The Neoproterozoic magmatism in the northern margin of the Yangtze Block: Insights from Neoproterozoic (950–706 Ma) gabbroic-granitoid rocks of the Hannan Complex

Precambrian Research 333 (2019) 105442

Contents lists available at ScienceDirect

Precambrian Research journal homepage: www.elsevier.com/locate/precamres

The Neoproterozoic magmatism in the northern margin of the Yangtze Block: Insights from Neoproterozoic (950–706 Ma) gabbroic-granitoid rocks of the Hannan Complex

T

⁎

Wenhao Aoa, , Yan Zhaoa, Yukun Zhangb, Mingguo Zhaia,c, Hong Zhanga, Ruiying Zhangd, Qian Wanga, Yong Suna a

State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China CNPC Logging, Xi’an 710000, China Key Laboratory of Computational Geodynamics, University of Chinese Academy of Sciences, Beijing 100049, China d College of Geographical Sciences, Shanxi Normal University, Shanxi 041000, China b c

A R T I C LE I N FO

A B S T R A C T

Keywords: Yangtze Block Hannan Complex Neoproterozoic magmatism Arc-back-arc tectonic setting Crustal evolution

The Hannan Complex, located in the northwestern margin of the Yangtze Block, South China, consists of numerous mafic-ultramafic and felsic plutons formed at ca. 950–700 Ma. However, their geotectonic setting and petrogenesis keep in controversy. This study presents whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf composition and whole-rock Hf isotope of gabbroic-granitoid rocks of the Hannan Complex, aiming to clarify their spatial-temporal distribution and discuss their geological significance. The Dahanshan gabbro in the Hannan region yields zircon U-Pb age of 793–779 Ma. The positive zircon εHf(t) values (+8.0–+10.4) and positive whole-rock εHf(t) values (+7.0–+12.6) suggest a relatively depleted mantle source of the gabbro. However, Hf model ages and whole-rock geochemical data suggest addition of enriched components to magma source. Thus, the magmas derived from decompression melting of MORB-like mantle and flux-induced melting of metasomatized lithospheric mantle wedge both contributed to generation of Dahanshan gabbro in a back-arc setting. The Hongmiao granite pluton, having crystallization age of 802–791 Ma, is characterized by aluminous A-type granite signatures and showing A2-type granite affinities. Taking negative εHf(t) values (–24.5 to −3.3) of zircons into account, the Hongmiao granite was generated by partial melting of pre-existing crustal materials in an extensional enviroment. The Xishenba trondhjemitic biotite granite formed at ca. 890 Ma. It belongs to metaluminous to peraluminous calc-alkaline I-type granitoid rock series with negative zircon εHf (t) values (–19.4 to −6.2), implying a magma source of pre-existing crustal materials in an arc setting. Thus, combined with previously published data, it can be concluded that the gabbroic-granitoid rocks of the Hannan Complex were generated in subduction-related arc-back-arc setting during Neoproterozoic (950–706 Ma). The Neoproterozoic (ca. 950–706 Ma) magmatism represents a significant crustal growth event in the northern margin of the Yangtze Block, simultaneously, accompanied by certain degree of crustal reworking. According to temporal-spatial distribution of different rock types, the formation of the Neoproterozoic (ca. 950–706 Ma) Hannan Complex can be subdivided into four stages: ca.950–890 Ma and ca.890–840 Ma in a continental arc setting and a continuous continental arc setting, respectively; whereas, ca.840–765 Ma and ca.765–706 Ma in a back-arc setting and a compression-extension tectonic setting, respectively.

1. Introduction Neoproterozoic magmatism is widely developed in the Yangtze Block, which is closely related to assembly and breakup of the Rodinia supercontinent (Li et al., 1995). Since the modified reconstruction scenario was proposed (Li et al., 1996, 1999; Li, 1999), the relationship

⁎

between the South China and the Rodina supercontinent in Neoproterozoic has become a key scientific issue of worldwide interesting. Li et al. (1995, 1996, 1999) suggested that the South China Block is situated in the center of the Rodinia linked the Laurentia and AustraliaEast Antarctica, which is evidenced by the amalgamation of the Yangtze Block and Cathysia Block during the Sibao movement (1100–1000 Ma)

Corresponding author. E-mail address: [email protected] (W. Ao).

https://doi.org/10.1016/j.precamres.2019.105442 Received 18 January 2019; Received in revised form 26 August 2019; Accepted 30 August 2019 Available online 31 August 2019 0301-9268/ © 2019 Elsevier B.V. All rights reserved.

Precambrian Research 333 (2019) 105442

W. Ao, et al.

considered that they were produced by multi-stage plate subduction in an active continental margin during Neoproterozoic (ca. 900–700 Ma) (Gao et al., 1990; Zhou et al., 2002a, 2002b; Ling et al., 2003; Zhao and Zhou, 2008; Dong et al., 2012; Bader et al., 2013; Ao et al., 2014; Li et al., 2018; Zhao et al., 2008, 2018). Among these, the mafic plutons were derived from partial melting of lithospheric mantle above a subduction zone (Zhou et al., 2002a; Zhao and Zhou, 2009a; Zhao et al., 2008), while most of the granitoids are I-type or A-type granites, with some even exhibiting adakitic geochemical features (Zhao and Zhou, 2008, 2009b; Luo et al., 2018). However, whether they are the response to the breakup of the Rodinia has long been debated, especially in regarding to the Late Neoproterozoic (ca. 700 Ma) magmatism (Ling et al., 2001, 2003; Zhao et al., 2006; Xia et al., 2009; Dong et al., 2011; Luo et al., 2018). Whether there exists a transition from subduction to extension in response to the breakup of the Rodinia is also not clear. Wang et al., (2013a) suggested that the age of ca. 635 Ma obtained from Zhouan ultramafic rocks in northern margin of the Yangtze Block represents the final stage of the breakup of the Rodina supercontinent. However, in this proposition, the time span (ca. 1300–600 Ma) of assembly and breakup of the Rodinia supercontinent seems too long. Furthermore, most of the magmatism in the Hannan region is slightly late when compared with their other equivalent of the Yangtze Block. Farther to the north, extensive Neoproterozoic rocks expose in the South Qinling Belt, such as the Wudang and Yaolinghe groups. The ca. 700–650 Ma mafic dikes intrude into the contemporaneous Yaolinghe and Wudang groups, within which the metavolcanic rocks yield zircon U-Pb age of ca. 750 Ma (Ling et al., 2008; Zhu et al., 2015; Li and Zhao, 2016). They were interpreted as the products of continental-rift setting or subduction-related arc setting (e.g. Zhang and Zhou, 1999; Ling et al., 2002a, 2007; Zhao and Asimow, 2018). In addition, the Mian-Lue Complex in the west of the Hannan region was considered as an oceanic accretionary wedge that formed outboard of an associated forearc-arc system represented by the Bikou-Hannan-Micangshan massifs along the northern (western) margin of the Yangtze Block (Bader et al., 2013). Wu et al. (2019) suggested the Mian-Lue Complex as a Neoproterozoic

in the Jiangnan Orogenic Belt. Therefore, plume-rift model was proposed to interpret Neoproterozoic magmatism in the South China (Li et al., 2002, 2003a, 2003b, 2003c, 2009; Wang et al., 2009). In this model, the upwelling of mantle plume led to the formation of the Kandian and Nanhua rifts in the western margin and the interior of the South China, respectively, and then resulted in the breakup of the Rodinia supercontinent (ca.820 Ma) (Li et al., 2003a). Nevertheless, further research reveal that the formation of the Jiangnan Orogenic Belt (ca. 830 Ma) is later than the Grenville Orogenic Belt (1300–1000 Ma), suggesting that the Jiangnan Orogenic Belt cannot represent the assembly of the Rodinia supercontinent as previously suggested (Zhao et al., 2011). Thereafter, Neoproterozoic plutons in the South China were generally linked with arc magmatism. It has long been considered that the Neoproterozoic magmatisms were generated in a plate subduction-related arc setting along the west, north and southeast of the Yangtze Block and the the Yangtze Block was located in the margin of the Rodinia supercontinent or external to the supercontinent (Zhou et al., 2002b, 2006a; Zhao and Zhou, 2007a,b; Dong et al., 2012; Zhao and Cawood, 2012; Wang et al., 2013b, 2014; Dong and Santosh, 2016; Li et al., 2018). Based on zircon Hf-O isotopes of Neoproterozoic granitoids in the South China, Zheng et al. (2008) summarized two episodes of magmatism: the first occurred at ca. 825 Ma in an orogenic collapse zone, related to ancient crust reworking; and the second took place at ca.750 Ma in a rifting setting, characterized by magmas derived from depleted mantle source. The geodynamic mechanism of the magmatism has long been in debate. However, the spatial-temporal variation of different rock types in different region may provide valuable information for understanding this scientific issue. In the Hannan region, northern margin of the Yangtze Block, Neoproterozoic ultramafic–mafic and granitoid intrusions were widely developed, providing a nature window to investigate the mechanism and petrogenesis of these plutons and a valuable opportunity to understand their relationship with the amalgamation and breakup of the Rodinia supercontinent. In this place, all the Neoproterozoic intrusions were called “Hannan Complex” (Fig. 1). Most researchers have

Fig. 1. Simplified geological map of the northwestern Yangtze Craton (modified after Zhao and Zhou, 2008). 2

Precambrian Research 333 (2019) 105442

W. Ao, et al.

unconformably overlying the Houhe Complex, has experienced greenschist-facies metamorphism and consists of the lower metasedimentary rocks (the Mawozi and Shangliang Formation) and the upper volcanic lavas and clastic rocks (the Tiechuanshan Formation) (Ling et al., 2003). The Tiechuanshan Formation in the upper unit was considered as typical bimodal basalt-rhyolite volcanic sequence, dated at 817 ± 5 Ma (Gao et al., 1990; Ling et al., 2003). The Neoproterozoic Xixiang Group, formed at ca. 950–730 Ma (e.g. Ling et al., 2002b, 2003; Xu et al., 2009, 2010; Cui et al., 2013; Deng et al., 2013), is a succession of metavolcanics-sediments with lower part of basalt and andesite and upper part of dacite and rhyolite (Gao et al., 1990; Ling et al., 2003). However, the tectonic setting of these metavolcanics-sediments is still in controversy (e.g. Xu et al., 2009, 2010; Deng et al., 2013). Coeval with the Neoproterozoic volcanism, mafic–ultramafic and granitoid plutons (the Hannan Complex) widely outcrop in the Hannan region. The Hannan Complex intrudes into the Archean-Mesoproterozoic strata and is locally overlain by Sinian strata, which is overlain by the Paleozoic-Cenozoic sedimentary sequences. The major granitoid rocks of the Hannan Complex include the Wudumen, Erliba, Zushidian and Tianpinghe plutons (Fig. 1), with crystallization ages of 789–718 Ma, 778–730 Ma, 728 Ma and 860–760 Ma, respectively (Ling et al., 2006; Zhao et al., 2006; Zhao and Zhou 2008, 2009b; Liu et al., 2009; Dong et al., 2012; Ao et al., 2014; Luo et al., 2018). The Wudumen and Erliba adakitic plutons (Zhao and Zhou, 2008), as well as the Tianpinghe Itype granite, were generated by partial melting of newly emplaced mafic rocks which thickened the lower crust (Zhao and Zhou, 2009b). The small volume of dioritic intrusion in the Xixiang area, with crystallization age of 764 Ma, was also generated by partial melting of newly formed mafic precursor (Zhao et al., 2010). Besides, A-type granites, with formation age of ca. 780–770 Ma, was recognized in the Tiechuanshan and Huangguan areas, suggestive of a local extensional environment (Luo et al., 2018). The Mafic-ultramafic rocks in the region mainly include the Wangjiangshan, Bijigou, Dahanshan and Beiba intrusions, having crystallization ages of 780–820 Ma, 750–790 Ma, 746 Ma, 814–880 Ma, respectively (Ling et al., 2001; Zhou et al., 2002a; Zhao and Zhou, 2009a; Dong et al 2011; Wang et al., 2016; Luo et al., 2018). It has been suggested that these intrusions were probably derived from a lithospheric mantle source under a subduction setting (Zhou et al., 2002a; Zhao and Zhou, 2009a; Dong et al., 2011), or an intra-continental rift setting that indicates a tectonic regime transition from convergence to extension (Ling et al., 2001, 2003).

(ca. 900 Ma) ophiolite of the Grenvillian oceanic subduction system. However, the petrogenesis of these volcanic-plutons is still under controversy, and the tectonic regime between the northern margin of the Yangtze Block and the South Qinling Belt in Neoproterozoic is still debated. Recently, several gabbroic plutons and granitic plutons have been recognized in the Hannan area, northern margin of the Yangtze Block (Fig. 1). In this study, we focus on the Dahanshan gabbroic pluton, Hongmiao and Xishenba granitoid plutons, which have rarely been investigated in detail. Combined with the published data, we attempt to delineate the spatial-temporal distribution of different rock types in the Hannan region, and to discuss the crustal and tectonic evolution of the northern margin of the Yangtze Block. Systematic studies of LA-ICP MS zircon U-Pb dating, whole-rock major and trace element analyses, zircon and whole-rock Hf isotopic analyses on representative samples of these plutons have been conducted. The results are of significance for understanding their petrogenesis, magma source and tectonic setting, as well as tectonic evolutionary history of the northern margin of the Yangtze Block. 2. Geological setting The South China Craton comprises the Yangtze Block to the northwest and the Cathaysian Block to the southeast, which were welded together during Mesoproterozoic-Neoproterozoic (Li and McCulloch, 1996; Zhao and Cawood, 2012; Wang et al., 2014). The Yangtze Block is separated from the North China Craton by the Qinling-Dabie Orogenic Belt to the north and the Tibetan Plateau to the west, consisting of basement complexes overlain by a Neoproterozoic to Cenozoic strata sequences. Several Archean zircon ages have been reported in the Yangtze Block (Xu et al., 2005; Liu et al., 2005; Zheng et al., 2006; Sun et al., 2008), and the Archean basement rocks mainly formed at ca. 3.45–2.70 Ga (Ling et al., 1998; Gao et al., 2001, 2011; Guo et al., 2014, 2015), ca. 2.7 Ga (Zhang et al., 2001; Hui et al., 2017; Zhou et al., 2018a,b) and 3.0–2.5 Ga (Hu et al., 2013; Shi et al., 2013; Wu et al., 2014; Nie et al., 2016) have been recognized within Kongling, Yudongzi and Douling complexes, respectively. A few 2.9–2.6 Ga potassic granite have also been identified in the Zhongxiang region within the northern Yangtze Block (Wang et al., 2013c, 2018; Zhou et al., 2017). Neoproterozoic volcanic-sedimentary sequences are discontinuously preserved in the Yanbian and Bikou terranes, along the western margin of the Yangtze Block (Zhou et al., 2006a; Sun et al., 2007; Yan et al., 2004). The Late Sinian-Middle Triassic sequences consist of tillites, shales, sandstones, carbonate-rich rocks, siltstones and clastic rocks (Yan et al., 2003). Additionally, Neoproterozoic mafic–ultramafic and granitoid plutons were also widely developed in the Yangtze Block (Zhou et al. 2002a,b; Li et al., 2003c; Zhou et al. 2006a,b), most of which emplaced into the Mesoproterozoic strata and are unconformably overlain by the Sinian strata. Petrogenesis of these Neoproterozoic intrusions has been hotly debated for years (Li et al., 1995, Li et al., 1999, 2003c; Li et al., 2003a; Zhou et al. 2002a,b, 2006a,b). Hannan is a key area situated in the transitional region between the northwestern margin of the Yangtze Block and the South Qinling Belt, and is separated from the Songpan-Ganze and Bikou terranes by the Longmenshan fault. Based on formation ages and rock types, rocks in this region can be divided into three units: (1) the oldest basement rocks of the Houhe Complex distribute along the the Beiba-Mayuan area, and the Meso-Neoproterozoic Huodiya Group near the Beiba area and the Neoproterozoic Xixiang Group near the Xixiang area; (2) the Neoproterozoic plutons, called “Hannan Complex”; (3) the Sinian to Paleozoic strata in the external place surrounding these Pre-Sinian rocks. Among these, the poorly exposed Houhe Complex experienced upper amphibolite-facies metamorphism and migmatization, mainly consists of trondhjemitic-tonalitic gneisses and migmatites with minor amphibolites and marbles (Gao et al., 1990; Ling et al., 2003). Zircon UPb dating results reveal that the TTG gneiss of the Houhe Complex has formation age of 2081 Ma (Wu et al., 2012). The Huodiya Group,

3. Sample petrography In this study, samples of the Dahanshan gabbro, Hongmiao potassic granite and Xishenba biotite granite (Fig. 2) were selected for systematically whole-rock geochemical and LA-ICP MS zircon U-Pb geochronological analyses. Representative samples were chosen for zircon and whole-rock Hf isotope analyses. The lithology, location and petrography of these samples are listed in Table 1. The Dahanshan gabbroic pluton outcrops over > 25 km2, occurring as a mountain with planation on its top and intruding the Late Mesoproterozoic strata (Fig. 2). The pluton consists of hornblende gabbro and hypersthene-hornblende gabbro from periphery to center. Sample DHS03, a sample of hypersthene-hornblende gabbro, was collected from the central part of the Dahanshan pluton (Fig. 2). It is dark grey in color (Fig. 3a) and medium-coarse-grained (Fig. 4a), predominantly consisting of plagioclase (45–50%), hornblende (30–35%), hypersthene (6–8%) and clinopyroxene (4–7%), with accessory minerals of zircon and apatite. The hornblende generally occurs as subhedral-euhedral crystals or growths around hypersthene. The small hypersthene crystals are generally granular and occur within hornblende. The coexistence of clinopyroxene and orthopyroxene indicate the petrography features of tholeiitic series (Chen et al., 2008). Samples DHS12 and DHS11, coarse-grained hornblende gabbro samples, were selected from northern part and southern part of the Dahanshan pluton, 3

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 2. Simplified geological map of the Dahanshan region.

the State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China. Major element contents were determined using a Rikagu RIX 2100 X-ray fluorescence (XRF) spectrometer, with analytical uncertainties lower than 5%. Trace element concentrations were analyzed by using an Agilent 7700a inductively coupled plasma mass spectrometer (ICP-MS) employing United States Geological Survey (USGS) and international rock standards (BHVO-2, AGV-2, BCR-2 and GSP-1). Most of the trace elements have relative deviation and relative standard deviation lower than 5% (Liu et al., 2007).

respectively (Fig. 2). They are dark grey in color (Fig. 3b and c), mainly consisting of hornblende (40–45%), plagioclase (45–50%) and clinopyroxene (3–5%), and accessory minerals of apatite, zircon and epidote (Fig. 4b and c). The hornblende is subhedral-euhedral and can be subdivided into two types: the dominant brown magmatic hornblende and the subordinate green altered hornblende. The granular clinopyroxene are randomly distributed along grain boundaries or within the hornblend. The plagioclase occurs as subhedral-euhedral crystals generally enclosed in hornblende, suggesting early crystallization. Samples NH-3 and XSB are potassic granite samples of Hongmiao pluton, intruding into the Late Mesoproterozoic strata (Fig. 2). They show massive structure (Fig. 3d and e) and coarse-grained texture (Fig. 4d and e), consisting mainly of microcline (35–43%), plagioclase (18–22%), quartz (25–30%) and biotite (< 5%), with accessory minerals of zircon and apatite (Fig. 4d and e). The plagioclase is subhedral to euhedral and platy, with well-developed polysynthetic twin. The microcline is also subhedral-euhedral and platy, having partially experienced kaolinization and displaying typical cross hatched twin. The interstitial quartz grains and biotite occurs irregularly (Fig. 4d and e). Sample GQ was a biotite granite sample collected from the Xishenba pluton, which intrudes into the Late Mesoproterozoic strata (Fig. 2). This granitic rock shows existence of dark enclaves (Fig. 3f) and are medium-coarse-grained (Fig. 4f), mainly composed of plagioclase (45–50%), quartz (25–30%), biotite (12–17%) and K-felspar (3%), with accessory minerals of apatite, magnetite and zircon. The plagioclase is subhedral and platy. The quartz occurs as irregular grains and the flaked biotite occurs within clearance of other minerals.

4.2. LA-ICP MS zircon U-Pb dating Zircon grains were separated from samples using conventional density and magnetic techniques and then hand-picked under a binocular microscope at the Institute of Regional Geology and Mineral Resources Survey, Langfang City, Hebei Province, China. Representative zircon grains were mounted together with epoxy, and then were polished to expose their centers. The internal texture of zircons was revealed by taking cathodoluminescence (CL) images using a Quanta 400FEG environmental scanning electron microscope equipped with an Oxford energy dispersive spectroscopy system and a Gatan CL3+ detector prior to U-Pb dating. Zircon U-Pb isotopic compositions were analyzed using Agilent 7700a ICP-MS instrument equipped with a 193 nm ArF-excimer laser and a homogenizing, imaging optical system at State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China. The spot size and laser repetition rate were set as 32 μm and 6 Hz, respectively throughout analytical process. Helium was used as carrier gas to provide efficient aerosol delivered to the torch. The standard silicate glass NIST 610 was used to optimize the instrument to obtain a maximum signal intensity (238U signal intensity is 1000–1600 cps/ppm) and a low oxide production (ThO/Th < 1%). Isotopic ratios of 207Pb/206Pb, 206Pb/238U, 207 Pb/235U and 208Pb/232Th were calculated using the Glitter 4.0

4. Analytical methods 4.1. Whole-rock geochemical analyses Whole-rock major and trace element compositions were analyzed at 4

Precambrian Research 333 (2019) 105442

program. The Harvard zircon 91,500 was used as external standard for correction of both instrumental mass bias and depth dependent elemental and isotopic fractionation. Element concentrations of U, Th and Pb were calibrated by using 29Si as an internal standard and NIST SRM 610 as an external standard. Concordia diagrams and weighted mean calculations were completed using the Isoplot 3.0 software (Ludwig, 2003). 4.3. Whole-rock Hf isotope analyses Whole-rock high precision Hf isotope measurements were analyzed using Agilent Technologies 7700x quadrupole ICP-MS (Hachioji, Tokyo, Japan) at Nanjing FocuMS Technology Co. Ltd. Hafnium was purified from the same digestion solution by two steps column chemistry: The first exchange column combined with BioRad AG50W-X8 was used to separate HFSE, and Hf was separated from the other HFSE on the second LN-specific column (HDEHP-coated Teflon powder). Raw data of isotopic ratios were corrected for mass fractionation by normalizing to 179Hf/177Hf = 0.7325. International isotopic standard of Alfa Hf was periodically analyzed to correct instrumental drift. Geochemical reference materials of USGS BCR-2, AGV-2, BHVO-2 and STM-2 were used as quality control, with determined 176Hf/177Hf ratios of 0.282870, 0.282984, 0.283105 and 0.283021, respectively. The εHf(t) values was calculated using present-day chondritic 176Lu/177Hf and 176 Hf/177Hf ratios of 0.0332 and 0.282772, respectively (Blichert-Toft and Albarède, 1997). Whole-rock Hf model ages were calculated using present-day 176Lu/177Hf = 0.0384 and 176Hf/177Hf = 0.28325 for depleted mantle (Griffin et al., 2000).

Mineral: Pl = plagioclase, Mc = microcline, Hbl = hornblende, Qtz = quartz, Bt = biotite, Cpx = clinopyroxene, Hy = hypersthene

Zircon, Apatite Zircon, Apatite, Fe-Ti oxide Mc(43%) + Pl(22%) + Qtz(30%) + Bt(5%) Pl(50%) + Qtz(30%) + Bt(17%) + K-feldspar(3%) 106°55′18.7″ 106°53′45.3″ 32°49′21.8″ 32°46′19.2″ Xishenba biotite granite K-feldspar granite biotite granite NH-3 GQ

Hongmiao Potassic granite

106°56′21.5″ 106°57′32.6″ 106°55′32.3″ 32°56′17.8″ 32°57′40.2″ 32°49′02.2″ DHS11 DHS12 XSB

Dahanshan gabbro

Hypersthene-hornblende gabbro Hornblende gabbro Hornblende gabbro K-feldspar granite DHS03

Coarse-grained granitic texture/Massive structure Medium-coarse-grained granitic texture/Massive structure

Zircon, Apatite Zircon, Apatite Zircon, Apatite Pl(50%) + Hbl(45%) + Cpx(5%) Pl(50%) + Hbl(45%) + Cpx(5%) Mc(43%) + Pl(22%) + Qtz(30%) + Bt(5%)

Zircon, Apatite Pl(50%) + Hbl(35%) + Cpx(7%) + Hy(8%)

Medium-coarse-grained gabbroic texture/Massive structure Coarse-grained gabbroic texture/Massive structure Coarse-grained gabbroic texture/Massive structure Coarse-grained granitic texture/Massive structure 106°56′23.3″ 32°56′58.8″

Mineral assemblage Texture/structure Longitude (E) Latitude (N) Location Lithology Sample no.

Table 1 Simplified geological and petrological characteristics for samples of gabbros and granites of the Hannan Complex.

Accessory minerals

W. Ao, et al.

4.4. Zircon Lu-Hf isotopic analyses In-situ zircon Hf isotope analyses were performed using a Nu Plasma HR MC-ICP-MS (Nu Instrument Ltd., UK) equipped with a GeoLas 193 nm excimer laser-ablation system at State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China. The beam size of 44 μm and a repetition rate of 10 Hz were adopted throughout analytical process. The applied energy density is 15–20 J/cm−2. Raw count rates for 172Yb, 173Yb, 175Lu, 176(Hf + Yb + Lu), 177Hf, 178Hf, 179 Hf and 180Hf were collected simultaneously. The isobaric interference of 176Lu on 176Hf was corrected by measuring the intensity of an interference-free 175Lu isotope, and a recommended 176Lu/175Lu ratio of 0.02655 was used to calculate 176Lu/177Hf ratios. The interference of 176 Yb on 176Hf was corrected by measuring an interference-free 172Yb isotope, and 176Hf/177Hf ratio was calculated using a 176Yb/172Yb ratio of 0.5886 (Chu et al., 2002). Time dependent drifts of Lu-Hf isotopic ratios were corrected using a linear interpolation according to the variations of standards 91,500 and GJ-1. The referenced values of 1.867 × 10-11 a-1 for the decay constant for 176Lu (Albarède et al., 2006), and 0.282772 and 0.0332 for present-day chondritic ratios of 176 Hf/177Hf and 176Lu/177Hf (Blichert-Toft and Albarède, 1997) were adopted to calculate εHf values at the time when zircon crystallized from magma. Single-stage zircon Hf model ages (TDM1) were calculated relative to the depleted mantle with a present-day 176Hf/177Hf ratio of 0.28325 and 176Lu/177Hf ratio of 0.0384 (Griffin et al., 2000). Twostage zircon Hf model ages (TDM2) were calculated by projecting the initial 176Hf/177Hf back to the depleted mantle growth curve using 176 Lu/177Hf = 0.015 for the average continental crust (Rudnick and Gao, 2003). 5. Analytical results 5.1. Major and trace elements The analytical results of whole-rock major and trace element compositions are listed in Table 2 and shown in Fig. 5. 5

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 3. Photographs showing field features of (a), (b) and (c) Dahanshan gabbro; (d) and (e) Hongmiao potassic granite; and (f) Xishenba biotite granite.

enrichment of light rare earth element (LREE) ([La/Yb]N = 1.95–2.99) and show insignificant Eu anomalies (Eu/Eu* = 0.93–1.11), similar as that of E-MORB (Sun and McDonough, 1989), with heavy rare earth element (HREE) profiles nearly flat. In the primitive mantle-normalized trace element spider diagram (Fig. 6b), they are characterized by weak depletion of high field strength element (HFSE) (e.g. Nb, Ta, Zr, Hf and Ti) and HREE, and relatively slight enrichment of large ion lithophile element (LILE), e.g. Rb, Ba, Th, U and Pb.

5.1.1. Dahanshan gabbro As described before, the Dahanshan gabbroic pluton consists of hypersthene-hornblende gabbro and hornblende gabbro. They have identical major and trace element concentrations, characterized by low contents of SiO2 (47.0–52.5 wt%), K2O (0.22–0.57 wt%), total alkalis (K2O + Na2O) (2.14–2.71 wt%) (Fig. 5a), TiO2 (0.63–1.15 wt%) and P2O5 (0.09–0.21 wt%) and relatively high contents of MgO (6.69–9.05 wt%) and Al2O3 (15.7–18.0 wt%), with Mg# values ranging from 59 to 69 (Table 2). On the (Na2O + K2O)-Fe2O3T-MgO triangular diagram and Fe2O3T/MgO versus SiO2 diagram, all the samples fall into the fields along the tholeiitic magma evolution trend, exhibiting tholeiitic affinity (Fig. 5b and c). The studied gabbro samples have low and variable concentrations of Cr (59.2–275 ppm) and Ni (38.0–86.9 ppm), as well as low contents of rare earth elements (∑REE = 34.3–66.1 ppm). In the chondrite-normalized REE distribution diagram (Fig. 6a), they display a slight

5.1.2. Hongmiao potassic granite The samples of Hongmiao potassic granite have high contents of SiO2 (74.2–77.9 wt%), K2O (4.67–5.75 wt%) and K2O + Na2O (8.09–8.82 wt%) (Fig. 5a), and low contents of Na2O (2.93–3.54 wt%), MgO (0.06–0.22 wt%), CaO (0.15–0.44 wt%), Al2O3 (11.5–13.4 wt%), Fe2O3T (1.25–1.97 wt%) and TiO2 (0.09–0.21 wt%). Their Mg# values range from 9 to 21, with K2O/Na2O, A/CNK and A/NK ratios of 6

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 4. Photomicrographs showing petrographic features of the studied samples.

and low contents of MgO (0.42–1.17 wt%), Fe2O3T (1.94–3.97 wt%), CaO (2.02–3.07 wt%) and K2O (1.20–3.10 wt%), having low and variable Mg# values of 21–44 and K2O/Na2O ratios of 0.14–0.47 (Table 1). They have intermediate-high values of total alkali (Fig. 5a), with A/ CNK and A/NK values ranging from 0.95 to 1.05 and 1.35 to 1.47, respectively, mostly belonging to weak peraluminous (Fig. 5d) and medium-K calc-alkaline rock series (Fig. 5e). Geochemically, these rocks are characterized by Na-rich features of trondhjemite (Fig. 5f). These biotite granite samples have variable ∑REE concentrations ranging from 53.6 to 532.3 ppm. In the chondrite-normalized REE patterns, they are mostly characterized by enrichment of LREE ([La/ Yb]N = 2.07–26.41) and relatively depletion of HREE, with positive to negative Eu anomalies (Eu/Eu*=0.68–2.18) (Fig. 6e). In the primitive mantle-normalized trace element diagram, these samples show relatively enrichment of LILEs, such as Rb, Ba, Th, and Pb, but relatively depletion of HFSEs, such as Nb, Ta and Ti (Fig. 6f).

0.88–1.28, 1.00–1.15 and 1.05–1.20, respectively (Table 1), belonging to light peraluminous (Fig. 5d) and medium- to high-K calc-alkaline rock series (Fig. 5e). These potassic granite samples contain high ∑REE concentrations of 174–396 ppm. Their chondrite-normalized REE patterns are characterized by LREE enrichment ([La/Yb]N = 7.00–18.32), relatively HREE depletion and pronounced negative Eu anomalies (Eu/Eu* = 0.07–0.29) (Fig. 6c), indicating plagioclase fractionation or plagioclase in residual. In the primitive mantle-normalized trace element diagram, these granite samples display enrichment of LILEs, e.g. Rb, Th, U and Pb, but relatively depletion of HFSEs (e.g. Nb, Ta and Ti) (Fig. 6d). The pronounced negative Sr anomalies indicate plagioclase fractionation or low pressure of partial melting of the magma source. 5.1.3. Xishenba biotite granite The samples of Xishenba biotite granite have high contents of SiO2 (67.2–72.5 wt%), Al2O3 (14.4–15.5 wt%) and Na2O (4.26–5.51 wt%), 7

49.3 0.71 18.0 8.61 0.14 7.34 11.6 2.14 0.52 0.14 1.15 99.5 1.13 66.5 1.26 6.65 0.45 33.2 215 187 52.6 86.9 88.5 57.2 15.4 1.29 9.96 384 16.1 81.0 1.87 0.21 158 6.58 15.1 2.15 10.4 2.68 0.91 2.75 0.44 2.74 0.56 1.59 0.23 1.48 0.22 1.85 0.14 2.47 0.82 0.22

SiO2 TiO2 Al2O3 Fe2O3T MnO MgO CaO Na2O K2O P2O5 LOI TOTAL δ Mg# A/CNK Li Be Sc V Cr Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

49.0 0.80 17.5 9.40 0.15 7.34 11.4 2.19 0.50 0.13 1.13 99.6 1.20 64.5 1.23 6.62 0.51 33.5 237 147 58.6 77.8 91.4 58.7 16.1 1.35 8.90 375 20.8 50.1 2.16 0.21 145 6.86 17.4 2.51 12.5 3.32 1.03 3.45 0.56 3.56 0.74 2.10 0.31 1.94 0.29 1.55 0.15 2.45 0.78 0.19

47.3 1.11 16.2 12.3 0.19 7.61 11.2 2.04 0.57 0.21 0.94 99.6 1.58 59.1 1.17 14.2 0.54 42.2 309 59.2 58.8 38.0 92.3 77.1 17.7 1.50 10.9 403 22.7 55.8 2.89 0.38 139 8.25 21.1 3.10 14.7 3.75 1.24 3.78 0.61 3.85 0.79 2.27 0.33 2.07 0.31 1.72 0.16 1.86 0.31 0.07

DHS12-1

DHS11-1

Sample no.

DHS11-2

Dahanshan hornblende gabbro

Rock type

47.2 1.10 16.4 12.0 0.19 7.96 11.5 2.07 0.39 0.18 0.72 99.7 1.44 60.7 1.18 7.59 0.49 41.4 295 70.1 55.2 46.9 95.0 75.7 17.5 1.44 5.36 387 22.6 55.7 2.70 0.11 104 6.62 16.3 2.46 11.5 3.18 1.12 3.41 0.58 3.65 0.77 2.23 0.33 2.04 0.31 1.71 0.15 1.61 0.24 0.06

DHS12-2 47.5 1.09 16.5 11.9 0.19 7.92 11.4 2.05 0.38 0.18 0.77 100.0 1.30 60.7 1.19 7.34 0.50 41.9 299 68.8 59.3 45.8 98.1 75.8 17.5 1.48 4.75 390 22.8 57.3 2.77 0.10 93.9 6.54 16.2 2.45 11.7 3.19 1.11 3.45 0.58 3.76 0.78 2.26 0.34 2.11 0.31 1.71 0.16 1.61 0.23 0.06

DHS12-3 48.8 0.80 16.1 10.0 0.14 8.10 11.8 2.42 0.29 0.09 1.00 99.6 1.26 65.3 1.11 4.36 0.36 38.0 261 218 78.0 80.0 107 62.2 16.0 1.29 4.73 364 15.5 43.1 1.65 0.10 101 4.96 12.2 1.68 8.02 2.14 0.79 2.56 0.41 2.63 0.56 1.60 0.23 1.48 0.22 1.27 0.14 1.62 0.42 0.09

DHS02-1 47.8 0.93 16.4 10.9 0.17 8.21 12.2 2.27 0.23 0.12 0.97 100.1 1.31 63.6 1.12 3.57 0.36 38.8 264 203 63.9 68.0 101 70.0 16.8 1.30 2.05 386 17.3 43.5 1.96 0.06 83.7 5.09 13.0 1.88 9.20 2.44 0.92 2.90 0.46 2.99 0.63 1.79 0.26 1.65 0.24 1.36 0.13 1.39 0.25 0.06

DHS02-2 47.0 1.15 15.7 12.9 0.19 8.03 11.6 1.90 0.24 0.16 0.81 99.7 1.15 59.2 1.14 11.9 0.47 41.8 343 68.4 67.6 41.8 91.4 75.0 17.3 1.47 2.48 374 19.7 44.7 2.33 0.08 90.8 5.36 13.8 2.02 10.2 2.78 1.00 3.03 0.53 3.40 0.72 1.99 0.29 1.85 0.27 1.38 0.15 1.57 0.20 0.05

DHS02-3

Dahanshan hypersthene-hornblende gabbro

Table 2 Whole-rock major and trace element compositions for samples of gabbros and granites of the Hannan Complex.

47.2 1.14 15.8 12.8 0.19 7.99 11.7 1.92 0.24 0.16 0.82 99.9 1.11 59.3 1.14 3.96 0.47 43.2 346 69.7 66.5 41.7 90.0 76.2 17.4 1.48 2.37 373 19.9 44.4 2.34 0.08 90.9 5.36 13.8 2.04 10.2 2.78 0.99 3.06 0.52 3.34 0.71 2.02 0.29 1.84 0.27 1.38 0.14 1.60 0.19 0.05

DHS02-4 49.0 0.63 16.3 9.66 0.18 9.05 12.5 1.95 0.23 0.09 0.51 100.1 0.79 68.6 1.11 3.64 0.37 42.9 235 275 60.2 81.6 89.1 57.9 15.4 1.43 2.46 371 14.4 35.2 1.34 0.10 77.0 4.24 10.3 1.49 7.05 1.98 0.73 2.16 0.37 2.44 0.50 1.45 0.21 1.35 0.20 1.05 0.09 1.69 0.18 0.04

DHS02-5 49.1 0.68 16.3 9.85 0.17 8.80 12.2 1.90 0.25 0.10 0.57 99.9 0.76 67.6 1.14 4.10 0.37 40.8 247 238 62.0 76.6 109 58.6 15.5 1.44 2.91 362 14.2 37.4 1.41 0.12 80.8 4.30 10.4 1.50 7.08 1.92 0.72 2.12 0.37 2.36 0.50 1.43 0.21 1.33 0.20 1.06 0.10 1.78 0.26 0.06

DHS03-1 49.0 0.63 16.5 9.57 0.17 8.89 12.5 1.92 0.22 0.09 0.52 100.0 0.76 68.4 1.12 4.08 0.38 41.3 235 257 65.3 77.3 90.6 56.4 15.5 1.40 2.31 376 14.3 34.9 1.33 0.10 77.2 4.22 10.2 1.48 7.05 1.95 0.74 2.16 0.37 2.37 0.50 1.45 0.21 1.35 0.20 1.04 0.09 1.64 0.19 0.04

DHS03-2 48.1 1.02 16.2 11.8 0.18 8.16 11.6 1.92 0.29 0.16 0.55 99.9 0.96 61.7 1.17 4.72 0.46 41.9 284 84.3 57.7 53.1 96.7 71.9 16.8 1.45 3.08 378 20.6 52.8 2.51 0.08 98.4 5.82 14.9 2.21 10.7 2.95 1.03 3.18 0.54 3.44 0.73 2.07 0.30 1.92 0.28 1.55 0.15 1.92 0.30 0.07

DHS03-3

8

48.5 0.71 16.5 9.96 0.17 8.60 12.1 1.88 0.33 0.10 0.97 99.8 0.89 66.8 1.16 5.02 0.38 39.0 240 258 57.0 75.2 111 59.9 15.6 1.36 4.44 364 14.8 42.4 1.57 0.21 93.9 4.70 11.1 1.62 7.69 2.09 0.75 2.25 0.38 2.47 0.52 1.50 0.22 1.40 0.21 1.21 0.10 1.91 0.32 0.07

DHS03-5

(continued on next page)

52.5 0.85 15.9 10.2 0.13 6.69 9.54 1.96 0.50 0.17 1.46 99.9 0.64 60.4 1.33 9.90 0.41 36.4 284 78.1 57.3 42.7 119 60.3 16.0 1.38 20.6 330 17.9 58.2 2.22 0.56 147 6.78 14.3 2.02 9.41 2.57 0.83 2.76 0.46 2.99 0.63 1.79 0.27 1.64 0.24 1.52 0.20 2.56 3.03 0.49

DHS03-4

W. Ao, et al.

Precambrian Research 333 (2019) 105442

1.02 47.9 2.99

δEu ∑REE (La/Yb)n

74.8 0.20 12.7 1.96 0.03 0.20 0.42 3.42 4.67 0.04 1.15 99.6 2.06 19.2 1.11 4.79 2.34 2.49 7.37 4.16 141 2.17 3.02 50.5 19.3 1.65 85.2 42.5 64.2 266 9.97 1.63 327 63.7 73.4 17.4 70.9 14.5 0.93 13.1 1.97 11.5 2.30 6.43 0.94

SiO2 TiO2 Al2O3 Fe2O3T MnO MgO CaO Na2O K2O P2O5 LOI TOTAL δ Mg# A/CNK Li Be Sc V Cr Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm

74.6 0.21 12.6 1.97 0.03 0.22 0.44 3.34 4.78 0.05 1.31 99.6 2.09 20.7 1.10 5.03 2.05 3.62 7.24 4.92 133 3.21 3.55 51.7 19.7 1.59 87.6 47.2 64.5 243 10.1 1.17 361 63.2 89.2 17.0 70.0 14.4 0.96 13.1 1.94 11.2 2.21 6.10 0.87

1.01 66.1 2.68

75.0 0.19 12.8 1.79 0.02 0.20 0.37 3.43 4.76 0.04 0.95 99.5 2.10 20.7 1.11 4.94 1.85 3.19 6.51 4.80 153 2.19 2.78 42.0 19.2 1.57 90.0 43.6 60.6 238 10.0 1.17 351 61.1 80.7 15.6 62.3 12.3 0.84 11.3 1.72 10.2 2.05 5.78 0.85

XSB-3

XSB-1

Sample no.

XSB-2

Hongmiao potassic granite

Rock type

0.93 56.6 2.39

DHS12-1

DHS11-1

Sample no.

DHS11-2

Dahanshan hornblende gabbro

Rock type

Table 2 (continued)

74.6 0.19 12.9 1.84 0.02 0.20 0.37 3.44 4.88 0.04 1.01 99.5 2.19 20.2 1.11 5.26 1.56 3.40 7.18 3.73 121 1.72 2.63 41.4 19.4 1.49 88.2 44.2 47.1 279 9.06 0.75 381 45.9 89.5 12.0 48.6 10.1 0.74 9.07 1.41 8.48 1.68 4.82 0.71

XSB-4

1.04 54.5 2.18

74.2 0.21 13.4 1.68 0.03 0.16 0.25 3.30 5.28 0.03 1.10 99.6 2.36 18.2 1.15 6.57 1.62 3.50 8.28 6.92 130 3.24 4.70 64.6 21.4 1.62 99.7 40.9 52.0 307 11.5 1.02 399 70.6 126 16.9 65.1 11.3 0.76 9.66 1.40 8.33 1.68 4.84 0.71

XSB-5

DHS12-2

74.8 0.19 12.8 1.86 0.02 0.18 0.33 3.17 4.99 0.02 1.21 99.5 2.10 18.4 1.14 3.14 1.58 2.32 7.01 4.22 210 1.90 3.18 43.5 17.7 1.39 89.9 41.7 28.4 249 6.29 1.23 367 34.5 74.0 8.11 32.4 6.25 0.56 5.65 0.80 4.64 0.94 2.65 0.39

XSB-6

1.03 54.8 2.09

DHS12-3

74.6 0.17 12.7 1.77 0.02 0.19 0.32 3.45 4.84 0.03 1.96 100.1 2.17 20.0 1.10 4.39 1.83 3.08 6.62 9.33 128 4.88 2.46 41.2 19.3 1.53 91.4 43.8 34.9 232 9.96 1.21 371 47.2 90.5 12.8 50.6 9.60 0.65 7.99 1.12 6.46 1.27 3.64 0.56

XSB-7

1.03 39.5 2.26

DHS02-1

77.5 0.11 11.7 1.62 0.03 0.09 0.32 3.29 5.02 < 0.01 0.55 100.2 2.00 11.5 1.02 3.23 1.06 1.48 0.54 2.12 55.3 2.18 1.74 54.0 18.2 1.61 69.9 4.37 29.3 271 6.70 0.84 26.1 73.4 159 18.0 69.5 12.1 0.25 9.05 1.15 6.14 1.18 3.33 0.49

HN-3–1

1.06 43.4 2.08

DHS02-2

77.3 0.09 11.5 1.44 0.03 0.09 0.31 3.30 5.00 < 0.01 0.52 99.6 2.01 12.7 1.01 3.11 1.02 1.51 0.50 3.05 54.8 3.10 2.10 50.0 18.6 1.57 72.4 4.35 28.4 237 6.36 0.86 28.0 60.6 125 14.8 58.2 10.4 0.25 7.95 1.07 5.91 1.12 3.20 0.48

HN-3–2

1.05 47.2 1.95

DHS02-3 1.04 47.2 1.96

DHS02-4

77.2 0.10 11.6 1.57 0.04 0.09 0.37 3.54 4.75 < 0.01 0.51 99.7 2.01 11.8 1.00 3.41 1.42 1.73 0.62 1.48 58.6 1.76 2.68 57.5 19.8 1.77 68.6 6.79 32.3 294 7.10 0.79 25.4 80.8 180 19.4 75.0 13.0 0.26 9.84 1.26 6.71 1.28 3.70 0.56

HN-3–3

Dahanshan hypersthene-hornblende gabbro

77.9 0.07 11.6 1.25 0.03 0.08 0.32 3.52 4.71 < 0.01 0.44 99.9 1.94 13.0 1.01 2.96 1.19 1.31 0.48 2.78 48.4 2.56 2.85 45.1 17.6 1.48 66.4 5.41 23.8 206 5.41 0.62 25.1 55.2 119 13.4 51.0 8.90 0.21 6.84 0.87 4.75 0.92 2.70 0.40

HN-3–4

1.08 34.4 2.11

DHS02-5

77.3 0.13 11.7 1.38 0.01 0.06 0.19 2.93 5.69 < 0.01 0.42 99.7 2.17 9.2 1.03 1.40 0.80 0.56 2.38 3.97 49.6 2.71 1.44 32.6 15.9 1.26 75.0 5.92 11.0 331 2.78 1.26 37.7 41.4 141 11.3 42.1 6.98 0.22 4.57 0.49 2.49 0.46 1.42 0.22

HN-3–5

1.08 34.4 2.18

DHS03-1

77.7 0.12 11.8 1.35 0.01 0.06 0.15 3.07 5.75 < 0.01 0.42 100.5 2.24 9.4 1.02 2.12 1.01 0.61 2.54 5.58 50.3 3.54 2.37 34.3 17.3 1.35 80.6 6.34 12.8 285 3.50 1.26 41.1 36.9 148 10.4 39.0 6.54 0.20 4.44 0.50 2.63 0.51 1.70 0.28

HN-3–6

1.11 34.3 2.11

DHS03-2 0.95 46.7 2.78

DHS03-4

1.06 36.9 2.27

DHS03-5

67.2 0.58 15.1 3.97 0.09 1.17 3.07 4.26 3.06 0.17 1.65 100.4 2.21 40.7 0.95 10.0 1.56 9.16 49.4 7.22 95.8 6.06 6.50 61.4 17.7 1.23 69.8 235 27.3 236 9.98 1.55 830 36.7 71.2 7.86 29.6 5.56 1.36 5.09 0.76 4.53 0.91 2.65 0.39

GQ-1

9

(continued on next page)

69.8 0.37 15.2 3.97 0.09 0.45 2.23 4.92 2.45 0.10 0.52 100.1 2.03 20.9 1.03 8.47 1.22 8.22 26.5 16.1 165 12.5 2.34 62.2 19.0 1.51 34.1 280 24.9 497 4.67 1.12 1664 90.1 188 20.6 84.2 13.8 2.85 9.97 1.07 5.16 0.89 2.45 0.38

GQ-2

Xishenba trondhjemitic biotite granite

1.03 50.1 2.04

DHS03-3

W. Ao, et al.

Precambrian Research 333 (2019) 105442

5.69 0.88 7.11 0.79 12.9 11.1 2.81 0.21 284 7.54 2.88

Yb Lu Hf Ta Pb Th U δEu ∑REE (La/Yb)n 10000Ga/Al

69.6 0.32 15.2 3.69 0.08 0.42 2.13 4.79 3.10 0.09 0.18 99.6 2.34 21.0 1.00 7.92 1.17 7.75 24.0 2.83 102 1.24 2.52 57.4 19.2 1.64 38.5 284 24.7 417 4.52 1.08 2224 110 242 26.9 107

SiO2 TiO2 Al2O3 Fe2O3T MnO MgO CaO Na2O K2O P2O5 LOI TOTAL δ Mg# A/CNK Li Be Sc V Cr Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd

70.0 0.49 15.4 2.96 0.13 0.78 2.31 5.12 2.13 0.13 0.56 100.0 1.95 38.0 1.03 15.9 2.54 8.29 15.3 6.68 175 3.42 14.0 74.4 19.2 1.53 66.5 267 79.7 348 15.5 2.60 642 28.1 57.0 6.95 28.9

GQ-4

GQ-3

Sample no.

4.42 0.69 7.13 0.63 11.3 9.30 1.50 0.24 238 7.00 2.84

Xishenba trondhjemitic biotite granite

5.21 0.80 6.26 0.84 10.8 9.30 2.24 0.22 271 7.91 2.85

XSB-4

Rock type

5.24 0.79 6.14 0.79 12.1 9.18 2.34 0.21 296 8.14 2.94

XSB-3

XSB-1

Sample no.

XSB-2

Hongmiao potassic granite

Rock type

Table 2 (continued)

4.41 0.68 8.01 1.02 13.1 12.2 1.76 0.22 322 10.8 3.03

XSB-5

69.1 0.56 15.5 3.47 0.15 0.92 2.37 5.19 2.14 0.16 0.45 100.1 2.06 38.2 1.02 19.0 2.64 9.48 19.7 3.38 99.4 1.49 11.9 86.9 20.3 1.58 71.9 267 79.2 414 18.0 2.96 602 33.9 68.7 8.38 34.5

GQ-5

2.46 0.39 6.24 0.32 11.9 9.20 2.10 0.29 174 9.44 2.63

XSB-6 3.59 0.56 6.14 0.88 10.9 11.6 1.48 0.23 237 8.86 2.89

XSB-7

72.0 0.30 15.0 1.94 0.07 0.64 2.02 5.34 1.70 0.09 0.61 99.7 1.71 43.5 1.05 12.0 1.25 2.34 17.8 6.16 36.3 4.32 26.5 45.0 16.1 1.21 30.3 204 5.68 172 4.62 1.12 951 11.9 21.5 2.47 9.78

GQ-6

3.37 0.53 6.90 0.54 10.9 9.03 1.11 0.07 358 14.7 2.95

HN-3–1 3.17 0.51 6.02 0.48 10.6 7.25 0.96 0.09 293 12.9 3.04

HN-3–2

71.9 0.37 14.8 2.48 0.08 0.71 2.34 5.51 1.24 0.08 0.64 100.2 1.58 40.0 1.01 12.4 1.04 4.02 23.8 5.11 40.5 3.92 18.1 53.7 17.1 1.16 24.8 246 13.7 235 4.87 0.82 827 31.0 53.3 5.83 22.4

GQ-7

3.86 0.62 7.37 0.55 10.7 9.01 1.03 0.07 396 14.1 3.22

HN-3–3 2.76 0.45 5.35 0.43 12.3 6.50 0.82 0.08 268 13.5 2.89

71.3 0.32 15.2 2.18 0.08 0.65 2.04 5.45 1.86 0.10 0.57 99.7 1.89 41.0 1.04 11.5 1.26 2.42 19.8 5.19 37.6 3.76 6.19 46.5 16.3 1.22 32.9 207 6.24 174 4.80 1.20 1049 13.0 25.2 2.85 11.5

GQ-8

HN-3–4 1.52 0.26 8.25 0.44 10.1 10.2 1.26 0.12 254 18.3 2.58

HN-3–5

72.3 0.32 14.4 2.23 0.07 0.74 2.11 5.22 1.43 0.07 0.64 99.5 1.51 43.6 1.03 13.0 1.28 3.65 22.8 5.00 63.7 4.69 6.10 48.7 16.5 1.22 27.4 237 14.2 204 5.10 1.44 754 17.0 32.6 3.69 14.6

GQ-9

2.10 0.35 7.32 0.65 11.0 10.5 1.51 0.11 254 11.8 2.77

HN-3–6 2.54 0.39 5.69 0.64 12.5 7.96 1.27 0.78 169 9.76

GQ-1

71.4 0.31 15.3 2.16 0.08 0.68 2.04 5.48 1.86 0.10 0.61 100.0 1.90 42.3 1.04 12.2 1.28 2.50 20.1 5.19 40.1 4.04 4.44 48.6 16.5 1.22 33.7 206 6.27 200 5.04 1.20 1032 12.5 23.6 2.70 10.7

GQ-10

10

72.5 0.38 14.8 2.55 0.08 0.72 2.32 5.46 1.20 0.08 0.46 100.5 1.51 39.7 1.02 12.1 1.04 3.92 25.3 2.98 48.6 2.81 11.0 54.0 16.8 1.13 24.5 242 13.0 230 4.98 0.81 788 23.8 43.3 4.67 18.4

GQ-11

(continued on next page)

3.06 0.51 10.8 0.49 13.3 25.0 1.09 0.74 423 19.9

GQ-2

Xishenba trondhjemitic biotite granite

W. Ao, et al.

Precambrian Research 333 (2019) 105442

Precambrian Research 333 (2019) 105442

5.2. Zircon U-Pb dating results

3.26 1.43 2.97 0.40 2.35 0.47 1.28 0.19 1.26 0.20 5.21 0.36 7.38 2.75 0.35 1.40 104 12.8

GQ-11

W. Ao, et al.

1.86 1.23 1.78 0.23 1.18 0.23 0.65 0.11 1.17 0.22 4.60 0.41 8.55 0.99 0.46 2.07 58.2 7.21 2.00 1.26 1.87 0.24 1.25 0.23 0.65 0.11 1.07 0.21 3.95 0.41 8.73 1.06 0.43 1.99 61.5 8.25 3.75 1.45 3.30 0.44 2.52 0.49 1.36 0.20 1.29 0.20 5.32 0.33 7.55 3.44 0.35 1.26 128 16.2

2.73 1.25 2.57 0.38 2.34 0.50 1.42 0.20 1.24 0.18 4.66 0.41 7.28 1.57 0.55 1.44 80.6 9.26

5.2.1. Dahanshan gabbro Zircon grains from the Dahanshan gabbro are transparent, colorless and subhedral-euhedral stubby crystals, showing lengths and width/ length ratios of 100–200 um and 1:3–1:1, respectively (Fig. 7a, b and c). Their CL images display apparent sector zonings (Fig. 7a, b and c). Zircon trace element compositions reveal that they have variable Th and U contents of 8–175 ppm and 20–216 ppm, respectively, corresponding to Th/U ratios of 0.46–1.19 (Supplementary Table 1), indicative of a typical magmatic origin (Belousova et al., 2002; Hoskin and Schaltegger, 2003). A total of twenty-two analyses were conducted on zircons from sample DHS03, yielding 206Pb/238U ages from 751 ± 12 to 807 ± 9 Ma, corresponding to a weighted mean 206 Pb/238U age of 779 ± 6 Ma (MSWD = 1.8) (Fig. 8a). The 206 Pb/238U ages for twenty-five analyzed spots of sample DHS11 range from 761 ± 20 to 803 ± 13 Ma, corresponding to a weighted mean 206 Pb/238U age of 792 ± 4 Ma (MSWD = 2.0) (Fig. 8b). Twenty-three analyses on zircons from sample DHS12 have 206Pb/238U ages varying from 773 ± 13 to 811 ± 14 Ma, with a weighted mean 206Pb/238U age of 793 ± 4 Ma (MSWD = 1.8) (Fig. 8c). Thus, the crystallization age of the Dahanshan gabbro could be constrained at ca. 790–780 Ma.

5.2.2. Hongmiao potassic granite Zircon grains from Hongmiao potassic granite samples (XSB and NH-1) show similar morphological feature and internal structure. They are transparent, colorless and euhedral prismatic crystals, with lengths and aspect ratios of 90–120 um and 1:1–2:1, respectively, characterized by obvious oscillatory zoned structures (Fig. 7d and e). Totally twentythree analyses were performed on zircons from sample XSB. They have variable Th and U contents of 40–582 ppm and 66–659 ppm, respectively, corresponding to Th/U ratios of 0.29–0.97, suggestive of a typical magmatic origin (Belousova et al., 2002; Hoskin and Schaltegger, 2003). The 206Pb/238U ages of these analyzed spots range from 780 ± 19 to 812 ± 19 Ma (Supplementary Table 1), corresponding to a weighted mean 206Pb/238U age of 802 ± 4 Ma (MSWD = 0.47) (Fig. 8d). A total of twenty-five spots on zircons from sample NH-3 were analyzed. They have Th and U contents of 67–346 ppm and 158–458 ppm, respectively, corresponding to Th/U ratios of 0.42–0.80 (Supplementary Table 1). The 206Pb/238U ages for analytical spots range from 778 ± 10 to 801 ± 11 Ma, yielding a weighted mean 206 Pb/238U age of 791 ± 6 Ma (MSWD = 0.47) (Fig. 8e), which is identical with that of sample XSB within error. Thus, the crystallization age of the Hongmiao potassic granite can be restricted at ca. 802–791 Ma.

7.23 2.18 7.71 1.43 10.3 2.44 7.97 1.30 8.97 1.39 8.95 1.45 12.8 8.94 1.60 0.89 196 2.55 17.4 3.22 12.1 1.26 5.71 0.91 2.42 0.36 2.81 0.47 9.07 0.41 15.6 33.1 1.06 0.68 532 26.4 Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U δEu ∑REE (La/Yb)n

6.31 2.15 7.03 1.38 10.2 2.49 8.16 1.35 9.17 1.42 7.85 1.44 13.2 7.82 1.62 0.99 171 2.07

1.71 1.20 1.64 0.21 1.10 0.21 0.59 0.10 1.04 0.20 3.89 0.38 7.87 0.96 0.47 2.18 53.6 7.71

GQ-8 GQ-5 GQ-3 Sample no.

GQ-4

Xishenba trondhjemitic biotite granite Rock type

Table 2 (continued)

GQ-6

GQ-7

GQ-9

GQ-10

Three samples from the Dahanshan gabbro (DHS03, DHS11 and DHS12), two samples from the Hongmiao potassic granite (XSB and NH-3) and one sample from the Xishenba biotitegranite (GQ) were collected for LA-ICP MS zircon U-Pb dating. The dating results are listed in Supplementary Table 1 and shown in Figs. 7 and 8.

5.2.3. Xishenba biotite granite Zircon grains from Xishenba biotite granite sample (GQ) are euhedral and prismatic, with their lengths and width/length ratios ranging from 60 to 130 um and 2:3 to 1:1, respectively (Fig. 7f). Their CL images show apparent oscillatory zonings, with Th and U contents and Th/U ratios of 127–435 ppm, 175–503 ppm and 0.40–1.03, respectively (Supplementary Table 1), implying a magmatic origin (Belousova et al., 2002; Hoskin and Schaltegger, 2003). Totally twenty-one analytical spots yield 206Pb/238U ages from 868 ± 11 to 898 ± 12 Ma, correspongding to a weighted mean 206Pb/238U age of 887 ± 7 Ma (MSWD = 0.48) (Fig. 8f). The age of 887 ± 7 Ma is interpreted as the crystallization age of the Xishenba biotite granite. 11

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 5. Geochemical discrimination diagrams of studied samples: (a) Na2O + K2O vs. SiO2 (after Irvine and Baragar, 1971; LeBas et al., 1986); (b) (Na2O + K2O)Fe2O3T-MgO triangular diagram (after Irvine and Baragar, 1971); (c) Fe2O3T/MgO vs. SiO2 diagram (after Miyashiro, 1974); (d) A/NK vs. A/CNK diagram (after Maniar and Piccoli, 1989); (e) Na2O + K2O-CaO vs. SiO2 (after Frost et al., 2001); and (f) An-Ab-Or riangular diagram (after O'Connor, 1965).

DHS02-3 has 176Lu/177Hf and 176Hf/177Hf ratios of 0.027765 and 0.282938, respectively. Sample DHS03-4 has 176Lu/177Hf ratio of 0.022954 and 176Hf/177Hf ratio of 0.282821. Sample DHS11-1 has slightly lower 176Lu/177Hf of 0.017324 and 176Hf/177Hf ratios of 0.282892. Sample DHS12-2 has 176Lu/177Hf and 176Hf/177Hf ratios of

5.3. Whole-rock Hf isotope compositions of the Dahanshan gabbro Four representative samples (DHS02-3, DHS03-4, DHS11-1 and DHS12-2) of the Dahanshan gabbro were collected for whole-rock Hf isotope analyses. The results are listed in Table 3 and Fig. 9a. Sample 12

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 6. Chondrite-normalized REE patterns and primitive mantle-normalized trace element diagrams of the gabbros and granitoids from the Hannan region. The chondrite, primitive mantle, OIB, E-MORB and N-MORB values are from Sun and McDonough (1989).

5.4.2. Hongmiao potassic granite Eighteen analyses performed on zircon grains from sample XSB have 176 Lu/177Hf and 176Hf/177Hf ratios varying from 0.000875 to 0.002372 and 0.281615 to 0.282191, respectively. Their age-corrected εHf(t) values range from −24.5 to −3.3 at 802 Ma (Fig. 9b), corresponding to single-stage zircon Hf model ages (TDM1) and two-stage zircon Hf model ages (TDM2) of 2377–1491 Ma and 2750–1689 Ma, respectively (Supplementary Table 2).

0.025503 and 0.282908, respectively. It can be summarized that the 176 Hf/177Hf ratios of the Dahanshan gabbro vary from 0.282821 to 0.282938. Their age-corrected εHf (t) values range from + 7.0 to + 12.6 (Fig. 9a), corresponding to single-stage zircon Hf model ages (TDM1) of 1548–902 Ma (Table 3). 5.4. Zircon Lu-Hf isotope compositions Representative samples of the Dahanshan gabbro (DHS03), Hongmiao potassic granite (XSB) and Xishenba trondhjemitic biotite granite (GQ) have been chosen for zircon Hf isotope analyses. In situ Hf isotope analyses were performed on the same or near the same spots on which the U–Pb dating have been conducted. The results are listed in Supplementary Table 2 and shown in Fig. 9b.

5.4.3. Xishenba biotite granite Sixteen analytical results were obtained from zircon grains from sample GQ. One analyzed spot has relatively high 176Lu/177Hf ratio of 0.000566 and 176Hf/177Hf ratio of 0.282246, corresponding to εHf (t) value of + 0.6 at 886 Ma. Other analyzed spots have 176Lu/177Hf and 176 Hf/177Hf ratios of 0.001008–0.002115 and 0.281703–0.282061 respectively, with age-corrected εHf(t) values varying from −19.4 to −6.2 (Fig. 9b), corresponding to single-stage zircon Hf model ages (TDM1) of 2224–1403 Ma and two-stage zircon Hf model ages (TDM2) of 2562–1901 Ma (Supplementary Table 2).

5.4.1. Dahanshan gabbro Twenty-two analyses conducted on zircons from sample DHS03 have 176Lu/177Hf and 176Hf/177Hf ratios of 0.000259–0.002060 and 0.282475–0.282604, respectively. Their age-corrected εHf(t) values range from + 6.5 to + 10.7 at 779 Ma (Fig. 9b), corresponding to single-stage zircon Hf model ages (TDM1) of 1084–921 Ma, and twostage zircon Hf model ages (TDM2) of 1175–962 Ma (Supplementary Table 2). 13

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 7. Representative zircon cathodoluminescence (CL) images of studied samples.

6. Discussion

enriched mantle source or the magma source must have been contaminated by continental crustal materials. For zircons from granitic rock, their TDM(Hf) ages are greatly older than crystallization ages because the magma source is generally crustal rocks; however, if their TDM(Hf) ages are approximate to the crystallization ages, the magma source must be juvenile crustal materials (Wu et al., 2007). Fractional crystallization associated with crustal contamination (AFC) plays an important role during magma evolution (DePaolo, 1981). It is generally accepted that the primary magma of basaltic melts has Ni and Cr concentrations higher than 400 ppm and 1000 ppm, respectively (Wilson, 1989), with Mg# value higher than 73 (Sharma, 1997). However, the Dahanshan gabbro samples have low and variable Cr and Ni concentrations of 59.2–275 ppm and 38.0–86.9 ppm, respectively, with relatively low Mg# values of 59.1–68.6 (Table 2), suggesting that they were crystallized from varying degree of evolved magmas which may have undergone fractionation of olivine and

6.1. Petrogenesis, magma source and tectonic setting of Dahanshan gabbro Samples of the Dahanshan gabbro have LOI of 0.51–1.46 wt%, suggesting that these rocks are fresh and the major and trace element concentrations can truthfully reflect the composition and characteristic of their original magma. Thus, the geochemical compositions can be used to distinguish their petrogenesis and magma source, as well as the tectonic setting. Combined analyses of zircon U-Pb-Hf isotopes play as a powerful tool in revealing magma source and crustal evolutionary history (e.g. Wu et al., 2007; Hawkesworth et al., 2010; Kröner et al., 2014). Generally, for zircons from basaltic rock, if their Hf model ages are the same as crystallization ages, the basaltic rock was derived from the depleted mantle source; otherwise, if their Hf model ages are older than crystallization ages, the basaltic rock was probably generated by 14

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 8. Zircon U-Pb concordia diagrams of gabbros and granitoids from the Hannan region.

Table 3 Whole-rock Hf isotopic data of Dahanshan gabbro. Sample No.

Lu (ppm)

Hf (ppm)

Age (Ma)

176

DHS02-3 DHS03-4 DHS11-1 DHS12-2

0.268862 0.244998 0.224420 0.305076

1.380491 1.521628 1.846815 1.705392

779

0.027765 0.022954 0.017324 0.025503

792 793

Lu/177Hf

176

Hf/177Hf

0.282938 0.282821 0.282892 0.282908

15

2σ

(176Hf/177Hf)

0.000004 0.000005 0.000004 0.000005

0.282531 0.282484 0.282634 0.282527

i

εHf(t)

TDM1(Ma)

8.71 7.04 12.63 8.87

1548 1469 902 1404

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 9. (a) Whole-rock Hf isotope compositions of Dahanshan gabbro and (b) Zircon Hf isotope compositions of gabbroic-granitoid rocks from the Hannan region.

and weak differentiation between LREE and HREE (Fig. 6a and b), which is similar as that of enriched mid-ocean ridge basalt (E-MORB) or island arc basalt (IAB), but distinctive from OIB and normal mid-ocean ridge basalt (N-MORB). The slightly negative Nb and Ta anomalies, as well as relatively low TiO2 contents (0.63–1.15 wt%) are comparable with subduction-related magmas (Fitton et al., 1988; Saunders et al., 1988). The N-MORB usually has higher Zr/Nb ratio (40) than E-MORB (10) and OIB (< 10) (Pearce and Norry, 1979). Most of the gabbro samples have intermediate Zr/Nb ratios (18.96–27.08), suggesting that they couldn’t have been derived from N-MORB- or/and E-MORB- and OIB-type lithospheric mantle. Additionally, these gabbro samples have Nb/Yb ratios of 0.99–1.40, higher than that of N-MORB (Nb/ Yb = 0.76), but lower than that of E-MORB (Nb/Yb = 3.5) and OIB (11.2) (Sun and McDonough, 1989), also indicating that they couldn’t have been derived from N-MORB- or/and E-MORB- and OIB-type lithospheric mantle. However, addition of metasomatized lithospheric mantle materials can result in higher Zr/Nb ratios and lower Nb/Yb ratios. Therefore, combined with the virable zircon and whole-rock Hf isitopes, we suggest that the Dahanshan gabbro was produced by magma mixing process of depleted mantle source (MORB-like) with metasomatized lithospheric mantle wedge, which generally happened in an island arc setting, or back-arc setting. Trace element ratios, together with fluid-mobile element ratios can be used to constrain the contribution of fluid/melts component to magma source. Previous investigations have shown that magmas derived from the sources modified by subducted slab-derived melts exhibit elevated Th and LREE contents compared to N-MORB, as well as high ratios of Th/La (> 0.2) and Th/Yb (> 2) (Woodhead et al., 2001). In addition, the subducted slab-derived melts contain high concentrations of Th and LREEs with distinctly elevated Th/Ce ratios (Hawkesworth et al., 1997; Johnson and Plank, 2000; Plank, 2005). Most of the Dahanshan gabbro samples display depletion of Th relative to Ba (Fig. 6b), and have variable Th/La (mostly of 0.04–0.12, average of 0.06) and Th/Yb (mostly of 0.10–0.55, average of 0.20) ratios, indicating insignificant addition of subducted slab-derived melts to magma source. By contrast, subducted slab-released fluids are generally characterized by high contents of Ba, Rb, Sr, U and Pb, leading to elevated Ba/Th, Ba/Nb, U/Th or Sr/Th ratios in the magma (Condomines et al., 1988; Hawkesworth et al., 1997; Johnson and Plank, 2000). The gabbro samples are featured by strong enrichment of slab-released fluid-mobilized trace element, having high ratios of Sr/Th (109–2010), Ba/Th (48.6–476.0) and Ba/Nb (33.95–84.70), but low ratios of Th/U (3.62–4.80) and Th/Ce (0.01–0.21) (Hawkesworth et al., 1997; Jiang et al., 2009). Diagrams of La/Sm versus Ba/Th and Th/Yb versus Sr/Nd (Fig. 11a and b) also demonstrate slab dehydration trend (Woodhead et al., 1998; Labanieh et al., 2012). Furthermore, mineral

pyroxene. The positive correlations of CaO with MgO (Fig. 10a) and Cr with Ni (Fig. 10g) indicate the fractionation of clinopyroxene. The positive correlations of Cr with MgO and Ni with MgO suggest fractionation of olivine and clinopyroxene (Fig. 10e and f). Most samples have homogeneous concentrations of Al2O3 (Fig. 10b) and without obvious Eu anomalies (Fig. 6a), indicating insignificant plagioclase fractionation. Relatively homogeneous concentrations of Fe2O3T (Fig. 10c), TiO2 (Fig. 10d) and V (Fig. 10h) indicate negligible fractionation of Fe-Ti oxides. Thus, the above geochemical features suggest that olivine and clinopyroxene are the principal fractionating minerals during magma crystallization process. Crustal contamination may also play an important role during magma upwelling process and it is always inevitable for mantle-derived melts during their ascent through continental crust or their evolution within a crustal magma chamber. Continental crust is rich in K2O, Na2O, Th-Zr-Hf and LILE, but depleted in Nb-Ta, TiO2 and P2O5. Therefore, crustal contamination may increase K2O, Na2O and LILE, but decrease P2O5 and TiO2 contents of the rock. Minor crustal contamination can lead to observably negative NbTa-Ti anomalies and positive Zr-Hf anomalies in the primitive mantlenormalized trace element pattern (Sun and McDonough, 1989; Zhao and Zhou, 2007a). Samples of the Dahanshan gabbro have relatively low contents of K2O and Na2O, TiO2 and P2O5 (Table 2), probably implying negligible crustal contamination. This also can be supported by slightly negative Nb-Ta-Ti and Zr-Hf anomalies (Fig. 6b). Besides, these gabbro samples have relatively low ratios of Th/Yb (0.10–1.84) and high ratios of Nb/Th (0.73–12.27), also suggesting insignificant crustal contamination. In summary, the magma of Dahanshan gabbro has experienced significant fractionation of olivine and clinopyroxene, but insignificant crustal contamination. Whole-rock samples of Dahanshan gabbro have positive εHf(t) values from +7.0 to +12.6 (Table 3), suggestive of a relatively depleted magma source. Zircons from sample of the Dahanhan gabbro have positive εHf(t) values from +6.5 to +10.7 (Supplementary Table 1) and display an evolutionary trend between the depleted mantle and chondrite (Fig. 9), also indicating that the primary magmas were possibly originated from a relatively depleted mantle source. However, the whole-rock and zircon samples have Hf model ages older than their crystallization ages (Table 3; Supplementary Table 1), suggesting addition of enriched components. As discussed before, crustal contamination is negligible during magma evolition of the gabbro. Thus, the enriched component is most likely associated with low-degree fluid/melt metasomatism. Generally, the primitive mantle-normalized trace element pattern of ocean island basalt (OIB) shows apparent enrichment of LREEs and HFSEs, with weakly positive Nb and Ta anomalies, and highly fractionated Zr/Hf ratios (Hollings, 2002). Samples of the Dahanshan gabbro exhibit slight enrichment of LILEs 16

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 10. Harker diagrams of the Dahanshan gabbro samples.

17

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 11. Discrimination diagrams of (a) Ba/Th vs. La/Sm (after Labanieh et al., 2012) and (b) Th/Yb vs. Sr/Nd (after Woodhead et al., 1998) of the Dahanshan gabbro samples.

of La/Sm versus Sm/Yb and Sm/Yb versus La/Sm, samples of the Dahanshan gabbro fall near the partial melting evolutionary trend of spinel-garnet lherzolite source and display moderate-high degree (20–30%) of partial melting (Fig. 12a and b), indicating a relatively moderate-deep mantle source, probably in the transition zone from garnet to spinel stability facies (~100 km; Xu et al., 2007). The relatively high degree of partial melting is in agreement with their geochemical feature of high contents of HFSEs contents and low ratios of [La/Yb]N. However, the Dahansahn gabbro samples have relatively low ratios of Rb/Sr (mostly < 0.1) and high ratios of Ba/Rb (mostly > 10), suggesting contribution of amphibole–bearing mantle source (Furman and Graham, 1999). This conclusion is also in accordance with the fact that the Dahanshan gabbro was produced by magma mixing process of depleted mantle source (MORB-like) with metasomatized lithospheric mantle wedge. The samples of Dahanshan gabbro have variable Th/Yb ratios (mostly of 0.10–0.55) and relatively low Nb/Yb ratios (mostly of 0.99–1.40), falling between N-MORB and E-MORB field along subduction enrichment array in the Nb/Yb versus Th/Yb distinguish diagram (Fig. 13a), with Nb and Th normalized by Yb in order to remove the effects of partial melting and fractional crystallization (Pearce and Peate, 1995). This suggests that the primary magma was generated by magma mixing of depleted mantle sources (MORB-like) and

assemblage of the Dahanshan gabbro, such as abundant of hornblende and anorthitic plagioclase, also imply that it was generated in waterrich environment. The crystallization temperature of Dahanshan hypersthene-hornblende gabbro (DHS03) can be constrained at 837–944 °C by utilizing Opx-Cpx thermometer (Our unpublished data), which is lower than crystallization temperature of normal basaltic magma (> 1200 °C) (Lee et al., 2009). Thus, we suppose that the subducted slab- dehydrated fluids contributed to magma source, which reduced the solidus temperature and caused the widespread melting of lithospheric mantle. This subducted slab- dehydrated fluids also contributed to metasomatism of lithospheric mantle. Partial melting degree of magma source of gabbros can be determined based on abundances and ratios of whole-rock REEs and HFSEs (Weaver, 1991; Zhao and Zhou, 2007a). Generally, Sm/Yb ratios of basaltic rocks are sensitive to source mineralogy (Genc and Tuysuz, 2010). Partial melting of a spinel lherzolite mantle source does not change Sm/Yb ratio but may decrease La/Sm ratios and Sm contents in melts because both Sm and Yb have similar partition coefficients (Aldanmaz et al., 2000). However, magmas generated by partial melting of garnet-lherzolite mantle source with garnet in residual could produce a more steeply sloping trend on the diagram of Sm/Yb versus Sm than that generated by partial melting of spinel lherzolite magma source (Zhao and Zhou, 2007a; and references therein). In the diagrams

Fig. 12. Discrimination diagrams of (a) Sm/Yb vs. Sm and (b) Sm/Yb vs. La/Sm of the Dahanshan gabbro samples (after Zhao and Zhou, 2007a; and references therein). 18

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 13. Tectonic discrimination diagrams of (a) Th/Yb vs. Nb/Yb (after Pearce, 2008); (b) Ti*100 vs. Zr (after Pearce, 1982); (c) V*1000 vs. Ti/1000 (after Shervais, 1982); (d) Zr/Y vs. Zr (after Pearce and Norry, 1979); (e) Hf-Th-Ta triangular diagram (after Wood, 1980); and (f) Ti/V vs. Zr (after Gribble et al., 1996) of the Dahanshan gabbro.

overlapping field of volcanic arc basalts (VAB) and MORB (Fig. 13b). In the Ti versus V diagram (Shervais, 1982), most of the samples plot from the overlapping field of VAB and MORB to the MORB field (Fig. 13c). Additionally, these gabbro samples display Zr/Nb ratios ranging from 19.0 to 43.4, similar as those generated in subduction-related arc

metasomatized lithospheric mantle wedge with subduction-related hydrous fluid inputted, which is in accordance with conclusions evidenced before. These gabbro samples have relatively low contents of TiO2 (0.63–1.15 wt%), as well as low ratios of Ti/V (16.1–22.4). In the Zr versus Ti diagram (Pearce, 1982), most of the samples plot in the 19

Precambrian Research 333 (2019) 105442

W. Ao, et al.

derived mafic igneous rocks (e.g. Dahanshan gabbro) in the study area, it seems that mafic magma might have contributed to the Hongmiao Atype granites. Nonetheless, this model is not acceptable. First, the volume of the Hongmiao A-type granite is over the mafic rocks and the intermediate rocks are relatively scarce, excluding a magma differentiation model (Frost and Frost, 2011). Furthermore, these A-type granite samples have negative εHf(t) values varying from −24.5 to −3.3, and mostly plot on 1.9–2.1 Ga crustal evolutionary line (Fig. 9b), indicative of continental crustal magma source, rather than mantlecrustal magma mixing source. Additionally, high Rb/Sr and Rb/Ba ratios, as well as low Al2O3 + Fe2O3T + MgO + TiO2, MgO, Cr and Ni contents but relatively high Al2O3/(Fe2O3T + MgO + TiO2) ratios also support the above conclusion. The Hongmiao A-type granites display relatively high and flat HREE patterns, have low ratios of Sr/Y (0.15–1.47), Gd/Yb (2.05–3.00) and Dy/Yb (1.25–2.02), and low CaO contents and high Ga/Al ratios, and show pronounced negative Eu and Sr anomalies, suggesting a lower pressure of partial melting, shiefly with plagioclase and amphibole, rather than garnet in the residual. The low MgO and high Fe/Mg ratios, as well as significantly negative Ti anomalies indicate the orthopyroxene and rutile in the residual (Jia, 2009). Thus, the Hongmiao A-type granite was generated by partial melting of pre-existing crustal rocks at a relatively shallow crustal depth. A-type granites do not affirmatively indicate anorogenic or rifting environment. Eby (1992) has subdivided A-type granites into two groups. The A1-type is characterized by element ratios consistent with those of oceanic-island basalts (OIB), representing differentiates of magmas derived from OIB-like sources but emplaced in non-orogenic settings (e.g. continental rifts or during intra-plate magmatism). The A2-type is characterized by element ratios varying from those of continental crust to those of island-arc basalts (IAB), representing magmas derived from continental crust or underplated mafic crust that has been through a cycle of continent–continent collision or island-arc magmatism (Eby, 1992). In the Nb-Y-Ce triangular diagram (Eby, 1992), the Hongmiao A-type granite samples plot into A2-type granite field (Fig. 14d), indicating that the magmas of Hongmiao A-type granite were probably derived from an arc-related setting similar as post-collisional or post-orogenic extensional environment. Considering the tectonic setting of coeval mafic igneous rocks in this area, the Hongmiao A-type granites were possibly originated from partial melting of Archean-Paleoproterozoic crustal materials in a subduction-related back-arc extensional setting. Meanwhile, the adjacent Huangguan and Tiechuanshan plutons also exhibit features of A-type granites, suggesting an important extensional event during 774–800 Ma (Dong et al., 2012; Luo et al., 2018).

system or back-arc system (Pearce and Peate, 1995). In the Zr versus Zr/Y diagram (Meschede, 1986), most of the samples plot into the fields from IAB to MORB fields (Fig. 13d). In the Hf/3-Th-Ta triangle diagram (Wood, 1980), the samples mostly plot in the fields from VAB, IAT to MORB (Fig. 13e). However, in the Zr versus Ti/V discrimination diagram (Gribble et al. 1996), most samples plot in superimposed field of IAB and back-arc basin basalt (BABB) (Fig. 13f). Generally, arc gabbros have Nb/Th values lower than 7.5, whereas non-arc gabbros have Nb/ Th values higher than 8.5 (Jenner et al. 1991). The Dahanshan gabbro has variable Nb/Th values (0.73–12.27), showing transitional features. The phenomenon of hybrid mixing between MORB-like and arc-like signatures is generally acknowledged being unique in fore-arc or backarc basin tectonic regime (Taylor and Martinez, 2003; Teklay, 2006). All these evidences probably suggest an extensional setting related to slab-subduction. Thus, considering the field distribution of this rock type, we suggest that the Dahanshan gabbroic pluton was probably generated in a back-arc tectonic setting. Their arc-type geochemical features were inherited from the strong subduction input at the initiation of back-arc rifting. It can be concluded that the Dahanshan gabbro was produced by magma mixing process of depleted mantle source (MORB-like) with metasomatized lithospheric mantle wedge that metasomatized by slabderived aqueous fluids in a back-arc system, and the Dahanshan gabbro has experienced significant fractionation of olivine and clinopyroxene, but insignificant crustal contamination during magma evolution. 6.2. Petrogenesis, magma source and tectonic setting of Hongmiao potassic granite Granitic rocks play an important role in evaluating the evolution of continental crust, especially when they outcrop together with coeval mafic rocks. In addition, their geochemical composition, together with zircon Hf isotopes can be used to constrain the magma source and tectonic setting. According to the protolith nature, the granitic rocks are generally devided into I-, S-, A- and M−types (Whalen et al. 1987; Barbarin, 1999; Frost et al. 2001; Chappell and White 2001). The Hongmiao potassic granite samples (XSB and NH-3) have high contents of SiO2, K2O and Fe2O3T, but low contents of CaO, P2O5 and MgO, cooresponding to high ratios of K2O/Na2O, Fe2O3T/ MgO and Ga/Al. Besides, they show strong negative Eu anomalies (Fig. 6c), and display depletions in Ba, Sr and Ti (Fig. 6d). These geochemical features are typical characteristics of A-type granites (Frost and Frost, 2011). The crystallization temperature of the Hongmiao potassic granite was constrained at 812–860 °C using zircon saturation geothermometer, consistent with that of A-type granites. The higher Zr + Nb + Ce + Y values (354–513 ppm) are also comparable with A-type granites and different from highly fractionated granites (Whalen et al., 1987). Thus, the Hongmiao potassic granite is geochemically of A-type granite. This is manifest in their exclusive distribution into the A-type field on the discrimination diagrams of Whalen et al. (1987) (Fig. 14a, b and c). A-type granite has long been discussed since it was referred to the initial concept of “alkaline”, “anhydrous” and “anorogenic”. Several models have been proposed to explain the petrogenesis of A-type granite, including (1) extremely high differentiation of mantle-derived tholeiitic or alkaline basaltic magma precursor (Turner et al., 1992; Mushkin et al., 2003); (2) low degree partial melting of crustal rocks (Whalen et al., 1987; Bonin, 2007); and (3) combination of crustal and mantle sources, in the form either crustal assimilation and fractional crystallization of mantle-derived magmas, or magma mixing of mantlederived melts and crustal magmas (Kemp et al., 2005). Meanwhile, it is widely accepted that A-type granites are produced in an extensional tectonic setting (Whalen et al., 1987; Turner et al., 1992). Furthermore, it has been suggested that aluminous A-type granites are usually formed in a post-orogenic environment, whereas the alkaline and peralkaline A-type granites are mainly produced in a within-plate anorogenic setting (Creaser et al., 1991; Rajesh, 2000). Considering the coeval mantle-

6.3. Petrogenesis, magma source and tectonic setting of Xishenba biotite granite Samples of the Xishenba biotite granite are geochemically trondhjemite (Fig. 5f), with calc-alkaline I-type granite signatures, characterized by high contents of SiO2 (67.2–72.5 wt%), Na2O (4.26–5.51 wt%) and Al2O3 (14.4–15.5 wt%), but low contents of K2O (1.20–3.10 wt%) and MgO (0.42–1.17 wt%) (Table 2). On the other hand, they have relatively low and variable ratios of [La/Yb]N (2.07–26.41) and Sr/Y (3.35–35.9), inconsistent with the adakites and TTGs, but comparable with modern arc rocks (Petford and Atherton, 1996; Defant and Drummond, 1990). This also can be evidenced by relatively low contents of MgO (0.42–1.17 wt%), Cr (2.83–16.1 ppm) and Ni (1.24–12.5 ppm), as well as low Mg# values (20.9–43.6) compared with typical adakites. Thus, the Xishenba biotite granite belongs to typical arc granitoid rocks. Calc-alkaline I-type granite is generally considered to be produced by 1) mixing of mantle- and crust-derived magmas (Barbarin, 2005; Yang et al., 2007); 2) fractional crystallization of mantle derived basaltic magma (Barth et al., 1995); or 3) partial melting of metabasaltic 20

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 14. Discrimination diagrams of (a) Fe2O3T/MgO vs. (Zr + Nb + Ce + Y), (b) (Na2O + K2O)/CaO vs. (Zr + Nb + Ce + Y) and (c) 10000*Ga/Al vs. (Zr + Nb + Ce + Y) (after Whalen et al., 1987); and (d) Nb-Y-Ce (after Eby, 1992) of the Hongmiao A-type granites. The geochemical data of ca. 774 Ma Huanguan and ca. 782 Ma Tiechuanshan plutons were cited from Luo et al. (2018) and those of ca. 777 Ma Huanguan pluton were cited from Dong et al. (2012).

relatively flat HREE patterns indicate that mineral assemblage of amphibole and garnet, rather than the garnet is the major component in the residual. The variable and relatively high Sr/Y ratios (3.34–35.9) and low Gd/Yb (0.76–4.30) and Dy/Yb (1.00–2.03) ratios also provide evidence for this conclusion. Negative Nb, Ta and Ti anomalies, together with variable Nb/Ta (9.58–15.62), Zr/Hf (41.47–46.24) and Zr/ Sm (23.93–108.32) ratios, probably imply rutile in the residual. Thus, these geochemical features suggest that partial melting of magma source has occurred at a relative deep-moderate crustal depth, with mineral assemblage of garnet amphibolite-facies in the residual. This kind of I-type granite can be produced by partial melting of (1) lower crust (Rapp and Watson, 1995; Rapp et al., 1999); (2) subducted oceanic crust (Martin et al., 2005; Moyen, 2009); and/or (3) delaminated lower crust. The Xishenba biotite granite samples are characterized by depletion of HFSEs (e.g. Nb, Ta and Ti), and enrichment of LILEs (e.g. Rb, Ba, Th and Pb), similar as volcanic arc granites. In addition, they have relatively low Yb and Ta contents (Fig. 15a), as well as low Y + Nb and Rb contents (Fig. 15b), also consistent with volcanic arc granites (Pearce et al., 1984). However, these samples show high SiO2 (67.2–72.5 wt%) contents but low-moderate Mg# values (21–44), as well as low Cr (2.83–16.1 ppm) and Ni (1.24–12.5 ppm) contents, similar as those of magmas derived by partial melting of thickened lower crust. Taking arc signatures into account, it is suggested that the Xishenba biotite granite was generated by partial melting of pre-existing thickened lower crust in an island arc setting. The geochemical data of cotemporary Tianpinghe and Nanjiang felsic plutons (Dong

rocks (Rapp et al., 1999). Samples of the Xishenba biotite granite have low ratios of Rb/Sr (0.10–0.30) and Rb/Ba (0.02–0.12), and relatively high contents of Al2O3 + Fe2O3T + MgO + TiO2 (17.7–20.9 wt%) but low ratios of Al2O3/(Fe2O3T + MgO + TiO2) (2.65–5.19), suggestive of magma produced by partial melting of basaltic rocks or amphibolite rocks. Zircon Hf isotopes reveal that zircon grains from the Xishenba biotite granite samples mostly have negative εHf(t) values ranging from −19.4 to −6.2, with TDM1 and TDM2 zircon Hf model ages of 2.22–1.68 Ga and from 2.56 to 1.90 Ga (Supplementary Table 2), indicating partial melting of pre-existing crust. Besides, the biotite grante samples have low MgO, Cr and Ni contents and Mg# values, similar as those of magmas generated by partial melting of thickened lower continental crust. Although some mafic or dioritic microgranular enclaves within the biotite granite pluton have been observed in the field, zircon Hf isotope compositions and whole-rock geochemical compositions do not support the hypotheses of mantle-crust magma mixing or fractional crystallization of mantle derived basaltic magma, which may generate variable and relatively high Mg# values (> 45), and high MgO, Cr and Ni contents, and negative to positive or positive εHf(t) values. The mafic enclaves can be interpreted as limited mafic magma injected into magmatic chamber but didn’t alter the geochemical composition of parent magma. These biotite granite samples display positive to negative Eu anomalies on chondrite-normalized RRE patterns, indicating that there was insignificant plagioclase in residual and the granite magma have experienced plagioclase fractional crystallization. The variable and 21

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 15. Tectonic discrimination diagrams of the Xishenba biotite granite. (a) Ta vs. Yb; and (b) Rb vs. (Y + Nb) (after Pearce et al., 1984). The geochemical data of ca. 860 Ma Tianpinghe pluton were cited from Luo et al., (2018) and those of ca. 840 Ma Nangjiang pluton were cited from Dong et al., (2012).

crustal evolution. In this paper, all available U-Pb-Hf isotopic data, as well as whole-rock Nd isotope data of the Hannan Complex have been summarized to provide evidence for crustal evolution of the northern margin of the Yangtze Block (Fig. 16; Supplementary Table 3). It is notable that the northern Hannan region (the Hannan massif), to the north of the Xishenba area, is characterized by gabbros formed at ca. 900–890 Ma, ca. 830–780 Ma and ca. 760–740 Ma, and diorites and Na-rich granites formed at ca. 950–860 Ma, 835–790 Ma and ca. 760–730 Ma, and potassic granite (especially A-type granite)-alkaline rocks formed at ca. 810–770 Ma and ca. 706 Ma (Fig. 16a). Zircons from

et al., 2012; Luo et al., 2018) are also included in the diagram (Fig. 15), indicating an island arc setting in the early evolutionary stage of the Hannan Complex.

6.4. Crustal evolution of the northern margin of the Yangtze Block during Neoproterozoic (ca. 950–706 Ma) As mentioned before, combined analyses on zircon U-Pb-Hf isotopes can be used to distinguish magma source, as well as crustal evolution. Analogously, whole-rock Nd isotope analyses can also be used to track

Fig. 16. Summary and comparison on formation age, zircon Hf compositions and whole-rock Nd isotopes of the Hannan Complex and the Micangshan Complex (Data from Ling et al., 2001, 2003, 2006; Zhou et al., 2002a, 2018; Zhao et al., 2006, 2010; Zhao and Zhou, 2008, 2009a,b; Xia et al., 2009; Liu et al., 2009; Cui et al., 2013; Li, 2010; Geng, 2010; Xu et al., 2011; Dong et al., 2011, 2012; Deng et al., 2013; Ao et al., 2014; Wang et al., 2016; Luo et al., 2018 and this study). 22

Precambrian Research 333 (2019) 105442

W. Ao, et al.

the ca. 830–780 Ma and ca. 760–730 Ma gabbros have positive εHf(t) values between the evolutionary trend of depleted mantle and chondrite, with some of them approaching depleted mantle trend. Zircon grains from ca. 835–730 Ma diorites and Na-rich granites have similar zircon Hf isotopes with those of ca. 830–730 Ma gabbros. However, zircons from the 887 Ma trondhjemitic biotite granite have negative εHf(t) values below chondrite. Zircons from the ca. 810–770 Ma potassic granites have negative or positive εHf(t) values (Fig. 16b). In addition, most of gabbro samples have positive εNd(t) values close to evolutionary trend of depleted mantle, while the granitoid rock samples mostly have positive εNd(t) values close to evolutionary trend of chondrite (Fig. 16c). All these data suggest a predominant crustal growth event, with small volume of pre-existing crustal materials reworked. The southern Hannan region (the Micangshan massif) is characterized by gabbros formed at ca. 880–850 Ma, ca. 825–810 Ma and ca. 770–750 Ma, and diorites and Na-rich granites crystallized at ca. 875–860 Ma, ca. 843–810 Ma and ca. 780–750 Ma, and potassic granite-alkaline rocks intruded at ca. 840–820 Ma, ca. 780 Ma and ca. 740 Ma (Fig. 16d). Zircon Hf isotopes reveal that zircons from the oldest gabbros have positive εNd(t) values between the evolutionary trend of depleted mantle and chondrite or close to evolutionary trend of chondrite, suggestive of crustal growth event, however, with recycling of minor amount of crustal materials. Zircons from ca. 820–810 Ma gabbros have variable and mostly positive εHf(t) values, indicating dominant crustal growth, accompanied by reworking of minor amount of crustal materials. Zircons from ca. 770–750 Ma gabbros have positive εHf(t) values close to evolutionary array of depleted mantle (Fig. 16e), implying significant crustal growth. Zircons from ca. 875–860 Ma diorites and Na-rich granites have negative to positive εHf(t) values but negative whole-rock εNd(t) values (Fig. 16f), indicating significant crustal reworking event. The ca. 843–810 Ma diorites and Na-rich granites also have negative εNd(t) values. Zircons from ca. 780–750 Ma diorites and Na-rich granites have mostly positive εHf(t) values (Fig. 16e), in consistent with positive whole-rock εNd(t) values. The potassic granite-alkaline rocks have positive zircon εHf(t) values (Fig. 16f), but negative or negative to positive εNd(t) values, obviously indicating crustal reworking. The Neoproterozoic volcanic rocks of the Xixiang Group (ca. 950–730 Ma) also present positive εNd(t) values, having TDM(Nd) ages identical with those of coeval gabbros (Ling et al., 2003). Thus, it can be concluded that the Neoproterozoic tectonic events in the northern margin of the Yangtze Block predominantly represent crustal growth processes, accompanied by certain degree of reworking of pre-existing crustal materials.

more complicated spatial-temporal variation, without a definite lithological-spatial-temporal relationship (Gao et al., 1990; Zhou et al., 2002a, 2002b; Ling et al., 2003; Zhao and Zhou, 2008; Dong et al., 2012; Ao et al 2014; Luo et al., 2018; Zhao et al., 2008). Neoproterozoic magmatic complex in the northwestern margin of the Yangtze Block has ever been considered as evidence for long-lived subduction system in Neoproterozoic, known as the Panxi-Hannan arc (Zhou et al., 2002b). But the tectonic settings of those ultramafic–mafic and felsic plutons of the Hannan Complex have long been debated. They were interpreted to be formed in continental rift or island arc settings (Zhou et al., 2002a, 2002b; Ling et al., 2003; Zhao and Zhou, 2008; Dong et al., 2012; Bader et al., 2013; Zhao et al., 2008, 2018). Thus, it is very important to take combined geochronological, petrological and geochemical data into account to clarify tectonic evolutionary history of the northern margin of the Yangtze Block. According to previously published data, the Xixiang Group comprises the oldest Neoproterozoic volcanic rocks formed at ca. 950–890 Ma in the Hannan region. These rocks are predominantly of low-Ti tholeiitic basalts, dacites and rhyolites characterized by island arc signatures, suggesting that subduction of oceanic lithosphere beneath the northern margin of the Yangtze Block probably occurred at ca. 950 Ma (Ling et al. 2003). Consistent with the oldest volcanic rocks of the Xixiang Group, the gabbros exposed in the Liushudian area has formation age of ca. 900 Ma and shows typical arc signatures (Dong et al., 2011; Zhou et al., 2018a,b). During ca. 890–840 Ma, large volumes of gabbros, as well as calc-alkaline granitoids, including diorites, granodiorites and Na-rich granites were mostly produced in the Tianpinghe-Beiba-Shatan-Wangcang (Daheba)-Zhenyuan areas in the southwestern Xixiang Group (Ling et al., 2006; Wang et al., 2016; Dong et al., 2012; Luo et al., 2018). They are featured by continental arc signatures and were possibly produced in a continental arc tectonic setting (Ling et al., 2006; Dong et al., 2012). The granitoid rocks have extremely low contents of MgO, Cr and Ni, indicating that they were chiefly produced by partial melting of pre-existing continental crust. Simultaneously, small volume of trondhjemitic biotite granites was produced in the Xishenba area at ca. 887 Ma (this study). As metioned before, this kind of rock has negative zircon εHf(t) values (Fig. 9 and Fig. 16b) and was generated by partial melting of pre-existing thickened lower crust in a continental arc setting. Thus, there was a continuous plate subduction process during ca. 950–840 Ma in the northern margin of the Yangtze Block (Fig. 17a and b). Small volume of contemporary alkaline complex developed in the southernmost margin of the Hannan region (e.g. Pinghe alkaline complex), possibably suggesting local extension during subduction. The occurrence of ca. 817 Ma bimodal volcanic rocks in the Tiechuanshan area, chiefly composed of basalt and dacite-rhyolite, indicate an intra-continental (Ling et al., 2003) or a back-arc setting (Luo et al., 2018). The ca. 838 Ma syenogranites in the Guangwushan (Daheba) area and the ca. 829 Ma A-type granites in the Xihe area suggest an extensional environment (Dong et al., 2012). The ca. 782 Ma alkaline rocks in the Tiechuanshan area and ca. 780–774 Ma A-type granites in the Huangguan area also manifest an extensional setting (Zhao et al., 2006; Dong et al., 2012; Luo et al., 2018). Geochemical and geochronological study on the Dahanshan gabbro and the Hongmiao A-type granite suggest that they were produced in a subduction-related backarc extensional environment at ca. 802–779 Ma (this study). The Wangjiangshan gabbro, showing typical arc signatures, were produced through two stages of ca. 830–800 Ma and ca. 785 Ma, and have been suggested to be formed in a subduction-related environment (Ling et al., 2001; Zhou et al., 2002a; Zhao and Zhou, 2009a; Dong et al., 2012; Wang et al., 2016). The ca. 785–780 Ma Bijigou gabbro was also formed in a subduction-related arc setting (Zhao and Zhou, 2009a; Zhou et al., 2002a). Additionally, the ca. 823–770 Ma granitoid rocks of diorites, tonalites, trondhjemites and granodiorites distributed in the Mengzi-Taojiaba-Zushidian-Erliba-Wudumen-Wangjiangshan-Bijigou areas were suggested to be formed in a subduction-related island arc

6.5. Neoproterozoic (ca. 950–706 Ma) tectonic evolution of the northern margin of the Yangtze Block As mentioned before, the Neoproterozoic (ca. 950–706 Ma) magmatic rocks, namely the Hannan Complex, are well preserved in the northern margin of the Yangtze Block (Fig. 16a and d) (Zhou et al., 2002a, 2002b; Ling et al., 2003; Zhao and Zhou, 2009a,b; Dong et al., 2011, 2012; Ao et al., 2014; Luo et al., 2018; Zhou et al., 2018a,b). Traditionally, the formation process of these ultramafic–mafic and granitoid plutons were subdivided into three stages (Gao et al., 1990). The first stage generated gabbros and small amount of diorites represented by the Wangjiangshan, Bijigou, Dahanshan and Beiba plutons; the second stage is characterized by tonalites, trondhjemites and quartz diorites (TTG-like) such as the Wudumen, Erliba, Zushidian and Tianpinghe plutons; and the third stage predominantly produced potassic granites represented by the Xishenba, Xixiang and Huangguan plutons, together with some potassic granite-alkaline rocks distributed in the Micangshan area. It seems that different rock units generated during the above three stages display an evolutionary trend from basic to intermediate, and then to acidic rocks with increasing alkalinity. However, the detailed geochronological studies on these plutons show a 23

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Fig. 17. Tectonic evolutionary history of the northern margin of the Yangtze Block during Neoproterozoic.

crystallization age of ca. 765–718 Ma were suggested to be formed by partial melting of thickened continental crust (Zhao et al., 2006; Zhao and Zhou, 2008; Dong et al., 2012). The ca. 728 Ma trondhjemitic rock in the Zushidian area have inherited zircon U-Pb age of ca. 786 Ma, with low Mg# values and low contents of Cr and Ni, as well as positive εHf(t) values, implying that it might have been produced by partial melting of thickened lower continental crust of juvenile materials (Ao et al., 2014). The ca. 762–706 Ma potassic (A-type) granites in the

setting (Ling et al., 2006; Liu et al., 2009; Geng, 2010; Dong et al., 2011; Xu et al., 2011; Wang et al., 2016; Luo et al., 2018). Thus, considering spatial–temporal distribution of the above different types of rock units, the northern margin of the Yangtze Block was possibly in a subduction-related arc-back-arc setting during ca. 840–765 Ma, which might be caused by roll back of subducted oceanic slab southeastward beneath the Yangtze Block (Fig. 17c). The adakitic (TTG) rocks in the Xixiang-Wudumen-Erliba areas with 24

Precambrian Research 333 (2019) 105442

W. Ao, et al.

constructive comments and suggestions in improving our work. We wish to thank Dr. P.M. George for his kind help with English language. Mr. Jianqi Wang and Dr. Zhian Bao are greatly appreciated for their kind help with whole-rock major element analyses and zircon Hf isotope analyses.

Mengzi-Xishenba-Tianpinghe-Xixiang areas were produced by partial melting of newly formed lower crust at lower pressure, indicating an extensional tectonic setting (Zhao and Zhou, 2009b; Li, 2010; Dong et al., 2012). The ca. 764–757 Ma gabbros in the Wangcang area and the ca. 751–746 Ma gabbros in the Bijigou-Dahanshan-Luojiaba areas were also generated in extensional setting (Zhao and Zhou, 2009a; Xu et al., 2011; Dong et al., 2011, 2012). Thus, it can be concluded that the northern margin of the Yangtze Block was in a crustal thickening-extensional tectonic setting during ca. 765–706 Ma (Fig. 17d). Further to the north, consistent with the Yangtze Block, the basement complex of the South Qinling Belt is unconformably overlain by the Neoproterozoic Sinian strata, such as the Doushantuo and Dengying formations, indicating that the Yangtze Block and the South Qinling Belt were welded together before Sinian. Comparable with the northern margin of the Yangtze Block, Neoproterozoic (ca. 970–750 Ma) subduction-related mafic-felsic rocks also widely outcrop in the South Qinling Belt, suggesting that both the South Qinling Belt and the northern margin of the Yangtze Block have experienced long-term subduction-related tectonic processes during Neoproterozoic (Zhang et al., 2016; and references therein). Based on petrological and geochronological study, the occurrences of voluminous volcanic-sedimentary sequences and mafic dike swarms indicate that the South Qinling Belt was in a continental rift setting at ca. 750 Ma (Ling et al., 2008), which is in agreement with the geological fact that the northern margin of the Yangtze Block was in a crustal thickening-extensional setting during ca. 765–706 Ma. Thus, plate-subduction model support the hypothesis that the South Qinling Belt and the northern margin of the Yangtze Block areas may have been dominanted by subduction with local rifting processes during Neoproterozoic (Gao et al., 1990; Zhang et al., 2016) and they were possibly welded together through these Neoproterozoic subduction-related tectonic processes (Fig. 17d).

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.precamres.2019.105442. References Ao, W.H., Zhang, Y.K., Zhang, R.Y., Zhao, Y., Sun, Y., 2014. Neoproterozoic Crustal Accretion of the Northern Margin of Yangtze Plate: Constrains from Geochemical Characteristics, LA-ICP-MS Zircon U-Pb Chronology and Hf Isotopic Compositions of Trondhjemite from Zushidian Area, Hannan Region. Geol. Rev. 60 (6), 1393–1408 (in Chinese with English abstract). Albarède, F., Scherer, E.E., Blichert-Toft, J., Rosing, M., Simionovici, A., Bizzarro, M., 2006. γ-ray irradiation in the early Solar System and the conundrum of the 176Lu decay constant. Geochim. Cosmochim. Acta 70, 1261–1270. Aldanmaz, E., Pearce, J.A., Thirlwall, M.F., Mitchell, J.G., 2000. Petrogenetic evolution of late Cenozoic, post-collision volcanism in western Anatolia, Turkey. J. Volcan. Geotherm. Res. 102, 67–95. Bader, T., Ratschbacher, L., Franz, L., Yang, Z., Hofmann, M., Linnemann, Ulf, Yuan, H.L., 2013. The heart of China revisited, I. Proterozoic tectonics of the Qin mountains in the core of supercontinent Rodinia. Tectonics 32 (3), 661–687. Barbarin, B., 1999. A review of the relationships between granitoid types, their origins and their geodynamic environments. Lithos 46, 605–626. Barbarin, B., 2005. Mafic magmatic enclaves and mafic rocks associated with some granitoids of the central Sierra Nevada batholith, California: nature, origin, and relations with the hosts. Lithos 80, 155–177. Barth, A.P., Wooden, J.L., Tosdal, R.M., Morrison, J., 1995. Crustal contamination in the petrogenesis of a calc-alkalic rock series: Josephine Mountain intrusion, California. Geol. Soc. Am. Bull. 107, 201–212. Belousova, E.A., Griffin, W.L., O’Reilly, S.Y., Fisher, N.L.L., 2002. Igneous zircon: Trace element composition as an indicator of source rock type. Contrib. Mineral. Petrol. 143, 602–622. Blichert-Toft, J., Albarède, F., 1997. The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system. Earth Planet. Sci. Lett. 148, 243–258. Bonin, B., 2007. A-type granites and related rocks: evolution of a concept, problems and prospects. Lithos 97 (1), 1–29. Chappell, B.W., White, A.J.R., 2001. Two contrasting granite types: 25 years later. Aust. J. Earth Sci. 48, 489–499. Chen, L.M., Song, X.Y., Nie, X.Y., Zhou, G.F., Liu, S.R., Zheng, W.Q., Li, S.B., 2008. Mineral chemistry and geological significance of pyroxene from segmentⅡof the Jinchuan intrusion, Gansu province. J. Mineral. Petrol. 28, 88–96 (in Chinese with English abstract). Chu, N.C., Taylor, R.N., Chavagnac, V., Nesbitt, R.W., Boella, R.M., Milton, J.A., German, C.R., Bayon, G., Burton, K., 2002. Hf isotope ratio analysis using multicollector inductively coupled plasma mass spectrometry: an evaluation of isobaric. J. Anal. Atom. Spectrom. 17, 1567–1574. Condomines, M., Hemond, C., Allègre, C.J., 1988. U-Th–Ra radioactive disequilibria and magmatic processes. Earth Planet. Sci. Lett. 90, 243–262. Creaser, R.A., Richard, C.P., Wormald, R.J., 1991. A-type granites revisited: assessment of a residual-source model. Geology 19, 163–166. Cui, J.T., Wang, F., Duan, J.G., Zhao, S.L., Cui, H.T., Cui, H.M., 2013. The Sunjiahe Formation of the Xixiang Group, southern Qinling Ranges: SHRIMP zircon U-Pb age and its tectonic implications. Sedim. Geol. Tethyan Geol. 33, 1–5 (in Chiniese with English abstract). Defant, M.J., Drummond, M.S., 1990. Derivation of some modern arc magmas by melting of young subduction lithosphere. Nature 347, 662–665. Deng, Q., Wang, J., Wang, Z.J., Jiang, X.S., Du, Q.D., Wu, H., Yang, F., Cui, X.Z., 2013. Zircon U-Pb ages for tuffs from the Dashigou and Sanlangpu Formations of the Xixiang Group in the northern margin of the Yangtze block and their geological significance. J. Jilin University 43, 797–808 (in Chiniese with English abstract). DePaolo, D.J., 1981. Trace element and isotopic effects of combined wallrock assimilation and fractional crystallisation. Earth Planet. Sci. Lett. 53, 189–202. Dong, Y.P., Liu, X.M., Santosh, M., Chen, Q., Zhang, X.N., Li, W., He, D.F., Zhang, G.W., 2012. Neoproterozoic accretionary tectonics along the northwestern margin of the Yangtze Block, China: constraints from zircon U-Pb geochronology and geochemistry. Precambr. Res. 196, 247–274. Dong, Y.P., Liu, X.M., Santosh, M., Zhang, X.N., Chen, Q., Yang, C., Yang, Z., 2011. Neoproterozoic subduction tectonics of the northwestern Yangtze Block in South China: constrains from zircon U-Pb geochronology and geochemistry of mafic intrusions in the Hannan Massif. Precambr. Res. 189, 66–90. Dong, Y.P., Santosh, M., 2016. Tectonic architecture and multiple orogeny of the Qinling Orogenic Belt, Central China. Gondwana Res. 29, 1–40. Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644. Journal of Petrology Special_Volume (1), 331–349. https://doi.org/10.1093/petrology/ Special_Volume.1.331.

7. Conclusions 1) The Dahanshan gabbroic pluton in the Hannan region has LA-ICP MS zircon U-Pb age of 793–779 Ma. It was probably formed in a back-arc tectonic setting modified by slab-derived aqueous fluids. The primary magma was possibly generated by magma mixing of depleted mantle source (MORB-like) with metasomatized lithospheric mantle wedge, with 20–30% partial melting of garnet-spinel lherzolite. 2) The Hongmiao potassic granite in the Hannan region yield crystallization age of ca. 802–791 Ma. It is geochemically A2-type granite and was generated by partial melting of pre-existing crust at a relatively shallow crustal depth in a back-arc setting. 3) The Xishenba trondhjemitic biotite granite in the Hannan region formed at ca. 887 Ma. It was derived from partial melting of preexisting thickened lower crust in continental arc setting. 4) In the northern margin of the Yangtze Block, Neoproterozoic (ca. 950–700 Ma) magmatic activities represent significant crustal growth event, which is accompanied by certain degree of crustal reworking. 5) According to temporal-spatial distribution of different rock types, the Neoproterozoic (ca. 950–706 Ma) Hannan Complex were generated in continental arc setting, continuous continental arc setting, back-arc setting and transitional tectonic setting from compression to extension at ca.950–890 Ma, ca.890–840 Ma, ca.840–765 Ma and ca.765–706 Ma, respectively. Acknowledgements This work was jointly supported by the National Natural Science Foundations of China (Grants: 41421002 and 41802199) and MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University. We are very grateful to Prof. Guochun Zhao, Editor, as well as two anonymous reviewers for their encouraging and 25

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Neoproterozoic supercontinent Rodinia. Aust. J. Earth Sci. 43, 593–604. Li, Z.X., Zhang, L., Powell, C.M., 1995. South China Rodinia: part of the missing link between Australia-East Antarctica and Laurentia. Geology 23, 407–410. Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., Zhang, S., Zhou, H., 2003a. Geochronology of Neoproterozoic syn-rift magmatism in the Yangtze Craton, South China and correlations with other continents: evidence for a mantle superplume that brokeup Rodinia. Precambr. Res. 122, 85–109. Li, J.Y., Wang, X.L., Gu, Z.D., 2018. Early Neoproterozoic arc magmatism of the Tongmuliang Group on the northwestern margin of the Yangtze Block: implications for Rodinia assembly. Precambr. Res. 308, 181–197. Li, T., 2010. The Study of Neoproterozoic Tectonic-Magmatic Events in the Northern Margin of the Yangtze Continental. Master's Degree Thesis. Chang'an University Xi'an, China, pp. 55. Li, X.H., McCulloch, M.T., 1996. Secular variation in the Nd isotopic composition of Neoproterozoic sediments from the southern margin of the Yangtze Block: evidence for a Proterozoic continental collision in south China. Precambr. Res. 76, 67–76. Li, X.H., 1999. U-Pb zircon ages of granites from the southern margin of the Yangtze Blocks: timing of Neoproterozoic Jinning: orogeny in SE China and implications for Rodinia Assembly. Precambr. Res. 97, 43–57. Li, X.H., Li, Z.X., Zhou, H.W., Liu, Y., Kinny, P.D., 2002. U-Pb zircon geochronology, geochemistry and Nd isotopic study of Neoproterozoic bimodal volcanic rocks in the Kangdian Rift of South China: implications for the initial rifting of Rodinia. Precambr. Res. 113, 135–154. Li, X.H., Li, Z.X., Ge, W.C., Zhou, H.W., Li, W.X., Liu, Y., Wingate, M.T.D., 2003b. Neoproterozoic granitoids in South China: crustal melting above a mantle plume at ca. 825 Ma? Precambr. Res. 122, 45–83. Li, X.H., Li, Z.X., Zhou, H.W., Liu, Y., Liang, X.R., Li, W.X., 2003c. SHRIMP U-Pb zircon age, geochemistry and Nd isotope of the Guandaoshan pluton in SW Sichuan: petrogenesis and tectonic significance. Sci. China D: Earth Sci. 46 (Supp.), 73–83. Li, X.H., Li, W.X., Li, Z.X., Lo, C.H., Wang, J., Ye, M.F., Yang, Y.H., 2009. Amalgamation between the Yangtze and Cathaysia Blocks in South China: constraints from SHRIMP U-Pb zircon ages, geochemistry and Nd–Hf isotopes of the Shuangxiwu volcanic rocks. Precambr. Res. 174, 117–128. Li, W.Q., Zhao, J.H., 2016. Petrogenesis of the Wudang mafic dikes: Implications of changing tectonic settings in South China during the Neoproterozoic. Precambr. Res. 272, 101–114. Ling, W.L., Gao, S., Zhang, H.F., Zhou, L., Zhao, Z.B., 1998. An Sm-Nd isotopic dating study of the Archean Kongling Complex in the Huangling area of the Yangtze Craton. Chin. Sci. Bull. 43, 1187–1191. Ling, W.L., Wang, X.H., Cheng, J.P., 2001. Geochemical features and its tectonic implication of the Jinningian Wangjiangshan Gabbros in the north margin of Yangtze Block. Bull. Miner. Petrol. Geochem. 20, 218–221 (in Chinese with English abstract). Ling, W.L., Cheng, J.P., Wang, X.H., Zhou, H.W., 2002a. Geochemical features of the Neoproterozoic igneous rocks from the Wudang region and their implications for the reconstruction of the Jinning tectonic evolution along the south Qinling orogenic belt. Acta Petrol. Sin. 18 (1), 25–36 (in Chiniese with English abstract). Ling, W.L., Gao, S., Ouyang, J.P., Zhang, B.R., Li, H.M., 2002b. Timing and tectonic setting of the Xixiang Group: Constraints from the zircon U-Pb geochronology and geochemistry. Sci. China: Series D 32, 101–112 (in Chiniese with English abstract). Ling, W.L., Gao, S., Zhang, B.R., Li, H.M., Liu, Y., Cheng, J.P., 2003. Neoproterozoic tectonic evolution of the northwesternYangtze craton, South China: implications for amalgamation and break-up of the Rodinia Supercontinent. Precambr. Res. 122, 111–140. Ling, W.L., Gao, S., Cheng, J.P., Jiang, L.S., Yuan, H.L., Hu, Z.C., 2006. Neoproterozoic magmatic events within the Yangtze continental interior and along its northern margin and their tectonic implication: constraint from the ELA-ICM-MS U-Pb geochronology of zorcons from the Huangling and Hannan complexes. Acta Petrol. Sin. 22, 387–396 (in Chiniese with English abstract). Ling, W.L., Ren, B.F., Duan, R.C., Liu, X.M., Mao, X.W., Peng, L.H., Liu, Z.X., Cheng, J.P., Yang, H.M., 2008. Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication. Chin. Sci. Bull. 53, 2192–2199. Ling, W.L., Ren, B.F., Duan, R.C., Liu, X.M., Mao, X.W., Peng, L.H., Liu, Z.X., Cheng, J.P., 2007. Zircon U-Pb isotopic geochronology of Wudangshan Group, Yaolinghe Group and basic intrusions and its geological significance. Chin. Sci. Bull. 52 (12), 1445–1456. Liu, X.M., Gao, S., Ling, W.L., Yuan, H.L., Hu, Z.C., 2005. Identification of 3.5 Ga detrital zircons from Yangtze craton in south China and the implication for Archean crust evolution. Prog. Nat. Sci. 15, 1334–1337 (in Chinese with English abstract). Liu, Y., Liu, X.M., Hu, Z.C., Diwu, C.R., Yuan, H.L., Gao, S., 2007. Evaluation of accuracy and long-term stability of determination of 37 trace elements in geological samples by ICP-MS. Acta Petrol. Sin. 23, 1203–1210 (in Chinese with English abstract). Liu, R., Zhang, B.R., Zhang, H.F., Yuan, H.L., 2009. U-Pb zircon age, geochemical and SrNd-Hf isotopic compositions of Neoproterozoic granitoids in Northwestern margin of Yangtze Block (South China): implications for Neoproterozoic tectonic evolution. J. Earth Sci. 20, 659–680. Ludwig, K.R., 2003. ISOPLOT 3.0: A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center. Special publication No. 4. Luo, B.J., Liu, R., Zhang, H.F., Zhao, J.H., Yang, H., Xu, W.C., Guo, L., Zhang, L.Q., Tao, L., Pan, F.B., Wang, W., Gao, Z., Shao, H., 2018. Neoproterozoic continental back-arc rift development in the Northwestern Yangtze Block: evidence from the Hannan intrusive magmatism. Gondwana Res. 59, 27–42. Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geol. Soc. Am. Bull. 101 (5), 635–643. Martin, H., Smithies, R.H., Rapp, R., Moyen, J.F., Champion, D., 2005. An overview of adakite, tonalite-trondhjemite-granodiorite (TTG) and sanukitoid: relation-ships and

Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical classification for granitic rocks. J. Petrol. 42, 2033–2048. Frost, C.D., Frost, B.R., 2011. On ferroan (A-type) granitoids: their compositional variability and modes of origin. J. Petrol. 52 (1), 39–53. Furman, T., Graham, D., 1999. Erosion of lithospheric mantle beneath the East African Rift system: geochemical evidence from the Kivu volcanic province. Lithos 48, 237–262. Gao, S., Zhang, B.R., Li, Z.J., 1990. Geochemical evidence for Proterozoic continental arc and continental margin rift magmatism along the northern margin of the Yangtze Craton, South China. Precambr. Res. 47, 205–221. Gao, S., Qiu, Y.M., Ling, W.L., McNaughton, N.J., Groves, D.I., 2001. Single zircon U-Pb dating of the Kongling high-grade metamorphic terrain: evidence for > 3.2 Ga old continental crust in the Yangtze craton. Sci. China Ser. D 44, 326–335. Gao, S., Yang, J., Zhou, L., Li, M., Hu, Z.C., Guo, J.L., Yuan, H.L., Gong, H.J., Xiao, G.Q., Wei, J.Q., 2011. Age and growth of the Archean Kongling terrain, South China, with emphasis on 3.3 Ga granitoid gneisses. Am. J. Sci. 311, 153–182. Genc, S.C., Tuysuz, O., 2010. Tectonic setting of the Jurassic bimodal magmatism in the Sakarya Zone (Central and Western Pontides), Northern Turkey: a geochemical and isotopic approach. Lithos 118, 95–111. Geng, Y.Y., 2010. SHRIMP U-Pb Zircon Geochronology and Geochemistry Study of Neoproterozoic Granites in the NorthernMargin of Yangtze Continental. Master's degree thesis. China University of Geosciences, Beijing 60. Gribble, R.F., Stern, R.J., Bloomer, S.H., Stüben, D., O’Hearn, T., Newman, S., 1996. MORB mantle and subduction components interact to generate basalts in the southern Mariana Trough back-arc basin. Geochim. Cosmochim. Acta 60, 2153–2166. Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., Achterbergh, E.V., O’Reilly, S.Y., Shee, S.R., 2000. The Hf isotope composition of cratonic mantle: LA-MC-ICPMS analysis of zircon megacrysts in kimberlites. Geochim. Cosmochim. Acta 64, 133–147. Guo, J.L., Gao, S., Wu, Y.B., Li, M., Chen, K., Hu, Z.C., Liang, Z.W., Liu, Y.S., Zhou, L., Zong, K.Q., Zhang, W., Chen, H.H., 2014. 3.45 Ga granitic gneisses from the Yangtze Craton, South China: Implications for Early Archean crustal growth. Precambr. Res. 242, 82–95. Guo, J.L., Wu, Y.B., Gao, S., Jin, Z.M., Zong, K.Q., Hu, Z.C., Chen, K., Chen, H.H., Liu, Y.S., 2015. Episodic Paleoarchean-Paleoproterozoic (3.3-2.0 Ga) granitoid magmatism in Yangtze Craton, South China: implications for late Archean tectonics. Precambr. Res. 270, 246–266. Hawkesworth, C.J., Turner, S.P., McDermott, F., Peate, D.W., Van Clasteren, P., 1997. UTh isotopes in arc magmas: implications for element transfer from thesubducted crust. Science 276, 551–555. Hawkesworth, C.J., Dhuime, B., Pietranik, A.B., Cawood, P.A., Kemp, A.I.S., Storey, C.D., 2010. The generation and evolution of the continental crust. J. Geol. Soc. 167 (2), 229–248. Hollings, P., 2002. Archean Nb-enriched basalts in the northern superior province. Lithos 64, 1–14. Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and igneous and metamorphic petrogenesis. Rev. Mineral. Geochem. 53, 27–62. Hu, J., Liu, X.C., Chen, L.Y., Qu, W., Li, H.K., Geng, J.Z., 2013. A ~2.5 Ga magmatic event at the northern margin of the Yangtze craton: evidence from U-Pb dating and Hf isotope analysis of zircons from the Douling Complex in the South Qinling orogen. Chin. Sci. Bull. 58, 3564–3579. Hui, B., Dong, Y., Cheng, C., Long, X., Liu, X., Yang, Z., Sun, S., Zhang, F., Varga, J., 2017. Zircon U-Pb chronology, Hf isotope analysis and whole-rock geochemistry for the Neoarchean-Paleoproterozoic Yudongzi complex, northwestern margin of the Yangtze craton, China. Precambr. Res. 301, 65–85. Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical classification of the common volcanic rocks. Can. J. Earth Sci. 8, 523–528. Jenner, G.A., Dunning, G.R., Malpas, J., Brown, M., Brace, T., 1991. Bay of Islands and Little Port complexes, revisited: age, geochemical and isotopic evidence confirm supra-subduction zone origin. Can. J. Earth Sci. 28, 135–162. Jia, X.H., 2009. A-type Granites: Research Progress and Implications. Geotectonica Et Metallogenia 33, 465–480 (in Chinese with English abstract). Jiang, Y.H., Jiang, S.Y., Dai, B.Z., Liao, S.Y., Zhao, K.D., Ling, H.F., 2009. Middle to late Jurassic felsic and mafic magmatism in southern Hunan province, southeast China: implications for a continental arc to rifting. Lithos 107, 185–204. Johnson, M.C., Plank, T., 2000. Dehydration and melting experiments constrain the fate of subducted sediments. Geochem. Geophys. Geosyst. 1, 1007. Kemp, T., Paterson, B., Hawkesworth, C., 2005. A coupled Lu-Hf and O isotope in zircon approach to granite genensis. Geochim. Cosmochim. Acta 69, 243 (Supplement). Kröner, A., Kovach, V., Belousova, E., Hegner, E., Armstrong, R., Dolgopolova, A., Seltmann, R., Alexeiev, D.V., Hoffmann, J.E., Wong, J., Sun, M., Cai, K., Wang, T., Tong, Y., Wilde, S.A., Degtyarev, K.E., Rytsk, E., 2014. Reassessment of continental growth during the accretionary history of the Central Asian Orogenic Belt. Gondwana Res. 25, 103–125. Labanieh, S., Chauvel, C., Germa, A., Quidelleur, X., 2012. Martinique: a clear case for sediment melting and slab dehydration as a function of distance to the trench. J. Petrol. 53, 2441–2464. LeBas, M.J., LeMaitre, R.W., Streckeisen, A., Zanettin, B., 1986. A chemical classification of volcanic rocks based on the total alkalie-silica diagram. J. Petrol. 27, 745–750. Lee, C.T.A., Luffi, P., Plank, T., Dalton, H., Leeman, W.P., 2009. Constraints on the depths and temperatures of basaltic magma generation on Earth and other terrestrial planets using new thermobarometers for mafic magmas. Earth Planet. Sci. Lett. 279, 20–33. Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., 1999. The breakup of Rodinia: did it start with a mantle plume beneath South China? Earth Planet. Sci. Lett 173, 171–181. Li, Z.X., Zhang, L., Powell, C.M., 1996. Positions of the East Asian cratons in the

26

Precambrian Research 333 (2019) 105442

W. Ao, et al.

Wang, Y.J., Zhang, A.M., Cawood, P.A., Fan, W.M., Xu, J.F., Zhang, G.W., Zhang, Y.Z., 2013b. Geochronological, geochemical and Nd-Hf-Os isotopic fingerprinting of an early Neoproterozoic arc-back-arc system in South China and its accretionary assembly along the margin of Rodinia. Precambr. Res. 231, 343–371. Wang, Z.J., Wang, J., Du, Q.D., Deng, Q., Yang, F., 2013c. The evolution of the Central Yangtze Block during early Neoarchean time: evidence from geochronology and geochemistry. J. Asian Earth Sci. 77, 31–44. Wang, K., Li, Z.X., Dong, S.W., Cui, J.J., Han, B.F., Zheng, T., Xu, Y.L., 2018. Early crustal evolution of the Yangtze Craton, South China: new constraints from zircon U-Pb-Hf isotopes and geochemistry of ca. 2.9-2.6 Ga granitic rocks in the Zhongxiang Complex. Precambr. Res. 314, 325–352. Weaver, B.L., 1991. The origin of ocean island basalt end-member compositions: trace element and isotopic constraints. Earth Planet. Sci. Lett. 104, 381–397. Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib. Miner. Petrol. 95, 407–419. Wilson, M., 1989. Igneous Petrogenesis. Chapman & Hall, London, pp. 466. Wood, D.A., 1980. The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crust contamination of basaltic lavas of the British Tertiary volcanic province. Earth Planet. Sci. Lett. 50, 11–30. Woodhead, J.D., Eggins, S.M., Johnson, R.W., 1998. Magma genesis in the New Britain Island Arc: further insights into melting and mass transfer processes. J. Petrol. 39, 1641–1668. Woodhead, J.D., Hergt, J.M., Davidson, J.P., Eggins, S.M., 2001. Hafnium isotope evidence for ‘conservative’ element mobility during subduction zone processes. Earth Planet. Sci. Lett. 192, 331–346. Wu, F.Y., Li, X.H., Zheng, Y.F., Gao, S., 2007. Lu-Hf isotopic systematics and their applications in petrology. Acta Petrol. Sin. 23 (2), 185–220 (in Chinese with English abstract). Wu, Y.B., Gao, S., Zhang, H.F., Zheng, J.P., Liu, X.C., Wang, H., Gong, H.J., Zhou, L., Yuan, H.L., 2012. Geochemistry and zircon U-Pb geochronology of Paleoproterozoic arc related granitoid in the Northwestern Yangtze Block and its geological implications. Precambr. Res. 200, 26–37. Wu, Y.B., Zhou, G.Y., Gao, S., Liu, X.M., Qin, Z.W., Wang, H., Yang, J.Z., Yang, S.H., 2014. Petrogenesis of Neoarchean TTG rocks in the Yangtze Craton and its implication for the formation of Archean TTGs. Precambr. Res. 254, 73–86. Wu, P., Zhang, S.-B., Zheng, Y.-F., Fu, B., Liang, T., 2019. Amalgamation of South China into Rodinia during the Grenvillian accretionary orogeny: geochemical evidence from Early Neoproterozoic igneous rocks in the northern margin of the South China Block. Precambr. Res. 321, 221–243. Xia, L.Q., Xia, X.C., Ma, Z.P., XU, X.Y., Li, X.M., 2009. Petrogenesis of volcanic rocks from Xixiang Group in Middle Part of South Qinling Mountains. Northwest. Geol. 42, 1–37 (in Chiniese with English abstract). Xu, X.S., O'Reilly, S.Y., Griffin, W.L., Deng, P., Pearson, N.J., 2005. Relict Proterozoic basement in the Nanling Mountains (SE China) and its tectonothermal overprinting. Tectonics 24 (2). https://doi.org/10.1029/2004TC001652. Xu, Y.G., He, B., Huang, X.L., Luo, Zh.Y., Zhu, D., Ma, J.L., Shao, H., 2007. The debate over mantle plumes and how to test the plume hypothesis. Earth Sci. Front. 14 (2), 001–009. Xu, X.Y., Xia, L.Q., Chen, J.L., Ma, Z.P., Li, X.M., Xia, Z.C., Wang, H.L., 2009. Zircon U-Pb dating and geochemical study of volcanic rocks from Sunjiahe formation of Xixiang Group in northern margin of Yangtze Plate. Acta Petrol. Sin. 25, 3309–3326 (in Chiniese with English abstract). Xu, X.Y., Chen, J.L., Li, X.M., Ma, Z.P., Wang, H.L., Xia, L.Q., Xia, Z.C., Li, P., 2010. Geochemistry and petrogenesis of volcanic rocks from Sanlangpu Formation and Dashigou Formation. Acta Petrol. Sin. 26, 617–632 (in Chiniese with English abstract). Xu, X.Y., Li, T., Che, X.L., Li, P., Wang, H.L., Li, Z.P., 2011. Zircon U-Pb age and petrogenesis of intrusions from Mengzi area in their northern margin of Yangtze plate. Acta Petrol. Sin. 27, 699–720 (in Chinese with English abstract). Yan, D.P., Zhou, M.F., Song, H.L., Wang, X.W., Malpas, J., 2003. Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China). Tectonophysics 361, 239–254. Yan, Q.R., Hanson, A.D., Wang, Z.Q., Druschke, P.A., Yan, Z., Wang, T., Liu, D.Y., Song, B., Pan, P., Zhou, H., Jiang, C.F., 2004. Neoproterozoic subduction and rifting on the northern margin of the Yangtze Plate, China: implications for Rodinia reconstruction. Int. Geol. Rev. 46, 817–832. Yang, J.H., Wu, F.Y., Wilde, S.A., Liu, X.M., 2007. Petrogenesis of Late Triassic granitoids and their enclaves with implications for post-collisional lithospheric thinning of the Liaodong Peninsula, North China Craton. Chem. Geol. 242, 155–175. Zhang, C.L., Zhou, D.W., 1999. Rifting of Wudang Block during Chenjiang Period of Neoproterozoic in South Qinling of China: geochemical evidence from Wudang Basic Dyke Swarm. Gondwana Res. 2 (4), 529–532. Zhang, R.Y., Sun, Y., Zhang, X., Ao, W.H., Santosh, M., 2016. Neoproterozoic magmatic events in the South Qinling Belt, China: implications for amalgamation and breakup of the Rodinia supercontinent. Gondwana Res. 30, 6–23. Zhang, Z.Q., Zhang, G.W., Tang, S.H., Wang, J.H., 2001. On the age of metamorphic rocks of the Yudongzi Group and the Archean crystalline basement of the Qinling Orogen. Acta Geol. Sin. 75, 198–204 (in Chinese with English abstract). Zhao, F.Q., Zhao, W.P., Zhuo, Y.C., Li, Z.H., Xue, K.Q., 2006. U-Pb geochronology of Neoproterozoic magmatic rocks in Hanzhong, southern Shaanxi. China. Geol. Bull. China 25, 383–388 (In Chiniese with English Abstract). Zhao, G.C., Cawood, P.A., 2012. Precambrian geology of China. Precambr. Res. 222–223, 13–54. Zhao, J.H., Zhou, M.F., 2007a. Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): implications for subduction-related metasomatism in the upper mantle. Precambr. Res. 152, 27–47.

some implications for crustal evolution. Lithos 79, 1–24. Meschede, M., 1986. A method of discrimination between different types of mid-oceanic ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. Chem. Geol. 56, 207–218. Miyashiro, A., 1974. Volcanic rock series in island arcs and active continentalmargins. Am. J. Sci. 274, 321–355. Moyen, J.F., 2009. High Sr/Y and La/Yb ratios: the meaning of the adakitic signature. Lithos 112, 556–574. Mushkin, A., Navon, O., Halica, L., Hartmann, G., Stein, M., 2003. The petrogenesis of Atype magmas from the Amram Massif, Southern Israel. J. Petrol. 44 (5), 815–832. Nie, H., Yao, J., Wan, X., Zhu, X.Y., Siebel, W., Chen, F.K., 2016. Precambrian tectonothermal evolution of South Qinling and its affinity to the Yangtze Block: evidence from zircon ages and Hf-Nd isotopic compositions of basement rocks. Precambr. Res. 286, 167–179. O'Connor, J.T., 1965. A classification of quartz-rich igneous rocks based on feldspar ratios. U.S. Geological Survey Professionnal Paper 525, 79–84. Pearce, J.A., Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks. Contrib. Mineral. Petrol. 69, 33–47. Pearce, J.A., 1982. Trace element characteristics of lavas from destructive plate boundaries. In: Thorpe, R.S. (Ed.), Andesites: Orogenic Andesites and Related Rocks. Wiley, Chichester, pp. 525–548. Pearce, J.A., Harris, B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretations of grantic rocks. J. Petrol. Geol. 25, 956–983. Pearce, J.A., Peate, D.W., 1995. Tectonic implications of the composition of volcanicarc magmas. Annu. Rev. Earth Planet. Sci. 23, 251–285. Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos 100 (1–4), 14–48. Petford, N., Atherton, M., 1996. Na–rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith. Peru. J. Petrol. 37 (6), 1491–1521. Plank, T., 2005. Constraints from thorium/lanthanum on sediment recycling at subduction zones and the evolution of the continents. J. Petrol. 46, 921–944. Rajesh, H.M., 2000. Characterization and origin of a compositionally zoned aluminous Atype granite from South India. Geol. Mag. 137, 291–318. Rapp, R.P., Watson, E.B., 1995. Dehydration melting of metabasalt at 8–32 kbar: implications for continental growth and crust-mantle recycling. J. Petrol. 36 (4), 891–931. Rapp, R.P., Shimizu, N., Norman, M.D., Applegate, G.S., 1999. Reaction between slabderived melts and peridotite in the mantle wedge: experimental constraints at 3.8 GPa. Chem. Geol. 160, 335–356. Rudnick, R.L., Gao, S., 2003. Composition of the continental crust. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry. Pergamon, Oxford, pp. 1–64. Saunders, A.D., Norry, M.J., Tarney, J., 1988. Origin of MORB and chemically depleted mantle reservoirs: trace element constraints. J. Petrol. 415-445 (Special Lithosphere Issue). Sharma, M., 1997. Siberian traps. In: Mahoney, J.J., Coffin, M.F. (Eds.), Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism, vol. 100. American Geophysical Union Geophysical Monograph, pp. 273–295. Shervais, J.W., 1982. Ti-V plots and the petrogenesis of modern ophiolitic lavas. Earth Planet. Sci. Lett. 59, 101–118. Shi, Y., Yu, H.J., Santosh, M., 2013. Tectonic evolution of the Qinling orogenic belt, Central China: new evidence from geochemical, zircon U-Pb geochronology and Hf isotopes. Precambr. Res. 231, 19–60. Sun, M., Chen, N., Zhao, G., Wilde, S.A., Ye, K., Guo, J., Chen, Y., Yuan, C., 2008. U-Pb zircon and Sm-Nd isotopic study of the Huangtuling granulite, Dabie-Sulu belt, China: implication for the paleoproterozoic tectonic history of the Yangtze Craton. Am. J. Sci. 308, 469–483. Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes, Magmatism in the Ocean Basins. Geol. Soc. Special Publ. 313–345. Sun, W.H., Zhou, M.F., Zhao, J.H., 2007. Geochemistry and tectonic significance of basaltic lavas in the Neoproterozoic Yanbian Group (Southern Sichuan Province, SW China). Inter. Geo. Rev. 49, 554–571. Taylor, B., Martinez, F., 2003. Back-arc basin basalt systematics. Earth Planet. Sci. Lett. 210, 481–497. Teklay, M., 2006. Neoproterozoic arc-back-arc system analog to modern arc-back-arc systems: evidence from tholeiite-boninite association, serpentinite mudflows and across-arc geochemical trends in Eritrea, southern Arabian-Nubian shield. Precambr. Res. 145 (5), 81–92. Turner, S.P., Foden, J.D., Morrison, R.S., 1992. Derivation of some A-type magmas by fractionation of basaltic magma—an example from the Padthaway Ridge, South Australia. Lithos 28 (2), 151–179. Wang, M.X., Wang, C.Y., Zhao, J.H., 2013a. Zircon U/Pb dating and Hf-O isotopes of the Zhouan ultramafic intrusion in the northern margin of the Yangtze Block, SW China: constraints on the nature of mantle source and timing of the supercontinent Rodinia breakup. Chin. Sci. Bull. 58 (7), 777–787. Wang, M.X., Nebel, O., Wang, C.Y., 2016. The flaw in the crustal ‘Zircon Archive’: mixed Hf isotope signatures record progressive contamination of late-stage liquid in maficultramafic layered intrusions. J. Petrol. 57, 27–52. Wang, X.C., Li, X.H., Li, W.X., Li, Z.X., 2009. Variable involvements of mantle plumes in the genesis of mid-Neoproterozoic basaltic rocks in South China: a review. Gondwana Res. 15, 381–395. Wang, X.L., Zhou, J.C., Griffin, W.L., Zhao, G.C., Yu, J.H., Qiu, J.S., Zhang, Y.J., Xing, G.F., 2014. Geochemical zonation across a Neoproterozoic orogenic belt: isotopic evidence from granitoids and metasedimentary rocks of the Jiangnan orogeny, China. Precambr. Res. 242, 154–171.

27

Precambrian Research 333 (2019) 105442

W. Ao, et al.

granitic rocks in the Jiangnan Orogen, South China. Precambr. Res. 163, 351–383. Zhou, G.Y., Wu, Y.B., Wang, H., Qin, Z., Zhang, W., Zheng, J., Yang, S., 2017. Petrogenesis of the Huashanguan A-type granite complex and its implications for the early evolution of the Yangtze Block. Precambr. Res. 292, 57–74. Zhou, G.Y., Wu, Y.B., Li, L., Zhang, W.X., Zheng, J.P., Wang, H., Yang, S.H., 2018a. Identification of ca. 2.65 Ga TTGs in the Yudongzi complex and its implications for the early evolution of the Yangtze Block. Precambr. Res. 314, 240–263. Zhou, J.L., Li, X.H., Tang, G.Q., Gao, B.Y., Bao, Z.A., Ling, X.X., Wu, L.G., Lu, K., Zhu, Y.S., Liao, X., 2018b. Ca. 890 Ma magmatism in the northwest Yangtze block, South China: SIMS U-Pb dating, in-situ Hf-O isotopes, and tectonic implications. J. Asian Earth Sci. 151, 101–111. Zhou, M.F., Kennedy, A.K., Sun, M., Malpas, J., Lesher, C.M., 2002a. Neoproterozoic arcrelated mafic intrusions in the northern margin of South China: implications for accretion of Rodinia. J. Geol. 110, 611–618. Zhou, M.F., Yan, D.P., Kennedy, A.K., Li, Y.Q., Ding, J., 2002b. SHRIMP zircon geochronological and geochemical evidence for Neoproterozoic arc-related magmatism along the western margin of the Yangtze Block, South China. Earth Planet. Sci. Lett. 196, 51–67. Zhou, M.F., Ma, Y.X., Yan, D.P., Xia, X.P., Zhao, J.H., Sun, M., 2006a. The Yanbian Terrane (Southern Sichuan Province, SW China): a Neoproterozoic arc assemblage in the western margin of the Yangtze Block. Precambr. Res. 144, 19–38. Zhou, M.F., Yan, D.P., Wang, C.L., Qi, L., Kennedy, A., 2006b. Subduction-related origin of the 750Ma Xuelongbao adakitic complex (Sichuan Province, China): implications for the tectonic setting of the giant Neoproterozoic magmatic event in South China. Earth Planet. Sci. Lett. 248, 286–300. Zhu, X.Y., Chen, F.K., Liu, B.X., Zhang, H., Zhai, M.G., 2015. Geochemistry and zircon ages of mafic dikes in the South Qinling, central China: evidence for late Neoproterozoic continental rifting in the northern Yangtze Block. Int. J. Earth Sci. 104, 27–44.

Zhao, J.H., Zhou, M.F., 2007b. Neoproterozoic adakitic plutons and arc magmatism along the western margin of the Yangtze Block, South China. J. Geol. 115, 675–689. Zhao, J.H., Zhou, M.F., 2008. Neoproterozoic adakitic plutons in the northern margin of the Yangtze Block, China: partial melting of a thickened lower crust and implications for secular crustal evolution. Lithos 104, 231–248. Zhao, J.H., Zhou, M.F., Yan, D.P., Yang, Y.H., Sun, M., 2008. Zircon Lu-Hf isotopic constraints on Neoproterozoic subduction-related crustal growth along the western margin of the Yangtze Block, South China. Precambr. Res. 163, 189–209. Zhao, J.H., Zhou, M.F., 2009a. Secular evolution of the Neoproterozoic lithospheric mantle underneath the northern margin of the Yangtze Block, South China. Lithos 107, 152–168. Zhao, J.H., Zhou, M.F., 2009b. Melting of newly formed mafic crust for the formation of Neoproterozoic I-type granite in the Hannan Region, South China. J. Geol. 117, 54–70. Zhao, J.H., Zhou, M.F., Zheng, J.P., Fang, S.M., 2010. Neoproterozoic crustal growth and reworking of the Northwestern Yangtze Block constraints from the Xixiang dioritic intrusion, South China. Lithos 120, 439–452. Zhao, J.H., Zhou, M.F., Yan, D.P., Zheng, J.P., Li, J.W., 2011. Reappraisal of the ages of Neoproterozoic strata in South China: no connection with the Grenvillian orogeny. Geology 39, 299–302. Zhao, J.H., Li, Q.W., Liu, H., Wang, W., 2018. Neoproterozoic magmatism in the western and northern margins of the Yangtze Block (South China) controlled by slab subduction and subductiontransform-edge-propagator. Earth-Sci. Rev. 187, 1–18. Zhao, J.H., Asimow, P.D., 2018. Formation and Evolution of a Magmatic System in a Rifting Continental Margin: Neoproterozoic Arc-and MORB-like Dike Swarms in South China. J. Petrol. 59, 1811–1844. Zheng, J.P., Griffin, W.L., O’Reilly, S.Y., Zhang, M., Pearson, N., Pan, Y.M., 2006. Widespread Archean basement beneath the Yangtze craton. Geology 34, 417–420. Zheng, Y.F., Wu, R.X., Wu, Y.B., Zhang, S.B., Yuan, H.L., Wu, F.Y., 2008. Rift melting of juvenile arc-derived crust: geochemical evidence from Neoproterozoic volcanic and

28