Petrogenesis of the Jiaoziding granitoids and associated basaltic porphyries: Implications for extensive early Neoproterozoic arc magmatism in western Yangtze Block

Accepted Manuscript Petrogenesis of the Jiaoziding granitoids and associated basaltic porphyries: Implications for extensive early Neoproterozoic arc magmatism in western Yangtze Block

Jun-Yong Li, Xiao-Lei Wang, Zhi-Dong Gu PII: DOI: Reference:

S0024-4937(17)30419-X doi:10.1016/j.lithos.2017.11.034 LITHOS 4495

To appear in: Received date: Accepted date:

23 May 2017 28 November 2017

Please cite this article as: Jun-Yong Li, Xiao-Lei Wang, Zhi-Dong Gu , Petrogenesis of the Jiaoziding granitoids and associated basaltic porphyries: Implications for extensive early Neoproterozoic arc magmatism in western Yangtze Block. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Lithos(2017), doi:10.1016/j.lithos.2017.11.034

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Petrogenesis of the Jiaoziding granitoids and

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associated basaltic porphyries: implications for

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extensive early Neoproterozoic arc magmatism in

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western Yangtze Block

State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and

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a

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Jun-Yong Lia, Xiao-Lei Wanga,*, Zhi-Dong Gub

Research Institute of Petroleum Exploration and Development, PetroChina, Beijing

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10083, China

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b

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Engineering, Nanjing University, Nanjing 210046, China

*

Corresponding author. E-mail address: [email protected] (X.-L. Wang)

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Abstract Middle Neoproterozoic (ca 860–750 Ma) granitoids are widely distributed in the western margin of the Yangtze Block, China, yet their magma sources and tectonic settings are unclear. The geochronology and geochemistry of the granitoids and

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associated basaltic porphyries, which intruded the ~970 Ma Tongmuliang arc volcanic

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rocks in the Jiaoziding area (east of Pingwu county), were investigated in this study.

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LA–ICP–MS zircon U–Pb dating indicates that the Jiaoziding granitoids and basaltic

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porphyries were formed at 795 ± 6 Ma and 790 ± 20 Ma, respectively. The granitoids have high SiO2 (69.2–76.9 wt%), K2O (2.3–5.6 wt%), and Na2O (3.2–5.1 wt%)

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contents, and a low Al2O3 (12.4–14.5 wt%) content. The basaltic porphyries contain high concentrations of TiO2 (~3 wt%) and high field strength elements, have steep

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rare earth element patterns, and are depleted in Nd and Hf isotopes. Batch partial-melting modelling indicates that the Jiaoziding granitoids could have been

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derived by ~5% and 50–70% partial melting of Tongmuliang mafic rocks and quartz-keratophyres, respectively. Formation of the basaltic porphyries by melting of

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upwelling asthenospheric mantle would have been facilitated by extensive lithospheric delamination during the Neoproterozoic. This study established a link between mid-Neoproterozoic granitic magmatism and ~970 Ma juvenile arc crust, indicating that extensive early Neoproterozoic juvenile arc crust, and partial melting of this crust in an extensional setting, favoured the formation of middle Neoproterozoic granitic rocks along the W–NW margin of the Yangtze Block.

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Keywords: Western Yangtze Block; Neoproterozoic; Juvenile crust; Partial melting; Jiaoziding granitoids

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1. Introduction

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Granitoids are one of the major constituents of continental crust and bear important

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information on fundamental geological processes such as continental growth and reworking, mantle–crust interaction, and lithospheric evolution (Kemp et al., 2007;

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Menand et al., 2011). Voluminous granitoid rocks along continental margins are believed to be linked to the amalgamation and break-up of supercontinents during

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Earth’s history (Bonin, 2007; Goodge and Vervoort, 2006). Among them, the Neoproterozoic Rodinia supercontinent is characterized by early to middle

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Neoproterozoic granitic magmatism on its margins, and such rocks are particularly concentrated on the margins of the Yangtze Block. Zircon U–Pb dating studies have

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shown that Neoproterozoic granitoids around the Yangtze Block were formed mainly during the period 860–750 Ma (e.g. Chen et al., 2015; X.H. Li et al., 2003a, 2003b; Zhao et al., 2011), and the rocks contain crucial information on Neoproterozoic crustal recycling and tectono-magmatic evolution. Nonetheless, their petrogenesis and tectonic settings are debated. Previous studies have proposed that these granitic rocks are related to crustal melting driven by lithospheric extension and heating driven by a

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(super-) mantle plume (e.g. X.H. Li et al., 2003a, 2008; Z.X. Li et al., 1999, 2003; Wang et al., 2007, 2011), while others have argued that they formed in a setting of Neoproterozoic subduction and related orogenesis (e.g. Du et al., 2014; Geng et al., 2008; Wang et al., 2014; Wang et al., 2016; Yao et al., 2015, 2016; Zhao and Zhou,

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2008; Zhao et al., 2011; Zhou et al., 2002a, 2002b; Zhou et al., 2006).

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The western margin of the Yangtze Block is a key area for study in resolving this

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long-standing debate, as Neoproterozoic granitoids in this region are diverse in

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composition (dioritic to granitic) and yield from ca 860 Ma to ca 750 Ma, while those at the southeastern margin of the block yield ages of 830–790 Ma and comprise

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mainly granodiorite and biotite granite (e.g. Wang et al., 2006; Zhao et al., 2013). The tectonic setting of Neoproterozoic granitoids in the western Yangtze Block is also

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debated. For example, Zhou et al. (2006) suggested long-term subduction from 860 to 750 Ma in the western Yangtze Block, and proposed that the 748 ± 7 Ma Xuelongbao

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adakitic rocks in this region were derived from partial melting of a subducted oceanic slab. However, the ca 780 Ma Mopanshan adakitic rocks and Mianning A-type

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granites are considered to have been formed by partial melting of a thickened lower crust in an extensional setting (Huang et al., 2008, 2009). In addition, 803 ± 12 Ma bimodal volcanic rocks and ocean island (OIB)-like basalts within the Suxiong Formation in the western margin of the Yangtze Block are thought to have been formed in a rift setting (Li et al., 2002). This variety of interpretations means that careful evaluations are needed to unravel the tectonic setting of Neoproterozoic

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granitoids in the area. In particular, the associated mafic rocks are crucial to the issue, as the geochemistry of granitoids may not always be considered diagnostic of the tectonic setting (e.g. Frost and Frost, 2008; Wang et al., 2009; Zhang et al, 2016). Another issue concerning the Neoproterozoic evolution of the western margin of

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the Yangtze Block is the lack of early Neoproterozoic magmatic rocks. Arc-related

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volcanic rocks (ca 970–860 Ma) have been reported from the southeastern margin of

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the block (Li et al., 2009), but contemporaneous arc magmatism has not previously

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been found in the western part of the block. Li et al. (2017) reported ca 970 Ma spilite–keratophyre associations in the Tongmuliang area, but the volume of similar

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arc crust in the western margin of the block is uncertain. Given that granitoids are derived mainly from crustal reworking, and most Neoproterozoic granitoids in the

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western Yangtze Block have depleted Nd–Hf isotopic features (e.g. Chen et al., 2015; Huang et al., 2008; Li et al., 2002; Zhou et al., 2006), the volume of juvenile arc crust

sources.

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involved in the formation of the granitoids may be deduced though evaluation of their

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Here we present laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U–Pb ages, major- and trace-element compositions, Sm–Nd isotopic signatures, and zircon Hf isotopic compositions for granitoids and associated basaltic porphyries in the Jiaoziding area. The aim is to constrain the tectonic setting of the Neoproterozoic granitoids and to establish the genetic relationship between middle Neoproterozoic granitoids and early Neoproterozoic arc rocks. The results are

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used to elucidate the early stages of subduction at the western margin of the Yangtze Block and to advance our understanding of the amalgamation and break-up of the Rodinia supercontinent.

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2. Geological background and sampling

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The Yangtze Block is separated from the Songpan–Ganze terrane in NW Sichuan

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Province by the Longmenshan Thrust Belt (Fig. 1B). The Neoproterozoic Panxi and Hannan belts converge in the area, and Indosinian overthrusting is well developed

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(Pei et al., 2009). Neoproterozoic rocks occur along the Longmenshan Thrust Belt, including the Neoproterozoic Pengguan, Baoxing, and Xuelongbao Complexes in the

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southern part of the belt (Fig. 1B), and the Jiaoziding granitic dome in the north (Fig. 1C). The latter comprises mainly the Jiaoziding granitic pluton and minor associated

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mafic rocks, which intrude the Tongmuliang Group and are unconformably overlain by Nanhua–Sinian supracrustal rocks. The Tongmuliang volcanic rocks consist of

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spilite–keratophyre and quartz-keratophyre associations that formed at ca 970 Ma in an intra-oceanic arc setting (Li et al., 2017). The Jiaoziding granitoids comprise mainly biotite granodiorite, biotite quartz monzonite, quartz monzonite, and potassium granite, and are dated at 792 ± 11 Ma (Pei et al., 2009). The Jiaoziding granitoids are intruded by the basaltic porphyry dykes (Fig. 2A–C), although only two dykes were found in present field study. Nine granitoid and two

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basaltic porphyry samples were collected on the basis of detailed geological field investigations. The granitic samples are light gray in the field and consist of fine- to medium-grained biotite granodiorites and biotite quartz monzonite. The dominant rock-forming minerals include quartz, plagioclase, K-feldspar and biotite, with

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plagioclase generally being replaced by tiny sericite and epidote crystals (Fig. 2E–F).

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The basaltic porphyries contain 30–40 vol.% plagioclase phenocrysts that are

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euhedral to subhedral and occur as prisms of length 0.1–0.5 cm. The groundmass

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consists of plagioclase, pyroxene, and secondary minerals such as calcite, chlorite,

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sericite, and epidote.

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3. Analytical procedures

All of the analytical processes were carried out at the State Key Laboratory for

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Mineral Deposits Research of Nanjing University. For the three granitoid and one basaltic porphyry samples that were selected for

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LA–ICP–MS zircon U–Pb dating, zircons were separated from the crushed samples using heavy liquid and magnetic techniques and then were mounted in epoxy resin and polished to expose their centers. Based on transmitted-light and reflected-light microphotographs and cathodoluminescence (CL) images, U–Pb dating of zircons from the samples were carried out by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) using an Agilent 7500a ICP–MS system with a Geolas

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193 nm laser ablation system, following the descriptions of Zhang et al. (2017). Zircon U–Pb isotopic data are listed in Table 1. In situ Lu–Hf isotopic analyses of zircon were conducted using a GeoLas 193 nm ArF3 laser ablation system attached to a Neptune Plus MC–ICP–MS. For all of the

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zircons show small sizes, a beam diameter of 44 μm was adopted at a repetition rate

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of 10 Hz and pulse energy density of 10.5 J/cm2. The detailed procedures and data

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isotopic compositions are given in Table 2.

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processing are also similar to Zhang et al. (2017). Analytical results of the Lu–Hf

Major element concentrations were measured by a Thermo ARL9900XP X–ray

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fluorescence (XRF) spectrometer. The analytical precision is generally better than 2% for all elements. Whole-rock rare earth and other trace elements were analyzed using

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an ICP–MS (Finnigan MAT–Element II) instrument. Analytical precision for most elements by ICP–MS is better than 5%. Whole-rock major and trace element analyses

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for all samples are listed in Table 3. Whole-rock Sm–Nd isotopic compositions were measured using a Finnigan Triton

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TI thermal ionization mass spectrometer (TIMS), following the methods of Pu et al. (2004, 2005) and the data processing similar to Li et al. (2017) and Zhang et al. (2017). Whole-rock Sm–Nd isotopic data of the samples are given in Table 4.

4. Results

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4.1. Zircon U–Pb geochronology and Hf isotopic compositions

Zircon grains from the three granitoid samples (15QX-1-1, 15QX-1-2, 15QX-13-1) show similar characteristics during CL imaging. They are euhedral to subhedral

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prisms, 100–150 m long and 50–100 μm wide. Although they are generally dark in

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CL images, clear oscillatory zoning can also be observed. In contrast, zircons from the

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basaltic porphyry sample, 15QX-3-1, are dark in CL images with indistinct wide

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oscillatory zoning. All of analysed zircons have Th/U ratios range of 0.4–1.4, confirming a magmatic origin.

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Three of the granitoid samples yield similar ages of 796 ± 10 Ma (MSWD = 0.023, n = 10) for sample 15QX-1-1, 793±7 Ma (MSWD = 0.086, n = 15) for 15QX-1-2, and

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795 ± 6 Ma (MSWD = 0.2, n = 15) for 15QX-13-1 (Table 1; Fig. 3), consistent with the SHRIMP dating results of Pei et al. (2009). The overall mean age is 795 ± 6 Ma.

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Three zircon grains from the basaltic porphyry yield concordant early Paleoproterozoic to late Neoarchean ages of 2136 ± 46, 2501 ± 48, and 2524 ± 41 Ma,

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and two yield early Neoproterozoic ages of 914 ± 37 and 861 ± 20 Ma, with all five grains possibly having been captured during magma ascent. Four LA spot analyses yielded a weighted mean

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Pb/238U age of 790 ± 20 Ma (MSWD = 0.03; n = 4),

possibly representing the formation age of the basaltic porphyry, while other grains with discordant ages had possibly lost Pb (Table 1; Fig. 3).

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Nineteen dated zircons from two granitoid samples (15QX-1-1 and 15QX-13-1) were analysed for Hf isotopes, and the mean age of 795 Ma was chosen as the crystallization age for calculations of isotopic compositions. All of the analysed 176

outlier (sample QX-13-1#03;

Hf/177Hf ratios of 0.282510–0.282658 except for one 176

Hf/177Hf = 0.282274) that is light in CL images; data

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zircons show high initial

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from this zircon were omitted from subsequent calculations. Calculated εHf(t) values

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are +8.0 to +13.2, with corresponding two-stage model ages of 1176–838 Ma and a

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weighted-mean age of ca 990 Ma, suggesting that these zircons were derived from

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juvenile crust.

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4.2. Whole-rock geochemistry

The Jiaoziding granitoids have high SiO2 (69.2–76.9 wt%), K2O (2.3–5.6 wt%),

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and Na2O (3.2–5.1 wt%) contents, and low Al2O3 content (12.4–14.5 wt%). In Harker diagrams (Fig. 4A–H), they show negative correlations between SiO2 and Al2O3,

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MgO, Fe2O3T, CaO, TiO2, and MnO, and a positive correlation with K2O, indicating fractional crystallization. However, the Na2O content remains fairly constant at ~4.0 wt%) with increasing SiO2 content (Fig. 4I). The ASI index values (i.e., the A/CNK ratio) of all samples are in the range varies from 0.99–1.15 (Table 3), indicating slightly peraluminous characteristics.

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The chondrite-normalized rare earth element (REE) patterns (Fig. 5A) of the granitoid samples show enrichment in light REE (LREE) and flat heavy REE (HREE) patterns, with negative Eu anomalies (Eu/Eu* = 0.3–0.7). The samples also exhibit slightly negative correlations between SiO2 content and Eu anomalies, total REE,

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LREE, and HREE contents, which are consistent with fractional crystallization. In

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primitive mantle-normalized spidergrams (Fig. 5B), all of the granitoids exhibit

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enrichment in large-ion lithophile elements (LILE) such as Rb, Ba, and K, and strong

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negative anomalies high field strength elements (HFSE) such as Nb, Ta, and Ti. The Two basaltic porphyry samples have almost identical major- and trace-element

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characteristics, even though they were collected from different intrusions. Both are characterized by low SiO2 (~49.5 wt%) contents and Mg number (Mg# = 38), high

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TiO2 (~3 wt%) and Fe2O3T (~13.0 wt%) contents, total alkalis (Na2O+K2O) of >3.7 wt%, and moderate CaO (~7.5 wt%) and Al2O3 (~14.5 wt%) contents. They have high

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Nb/Y ratios (~1.0), indicating an alkaline affinity. Their REE patterns (Fig. 5C) are consistent with that of typical OIB (Sun and McDonough, 1989) and display

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enrichment in LREEs, without Eu anomalies. HFSEs (Nb, Ta, Zr, Hf and Ti) are generally not depleted in primitive mantle-normalized diagrams (Fig. 5D). It is possible that Rb and Ba were derived from secondary alteration, the positive Pb anomalies reflect crustal contamination, and the negative P anomalies resulted from the fractional crystallization of apatite.

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4.3. Whole-rock Sm–Nd isotopic compositions

The εNd(t) values of the granitoids are relatively constant at about +2.6, with a corresponding two-stage (TDM2) Nd model age of ~1250 Ma, indicating a relatively

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depleted source (Table 4). The two basaltic porphyries have similar εNd(t) values

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about +5.7 with a corresponding single-stage (TDM) Nd model ages of ~1000 Ma.

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5. Discussion

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5.1. Post-magmatic alteration

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Many Neoproterozoic rocks of the western Yangtze Block show evidence of dynamic overprinting and hydrothermal alteration. In the present study, microscopic

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study of the Jiaoziding granitoids revealed that plagioclases have generally been replaced by tiny sericite and epidote crystals, indicating alteration that might have

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affected the concentrations of mobile elements in the rock. Zr is considered immobile during low-grade alteration of magmatic rocks and so may be used in tracing the magmatic evolution (e.g. Polat et al., 2002; Polat and Hofmann, 2003). Concentrations of major and trace elements in the Jiaoziding granitoids were plotted against Zr contents (Fig. 6) to evaluate their mobilities, with most showing significant correlation with Zr (e.g. Hf, Y and Sr), while some show no such correlation (e.g. Na,

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Ba, Pb and U), suggesting the effects of alteration. The following sections focus on the immobile elements (i.e., those that show a correlation with Zr) in probing the petrogenesis and tectonic settings of the granitoids. The basaltic porphyries consistently have REE and HFSE contents very similar to

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those of typical OIB, although their Rb, Ba, and K contents vary (Fig. 5D). Their

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positive Pb anomalies may have resulted from crustal contamination, but this is not

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considered significant as they are strongly depleted in Nd isotopes.

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5.2. Petrogenesis of the Jiaoziding granitoids

The geochemical characteristics of granitoids are ultimately controlled by the

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nature of their source, the degree of partial melting, fractional crystallization, magma mixing, wall-rock assimilation during magma ascent, and possibly post-magmatic

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alteration discussed in Section 5.1 (e.g. Barbarin, 2005; Clemens and Stevens, 2012; Stevens et al., 2007; Wu et al., 2017). The consistent Nd(t) values (~ +2.6) and lack

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of captured zircons in the Jiaoziding granitoids preclude significant crustal assimilation. In addition, no geological and petrographic evidence has been found for magma mixing and mingling. Accordingly, the discussion here focuses on the significance of fractional crystallization, the nature of the source, and partial melting as controls on the petrogenesis of the Jiaoziding granitoids.

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5.2.1 Effects of fractional crystallization and identification of silicic parental melt

Fractional crystallization (crystal–liquid segregation) occurs readily in low-silica mafic magmas but can also occur in silicic viscous magmas (Gelman et al., 2014; Lee

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and Morton, 2015; Wu et al., 2017), although the processes involved are complicated.

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Fractionally crystallized granitic melts are difficult to recognize in the field because

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the densities of crystallizing minerals and co-existing melts are similar (e.g. Clemens

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and Petford, 1999; Wu et al., 2017), meaning there is no significant separation between accumulating minerals and residual differentiated melts. Both high-silica

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liquid-dominated and complementary cumulate-dominated facies are derived from pre-existing silicic parental melt (Lee and Morton, 2015). Although difficult to

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distinguish in the field, subtle changes between the two phases can be traced by geochemical variations, especially for incompatible elements and their ratios. For

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example, Rb, Sr, SiO2, Eu/Eu*, Rb/Sr and Zr/Nb show subtle variations with decreasing Zr content (Fig. 6), corresponding to crystal–liquid segregation during the

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evolution of silicic magma. The point of inflection (Fig. 6), which is consistently at Zr = 140 ppm for the Jiaoziding granitoids, may represent the composition of silicic parental melt. Samples with Zr < 140 ppm represent liquid-dominated facies that have experienced fractional crystallization of K-feldspar, plagioclase, and zircon, while those with Zr > 140 ppm represent cumulate-dominated facies with crystal accumulations of plagioclase and/or zircons. It is therefore suggested that the

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liquid–crystal segregation played an important role in determining the geochemical compositions of the high-silica Jiaoziding granitoids, and sample 15QX-1-3 (Zr = 134

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5.2.2 Nature of source rocks of the Jiaoziding granitoids

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ppm) could approximate the silicic parental melt.

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Experimental studies have indicated that peraluminous granites can be produced

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either by partial melting of metasedimentary rocks (S-type granites) or meta-igneous rocks (I-type) (P. Gao et al., 2016, and references therein). In addition, some I-type

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granites can also be generated from the melting of metasediments (Kemp et al., 2006). Pei et al. (2009) proposed that the Jiaoziding granitoids are S-type, following the

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classifications of Chappell and White (1974), and formed by partial melting of a greywacke source. However, mobile elements such as Na and Ba were used in their

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geochemical evaluations, which cast doubts on the conclusions. Previous studies have found that I- and S-type granites can be distinguished in SiO2 vs P2O5 (Chappell and

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White, 1992, Chappell, 1999), SiO2 vs A/CNK (Clemens and Stevens, 2012), Rb vs Th and Y (Li et al., 2007), SiO2 vs Zr, and Zr vs TiO2 (Wang et al., 2015) plots. The Jiaoziding granitoids resemble typical I-type granites in SiO2 vs P2O5 and Zr and Rb vs Th diagrams (Fig. 7). In addition, they have medium A/CNK values (~1.05) that are lower than those of typical S-type granites (A/CNK > 1.1) (e.g. Chappell, 1999). However, some of the geochemical approaches to distinguishing I- from S-type

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granites may be unreliable due to factors such as secondary alteration. The most important aspect of distinguishing between I- and S-type granites is to discriminate between their source features (i.e., meta-igneous vs meta-sedimentary) (e.g. P. Gao et al., 2016). There may be a transition from I- to S-type during the magmatic evolution

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due to the addition of new supracrustal melts (X.L. Wang et al., 2013). Magma

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sources can thus be difficult to constrain, and the source characteristics of

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Neoproterozoic granitoids in the western Yangtze Block remain unresolved.

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The Tongmuliang volcanic rocks in the study area have been dated at ca 970 Ma, and they show arc geochemical features with depletion in Nd–Hf isotopes (Li et al.,

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2017). These rocks are wall rocks of the ca 795 Ma Jiaoziding granitoids, and the genetic relationship between them needs to be evaluated.

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The Jiaoziding granitoids exhibit similar Nd–Hf isotopic features to the Tongmuliang volcanic rocks. Zircon from quartz-keratophyres of the Tongmuliang

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Group yield εHf(970 Ma) values of +12.7 to +18.0 (Fig. 7), with a mean of +15.1. If calculated at the same age as the Tongmuliang volcanic rocks, the Jiaoziding

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granitoid zircons will yield εHf (t) values of +11.8 to +16.9, with a mean of +14.0, which is consistent with the former. Whole-rock Nd isotopic analyses give similar results. The Jiaoziding granitoids yield εNd(970 Ma) values of +3.6 to +5.6, with a mean of +4.3, which is consistent with the mean whole-rock

Nd value (+4.1) for

the Tongmuliang volcanic rocks. During equilibrium melting, magmas inherit the isotopic characteristics of their source, and radiogenic isotopic compositions

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commonly remain stable during subsequent magmatic evolution at normal crustal depth (e.g. Xu et al., 2005). Thus, the similar zircon Hf and whole-rock Nd isotopic compositions of the Tongmuliang volcanic rocks and their equivalents indicate that these rocks are potential sources of the Jiaoziding granitoids.

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The geochemistry of the Jiaoziding granitoid samples indicate a genetic

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relationship with the Tongmuliang arc volcanic rocks. Melting experiments (Jung et

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al., 2007 and references therein) indicate that partial melts of meta-basalts and

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meta-greywackes have high CaO/Na2O ratios (>0.3), while mature crust has higher Al2O3/CaO ratios. Some of the Jiaoziding granitoids have high CaO/Na2O (~0.3) and

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Al2O3/CaO (~14) ratios (Fig. 9), similar to the Tongmuliang felsic volcanic rocks. Other Jiaoziding granitoids, with higher Al2O3/CaO, CaO/(MgO+FeOt), and

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Al2O3/(MgO+FeOt) ratios, were possibly sourced from materials similar to the Tongmuliang mafic–intermediate volcanic rocks. Modelling of partial melting is

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considered in the next section.

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5.2.3. Partial melting

REE distribution patterns were used to simulate partial-melting processes to verify the genetic relationship between the Jiaoziding granitoids and the Tongmuliang volcanic rocks. Partial-melting processes were modelled by batch-melting mode, which is suitable for application to viscous felsic melts. During batch melting,

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elemental and isotopic equilibria are maintained between residual solid and melt until the melt separates from its source. With regard to an individual element (e.g. La), the following equation is derived by mass balance: CiL/ CiO=1/［Di (1-F)+F］

(1)

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where i is the element of interest; CiO and CiL are concentrations of the element in the

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original (O) solid phase and the detached liquid (L), respectively; Di is the partition

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coefficient of the element; and F is the melt fraction. This equation, which is useful in

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determining enrichment or depletion of a trace element in liquid with various degrees of melting, was established on the premise that the original solid is homogeneous and

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made up of one simple phase. In most cases, however, the source comprises several phases (e.g. an assemblage of various minerals), and Di must be replaced with a bulk

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distribution coefficient (Do), which represents the weighted-mean distribution coefficient of the element in the original solid. However, the molten minerals

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generally do not follow the proportions found in original solid. Therefore, the parameter P is introduced to define the weighted-mean distribution coefficient of the

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element in molten minerals. A more realistic equation is therefore given as: CiL/ CiO=1/［Do+F(1-P)］

(2)

As the Tongmuliang volcanic rocks are regarded here as possible source rocks for the Jiaoziding granitoids, the modelling was based on the assumptions that the source rocks are mafic rocks of the Tongmuliang group, and minerals enter the melt in the proportion of 28% clinopyroxene, 60% plagioclase, 10% amphibole and 2% apatite

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(used for calculating P). The mean primitive mineral composition of the mafic rocks was roughly as 48% clinopyroxene, 42% plagioclase, 4% amphibole, and 6% apatite (as observed microscopically and used for calculating Do). The mean REE contents of mafic rocks were adopted in modelling of the REE compositions (Table 5), while the

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REE composition of the Jiaoziding granitoids was based on that of sample 15QX-1-3

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(as r it could represent the silicic parental melt).. The resulting modelled degree of

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partial melting is 5%–20%, and details of modelling process are given in Table 5.

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Modeling results (Fig. 10A) indicate that REE patterns calculated after ~5% partial melting of the Tongmuliang mafic rocks are consistent with those of the Jiaoziding

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granitoids, as represented by sample 15QX-1-3.

In the same way, the Tongmuliang quartz-keratophyres were chosen as the source

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composition for modelling partial melting, as some of the Jiaoziding granitoids are geochemically similar to felsic volcanic rocks of the Tongmuliang Group. The

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quartz-keratophyres are relatively unaltered, and their primitive minerals are inferred to comprise 60% plagioclase, 38% quartz, and 2% biotite (according to microscopic

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observations). It was assumed that the minerals entered the melt in the proportion of 60% quartz, 35% plagioclase, and 5% biotite. Partition coefficients of REEs in rhyolite were used for

the modelling,

the mean REE

composition

of

quartz-keratophyres was taken as that of source rocks (Table 6), and the REE content of sample 15QX-1-3 was taken as that of the resulting melt. The resulting modelled degree of partial melting is 50%–70%, and details of the modelling process are given

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in Table 6. Thus, the modelling results indicate that the high-silica Jiaoziding granitoids could have been produced by ~50–70% partial melting of the Tongmuliang quartz-keratophyres (Fig. 10B). In summary, the modelling results indicate that the Jiaoziding granitoids could be from

~5%

and

50–70%

partial

melting

of

mafic

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derived

rocks

and

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quartz-keratophyres of the Tongmuliang Group, respectively, with materials such as

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the Tongmuliang volcanic rocks in the deep crust possibly being their source rocks.

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Accordingly, the Jiaoziding granitoids should be chassed as I-type granites, and their arc-signature geochemical characteristics are likely to have been inherited from the

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source.

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5.3. Petrogenesis of associated basaltic porphyries

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The petrogenesis of associated mafic rocks is important in elucidating the tectonic settings of granitoids (e.g. Wang et al., 2009; Zhang et al., 2016). As mentioned in

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Section 5.1, the two basaltic porphyry samples exhibit OIB-like geochemical characteristics and are contemporaneous with the Jiaoziding granitoids. Their REE and HFSE contents are identical to those of typical OIB, and their initial Nd isotopic ratios are similar to those of depleted mantle, indicating a depleted mantle source. Moreover, their geochemical characteristics of high Ti/V (~ 60), Zr/Ba (> 0.2), Zr/Y (> 6) and Ti/Y (> 410) ratios and low La/Nb (< 1.5) and La/Ta (< 22) ratios all support a

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derivation from asthenospheric mantle. Their geochemistry was modelled using PriMelts program (Herzberg and Asimow, 2008), yielding results similar to measured whole-rock compositions, enabling modelling of their origin and source characteristics by the methods of Shaw (1970) (Fig. 11).

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The La/Yb vs Dy/Yb and Y diagrams enable the distinction between melting

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processes in the stability field of garnet peridotite and spinel peridotite (Baker et al.

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1997). If both sources contributed to the melting process, the melts should lie in the

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transition area between the two fields. This is the case for the basaltic porphyries of the present study, which cannot be explained solely by variable degrees of partial

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melting of an exclusively garnet-bearing or spinel-bearing lherzolite source (Fig. 11A, B). Modelling indicates that mixing of 2% garnet peridotite and 0.5% spinel peridotite

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partial melts could produce the Jiaoziding basaltic porphyries, with 80–85% of the melt being from garnet peridotite. Furthermore, the degree of fractionation of REEs

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may constrain melting depth, and the Sm/Yb vs Ce/Yb diagram indicates that the primary melts that formed the Jiaoziding basaltic porphyries were generated at a depth

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of ~80 km (Fig. 11C; Ellam, 1992). This indicates that the basaltic porphyries were derived mainly from melting of asthenospheric mantle at a depth of <80 km, and that the thickness of the lithosphere must have decreased to <80 km prior to 790 Ma. The present-day thickness of the continental lithosphere is generally >100 km, so the upwelling of asthenospheric materials may have resulted from delamination in

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response to large-scale lithospheric extension along the western margin of the Yangtze Block.

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5.4. Implications for the Neoproterozoic tectonic setting of the western Yangtze Block

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The Neoproterozoic tectonic setting of the Yangtze Block is complex and is hotly

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debated. Li et al. (1999) proposed a mantle plume beneath South China at ca 820 Ma,

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based on a comparison of 827 Ma mafic–ultramafic dykes and sills in Guangxi Province with mantle-plume-induced Gairdner dyke swarms in Australia. Z.X. Li et al.

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(2003) reported 780–750 Ma Kangdian rift-related magmatism in the western Yangtze Block, and proposed two episodes of mantle-plume magmatic activity (830–795 and

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780–745 Ma), as supported by 820–796 Ma high-temperature picritic dikes and komatiitic basalts (X.H. Li et al., 2010; Wang et al., 2007), 820–810 Ma Bikou

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continental flood basalts (Wang et al., 2008), 860–790 Ma bimodal volcanic and intrusive rocks (W.X. Li et al., 2010; X.H. Li et al., 2002, 2008; Lyu et al., 2017) and

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widely distributed 790–760 Ma OIB-like mafic–ultramafic dyke swarms in the Yanbian and Kangding areas (Z.X. Li et al., 2003; Lin et al., 2007; Zhu et al., 2008). Contemporaneous felsic magmas were considered to have been derived from partial melting of different sources triggered by a (super-) mantle plume (X.H. Li et al., 2003b, 2008; Wang et al., 2010). Wang et al. (2011) studied Neoproterozoic sedimentary and volcanoclastic rocks in the Nanhua Basin and concluded that they

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received much detritus from mafic rocks resembling mantle-plume-related continental flood basalts. However, the mantle-plume model does not explain the petrogenesis of the 820–740 Ma mafic rocks that show an arc affinity (Zhao and Zhou, 2007a, 2009; Zhou et al., 2002b), or the ca 830–810 Ma back-arc mafic rocks (Li et al., 2013, 2016;

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Zhang FF et al., 2017) of the Yangtze Block. In contrast, arc-like geochemical

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characteristics were interpreted as being derived from a subcontinental lithospheric

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mantle that had previously been metasomatized by subduction-related melts and fluids

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(W.X. Li et al., 2010; X.H. Li et al., 2008; Lyu et al., 2017; Shen et al., 2003; Zhu et al., 2006, 2007). The slab-arc model (e.g. Wang et al., 2016; Zhao et al., 2008, 2011;

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Zhao and Zhou, 2008; Zhou et al., 2002a, 2002b; Zhou et al., 2006) describes a long-term subduction (950–735 Ma) along the western margin of the Yangtze Block.

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Mid-Neoproterozoic subduction is indicated by the existence of ca 860 Ma Guandaoshan diorites (Du et al., 2014) with strong arc affinities, ca 860 Ma Gongcai

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slab-derived adakitic tonalities (Chen et al., 2015), and back-arc magmatic and sedimentary rocks (Hu et al., 2007; Li et al., 2013, 2016; Wang et al., 2014). A fossil

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subduction belt at depth in the Sichuan Basin has recently been identified by dipping sub-Moho reflection profiles (R. Gao et al., 2016), with the belt interpreted as being a relict of Neoproterozoic subduction, possibly indicating mid-Neoproterozoic subduction activities. The slab-arc model may generally explain the tectonic setting of magmatic rocks older than ca 820 Ma, but fails to explain regional Neoproterozoic rift structures throughout the whole Sichuan Basin (Gu and Wang, 2014) or the

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occurrence of voluminous 790–760 Ma OIB-like mafic dyke swarms. Furthermore, Neoproterozoic orogeny-related middle- to high-grade regional metamorphism has not been identified in the Yangtze Block. Thus, the popular models outlined above have their advantages and disadvantages,

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but none fully explained all of the geological and geochemical features of the Yangtze

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Block. There exists strong petrological, sedimentary, geochemical, and geophysical

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evidence supporting a regional extensional setting for the Yangtze Block after ca 820

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Ma (e.g. Gu et al., 2014; Gu and Wang, 2014; Huang et al., 2008, 2009; Ren et al., 2013; J. Wang et al., 2013; Zhao et al., 2011; Zhou et al., 2002b; Zhu et al., 2008).

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This period of extension was commonly interpreted as being due to rifting, post-orogenic delamination, or back-arc spreading (e.g. Hu et al., 2007; X.H. Li et al.,

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2008, 2010; Zhao et al., 2008). On the other hand, the 860–830 Ma tectonic setting is more likely to have been compressional, related to oceanic slab subduction, as

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indicated by the large volume of arc-like intermediate–mafic rocks of this age but a lack of OIB-like radiating mafic dyke swarms. Considering the occurrence of

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subduction during 860–830 Ma, a post-orogenic extension model is favoured for the western margin of the Yangtze Block for the period after ca 820 Ma. Post-orogenic delamination may explain the coexistence of OIB-like and arc-like rocks, as the upwelling of depleted asthenospheric mantle and its subsequent partial melting can occur together with melting of early-metasomatized lithospheric mantle. Such a tectonic process resembles the early–middle Miocene orogenic event that affected the

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Niigata region in NE Japan (Shuto et al., 2006), although we cannot exclude the possibility of mantle-plume-related rifting after ca 820 Ma. It is therefore suggested that the Jiaoziding granitoids were derived from extension-induced partial melting of crustal materials, with the source characteristics

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most likely being similar to those of the wall rocks (the Tongmuliang arc volcanic

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rocks). Voluminous Neoproterozoic granites (numerous I-type with minor S- and

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A-type granitic plutons) were formed throughout the W and NW margins of the

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Yangtze Block after 860 Ma (e.g. Chen et al., 2015; Huang et al., 2008, 2009; Lin, 2010; Zhao and Zhou, 2007a, 2007b, 2008, 2009; Zhou et al., 2002a). Many of them,

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such as the Tianpinghe plutons, the Shimian, Daxiangling, Mianning, and Qinganlin intrusions, and the Kangding, Gongcai, and Miyi granitic gneiss, have depleted Nd-Hf

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isotopic characteristics (Chen et al., 2015; Huang et al., 2008; X.H. Li et al., 2003b; Lin, 2010; Zhao et al., 2008; Zhou et al., 2002a), as with the Jiaoziding granitoids.

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The present study of the Jiaoziding granitoids indicates a genetic relationship between Neoproterozoic granitoids and early Neoproterozoic arc magmatic rocks. Assuming

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that most of the Neoproterozoic granitoids of the W–NW margin of the Yangtze Block have sources similar to that of the Jiaoziding granitoids, it can be inferred that extensive early Neoproterozoic island arc magmatism occurred in the area, as represented by the Tongmuliang volcanic rocks. The potential existence of extensive early Neoproterozoic arc rocks indicates a widespread subduction zone along the W–NW margin of the Yangtze Block since the early Neoproterozoic. This subduction

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may have ended at ca 820 Ma, followed by the extensive delamination of lithospheric mantle and associated upwelling of deep asthenosphere that could feasibly have generated the OIB-like basaltic porphyries and other bimodal volcanic rocks (e.g. the Suxiong Formation; Li et al., 2002) in the region. Such extension is consistent with

SC

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Rodinia break-up need to be constrained by further study.

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that along the SE margin of the Yangtze Block, and its geological implications for

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6. Conclusions

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The ca 795 Ma Jiaoziding granitoids and associated contemporaneous basaltic porphyries appear to be closely related to newly reported ca 970 Ma arc-related

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volcanic rocks. The granitoids may have been generated by partial melting of the Tongmuliang volcanic rocks, as supported by their similar high initial zircon Hf and

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whole-rock Nd isotopic compositions, and partial-melting modelling results. The basaltic porphyries show OIB-type characteristics, and modelling indicates that

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mid-Neoproterozoic delamination occurred in response to large-scale lithospheric extension in the western Yangtze Block. Subduction at ca 860–830 Ma and subsequent (after ca 820 Ma) post-orogenic extension occurred in the western Yangtze Block. The ca 790 Ma OIB-like mafic rocks analysed here, along with many other 790–760 Ma OIB-like mafic dyke swarms in the western Yangtze Block and Neoproterozoic rift structures beneath the Sichuan basin, were possibly all formed by

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large-scale rifting induced by post-orogenic upwelling of asthenospheric mantle in the western Yangtze Block. Most granitoids of this period, including the Jiaoziding granitoids, and the Tianpinghe plutons, the Shimian, Daxiangling, Mianning and Qinganlin intrusions, and the Kangding, Gongcai and Miyi granitic gneiss, which

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display depleted Nd–Hf isotopic characteristics, may have been derived from partial

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melting of juvenile crustal materials that are geochemically similar to the

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Tongmuliang volcanic rocks. These conclusions indicate the likely occurrence of

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early Neoproterozoic arc rocks and widespread subduction along the W–NW margin

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of the Yangtze Block during early Neoproterozoic.

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Acknowledgements

This study was financially supported by the National Nature Science Foundation of

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China (41330208 and 41222016) and the Program for New Century Excellent Talents in University (NCET, to X.L. Wang). The manuscript benefits a lot from the

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thoughtful comments from three anonymous reviewers. We thank B. Wu for LA–ICP–MS dating, W.L. Xie for major elements, Q. Liu for trace elements and H.L. Lei for Sm–Nd isotope analyses.

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SHRIMP zircon U–Pb geochronology, elemental, and Nd isotopic geochemistry of the Neoproterozoic mafic dykes in the Yanbian area, SW China.

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Precambrian Research 164, 66–85. Figure Captions

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Fig.1. Geological sketch map of the Jiaoziding granitoids of the Yangtze Block (modified after Li et al., 2017). (A) Simplified tectonic map showing the location of the study area in northwestern Yangtze Block. (B) Simplified geological sketch map showing the distribution of Neoproterozoic rocks in northwestern Yangtze Block. QC–YPG Fault, Qingchuan–Yangpingguan Fault; BC–YX Fault, Beichuan–Yingxiu

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Fault; AX–DJY Fault, Anxian–Dujiangyan Fault. (C) Geological sketch map with sampling locations. Fig.2. Representative field photos and photomicrographs of the Jiaoziding granitoids and the associated basaltic porphyries.

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Fig.3. LA–ICP–MS zircon U–Pb Concordia plots of samples (15QX-1-1, 15QX-1-2,

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15QX-13-1 and 15QX-3-1) and representative cathodo-luminescence (CL) images for

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analyzed zircons. The analyzed 206Pb/238U ages are attached below the CL images.

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Fig.4. Harker diagrams of TiO2, Al2O3, Fe2O3T, MnO, MgO, CaO, K2O, P2O5 and Na2O versus SiO2.

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Fig.5. Chondrite-normalized REE patterns and primitive mantle-normalized diagram for the Jiaoziding granitoids and associated basaltic porphyries. Normalizing values of

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chondrite and primitive mantle are after Sun and McDonough (1989). Fig.6. Plots of Hf, Y, U, Rb, Eu/Eu*, Sr, SiO2, and Zr/Nb versus Zr for the Jiaoziding

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granitoids. Compositional shift was caused by crystal-liquid segregation. The kink represents the silicic parental melt.

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Fig.7. The discrimination diagrams for I-type and S-type granites. Fig.8. Initial zircon 176Hf/177Hf ratios versus U-Pb ages for the Jiaoziding granitoids and the Tongmuliang quartz-keratophyres. Fig.9. Al2O3/TiO2 versus CaO/Na2O and molar CaO/(MgO+FeOt) versus molar Al2O3/(MgO+FeOt) diagrams for the Jiaoziding granitoids and the Tongmuliang

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volcanic rocks. The Jiaoziding granitoids in this figure include the samples in this study and Pei et al. (2009). Fig.10. Partial melting modeling results for the spilites (A) and quartz-keratophyres (B) of the Tongmuliang Group.

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Fig.11. (A) – (B) Qualitative and semi-qualitative partial melting models based on

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La/Yb versus Yb and Dy/Yb, according to Tschegg et al. (2011). (C) Sm/Yb versus

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Ce/Yb, according to Ellam (1992).

Table 1 LA–ICP–MS zircon U–Th–Pb isotope analyses for zircons from the

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Jiaoziding granitoids and basaltic porphyry.

Table 2 LA–MC–ICP–MS Hf isotope compositions in zircons from the Jiaoziding

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granitoids.

Table 3 Major (wt%) and trace element (ppm) analyses for the Jiaoziding granitoids

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and the associated basaltic porphyries. Table 4 Whole-rock Sm–Nd isotope compositions of the Jiaoziding granitoids and the

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associated basaltic porphyries. Table 5 Modelling parameters of the volcanic rocks from the Tongmuliang Group. Table 6 Modelling parameters of the Tongmuliang quartz-keratophyres.

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ACCEPTED MANUSCRIPT Table 1 LA–ICP–MS zircon U–Th–Pb isotope analyses for zircons from the Jiaoziding granitoids and basaltic porphyry. Concentrations U-Th-Pb isotopic ratios

Isotopic age (Ma)

(ppm)

Spot analysis

Th/ Th

U

U

7/6

1σ

7/5

1σ

6/8

1σ

7/6

1σ

0.06

0.003

1.18

0.0

0.13

0.00

79

56

4

3

60

08

27

4

0.06

0.004

1.18

0.0

0.13

0.00

55

2

5

74

12

33

0.06

0.002

1.19

0.0

0.13

0.00

56

7

0

47

16

0.06

0.002

1.19

0.0

0.13

57

8

5

50

0.06

0.002

1.18

0.0

55

4

8

42

0.06

0.003

1.18

56

0

2

0.06

0.007

1.18

52

3

0.06 56

1

1

7/5

σ

6/8

σ

11

79

2

79

1

3

3

8

2

6

15QX-1-1, granite 24 3 25 7

15QX-1-1

22 138

-03 15QX-1-1

8 18

100 -04

17 107

-05 15QX-1-1

26 148

-06 15QX-1-1

3 25

128 -07

19 101

-08

30 332

-09 15QX-1-1

8 27

190 -10

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15QX-1-2, granite 17

117 -01

16

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126

21

176

23 178

-04

15 93

-05

28 237

-06

19 156

-07

79

2

79

1

6

2

7

4

79

2

79

1

8

3

9

4

79

1

79

1

5

9

6

2

79

2

79

1

79

87

24

7

0.13

0.00

79

15

22

1

0.0

0.13

0.00

79

52

07

25

4

97

2

4

2

4

0.1

0.13

0.00

78

24

79

5

79

2

1

27

13

51

2

5

2

9

5

9

0.008

1.18

0.1

0.13

0.00

79

29

79

7

79

3

8

7

55

10

61

4

8

4

2

4

5

0.002

1.18

0.0

0.13

0.00

79

79

2

79

1

92

77

55

5

6

45

13

23

1

83

4

1

5

3

0.06

0.004

1.18

0.0

0.13

0.00

79

14

79

3

79

1

55

3

9

76

17

33

0

2

6

5

8

9

0.06

0.005

1.18

0.0

0.13

0.00

79

17

79

4

79

2

55

17

1

89

08

38

0

1

2

1

3

1

0.06

0.003

1.18

0.0

0.13

0.00

79

10

79

2

79

1

56

26

7

57

15

26

2

7

5

6

6

5

0.06

0.002

1.19

0.0

0.13

0.00

79

79

2

79

1

57

85

2

50

17

24

7

93

7

3

7

4

0.06

0.005

1.18

0.1

0.13

0.00

81

19

79

4

78

2

62

85

7

00

02

44

2

2

5

6

9

5

0.06

0.001

1.19

0.0

0.13

0.00

79

79

1

79

1

57

87

3

33

18

19

5

7

5

8

1

0.06

0.001

1.18

0.0

0.13

0.00

79

79

1

79

1

55

6

0

29

06

19

2

1

3

1

1

0.06

0.002

1.17

0.0

0.13

0.00

79

78

2

78

1

55

66

5

46

01

23

1

9

2

8

3

61

0.8 9

15QX-1-2

9

0.6 5

15QX-1-2

5

0.7 8

15QX-1-2

4

0.8

6

15QX-1-2

4

0.8

4

15QX-1-2

0

0.7

7

15QX-1-2

1

0.7

5

15QX-1-2

0.06 1.1

1

20

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15QX-1-1

79

79

0.5 1

3

0.00

0.5 0

15QX-1-1

-03

0.6

79

4

0.6 5

14

24

0.5 7

15QX-1-1

-02

0.6

79

RI

-02

0.7

SC

181

NU

15QX-1-1

MA

-01

0.6

PT

157

D

15QX-1-1

52

0.8 6

87

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59 509

-08

0

15QX-1-2

14 85

4

15QX-1-2

0.6

21 147 6

15QX-1-2

30

0.0

0.12

0.00

79

78

2

78

1

55

83

1

49

96

25

0

93

7

3

6

4

0.06

0.004

1.19

0.0

0.13

0.00

79

15

79

3

79

2

57

56

5

80

19

36

8

0

8

7

9

0

0.06

0.002

1.17

0.0

0.13

0.00

79

78

1

78

1

55

27

4

40

00

22

0

74

9

9

8

3

0.06

0.004

1.17

0.0

0.13

0.00

78

16

79

3

79

2

55

86

9

84

06

37

9

1

1

9

1

1

0.06

0.003

1.18

0.0

0.13

0.00

79

10

79

2

79

1

56

21

7

56

14

26

0.06

0.003

1.18

0.0

0.13

0.00

56

85

3

66

12

29

0.06

0.002

1.18

0.0

0.13

55

12

4

37

12

0.06

0.002

1.18

0.0

56

46

9

44

0.06

0.001

1.19

0.0

60

7

4

31

0.06

0.002

1.18

60

5

0.06 54

0.9

-11

3

15QX-1-2

32 288

0

15QX-1-2

0.9

18 0.7

-13

4

15QX-1-2

21

-14

7

15QX-1-2

25 247

2

1.0

38

15QX-13-

61 371

1-02 15QX-13-

39 221

1-03

19 154

1-04

1

15QX-13114

94

1-05 19 277 1-06

21

256

8

15QX-13-

63

775

1-08

44

525 1-09

81 420

1-10

18 135

1-11

23 205

1-12 15QX-13-

5

6

79

1

79

1

3

7

5

1

79

2

79

1

6

0

7

3

79

1

79

1

8

4

4

1

79

2

78

1

1

0

6

4

79

1

79

1

0

7

1

3

79

1

79

1

5

8

6

3

78

2

78

1

9

3

8

5

80

2

80

1

5

5

0

5

79

1

79

1

9

1

9

1

80

1

80

1

23

3

0.13

0.00

80

10

20

7

0.0

0.12

0.00

80

0

44

98

25

5

0.002

1.17

0.0

0.13

0.00

78

0

7

36

05

23

8

1.18

0.0

0.13

0.00

79

0.002

69

81

55

80

64

56

2

8

39

14

22

4

72

0.06

0.002

1.17

0.0

0.13

0.00

79

55

9

5

50

00

26

1

0.06

0.003

1.20

0.0

0.13

0.00

81

64

1

9

54

22

27

8

0.06

0.001

1.19

0.0

0.13

0.00

79

57

2

6

24

20

19

8

0.06

0.002

1.20

0.0

0.13

0.00

80

59

1

7

38

28

22

4

68

4

7

4

2

0.06

0.006

1.19

0.1

0.13

0.00

80

21

79

5

79

2

58

6

2

15

14

49

1

9

7

3

6

8

0.06

0.001

1.19

0.0

0.13

0.00

79

79

1

79

1

58

9

4

35

17

21

8

63

8

6

7

2

0.06

0.003

1.18

0.0

0.13

0.00

79

10

79

2

79

1

55

2

1

56

08

29

0

5

2

6

2

6

0.06

0.001

1.17

0.0

0.12

0.00

80

79

1

78

1

59

3

7

25

96

19

2

44

0

2

6

1

0.06

0.001

1.19

0.0

0.13

0.00

79

46

79

1

79

1

94

98

40

0.9 1

137

1

0.7 4

15QX-13-

3

0.5 1

15QX-13-

7

1.2 4

15QX-13-

3

1.2

3

15QX-13-

1

1.2

AC

1-07

79

1.4

2

15QX-13-

3

1.2

CE

15QX-13-

0.06 0.8

79

15

PT E

15QX-13-

12

79

0.6 4

79

0.00

0.6 2

5

0.13

1.2 8

6

1

D

1-01

6

20

MA

485

5

79

15QX-13-1, granite 15QX-13-

5

0.00

1.0

SC

219

4

RI

131

PT

261

-15

1.17

0.7

-10

-12

0.002

NU

-09

0.06 0.9

15

0.9

ACCEPTED MANUSCRIPT 1-13

5

15QX-13-

31 292

1-14

28 138

1-15

4

3

27

17

20

7

7

2

7

1

0.06

0.001

1.20

0.0

0.13

0.00

80

80

1

80

1

59

5

4

29

25

21

4

3

3

2

2

0.06

0.001

1.17

0.0

0.13

0.00

79

79

1

79

1

55

3

9

25

05

20

1

42

1

1

1

1

0.06

0.005

0.61

0.0

0.07

0.00

70

17

48

3

44

1

28

1

5

48

09

21

3

8

6

0

2

2

0.06

0.006

0.82

0.0

0.09

0.00

78

20

61

4

56

1

54

0

9

73

17

29

0.06

0.004

1.45

0.0

0.15

0.00

98

4

9

89

16

33

0.06

0.007

1.16

0.1

0.12

52

1

4

22

94

0.06

0.009

0.65

0.0

49

2

9

91

0.13

0.007

7.19

0.3

23

1

4

0.06

0.006

1.18

0.9 4

15QX-13-

57

49

0.5 6

15QX-3-1, basaltic porphyry 15QX-3-1

23

-01

5

15QX-3-1

29 117

-02

0.5

15QX-3-1

0

0.4

10

8

0

3

1

6

7

92

13

91

3

91

1

1

2

4

7

0

8

0.00

78

23

78

5

78

2

45

2

8

4

7

4

6

0.07

0.00

77

31

51

5

45

1

36

27

1

5

4

6

8

6

0.39

0.01

21

21

4

21

4

68

40

05

29

96

36

6

41

9

0.1

0.13

0.00

78

20

79

4

79

2

5

0.8

15QX-3-1 -04

1.3

15QX-3-1 50

-05 15QX-3-1

70

0.7

12 106

-06

4

15QX-3-1

0.9

21 8

15QX-3-1

54

25 170

-08

0.6

15QX-3-1

0

0.7

55

1

1

06

10

43

7

4

2

9

4

5

0.06

0.004

1.17

0.0

0.13

0.00

78

15

78

3

79

2

52

6

5

79

06

35

2

2

9

7

1

0

0.002

1.33

0.0

0.14

0.00

87

86

2

85

1

4

6

46

22

25

2

1

0

7

4

0.16

0.007

11.0

0.4

0.48

0.01

25

25

4

25

5

63

7

1

90

01

17

21

80

24

1

28

1

0.06

0.006

0.84

0.0

0.09

0.00

77

20

62

4

58

1

51

1

4

76

42

31

9

6

1

2

0

8

0.16

0.009

10.7

0.5

0.47

0.01

24

25

4

24

5

42

0

37

57

36

33

99

95

01

8

99

8

0.06

0.008

1.17

0.1

0.12

0.00

79

28

78

6

78

3

56

4

5

44

98

55

4

2

9

7

7

2

0.06

0.002

0.78

0.0

0.08

0.00

79

58

1

53

55

7

2

32

66

15

0

7

8

6

0.06

302 4

15QX-3-1

10 85

-10

3 38 233

-11 15QX-3-1

50 -12

0.6

AC 1

15QX-3-1

207

1.2

40

328 206

6

0.8 207

235

Note: 7/6- Pb/ Pb, 7/5- Pb/ U, 6/8-206Pb/238U

74

66 14

163

-14

0.8

0.8

15QX-3-1 -13

6

81

CE

15QX-3-1

0.5

PT E

-09

D

-07

MA

135

SC

76

NU

96

RI

89 -03

PT

115

90

9

ACCEPTED MANUSCRIPT Table 2

LA–MC–ICP–MS Hf isotope compositions of zircons from the Jiaoziding

granitoids. t Analysis

(Ma )

176

Yb/17

176

Lu/17

7

7

Hf

Hf

176

Hf/17

7

176

2σ

Hf

Hf/17

7

Hfi

εHf(

εHf(

2

TD

TD

2

fLu/

0)

t)

σ

M1

M2

σ

Hf

11.

0.

88

93

3

-0.

7

8

5

7

5

93

15QX-1-1,

15QX-1-1 -03

795

15QX-1-1 -04

795

15QX-1-1 -05

795

15QX-1-1 -06

795

15QX-1-1 -07

795

15QX-1-1 -08

795

15QX-1-1 -09

795

68

84

49

024

5

0.0586

0.0019

0.2825

0.000

0.28251

43

03

38

024

0

0.0751

0.0021

0.2825

0.000

0.28256

77

79

94

021

2

0.0832

0.0025

0.2826

0.000

0.28263

56

06

70

022

3

0.0912

0.0029

0.2826

0.000

0.28261

29

84

59

023

5

0.0557

0.0016

0.2825

0.000

0.28255

20

87

84

023

8

0.0904

0.0026

0.2826

0.000

0.28265

93

82

93

022

4

0.0699

0.0020

0.2826

0.000

0.28259

95

72

26

021

5

0.1557

0.0040

0.2826

0.000

0.28260

42

15QX-13-1, granite

1-01

0.1048 795

15QX-13795

15QX-131-03

795

15QX-131-04

795

15QX-131-05

795

15QX-131-06

795

15QX-13-

0.

10

11

3

-0.

9

35

76

5

94

0.

96

10

3

-0.

9.8

8

1

57

1

93

12.

0.

85

89

3

-0.

-4.1

3

8

8

5

3

92

11.

0.

88

93

3

-0.

7

8

6

7

5

91

0.

96

10

3

-0.

9.7

8

3

65

2

95

13.

0.

82

84

3

-0.

1

8

8

8

2

92

11.

0.

91

98

3

-0.

0

7

2

1

0

94

11.

0.

90

95

3

-0.

4

8

2

6

6

88

11.

0.

87

92

3

-0.

9

8

8

3

4

90

0.

96

10

4

-0.

-8.7

-6.7

67

024

6

0.0031

0.2826

0.000

0.28262

-4.5

-7.1

-3.2

-5.6

-4.2

-4.2

8.0

83

60

68

023

1

0.1271

0.0039

0.2826

0.000

0.28256

34

53

24

027

5

-5.7

9.9

9

5

50

1

88

0.0370

0.0012

0.2822

0.000

0.28227

-17.

-0.

0.

13

17

3

-0.

61

07

92

023

4

4

4

8

63

09

2

96

0.0463

0.0014

0.2825

0.000

0.28256

0.

95

10

3

-0.

27

03

83

021

2

9.8

7

7

57

0

96

0.0872

0.0026

0.2826

0.000

0.28262

12.

0.

86

91

3

-0.

27

28

66

026

6

1

9

8

0

9

92

0.1120

0.0034

0.2826

0.000

0.28255

0.

97

10

4

-0.

74

13

05

027

4

9

8

74

0

90

0.0416

0.0012

0.2825

0.000

0.28252

0.

10

11

2

-0.

AC

1-02

87

CE

15QX-13-

-4.8

RI

795

0.28261

SC

-02

0.000

NU

15QX-1-1

0.2826

MA

795

0.0022

D

-01

0.0758

PT E

15QX-1-1

PT

granite

-7.1

-4.2

-6.4

9.6

1-07

795

81

56

42

021

3

-8.6

8.5

7

11

45

9

96

15QX-13-

795

0.0925

0.0028

0.2826

0.000

0.28260

-5.0

11.

0.

90

96

3

-0.

ACCEPTED MANUSCRIPT 1-08

65

43

44

022

2

2

8

5

6

2

91

15QX-13-

0.0775

0.0022

0.2826

0.000

0.28260

11.

0.

90

96

2

-0.

04

74

35

020

1

2

7

5

8

9

93

0.1082

0.0032

0.2827

0.000

0.28265

13.

0.

82

83

3

-0.

09

96

07

025

8

2

9

2

8

8

90

1-09

795

15QX-131-10

795

-5.3

-2.8

Note: 1) εHf(t) = 10,000×{[(176Hf/177Hf)S – (176Lu/177Hf)S×(et–1)]/[(176Hf/177Hf)CHUR,0 – (176Lu/177Hf)CHUR×(et–1)]–1}

PT

2) TDM = 1/ × ln{1 + [(176Hf/177Hf)S – (176Hf/177Hf)DM] / [(176Lu/177Hf)S – (176Lu/177Hf)DM]}

AC

CE

PT E

D

MA

NU

SC

RI

3) TDM2 = 1/ × ln{1 + [(176Hf/177Hf)S, t – (176Hf/177Hf)DM, t ] / [(176Lu/177Hf)C – (176Lu/177Hf)DM]} + t

ACCEPTED MANUSCRIPT Table 3 Major (wt. %) and trace element (ppm) analyses for the Jiaoziding granitoids and the associated basaltic porphyries. No.

1

2

3

4

5

6

7

15

15

15

15

15

15

15

QX

QX

QX

QX

QX

QX

1

-12

-13

-42

-8-

-9-

1

1

9

10

15Q

15Q

15Q

X-1

X-1

X-1

1-2

3-1

1-1

QX

-9-

-3-

2

1 bas

PT

gra bas

niti gra

gra

gra

gra

gra

c

Rock type nite

nite

nite

nite

enc

gra

nite

RI

nite

gra

nite

alti altic gra

c por

nite

por phy

lav

phy ry

72.

72.

71.

75.

69.

76.

72.5

76.0

49.7

49.

91

45

95

01

11

17

85

4

1

1

49

0.2

0.2

0.1

0.3

0.1 0.29

0.18

3.15

6

8

14.

14.

0.2

3

6

6

5

1

13.

13.

13.

14.

12.

06

83

74

02

46

36

1.6

2.0

2.6

2.0

1.2

3.4

0.7

7

5

7

4

2

2

0.0

0.1

0.1

0.2

0.0

0.1

0.0

D

6

9

0

1

3

5

2

4

0.2

0.3

0.3

0.5

0.2

1.1

0.1

13.9

13.0

6

6

1.66

1.32

14.

5

4

3

4

5

6

3

0.9

0.9

0.8

1.9

0.8

2.8

0.6

8

0

4

1

5

5

4.8

4.7

5.1

4.2

3.6

4.1

3.1

2

4

2

8

6

5

3.2

3.2

2.8

3.1

4.5

2.2

5.5

1

2

9

4

0.0

0.0

0.0

0.0

0.0

P2O5

7

7

5

7

3

1.5

1.4

1.1

2.8

1.2

44

0.07

0.21

0.27

3.98 6.7

0.49

8.77 5 2.5

3.67

2.63 7 3.8

4.08

1.16

5

7

0.0 0.1

6

6

3

2.39 8

13.

4.1

4.63 3

12.9

4

1.90 7

3

0.2

0.46

K2O

AC

3

0.07

Na2O

0.3 0.07

0.04

0.33

1 1.2

3

0.4

LOI

1.1 2.31

5

8

8

0

0

9

2

1.0

1.0

1.0

0.9

1.0

1.0

1.0

ASI 8

7

6

9

5

0

0

8.1

7.9

7.9

7.4

8.2

6.4

8.7

3

6

1

2

3

0

7.8

11.

10.

11.

15.

19.

2.6

2.17 0.6

1.15

0.69 8 6.4

7.02 1

1.00

4 1.02

Na2O+K2O

Li

3.1

14.7

05

PT E

CE

CaO

0.2

MA

Al2O3

NU

TiO2

MgO

ry

72. SiO2

MnO

SC

e

Fe2O3T

11 15

QX

Sample -1-

8

7.75

3.79 4

11.9

7.02

13.8

23.

ACCEPTED MANUSCRIPT 9

6

7

9

7

7

8

9

1.9

2.2

1.6

2.4

1.7

2.5

1.1

1.6

3

2

0

6

7

6

0

6.0

7.0

5.1

5.6

4.5

8.3

3.6

Be

Sc 3

6

2

7

2

7

2

9.7

12.

10.

13.

11.

64.

9.0

3

6

5

1

4

2

6

1.2

74.

4.5

0.9

3.9

15.

1.0

V

Cr 7

9

7

3

8

1.2

1.1

3.2

1.3

1.1

7.0

0.6

2

7

2

6

0

9

8

31.

0.9

0.4

1.5

7.0

Ni

9

2

7

2.1

4.2

3.0

3.5

5

2

3

43.

51.

9

2

14.

15.

2

7

4.19

1.76

39.3

294 42. 2

1.01

39.5

1.12

0.73

50.3

42.

0.3

8 49.

5

6

152

150

212

212

125

13.

15.

12.

16.

11.

5

1

3

8

3

14.8

14.2

25.4

1

129

109

101

66.7

102

42.9

124

130

125

611

513

NU

MA 6

8

8

D

CE

Nb

307

1

4

PT E

Zr

10.5

5

91.

7

14.4

2.4

78.

25.

Y

4

8.3

93.

131

23.

1.2

86.

Sr

24.5

1

Zn

Rb

5.14

7

7

Cu

Ga

5.82

1.21

SC

9

1.57

5

RI

Co

2.20

PT

3

2.61

73.

8 4.28

3.70

164

130

125

48.0

227

213 23.

84.

132

106

175

9

265

0

34.

25.

31.

19.

35.

17.

8

7

0

1

2

2

92.

29. 38.2

24.6

30.8

7

185

121

283

273

86.

163

177

134

154

3

201

3

9.2

10.

8.4

7.8

9.4

11.

9.0

5

5

6

2

0

0

8

3.5

3.4

4.8

2.5

2.7

4.0

0.9

0

1

6

1

9

1

8

1.90

1.67

5.49

9

642

739

691

705

910

682

654

863

874

197

510

29.

31.

24.

24.

26.

89.

13.

4

3

5

1

5

5

9

59.

64.

49.

48.

50.

1

5

0

8

0

151

3

7.0

7.5

5.7

5.4

4.9

17.

2.6

5

7

6

0

0

1

1

22.

26.

18.

19.

15.

50.

8.5

5

3

9

0

5

3

9

4.4

5.5

3.9

4.2

2.9

8.1

1.9

9

4

7

3

7

8

0

28. 10.0

9.15

30.3

6 11.

AC

Cs

Ba

35.

La

23.4

27.1

35.4

26.

7 77.

Ce 47.7

54.9

79.2

7 9.7

Pr 5.49

5.65

9.74

9 39.

Nd 20.5

19.7

41.7

9 8.2

Sm 4.66

3.76

8.91

9

ACCEPTED MANUSCRIPT 0.8

0.9

0.8

0.8

0.3

0.9

0.2

Eu

2.7 0.77

5

3

3

2

4

0

8

3.6

5.0

3.5

4.0

2.6

5.7

1.7

Gd

0.42

2.72 0 7.8

4.64

3.50

7.68

1

5

8

1

5

7

4

6

0.7

0.9

0.6

0.6

0.3

1.0

0.3

1.1

2

6

4

7

9

1

7

4.1

5.7

4.0

4.3

2.4

5.5

2.2

4

3

8

2

3

0

9

0.8

1.1

0.8

0.9

0.5

1.1

0.5

4

8

9

4

9

1

2.6

3.5

2.9

1.6

3.3

1.8

6

7

2.6

7

9

5

1

0.4

0.5

0.4

0.5

0.3

0.5

0.3

2

1

2

0

1

0

0

3.0

3.6

2.9

3.2

2.0

3.6

2.3

0

5

3

7

6

9

6

0.4

0.5

0.4

0.5

0.3

0.6

0.3

6

4

5

0

5

1

7

4.4

4.8

4.0

3.7

2.8

4.7

3.0

Tb 0.83

0.55

1.16

7 6.1

Dy

Lu

MA

Hf 0

9

6

9

3

6

2

0.6

0.7

0.6

0.4

0.7

0.7

0.9

7

7

1

2

0

0

1

16.

17.

78.

72.

9.7

11.

19.

7

7

1

8

2

6

1

8.4

9.4

8.7

7.5

12.

12.

12.

5

9

2

9

7

1

2

1.9

2.5

3.0

5

3

3

Ta

PT E

D

Pb

Th

1.6

AC

CE

U

NU

Yb

SC

Tm

RI

Er

0

1

1.1 1.2

9

2.1

3.81

6.27

5 1.1

PT

Ho

5.53

1.30

3.92

0.77

1.13

2 2.9

2.39

2.90

8 0.3

0.59

0.38

0.39

8 2.3

4.38

2.58

2.36

5 0.3

0.65

0.44

0.35

3 7.1

5.08

3.16

6.72

3 1.9

0.76

0.78

1.89

3 8.4

5.38

9.69

11.0

1 5.0

9.48

12.4

5.19

1 1.1

1.22

1.18

1.10

0

ACCEPTED MANUSCRIPT Table 4 Whole-rock Sm–Nd isotope compositions of the Jiaoziding granitoids and the associated basaltic porphyries. Rock

Age

Sm

Nd

Sample

147

Sm/144Nd

143

Nd/144Nd

2σ

Nd(i)

εNd(t)

TDM

TDM2

(Ma)

(Ma)

type

(Ma)

(ppm)

(ppm)

15QX-1-1

granite

795

4.49

22.5

0.12065

0.512379

0.000004

0.511750

2.7

1263

1252

15QX-4-2

granite

795

4.23

19.0

0.13460

0.512426

0.000003

0.511724

2.2

1395

1292

15QX-8-1

granite

795

2.97

15.5

0.11585

0.512410

0.000004

0.511806

3.7

1154

1163

795

8.18

50.3

0.09832

0.512261

0.000003

2.6

1175

1255

0.000007

0.511727

2.2

1384

1289

15QX-9-2

granite

795

1.90

8.6

0.13373

0.512424

PT

15QX-11-2

granite

795

4.66

20.5

0.13744

0.512443

0.000006

0.511726

2.2

1413

1289

15QX-13-1

granite

795

3.76

19.7

0.11540

0.512339

0.000003

0.511737

2.4

1258

1272

790

8.29

39.9

0.12562

0.512572

0.000002

0.511922

5.9

1001

986

790

8.91

41.7

0.12918

0.512570

0.000002

0.511901

5.5

1048

1019

enclave

porphyry basaltic 15QX-11-1

AC

CE

PT E

D

MA

porphyry

NU

basaltic 15QX-3-1

RI

0.511748

SC

granitic 15QX-9-1

ACCEPTED MANUSCRIPT Table 5 Modelling parameters of the volcanic rocks from the Tongmuliang Group. Partition coefficients

Gd

Tb

Ho

Yb

(ref.)

(ref.)

(ref.)

0.054

0.27

0.17

8.6

(1)

(1)

(1)

(2)

0.098

0.2

0.26

11.2

(1)

(1)

(1)

(2)

0.21

0.14

0.44

14

(1)

(1)

(1)

(2)

0.98

0.11

0.76

14.6

(3)

(1)

(1)

1.55

0.066

0.86

(4)

(1)

(1)

1.124

0.06

0.83

15.4

(5)

(1)

(1)

(2)

1.2

0.048

(6)

(1)

1.05

0.031

(3)

(1)

(2)

15.8 (2)

13.3

(1)

(2)

0.59

8.1

(1)

(2)

0.73

P

REE

ppm)

contents (CO,

F=5%

F=10%

F=20%

18.0

17.2

15.8

ppm) 0.66

0.81

0.37

12.5

PT

(ref.)

0.40

30.1

35.7

34.5

32.2

0.47

18.5

17.7

17.3

16.4

1.42

0.71

5.3

3.7

3.6

3.5

1.75

0.88

6.1

3.5

3.5

3.4

1.51

0.74

0.9

0.6

0.6

0.6

1.42

0.70

1.3

0.9

0.9

0.9

1.03

0.53

3.1

2.9

2.9

2.7

1.02

SC

Sm

Apatite

NU

Nd

Amphibole

MA

Ce

Plagioclase

D

La

Do Clinopyroxene

Melt REE contents (CL,

RI

Element

Source

PT E

Ref.: 1 – McKenzie and O'Nions (1991); 2 – Paster et al. (1974); 3 – Nagasawa (1973); 4 – Vannucci et al. (1998); 5 –

AC

CE

Skulski et al. (1994); 6 – Green and Pearson (1983).

ACCEPTED MANUSCRIPT Table 6 Modelling parameters of the Tongmuliang quartz-keratophyres. Source Partition coefficients

Dy

Yb

Lu

0.76

(1)

(2)

0.22

0.234

(1)

(3)

0.19

0.339

(1)

(3)

0.12

0.392

(1)

(3)

0.14

0.87

(1)

(2)

0.18

0.2

(2)

(3)

0.1

0.165

(1)

(3)

0.1

0.208

(1)

(3)

F=50%

F=60%

F=70%

26.8

23.9

ppm) 0.195

0.143

19.0

30.5

0.137

0.089

37.2

0.121

0.083

13.4

PT

Tb

0.3

(CO,

0.080

0.062

3.00

0.101

0.093

0.112

0.073

62.8

54.4

48.0

23.1

20.0

17.6

5.5

4.7

4.1

0.9

0.8

0.7

3.20

4.8

4.2

RI

Sm

(ref.)

contents

SC

Nd

(ref.)

P

0.50

NU

Ce

Biotite

5.6

0.063

0.043

2.34

4.3

3.7

3.2

0.064

0.045

0.36

0.7

0.6

0.5

D

La

Do Plagioclase

MA

Element

Melt REE contents (CL, ppm)

REE

AC

CE

PT E

Ref.: 1 – Bacon and Druitt (1988); 2 – Nash and Crecraft (1985); 3 – Schnetzler and Philpotts (1970).

ACCEPTED MANUSCRIPT

PT

RI SC NU MA D



PT E



CE



AC



Highlights The 795 Ma Jiaoziding granites were closely associated with OIB-like mafic rocks. These rocks formed in an extensional setting with mafic rocks from deep mantle. Modeling implies melting of ca. 970 Ma arc volcanic rocks to form the granites. This builds a link between the arc rocks and the widespread arc rocks in the area.