian area suggested that
369
the Mid-Neoproterozoic mafic magmatism initiated at ca. 825 Ma (Zhu et al., 2007).
370
5.2. Petrogenesis of the Xide diabase dykes
cr
us
Pb/238U age of 803 ± 3
pt
ed
M
an
206
Ac ce
371
ip t
356
The diabase samples used in this study experienced little metamorphism, but
372
they show various LOI values (Table 3), suggesting varying degrees of alteration.
373
Bivariate plots of Zr against selected trace elements can be used for evaluating the
374
motilities of such elements during alteration (e.g., Polat et al., 2002; Wang et al.,
375
2010a). As shown in Fig. 10, rare earth elements (REE, e.g., Nd, Yb), high field
376
strength elements (HFSE, e.g., Nb, Ta, Hf), and Y are all well correlated with Zr,
377
indicating that they were essentially immobile during alteration. In contrast, alkaline
18
Page 18 of 69
378
elements (e.g., Rb), alkaline earth elements (e.g., Sr), and transition metal elements do
379
not have co-vary with Zr, suggestive of variable degree of mobility. Therefore, only
380
the REE and HSFE are used for the discussions. Major and trace element distribution pattern has revealed the evolution of the
382
magma. The samples show pronounced negative Eu and Sr anomalies in trace element
383
distribution patterns (Fig. 8a), and suggest that fractionation crystallization of
384
plagioclase may have played an important role in these magma evolution. The Ni and
385
Cr decrease along with MgO, indicating fractional crystallization of olivine. Negative
386
correlations between CaO, CaO/Al2O3 and MgO do not support the fractionation of
387
clinopyroxene. The magma also underwent slight fractionation of apatite, which is
388
suggested by positive correlation between MgO and P2O5. Moreover, FeOT and TiO2
389
are generally negatively correlated with MgO in all the rocks, suggesting possible
390
Fe-Ti oxides fractionation crystallization.
ed
M
an
us
cr
ip t
381
Enriched LREE patterns and negative Nb and Ta anomalies of the samples show
392
that the Xide diabase dykes may have been subjected to crustal contamination.
393
However, the following lines of evidence showed that crustal contamination is
394
insignificant, if any, in the generation of these mafic dykes. The studied samples have
395
large range of major element compositions (SiO2 = 47.51 to 53.78 wt% and MgO =
396
6.02 to 12.72 wt%), but nearly constant Zr/Hf (37.3 to 47, with an average of 39.8)
397
and Nb/Ta (14.6 to 17.0, with an average of 15.3) ratios. Zr/Hf and Nb/Ta ratios are
398
insensitive to fractionation crystallization, but sensitive to crustal input due to contrast
399
values between asthenosphere mantle-derived melts and crustal materials (Weaver,
Ac ce
pt
391
19
Page 19 of 69
1991; Barth et al., 2000). Thus, if the major element variation was caused by crustal
401
contamination, considering the mass balance, the large range and crust-like Zr/Hf and
402
Nb/Ta ratios should be observed in the final magmas. However, the nearly constant
403
and OIB-like Nb/Ta and Zr/Hf ratios (OIB with Nb/Ta = 15.9 ± 0.6 and Zr/Hf = 36.3)
404
are inconsistent with the prediction of crustal contamination. It ruled out that the
405
possibility of intense crustal contamination. On the other hand, the analyzed samples
406
exhibit a large range of Nb/Th and Zr/Nb ratios but relatively constant Nb/La ratios
407
(Fig.11), also contradicting large input of crustal materials (Pearce, 2008; Zhang et al.,
408
2013b). Furthermore, the lack of country rock xenoliths in the dykes and the sharp
409
contact along dyke margins also suggest insignificant crustal contamination.
M
an
us
cr
ip t
400
The asthenosphere-lithosphere interaction plays a key role in producing
411
continental basalts (Turner and Hawkesworth, 1995; Wang et al., 2008a, 2009, 2014d).
412
The Nb/La ratio is effective to distinguish between asthenospheric mantle and
413
sub-continental lithospheric mantle (SCLM) contributions. The asthenospheric
414
mantle-derived melts are generally characterized by high Nb/La ratios, varying from
415
0.9 (N-MORB) to 1.3 (OIB and E-MORB) (Sun and McDonough, 1989). By contrast,
416
the SCLM-derived melts display low Nb/La ratios and similar to that of continental
417
crust (Wang et al., 2014d). The studied samples have large range in Nb/La ratios,
418
varying from 0.4 to 1.4. They can be further divided into two sub-types: high-Nb/La
419
types with Nb/La ratios ≥0.8, including 12DX-07 and 12DX-09 and low-Nb/La with
420
constant Nb/La ratios, varying from 0.4 to 0.6. Within them, the high-Nb/La sample
421
12DX-09 has highest Nb/La (1.4), Zr/Hf (43.8), and Nb/Ta (17.0) ratios, similar to
Ac ce
pt
ed
410
20
Page 20 of 69
OIB. The parental of this sample was mainly derived from asthenospheric mantle. The
423
other high-Nb/La sample 12DX-07 displays relatively low Nb/La (0.8), Nb/Ta (14.8),
424
and Zr/Hf (38.4). This source of this sample may record the asthenosphere-lithosphere
425
interaction. The low-Nb/La samples are characterized by nearly constant Nb/La ratios,
426
which are comparable to the typical SCLM-derived melts (lower to 0.3; Wang et al.,
427
2014d). Thus, the source of low-Nb/La types was most likely dominated by SCLM.
428
By contrast, most of the coeval Suxiong basalts display high Nb/La ratios (≥1.0),
429
suggesting their source was dominant by an OIB-like mantle (Li et al. 2002a).
430
5.3. Implications for continental rifting in the western Yangtze Block
an
us
cr
ip t
422
All the diabase samples display negative Nb-Ta anomalies in the primitive
432
mantle-normalized spidergrams (Fig. 8b), which are generally regarded as signatures
433
of arc related basalts (Pearce, 1982; Keppler, 1996). However, several lines of
434
geochemical evidence argue against an arc origin for the Xide diabase dykes. (1) The
435
contents of incompatible elements are relatively generally higher than those of IABs,
436
varying between the OIBs and IABs (Fig. 8b). (2) The Xide diabase dykes have
437
relatively high TiO2 (1.73-2.56 wt.%) and Ti/V ratios (> 45), different from arc related
438
basalts. (3) Most samples are characterized by high and various Th/U ranging from
439
6.06 to 45.00 with one exception of 0.67, in contrast to arc related basalts that are
440
generally low in Th/U (2.4 ± 0.8). (4) Contents of Ni (34.8-137 ppm; average = 73.4
441
ppm) and Cr (172-440 ppm; average = 317 ppm) are clearly higher than those of
442
typical island arc tholeiitic basalts (Ni = 25 ppm; Cr = 50 ppm) (Pearce, 1982; Wilson,
443
1989). (5) The Zr/Y ratios (3.72-7.51) are significantly higher than those of arc related
Ac ce
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ed
M
431
21
Page 21 of 69
basalts as they are plotted in the field of within plate basalts rather than the island arc
445
basalts in the Zr-TiO2 and Zr-Zr/Y diagrams (Fig. 12a,b). This is further supported by
446
the Ta/Hf-Th/Hf diagram proposed by Wang et al., (2001) (Fig.12c), as most of the
447
samples fall in the field of continental within plate basalts. Overall, the Xide diabase
448
dykes should be interpreted to generate in a continental rift environment. Furthermore,
449
the dominant N-S trend of the Xide diabase dykes is sub-parallel to the Kangdian Rift
450
(Fig. 2), which also coincides with this interpretation.
us
cr
ip t
444
As discussed above, there are widespread ca. 800-810 Ma bimodal magmatic
452
rocks in the western Yangtze Block, suggesting a possible continental rift environment
453
(Wilson, 1989; Xia et al., 2012). Based on geochemical and Nd isotopic data, Li et al.
454
(2002a) concluded that the Suxiong basalts were most likely derived from an OIB-like
455
mantle source, while the rhyolites were possibly generated by shallow dehydration
456
melting of hornblende-bearing granitoids, indicating that they should be formed in a
457
continental rift environment. Recently identified ca. 800 Ma high-MgO lavas, the
458
Tongde picrites, also suggested presence of a hot mantle plume beneath SCB (Li et al.,
459
2010a). The basalts of the Chengjiang Formation display lower SiO2, high K2O+Na2O
460
and TiO2 contents with Rittmann index (σ) > 3.3, similar to those alkaline basalts
461
generated in the continental rift (Zhu, 1990; Cui et al., 2015). Additionally, the
462
recently identified A-type Xiatianba granites have been demonstrated to be produced
463
within an intra-plate extension environment (Wu et al., 2014b).
Ac ce
pt
ed
M
an
451
464
Recent studies confirm that the sedimentary history of the Kangdian Rift in the
465
western Yangtze Block can be well correlated with the Nanhua Rift in the
22
Page 22 of 69
southeastern Yangtze Block (Wang and Li, 2003) and the Adelaide Rift in Australia
467
(Preiss, 2000). A SHRIMP zircon U-Pb age of tuffs from the lowermost part of the
468
Luliang Formation is 819±9 Ma, representing the initiation of the Kangdian rifting
469
(Zhuo et al., 2013). However, the rifting just produced narrow, deeply subsidence,
470
unidirectional N-S trending half-grabens before 800 Ma. Since 800 Ma, accompanied
471
with drastic bimodal magmatism, the rifting clearly widened the zone of continental
472
extension which made those mini half-grabens into a large united half-graben.
473
Accordingly, a large-scale transgressive overlap occurred (Zhuo et al., 2013; Cui et al.,
474
2014). Provenance analyses show that the clastic wedges were derived from the
475
western rift shoulder, which was mainly consisted of the Kunyang Group and its
476
equivalents, rather than synchronous andesitic volcanic rocks indicating the existence
477
of an Andean magmatic arc (Cui et al., 2014). More intriguingly, the latest proposed
478
tectonic model and filling pattern of the Kangdian Rift (Zhuo et al., 2013; Cui et al.,
479
2014) are comparable to those of the East Africa Rift, a typical continental rift
480
(Chorowicz, 2005).
cr
us
an
M
ed
pt
Ac ce
481
ip t
466
In summary, the Xide diabase dykes that underwent negligible crustal
482
contamination display geochemical characteristics of intra-plate basalts, instead of
483
arc-related basalts. Combined with the synchronous bimodal magmatism and
484
sedimentary history, it is suggested that the Mid-Neoproterozoic continental rifting
485
once occurred in the western Yangtze Block. The widespread Mid-Neoproterozoic
486
continental rifting and anorogenic magmatism are also preserved in other Rodinia
487
blocks, such as Tarim (e.g., Xu et al., 2013; Zhang et al., 2013a), Australia (e.g.,
23
Page 23 of 69
Powell et al., 1994; Wingate et al., 1998; Preiss, 2000; Li et al., 2006a; Wang et al.,
489
2010a), North America (e.g., Park et al., 1995; McClellan and Gazel, 2014) and
490
Southern Africa (e.g., Frimmel et a., 2001). All these observations indicate that the
491
Mid-Neoproterozoic continental rifting in the western Yangtze Block could be part of
492
a major global rifting event, which triggered the breakup of Rodinia supercontinent.
493
5.4. Reconsidering the proposed tectonic models of South China
cr
ip t
488
Aside from the plume-rift model proposed by Li and co-authors (Li et al., 1999,
495
2003a, 2008a; Li et al., 2002a, 2003b; Ling et al., 2003; Wang and Li, 2003; Wang et
496
al., 2007, 2008a, 2009, 2011a) and the slab-arc model proposed by Zhou and
497
co-authors (Yan et al., 2002; Zhou et al., 2002a,b, 2006a,b; Zhao and Zhou, 2007a,b;
498
Zhao et al., 2008, 2011), Zheng et al. (2007, 2008a,b) recently proposed the plate-rift
499
model. However, the plate-rift model was established merely on the basis of
500
Neoproterozoic felsic volcanic rocks and granites from the northeastern segment of
501
the Jiangnan Orogen. However, the felsic igneous rocks are not suitable to constrain
502
on tectonic setting due to their highly complex petrogenesis. At least, it still needs
503
further testing as to whether or not this model can be successfully applied to
504
understanding of the Neoproterozoic tectonic processes of the whole SCB.
an
M
ed
pt
Ac ce
505
us
494
The slab-arc model proposes that there was a long-lived (950-735 Ma) oceanic
506
subduction zone along the western-northern Yangtze Block and the rift basins in SCB
507
were attributed to back arc spreading (Yan et al., 2002; Zhou et al., 2002a,b, 2006a,b;
508
Zhao and Zhou, 2007a,b; Zhao et al., 2008, 2011; Dong et al., 2011, 2012; Wang and
509
Zhou, 2012). The slab-arc model overlooked some important observations of
24
Page 24 of 69
structural geology and metamorphism. For instance, the slab-arc model is inconsistent
511
with a general northward structural vergence of the Yanbian Group (Li et al., 2006b).
512
The first and second phases of metamorphism and deformation of the Tianli Schist
513
occurred respectively at 1.04-1.01 Ga and 0.97-0.94 Ga (Li et al., 2007), which are
514
broadly coincident with the ages of Northern Jiangxi Ophiolites (Chen et al., 1991)
515
and the Shuangxiwu magmatic arcs (Li et al., 2009). The petrographic observations
516
demonstrated ca. 820 Ma mafic rocks in the western Yangtze Block are dominated by
517
olivine-plagioclase-clinopyroxene (Li et al., 2006b). This suggests an anhydrous
518
parental magma for these mafic rocks, which is contracted with the predictions of the
519
slab-arc model.
M
an
us
cr
ip t
510
Recently, Chen et al. (2014) proposed that the ca. 1050 Ma Julin basalts might
521
formed in a passive continental margin, which is in accord with the subsequent
522
oceanic subduction since 950 Ma. However, as mentioned earlier, abundant
523
Grenville-aged subduction- or collision-related magmatism records are distributed
524
along the western-northern Yangtze Block. For example, the 1014 ± 8 Ma Yakou
525
granites display characteristics of those crust-derived collisional granites (Yang et al.,
526
2009); Andesitic tuffs from the Heishantou Formation give a SHRIMP U-Pb age of
527
1032 ± 9 Ma (Zhang et al., 2007), which further support the Kunyang Group was
528
deposited within a foreland basin associated with the collision events (Greentree et al.,
529
2006); In the northern Yangtze Block, the volcanic suites of the Shennongjia Group
530
yield zircon U-Pb ages between 1063 ± 16 and 1103 ± 8 Ma and have been interpreted
531
to be developed within subduction-related collision environments (Qiu et al., 2011,
Ac ce
pt
ed
520
25
Page 25 of 69
532
2015). These geologic records contradict the existence of a passive continental margin
533
along the western-northern Yangtze Block during 1100-960 Ma. Obviously, the interpretation of back-arc rift basins for the Neoproterozoic
535
tectonic setting of SCB remains open to question. The data present in this paper show
536
that the Xide diabase dykes emplaced at ca. 800-810 Ma and formed in a continental
537
rift setting. This suggests that a continental rift environment is relatively appropriate,
538
which is broadly in agreement with the plume-rift model. The following lines of
539
positive geological evidence also support this proposal.
us
cr
ip t
534
(1) The episodic bimodal magmatism were widespread throughout SCB, e.g., the
541
ca. 800 Ma bimodal magmatism suite recognized in this study, Shangshu and Puling
542
bimodal volcanic rocks (Li et al., 2008b; Wang et al., 2012b) and 780-760 Ma
543
Kangding mafic dykes and synchronous granites (Li et al., 2003a; Lin et al., 2007);
ed
M
an
540
(2) The Mid-Neoproterozoic (825-760 Ma) basaltic rocks in SCB have
545
continental intra-plate geochemical signatures and high mantle potential temperatures
546
(Li et al., 2008c; Wang et al., 2009), and some of them are most likely the remnants of
547
plume-related continental flood basalts (e.g., Wang et al., 2008a, Deng et al., 2013);
Ac ce
548
pt
544
(3) Many Mid-Neoproterozoic igneous rocks are characterized by exceptional
549
low-18O values, indicating intensive high-temperature water-rock interaction and
550
generation of the low-18O magmatism in rift tectonic zones (e.g., Zheng et al., 2008b;
551
Wang et a., 2011b; Liu and Zhang, 2013);
552
(4) In situ U-Pb, Hf and O isotopic analyses of detrital zircon grains from
553
sandstones across the Mid-Neoproterozoic unconformity in the Nanhua Basin, which
26
Page 26 of 69
554
was previously interpreted as orogenic origin, demonstrated that sediments across this
555
unconformity should be deposited within a continental rift setting (Yang et al., 2015); (5) The sedimentary overlap and filling process of the Neoproterozoic rift basins
557
in SCB are characterized by a deepening water trend and comparable with those
558
typical continental rifts (Wang and Li, 2003; Zhuo et al., 2013; Cui et al., 2014; Wang
559
et al., 2015).
cr
ip t
556
In short, SCB experienced continental rifting during 825-740 Ma, probably
561
linking with the breakup of Rodinia. Although the specific position of SCB in Rodinia
562
is not well constrained (e.g., Li et al., 1995, 1999, 2008a; Zhou et al., 2002a,b; Wang
563
et al., 2010a; Wang and Zhou, 2012; Cawood et al., 2013; Zhang et al., 2013d), we
564
proposed that SCB should play a key role in the assembly and breakup history of this
565
supercontinent.
566
6. Conclusions
569
an
M
ed
pt
568
Our geochronological and geochemical study on the Xide diabase dykes come into the following conclusions:
Ac ce
567
us
560
1. New SHRIMP and LA-ICP-MS zircon U-Pb dating results show that the
570
emplacement of the Xide diabase dykes occurred at ca. 800-810 Ma, coeval with the
571
widespread bimodal magmatism in the western Yangtze Block.
572
2. The Xide diabase dykes underwent insignificantly crustal contamination
573
during magma evolution and ascent, and were mainly derived from a sub-continental
574
lithospheric mantle.
575
3. The Xide diabase dykes formed in a continental rift setting, rather than
27
Page 27 of 69
576
arc-related or post-orogenic setting, indicating that the western Yangtze Block once
577
experienced the continental rifting during the Mid-Neoproterozoic.
579
4. SCB should play a significant role in the assembly and breakup history of Rodinia supercontinent.
ip t
578
580
Acknowledgments
cr
581
This research was supported by the National Natural Science Foundation of
583
China (41030315, 41402103, and 41202048), China Geological Survey project
584
(12120114067901 and 12120114005301), and the Australian Research Council (ARC)
585
Future Fellowship (FT140100826) for Xuan-Ce Wang. We thank Guoqing Xiong and
586
Junze Lu for their help with the field work. We thank Drs. Zhaochu Hu, Keqing Zong,
587
Mingzhu Ma, and Jianhui Liu for their assistance during zircon analysis and data
588
processing. Constructive comments and suggestions from Prof. Guochun Zhao and
589
two anonymous reviewers have helped to improve the manuscript substantially and
590
are gratefully acknowledged. This is TIGeR publication No. xx.
an
M
ed
pt
Ac ce
591
us
582
592
References
593
Barth, M.G., McDonough, W.F., Rudnick, R.L., 2000. Tracking the budget of Nb and Ta in the
594 595
continental crust. Chemical Geology 165, 197-213. Black. L.P., Kamo. S.L., Allen. C. M., Aleinifoff, J.N., Davis, D.W., Korsch, R.J., Foudoulis, C.,
596
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913
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921
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926
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936
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938
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945
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946 947 948 949
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968 969 970 971
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973
Proterozoic supercontinents. Journal of Asian Earth Sciences 28, 3-19.
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972
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980
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981
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986
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989
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990
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991
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992
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993
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997
Zhou, G.Y., Wu, Y.B., Gao, S., Yang, J.Z., Zheng, J.P., Qin, Z.W., Wang, H., Yang, S.H., 2015. The
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2.65 Ga A-type granite in the northeastern Yangtze craton: Petrogenesis and geological
999
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cr
ip t
994
Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y., Ding, J., 2002a. SHRIMP U-Pb zircon
1001
geochronological and geochemical evidence for Neoproterozoic arc-magmatism along the
1002
western margin of the Yangtze Block, South China. Earth and Planetary Science Letters 196,
1003
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an
us
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Zhou, M.F., Kennedy, A.K., Sun, M., Malpas, J., Lesher, C.M., 2002b. Neoproterozoic
1005
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1006
the Accretion of Rodinia. Journal of Geology 110, 611-618.
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1004
Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A.K., 2006a. Subduction-related origin of the
1008
750 Ma Xuelongbao adakitic complex (Sichuan Province, China): implications for the
1010
Ac ce
1009
pt
1007
tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth and Planetary Science Letters 248, 286-300.
1011
Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006b. The Yanbian Terrane
1012
(Southern Sichuan Province, SW China): A Neoproterozoic arc assemblage in the western
1013
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1014
Zhu, C.Y., 1990. The sequences of filling and tectonic evolution of Qiaojia-Shiping basin, Yunnan
1015
during early Sinian. Journal of Chengdu College of Geology 17, 76-82 (in Chinese with
47
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1016
English abstract). Zhu, W.G., Zhong, H., Deng, H.L., Wilson, A.H., Liu, B.G., Li, C.Y., Qin, Y., 2006. SHRIMP
1018
zircon U-Pb age, geochemistry and Nd-Sr isotopes of the Gaojiacun mafic-ultramafic
1019
intrusive complex, SW China. Int. Geol. Rev. 48, 650-668.
1020
ip t
1017
Zhu, W.G., Zhong, H., Li, X.H., Liu, B.G., Deng, H.L., Qin, Y., 2007. Age, geochemistry and Sr-Nd-Pb
isotopes
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Neoproterozoic
Lengshuiqing
Cu-Ni
1022
mafic-ultramafic complex, SW China. Precambrian Research 155, 98-124.
sulfide-bearing
us
cr
1021
Zhu, W.G., Zhong, H., Li, X.H., Liu, B.G., Deng, H.L., He, D.F., Wu, K.W., Bai, Z.J., 2008.
1024
SHRIMP zircon U-Pb geochronology, elemental, and Nd isotopic geochemistry of the
1025
Neoproterozoic mafic dykes in the Yanbian area, SW China. Precambrian Research 164,
1026
66-85.
M
an
1023
Zhuo, J.W., Jiang, X.S., Wang, J., Cui, X.Z., Xiong, G.Q., Lu, J.Z., Liu, J.H., Ma, M.Z., 2013.
1028
Opening time and filling pattern of the Neoproterozoic Kangdian Rift Basin, western
1029
Yangtze Continent, South China. Science China: Earth Sciences 56, 1664-1676.
pt
ed
1027
Zhuo, J.W., Jiang, X.S., Wang, J., Cui, X.Z., Xiong, G.Q., Lu, J.Z., Liu, J.H., Ma, M.Z., 2015.
1031
SHRIMP U-Pb age of tuff from the Neoproterozoic Kaijianqiao Formation and its geological
1032 1033
Ac ce
1030
significance. Journal of Mineralogy and Petrology 35(1), 91-99 (in Chinese with English abstract).
1034
48
Page 48 of 69
Figure captions
1035
Fig.1. Schematic map of the Precambrian South China Block emphasizing the three
1036
Mid-Neoproterozoic rift basins (after Li et al., 2003a; Wang and Li, 2003; Wang et al.,
1037
2011). The inset is a tectonic sketch of China showing the three Precambrian blocks
1038
(after Zhao and Cawood, 2012).
ip t
1034
cr
1039
Fig.2. Geological map of the Xide region in the western Yangtze Block showing the
1041
sampling locations.
us
1040
an
1042
Fig.3. Field occurrence and petrography of the Xide diabase dyke swarms in the
1044
western Yangtze Block. (a)-(b) Field photos showing the Xide diabase dykes intruded
1045
host meta-sedimentary rocks of the Dengxiangying Group; (c) Outcrop photo showing
1046
fresh surface color and massive structure of the sampling diabase; (d) Representative
1047
photomicrograph of diabasic texture and mineral assemblages including Plagioclase
1048
(Pl), Pyroxene (Py) and Magnetite (Mt).
ed
pt
Ac ce
1049
M
1043
1050
Fig.4. Representative CL images with SHRIMP and LA-ICP-MS U-Pb spots and ages
1051
for analyzed zircons of diabase samples. Scale bar in each diagram is 50 μm long.
1052 1053
Fig.5. SHRIMP zircon U-Pb concordia diagrams for diabase samples 12XD-D1,
1054
12XD-D4 and 12XD-D9. The red and green line spots represent xenocryst and
1055
discordant ages, respectively.
49
Page 49 of 69
1056 1057
Fig.6. LA-ICP-MS zircon U-Pb concordia diagrams for diabase samples 13XD-D12
1058
and 13XD-D13. The red line spots represent xenocryst ages.
ip t
1059
Fig.7. Rock classification diagrams for the diabase samples. (a) Nb/Y-Zr/TiO2*0.0001
1061
diagram distinguishing subalkaline and alkaline basalts (Winchester and Floyd, 1977);
1062
(b) FeOT/MgO-TiO2 diagram distinguishing tholeiitic and calc-alkaline series
1063
(Miyashiro, 1974).
us
cr
1060
an
1064
Fig.8. Chondrite-normalized REE patterns (a) and primitive mantle-normalized spider
1066
diagrams (b) for the Xide diabase dykes. The data for chondrite, primitive mantle,
1067
enriched mid-ocean ridge basalt (E-MORB), normal mid-ocean ridge basalt
1068
(N-MORB) and ocean island basalt (OIB) are from Sun and McDonough (1989). The
1069
data for island arc basalts (IAB) are from George et al. (2003).
ed
pt
Ac ce
1070
M
1065
1071
Fig.9. Weighted average of zircon U-Pb ages for the ca. 800-810 Ma magmatic rocks
1072
in the western Yangtze Block. The age data are list in Table 4.
1073 1074
Fig.10. Bi-elemental plots of Nd, Yb, Y, Nb, Ta, Hf, Rb and Sr versus Zr to evaluate
1075
the mobility of these elements of the Xide diabase dykes during alteration.
1076 1077
Fig.11. Nb/La-Nb/Th (a) and Nb/La-Zr/Nb (b) diagrams showing the negligible
50
Page 50 of 69
1078
crustal contamination of the parental magma for the Xide diabase dykes.
1079
Fig.12. Tectonic discrimination diagrams for the Xide diabase dykes. (a) Zr-Zr/Y
1081
diagram (after Pearce and Norry, 1979); (b) Ti-Zr diagram (after Pearce, 1982); (c)
1082
Ta/Hf-Th/Hf diagram (after Wang et al., 2001). The data for the Suxiong basalts (gray
1083
shadow) are from Li et al. (2002a).
cr
ip t
1080
1085
us
1084
Table captions
an
1086
Table 1 Zircon U-Pb isotopic data obtained by SHRIMP for diabase samples
1088
12XD-D1, 12XD-D4 and 12XD-D9. The data are the mean values of five consequent
1089
scans for each analytical spot.
ed
1090
M
1087
Table 2 Zircon U-Pb isotopic data obtained by LA-ICP-MS for diabase samples
1092
13XD-D12 and 13XD-D13.
1094 1095
Ac ce
1093
pt
1091
Table 3 Major and trace element contents of diabase samples from the Xide region.
1096
Table 4 Summary of published zircon U-Pb ages for the ca. 800-810 Ma magmatic
1097
rocks in the western Yangtze Block.
1098
51
Page 51 of 69
1098
Figures
1099 1100
1102 1103 1104 1105 1106
Ac ce
pt
ed
M
an
us
cr
ip t
1101
Fig. 1
1107 1108 1109 1110 1111
52
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1112
Ac ce
pt
ed
M
an
us
cr
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1113
1114 1115 1116
Fig. 2
1117 1118
53
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1119 1120
1124 1125 1126 1127 1128 1129 1130
pt
1123
Fig. 3
Ac ce
1122
ed
M
an
us
cr
ip t
1121
1131 1132 1133 1134 1135
54
Page 54 of 69
1136 1137
1140 1141 1142 1143
Ac ce
1139
pt
ed
M
an
us
cr
ip t
1138
Fig. 4
1144 1145 1146 1147 1148 1149 55
Page 55 of 69
1150
Ac ce
pt
ed
M
an
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cr
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1152 1153 1154
Fig. 5
1155 1156 56
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1161 1162 1163 1164 1165
pt
1160
Ac ce
1159
ed
M
an
us
cr
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1158
Fig. 6
1166 1167 1168 1169 1170 1171 57
Page 57 of 69
1172
1176 1177 1178 1179 1180
pt
1175
Ac ce
1174
ed
M
an
us
cr
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1173
Fig. 7
1181 1182 1183 1184 1185 1186 58
Page 58 of 69
1187 1188
us
cr
ip t
1189
1190
an
1191 1192
Fig. 8
M
1193
1197 1198 1199 1200 1201 1202 1203
pt
1196
Ac ce
1195
ed
1194
1204 1205 1206 1207 1208 1209 59
Page 59 of 69
1210 1211 1212
an
us
cr
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1213
1214 1215 1216
M
Fig. 9
1220 1221 1222 1223 1224 1225 1226
pt
1219
Ac ce
1218
ed
1217
1227 1228 1229 1230 1231 1232 60
Page 60 of 69
Ac ce
pt
ed
M
an
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1233
1234 1235 1236
Fig. 10 61
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1237 1238 1239
1242 1243 1244 1245 1246
Ac ce
1241
pt
ed
M
an
us
cr
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1240
Fig. 11
1247 1248 1249 1250 1251 1252 62
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1253 1254
1258 1259
pt
1257
Fig. 12
Ac ce
1256
ed
M
an
us
cr
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1255
63
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ip t Spot
Pbc/%
U/ppm
Th/ppm
Th/U
Pb*/
206
Pb/238U
207
Pb/206Pb
us
206 206
cr
Table 1
207
Pb*/206Pb*
207
Pb*/235U
206
Pb*/238U
ppm
Age/Ma
Age/Ma
±%
±%
±%
795±9
740±41
0.0639±1.9
1.16±2.3
0.131±1.2
2482±32
2481±15
0.1624±0.9
10.51±1.8
0.470±1.6
826±9
773±31
0.0650±1.5
1.22±1.9
0.137±1.2
0.41
137
150
1.13
15
12XD-D1-02
0.22
43
56
1.35
17
12XD-D1-03
0.35
159
70
0.46
19
12XD-D1-04
0.17
187
136
0.75
21
800±9
an
754±26
0.0644±1.2
1.17±1.7
0.132±1.2
12XD-D1-05
0.11
100
135
1.39
12
813±10
829±29
0.0667±1.4
1.24±1.9
0.134±1.3
12XD-D1-06
0.19
28
18
0.67
11
2418±35
2525±16
0.1667±1.0
10.46±2.0
0.455±1.7
12XD-D1-07
0.25
180
106
0.61
21
814±9
865±24
0.0679±1.2
1.26±1.6
0.135±1.2
12XD-D1-08
1.52
272
143
0.54
29
755±8
803±35
0.0659±1.6
1.13±2.0
0.124±1.1
12XD-D4-01
0.45
302
12XD-D4-02
0.26
148
12XD-D4-03
0.22
183
12XD-D4-04
0.13
150
12XD-D4-05
0.39
95
12XD-D4-06
0.00
124
12XD-D4-07
0.08
12XD-D4-08 12XD-D4-09
ep te
12XD-D4
M
12XD-D1-01
d
12XD-D1
0.52
27
637±10
810±41
0.0661±2.0
0.95±2.6
0.104±1.6
76
0.53
17
804±11
808±35
0.0661±1.7
1.21±2.2
0.133±1.5
102
0.57
21
796±11
827±43
0.0667±2.1
1.21±2.5
0.131±1.4
164
1.13
18
828±11
846±31
0.0673±1.5
1.27±2.1
0.137±1.5
315
3.44
11
803±12
746±51
0.0641±2.4
1.17±2.9
0.133±1.5
362
3.02
14
819±16
833±43
0.0669±2.0
1.25±2.9
0.136±2.0
64
136
2.20
7
825±13
672±104
0.0619±4.9
1.17±5.2
0.137±1.7
0.30
173
41
0.25
20
801±11
870±38
0.0680±1.8
1.24±2.3
0.132±1.4
0.12
96
275
2.94
11
808±13
796±38
0.0657±1.8
1.21±2.4
0.134±1.5
12XD-D9-01
0.15
367
130
0.37
43
825±9
844±18
0.0672±0.8
1.26±1.4
0.136±1.1
12XD-D9-02
0.07
206
91
0.46
24
820±9
840±21
0.0671±1.0
1.25±1.5
0.136±1.2
12XD-D9-03
0.18
92
43
0.48
11
838±10
806±36
0.0660±1.7
1.26±2.1
0.139±1.3
12XD-D9-04
0.10
459
96
0.22
53
810±8
808±14
0.0661±0.7
1.22±1.3
0.134±1.1
12XD-D9-05
0.29
158
113
0.74
19
831±9
751±46
0.0643±2.2
1.22±2.5
0.138±1.2
12XD-D9-06
0.28
247
137
0.57
29
834±9
869±40
0.0680±1.9
1.30±2.2
0.138±1.1
12XD-D9-07
0.14
291
64
0.23
34
826±9
811±20
0.0661±0.9
1.25±1.5
0.137±1.1
12XD-D9
Ac c
150
Page 64 of 69
ip t
1.99
46
25
0.55
5
814±12
602±138
0.0600±6.4
1.11±6.6
0.135±1.5
12XD-D9-09
0.12
198
145
0.75
23
831±9
836±23
0.0669±1.1
1.27±1.6
0.138±1.2
12XD-D9-10
0.58
365
146
0.40
41
793±8
816±29
0.0663±1.4
1.20±1.8
0.131±1.1
12XD-D9-11
0.12
370
162
0.45
44
843±9
794±18
0.0656±0.9
1.26±1.4
0.140±1.1
204
Pb. All errors are 1σ.
Ac c
ep te
d
M
an
Notes: The radiogenic lead Pb corrected for common Pb using
us
*
cr
12XD-D9-08
Page 65 of 69
ip t
Table 2 Th/ppm
U/ppm
Th/U
207
Pb/206Pb
±%
207
Pb/235U
±%
3.0
0.0661
6.6
1.2122
7.2
02
74
426
0.2
0.0680
4.0
1.2418
4.5
03
133
58
2.3
0.0642
8.3
1.2165
4.6
04
265
267
1.0
0.0695
4.3
1.2514
05
99
234
0.4
0.0667
3.7
1.2183
06
223
198
1.1
0.0684
3.1
1.2917
07
249
117
2.1
0.0658
5.7
1.1772
08
113
59
1.9
0.0669
6.5
09
56
317
0.2
0.0672
10
166
92
1.8
01
46
21
02
192
03 04
206
Pb/238U
2.0
809
139
806
40
802
15
0.1318
2.5
878
82
820
25
798
19
0.1363
2.6
746
181
808
26
824
20
±%
us
105
Pb/235U
0.1325
Pb/238U
an
312
207
1σ
206
13XD-D12 01
Pb/206Pb
cr
207
Spot
Age/Ma
Age/Ma
1σ
Age/Ma
1σ
0.1324
1.5
915
83
824
24
801
12
3.5
0.1327
1.5
828
76
809
20
803
11
3.2
0.1369
1.4
880
64
842
19
827
11
5.4
0.1321
1.9
800
119
790
30
800
14
1.2200
6.4
0.1328
1.7
835
136
810
36
804
13
3.1
1.2285
3.3
0.1324
1.4
843
65
814
18
801
11
0.0671
5.9
1.2569
3.4
0.1366
2.0
839
122
827
20
825
15
2.2
0.0716
11.1
1.3267
10.6
0.1411
2.7
976
227
857
61
851
22
168
1.1
0.0707
3.8
1.2979
4.1
0.1319
1.4
950
75
845
23
799
10
71
31
2.3
0.0687
8.1
1.2768
8.0
0.1337
2.0
900
164
835
45
809
16
45
23
1.9
0.0689
11.5
1.3591
11.4
0.1417
3.5
894
239
871
67
854
28
05
196
272
0.7
0.0701
3.8
1.2695
3.8
0.1306
1.1
931
78
832
22
791
8
06
195
86
2.3
0.0681
11.2
1.2787
10.5
0.1358
3.1
870
235
836
60
821
24
07
529
219
08
177
313
09
194
102
10
79
35
11
432
165
12
268
13 14
Ac c
d
ep te
13XD-D13
M
4.2
2.4
0.0688
4.3
1.2427
4.3
0.1315
1.8
892
95
820
24
797
14
0.6
0.0697
2.9
1.2615
3.2
0.1315
1.7
918
59
829
18
796
13
1.9
0.0655
7.7
1.1749
7.5
0.1306
1.9
791
162
789
41
791
14
2.3
0.0695
8.9
1.2908
8.7
0.1363
2.4
922
185
842
50
823
18
2.6
0.0686
5.1
1.2379
4.8
0.1312
1.4
887
100
818
27
795
11
506
0.5
0.0695
3.0
1.2601
3.1
0.1302
1.0
917
61
828
18
789
7
454
394
1.2
0.0669
2.7
1.2238
2.6
0.1325
1.1
833
56
812
15
802
9
57
300
0.2
0.0684
2.5
1.2402
2.5
0.1309
0.8
880
52
819
14
793
6
Page 66 of 69
ip t 12XD-01
12XD-02
12XD-03
12XD-04
12XD-05
12XD-06
12XD-07
Major (wt.%)
12XD-08
us
Sample
cr
Table 3
12XD-09
13XD-10
13XD-11
13XD-12
13XD-13
13XD-14
SiO2
47.51
48.19
41.64
51.94
49.65
49.57
50.30
34.80
50.04
53.78
48.44
48.96
49.93
47.82
Al2O3
15.17
14.86
14.78
15.66
15.5
15.47
16.87
20.04
18.67
15.74
17.05
17.24
15.97
15.13
Fe2O3
2.87
2.29
3.08
2.06
2.28
2.59
3.25
3.91
2.46
2.92
2.49
2.40
3.76
FeO
11.49
11.37
13.59
8.12
9.81
9.64
8.04
12.27
8.72
7.86
8.31
7.40
8.03
10.61
MgO
7.55
7.87
14.78
9.23
8.19
8.13
12.28
20.86
6.02
10.74
10.75
12.72
8.84
7.35
CaO
9.62
8.99
7.41
7.73
9.48
9.47
4.73
4.58
6.69
4.27
5.49
4.42
9.24
9.68
Na2O
2.23
2.58
1.10
1.73
2.03
2.06
0.92
0.21
1.18
0.97
0.99
0.96
2.09
2.50
K2O
0.83
0.88
0.40
1.33
0.68
0.73
1.70
0.57
2.28
1.57
3.15
2.85
1.15
0.51
MnO
0.23
0.21
0.21
0.18
0.18
0.19
0.07
0.11
0.19
0.07
0.15
0.16
0.20
0.24
TiO2
2.18
2.56
2.70
1.73
1.90
1.92
2.41
2.93
2.14
2.20
2.41
2.45
1.83
2.22
P2O5
0.19
0.34
0.37
0.25
0.26
0.28
0.37
0.40
0.20
0.35
0.35
0.34
0.24
0.19
TOTAL
99.87
100.14
100.06
100.05
100.09
100.02
100.04
100.01
100.01
99.99
99.92
100.01
0.92
1.81
5.15
Mg#
52.95
55.14
65.46
La
17.43
15.9
16.5
Ce
39.0
37.5
39.5
Pr
5.84
5.12
Nd
25.2
Sm
an
M
d
ep te
LOI
99.96
99.96
2.4
1.89
1.42
1.36
3.61
8.25
4.25
4.85
4.09
4.34
1.79
1.21
66.00
59.16
58.76
71.63
74.22
50.78
69.10
67.34
73.46
64.54
52.42
29.8
15.2
14.6
12.8
14.7
7.69
15.9
17.7
17.4
20.0
17.56
66.3
34.7
33.2
31.1
37.4
19.9
38.2
41.5
41.1
45.5
39.1
5.38
7.93
4.49
4.31
4.08
4.96
3.01
4.86
5.37
5.27
5.59
5.85
24.3
26.1
33.7
20.3
19.6
19.2
24.0
15.5
22.3
24.6
24.1
25.0
25.5
4.76
6.61
7.41
7.30
5.14
5.19
4.84
6.12
4.89
5.78
6.03
5.84
5.82
4.93
Eu
1.85
2.37
2.48
1.61
1.62
1.58
1.16
1.89
1.39
1.44
1.55
1.51
1.33
1.79
Gd
6.41
8.13
8.94
7.28
6.17
5.80
5.63
7.22
6.02
5.97
6.94
6.64
6.32
6.39
Ac c
Trace (ppm)
Tb
1.09
1.32
1.53
1.15
1.00
0.97
0.94
1.07
0.95
0.96
1.06
1.03
0.99
1.10
Dy
7.07
8.45
9.41
6.82
6.35
6.30
5.95
6.66
6.03
5.78
6.55
6.43
6.02
7.24
Ho
1.53
1.76
2.00
1.40
1.32
1.35
1.25
1.39
1.28
1.20
1.36
1.32
1.25
1.54
Er
4.78
5.55
6.13
4.30
4.08
4.01
3.78
4.28
3.93
3.47
4.16
4.02
3.74
4.77
Tm
0.64
0.69
0.81
0.57
0.56
0.54
0.50
0.55
0.53
0.46
0.56
0.53
0.51
0.66
Page 67 of 69
4.71
5.20
3.68
3.65
3.67
3.28
3.83
Lu
0.63
0.73
0.77
0.54
0.55
0.55
0.51
0.56
3.63
3.09
3.60
3.47
3.36
4.28
0.55
0.46
0.56
0.54
0.48
0.64
12XD-01
12XD-02
12XD-03
12XD-04
12XD-05
12XD-06
12XD-07
12XD-08
12XD-09
13XD-10
13XD-11
13XD-12
13XD-13
13XD-14
Sc
47.0
49.6
52.5
34.8
38.1
40.0
33.6
47.2
46.0
30.5
36.0
35.2
36.8
47.1
V
241
279
301
190
178
187
207
91.0
250
199
222
222
218
245
Cr
214
172
179
419
282
292
424
358
218
386
428
418
440
213
Co
53.5
48.7
45.5
44.2
45.0
48.1
38.0
38.2
55.6
32.8
47.8
46.1
49.2
50.7
Ni
44.4
39.5
34.8
126
72.6
75.8
83.4
88.0
50.1
76.3
80.8
79.2
137
39.3
148
144
253
134
102
105
121
192
362
114
116
119
83.0
129
22.6
22.9
22.8
19.5
20.5
21.0
20.5
21.3
21.5
19.1
20.6
20.4
20.0
23.1
Rb
39.2
32.2
13.6
51.2
22.2
24.8
64.4
25.1
104
62.7
145
149
45.4
19.2
Sr
166
152
58.0
130
178
173
45.7
9.78
141
60.6
64.3
65.6
160
169
Y
41.9
47.8
56.6
37.8
36.4
35.8
33.3
39.0
34.8
32.3
37.5
37.8
34.2
43.1
Zr
156
211
234
253
149
149
191
216
169
174
195
197
193
173
Nb
8.99
8.23
8.89
Cs
13.2
5.37
2.72
Ba
246
379
158
Hf
3.79
5.56
5.87
0.56
0.58
8.43
6.37
Th
3.52
1.72
U
0.13
Cu
19.4
ep te
0.58 8.04
10.8
8.66
8.52
9.94
11.8
10.88
9.22
10.1
10.3
8.53
9.04
15.5
7.82
9.71
8.02
1.99
14.0
9.33
17.7
17.9
11.4
6.01
419
331
345
1161
398
177
1000
1923
1935
414
193
6.42
3.99
3.95
4.97
5.49
3.86
4.63
5.05
4.90
5.01
3.68
0.72
0.56
0.54
0.67
0.75
0.64
0.62
0.69
0.67
0.57
0.77
25.4
33.8
20.1
21.5
16.4
13.0
21.7
30.4
29.5
18.0
12.9
1.88
10.1
2.16
2.11
3.42
3.84
5.06
3.15
3.53
3.43
6.06
4.50
0.24
0.31
0.88
0.32
0.32
0.46
5.70
0.17
0.44
0.48
0.44
0.50
0.10
29.9
14.9
32.3
28.5
35.6
6.34
3.16
2.59
11.4
4.11
5.32
24.5
24.0
Ac c
Ta Pb
d
Zn Ga
M
an
us
Table 3 (continued) Sample
ip t
4.20
cr
Yb
Page 68 of 69
ip t cr Location
Rock type
1
Kangding
Gneissic granites
2
Kangding
Gneissic granites
3
Kangding
Gneissic granites
SHRIMP U-Pb
4
Tongde
Picritic dykes
5
Songlinping
6
Changshiba
7
Xide
8
Xiatianba
9
Kaijianqiao
10
Zhonghe
13 14 15
SHRIMP U-Pb
795±11
Zhou et al., 2002a
SHRIMP U-Pb
796±13
Zhou et al., 2002a
797±10
Zhou et al., 2002a
SIMS U-Pb
796±5
Li et al., 2010a
Felsic tuffs
SHRIMP U-Pb
798±8
Jiang et al., 2012
Metabasalts
SHRIMP U-Pb
799±8
Ren et al., 2013
Diabases
LA-ICP-MS U-Pb
800-810
This study
A-type granites
LA-ICP-MS U-Pb
801±7
Wu et al., 2014b
Felsic tuffs
SHRIMP U-Pb
801±7
Zhuo et al., 2015
Felsic tuffs
SHRIMP U-Pb
803±9
Jiang et al., 2012
Suxiong
Rhyolites and Basalts
SHRIMP U-Pb
803±12
Li et al., 2002a
Xiacun
Granites
SHRIMP U-Pb
803±15
Guo et al., 2007
Luoci
Basalts
LA-ICP-MS U-Pb
804±3
Cui et al., 2015
Luliang
Felsic tuffs
SHRIMP U-Pb
805±14
Zhuo et al., 2013
Lengshuiqing
Gabbros
SHRIMP U-Pb
806±4
Zhou et al., 2006b
Lengqi
Gabbros
SHRIMP U-Pb
808±12
Li et al., 2002c
Yanjing
Rhyolitic tuffs
SHRIMP U-Pb
809±9
Geng et al., 2008
Ac c
16
Reference
17
d
ep te
12
Age (Ma)
an
No.
11
Dating method
M
us
Table 4
Page 69 of 69