The geochemical evolution of syncollisional magmatism and the implications for significant magmatic-hydrothermal lead–zinc mineralization (Gangdese, Tibet)

    The geochemical evolution of syncollisional magmatism and the implications for significant magmatic-hydrothermal lead–zinc mineralization (Gangdese, Tibet) Jinsheng Zhou, Zhusen Yang, Zengqian Hou, Yingchao Liu, Xiaoyan Zhao, Xiong Zhang, Miao Zhao, Wang Ma PII: DOI: Reference:

S0024-4937(17)30243-8 doi:10.1016/j.lithos.2017.07.004 LITHOS 4364

To appear in:

LITHOS

Received date: Accepted date:

4 November 2016 4 July 2017

Please cite this article as: Zhou, Jinsheng, Yang, Zhusen, Hou, Zengqian, Liu, Yingchao, Zhao, Xiaoyan, Zhang, Xiong, Zhao, Miao, Ma, Wang, The geochemical evolution of syncollisional magmatism and the implications for significant magmatic-hydrothermal lead–zinc mineralization (Gangdese, Tibet), LITHOS (2017), doi:10.1016/j.lithos.2017.07.004

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ACCEPTED MANUSCRIPT The geochemical evolution of syncollisional magmatism and the implications for significant magmatic-hydrothermal

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lead–zinc mineralization (Gangdese, Tibet)

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Jinsheng Zhoua, b, Zhusen Yangc, *, Zengqian Houa, Yingchao Liua, Xiaoyan Zhaoc, Xiong Zhangd, Miao Zhaoc, Wang Mad

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;

b

School of Earth and Space Sciences, Peking University, Beijing 100871, China; MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral

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c

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Resources, CAGS, Beijing, 100037, China;;

School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083,

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China

Abstract

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* Corresponding author. E-mail address: [email protected]

In addition to well-known subduction processes, the collision of two continents also generates abundant ore deposits, as in the case of the Tibetan Plateau, which is the youngest and most spectacular collisional belt on Earth. During the building history of the Gangdese magmatic belt, several magmatic flare-up events developed, however, significant magmatic-hydrothermal lead–zinc mineralization dominantly accompanied the magmatism during the syncollisional period (～65 - 41Ma). Based on integrated geochemical and isotopic data, we provide insights into the genesis and evolution of syncollisional magmas, and their

ACCEPTED MANUSCRIPT implications for significant magmatic-hydrothermal lead–zinc mineralization. The Sr–Nd isotopic compositions of most syncollisional igneous rocks (87Sr/86Sr = 0.7034–0.7123; εNd(t)

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= −9.0 to +1.8) indicate a mixing origin between mantle-derived basaltic magmas and ancient

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crustal melts, and fractional crystallization is a fundamental mechanism by which syncollisional magmas evolve towards intermediate to silicic compositions. Most lead-zinc mineralization-related plutons are high silica (76.14% wt.% SiO2 on average), high oxygen

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fugacity (average ΔFMQ +2.5) granites with highly evolved chemical signatures

[average

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Eun/Eun* = 0.33, high Rb/Sr (average = 3.9)], and they represent the final products from primary magmas. Due to the contribution of ancient crustal melts to the genesis of

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mineralization-related parent magmas, the spatial distribution of Pb-Zn deposits within the

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northern Gangdese magmatic belt is controlled by the lithospheric architecture. In

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compressional environments, magmas have low evacuation efficiency and long magma chamber lifespan, which is favorable for basaltic parents evolved to high silica granites

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through sufficient fractional crystallization. This scenario contributes to our understanding of the significant magmatic-hydrothermal lead-zinc mineralization that occurred in the syncollisional period.

Keywords: Gangdese; syncollision; magmatic-hydrothermal Pb-Zn deposit; high silica granite; magmatic evolution

1. Introduction Cenozoic convergence between the Indian and Asian plates produced the archetypical continental collision zone, composed of the Himalaya mountain belt and the Tibetan Plateau

ACCEPTED MANUSCRIPT (Yin and Harrison, 2000; van Hinsbergen et al., 2011). In addition to crustal deformation, mountain building and profound effects on global climate (Dupont‐Nivet et al., 2007;

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Royden et al., 2008), episodic metallogenetic events occurred with the procession of this

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continent-continent convergence (Hou et al., 2015a, b; Richards, 2015; Zheng et al., 2015). Some giant and large ore deposits were emplaced within the Gangdese magmatic belt in the southern Tibetan Plateau and their formation was associated with the continental collision

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(Hou et al., 2015b). Two principal ore belts are the Gangdese porphyry Cu-Mo belt and the

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northern Gangdese skarn Pb–Zn belt (Hou et al., 2015b; Zheng et al., 2015). The Miocene Gangdese porphyry Cu-Mo belt, located in the southern Gangdese

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magmatic belt of the Lhasa terrane, is considered to derive from either remelting of

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sulfide-bearing lower crust (Hou et al., 2015a; Richards, 2015) or high-pressure

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differentiation products of hydrous mafic partial melts of Tibetan mantle (Lu et al., 2015). In recent years, geochronological constraints on the timing of ore formation have revealed that

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many magmatic-hydrothermal Pb-Zn deposits were formed in the syncollisional period within the northern Gangdese magmatic belt (Fig. 1, Table. 1), showing genetic links to ancient continental material (Hou et al., 2015b; Zheng et al., 2015; Fu et al., 2017). During the past 120 Ma, three magmatic flare-up events (with corresponding peaks of ∼90 Ma, ∼50 Ma, ∼20 Ma) developed within the Gangdese magmatic belt (Ji et al., 2014), and Pb-Zn mineralization are dominantly accompanied with syncollisional magmatism [～65-41Ma (Hou and Cook, 2009)]. Thus, the origin and evolution of the syncollisional magmas and their association with mineralization-related granites are important for understanding the genesis of these magmatic-hydrothermal Pb-Zn deposits.

ACCEPTED MANUSCRIPT We report here some new geochemical, isotopic and mineral chemical data of the igneous rocks associated with Pb-Zn mineralization and without mineralization from the

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Narusongduo deposit, which is one of the largest magmatic-hydrothermal Pb-Zn deposits in

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the Gangdese magmatic belt. To understand the genesis and evolution of syncollisional magmas, we also conducted a statistical assessment of geochemical and isotopic data from the Paleocene and early Eocene magmatic rocks in the Gangdese magmatic belt. Combining our

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new data with literature data, we aim to understand the following: (i) the genesis and

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evolution of syncollisional magmas; (ii) the evolution processes of Pb-Zn mineralization related magmas; (iii) why significant magmatic-hydrothermal lead–zinc mineralization

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2. Geological setting

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developed in the syncollisional period.

2.1 Tectonic framework

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The Himalayan–Tibetan orogen is composed of several continental terranes, including the Himalayan, Lhasa, Qiangtang and Songpan–Ganze terranes (Fig. 1A; Yin and Harrison, 2000). The Lhasa terrane, located in the southern Tibetan Plateau, is bounded by the Bangong-Nujiang and Zangbo suture zone, respectively. The crystalline basement of the Lhasa terrane is Mesoproterozoic-early Cambrian Nyainqentanghlha Group (Yin and Harrison, 2000). During the Late Jurassic–Cretaceous, the Neo-Tethyan oceanic slab was subducted northward beneath the Lhasa terrane (Mo et al., 2007). Since the collision of India with Asia occurred as early as Paleocene (∼65 Ma) (Yin and Harrison, 2000; Ding et al., 2005; Mo et al., 2008; Cai et al., 2011), the Lhasa terrane was shortened by ∼180 km and has a

ACCEPTED MANUSCRIPT maximum crust thickness of ∼80 km (Murphy et al., 1997). 2.2 Magmatism in the Lhasa terrane

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Magmatic flare-up activity occurred episodically in the Lhasa terrane from the Mesozoic

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to Cenozoic, and this continuous magmatism produced the Gangdese magmatic belt, which is distributed in the southern Lhasa terrane and extends more than 1,500 km (Chung et al., 2005; Ji et al., 2014; Mo et al., 2007, 2008; Zhu et al., 2011; Zhang et al., 2013). Although the

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geochronological features between the western and eastern segments of the Gangdese

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magmatic belt do not match completely (Ji et al., 2014), in general, the magmatism can be divided into four stages, with corresponding peaks of ∼190 Ma, ∼90 Ma, ∼50 Ma, ∼20 Ma

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(Zhu et al., 2011; Ji et al., 2014). Among these periods of magmatism, the most voluminous

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and intense magmatic event occurred during the early Tertiary (peak age: ∼50 Ma) (Mo et al.,

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2008). The event was limited to the southern Lhasa terrane, with compositions varying from high-K calc-alkalic to shoshonitic (Zhu et al., 2011). As a product of this magmatic event, the

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Linzizong volcanic rocks (basaltic to rhyolitic in composition) extend for more than 1000 km along the southern Lhasa terrane and ages vary in a narrow range of 69–44 Ma (Zhu et al., 2015). The Linzizong volcanic rocks and the coeval intrusions represent a magmatic response to syncollision between the India and Asia continent (Mo et al., 2008). A suite of skarn Pb-Zn deposits are associated with this distinct magmatic flare-up event (Hou et al., 2015b; Zheng et al., 2015). Another important stage of magmatism in the Gangdese magmatic belt is of Oligocene-Miocene age (Ji et al., 2014). Part of them exhibit adakitic affinities and are considered products of partial melting of a hydrous amphibole eclogite or garnet amphibolite in the lower crust (Hou et al., 2004) or high-pressure differentiation products of hydrous

ACCEPTED MANUSCRIPT mafic partial melts of the Tibetan mantle (Lu et al., 2015). This magmatic event was accompanied by the development of many porphyry Cu-Mo deposits in the Gangdese

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magmatic belt (Hou et al., 2015a, b; Lu et al., 2015, 2016; Wang et al., 2015; Yang et al.,

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2015, 2016).

3. Mineralization-related granites

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Within the northern Gangdese Pb–Zn belt, skarn is the principal types of mineralization,

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with minor amounts of breccia pipe, vein-type and manto deposits (Zheng et al., 2015). The occurrence of skarn alteration in contact zones between granites and the surrounding rocks is

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evidence of ore-related intrusions. Most (though not all) mineralization-related granites and

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mineralization ages are in the range of 65-50 Ma (Table. 1; Zheng et al., 2015; L. Wang et al.,

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2015; Fu et al., 2017). Mineralization-related granites from three representative deposits are introduced here, and petrographic descriptions are based on the previous work of Duan et al.

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(2015) and Zheng et al. (2015) as well as the results of the present study. The Narusongduo granite porphyries, dated at 62.54 ± 0.77 Ma (zircon U-Pb) (Ji et al., 2012), is monotonous porphyritic and dominated by quartz, alkali feldspar and biotite (1.5-4.0 mm), surrounded by a groundmass of smaller quartz and alkali feldspar (0.1-0.5 mm) (Fig. 2A, B). Accessory minerals are apatite and zircon. Mineralization-related rocks in the Yaguila deposit are quartz porphyries (Fig. 2C), and available data indicate that they intruded at 62.4 ± 0.6 Ma (Huang et al., 2012). The quartz porphyries show porphyritic texture with phenocrysts and groundmass dominated by quartz. The only igneous rock in the Chagele deposit is granite porphyry dated at 62.9 ± 1.0 Ma (Duan et al., 2015). The granite porphyry is mainly composed of quartz,

ACCEPTED MANUSCRIPT plagioclase, K-feldspar and biotite phenocrysts set in a groundmass of fine-grained quartz and feldspar. Accessory minerals include apatite, zircon, titanite and Fe-Ti oxides. In the

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Narusongduo deposit, mineralization-related granites show spatial and temporal association

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with a volcanic sequence.

4. Data compilation and analytical methods

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Eleven samples of intrusive rocks were collected from outcrops in the Narusongduo

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mine. The weathered rinds were removed in the field. All the samples were determined by whole rock major and trace elements analysis. Five samples were chosen for bulk-rock Sr–Nd

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isotopic analysis, and one sample was used for zircon trace element determinations. Datasets

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of igneous rocks in other skarn deposits are previously published. To explore the magmatic

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genesis and evolution of syncollisional magmatism, a large number of geochemical and isotopic data of igneous rocks without mineralization in the Gangdese magmatic belt were

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compiled from the literature.

Major and trace element geochemical analyses were performed at the National Research Centre for Geoanalysis, Chinese Academy of Geological Science (Beijing). Rock powder was mixed with Li2B4O7 + LiF + NH4NO3, and fused in a Pt crucible for major elements analysis using X-ray fluorescence spectrometry (XRF). The analytical uncertainty of XRF for major elements was within 5%. For trace element analyses, powder was dissolved in high-pressure Teflon bombs using an HF + HNO3 mixture for ICP-MS analyses. Uncertainty of the trace elements was less than 5% for ICP-MS analysis. Whole-rock Sr–Nd isotopic analysis were conducted by a Triton mass spectrometer

ACCEPTED MANUSCRIPT (TIMS) at the Isotope Geology Lab, Chinese Academy of Geological Science (Beijing). The SRM 987 SrCO3 standard yielded

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Sr/86Sr = 0.710247 ± 2 (2σ) (the recommended value is

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Sr/86Sr = 8.37521. The JMC Nd2O3 yielded

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of Sr isotopes was corrected by using

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0.710245). The accuracy of the Rb/Sr ratio was better than 0.1 % and the mass fractionation

Nd/144Nd = 0.511842 ± 4 (2σ) (the recommended value is 0.511850), and the accuracy of

the Sm/Nd ratio was better than 0.1%, and the mass fractionation of Nd isotopes was 146

Nd/144Nd = 0.7219. The initial εNd values and

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corrected using

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Sr/86Sr ratios for the

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granites were calculated using t = 62.5 Ma (Ji et al., 2012). A total of 19 zircon grains were selected for trace element analysis using LA-ICP-MS at

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the State Key Laboratory of Geological Processes and Mineral Resources, China University

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of Geosciences, Wuhan. Detailed operating conditions for the laser ablation system and the

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ICP-MS instrument are same as described by Liu et al. (2008). Laser sampling was conducted using a GeoLas 2005 with spot diameter of 32 µm. An Agilent 7500a ICP-MS instrument was

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used to acquire ion-signal intensities. Helium was used as the carrier gas to ensure efficient aerosol delivery to the torch. Trace element compositions of zircons were calibrated against multiple-reference materials (BCR-2G and BIR-1G) combined with internal standardization (Liu et al., 2010). Zircon standards 91500 were analyzed as unknown samples. 5. Results

5.1 Mineralization-related igneous rocks New major, trace element and Sr–Nd isotopic compositions of the Narusongduo mineralization-related igneous rocks are listed in Table. 2. The compiled datasets of other deposits are listed in Table. A1, A2. Because most mineralization-related igneous rocks have

ACCEPTED MANUSCRIPT similar geochemical signatures, their results are introduced together as follows. Compared with the average composition of the upper continental crust (Fig. 3), the

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mineralization-related rock samples are characterized by high SiO2 (72.33–80.71 wt. %) and

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K2O (3.09–6.30 wt. %), moderate Al2O3 (9.92–15.46 wt. %), and low MgO (0.08–0.54 wt. %), Na2O (0.08–4.13 wt.%), total Fe2O3 (0.36–3.80 wt.%), CaO (0.12–1.82 wt.%), and P2O5 (0.01–0.06 wt.%). Geochemically, the rocks are high-K, calc-alkaline and high silica granites.

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In the primitive mantle-normalized spidergram (Fig. 4A), all of the samples are enriched

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in some incompatible trace elements, including K and Pb, depleted in Ba, Sr and Ti. In chondrite-normalized rare earth elements (REEs) plots (Fig. 4B), they are enriched in light

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rare earth elements (LREEs), slightly depleted heavy rare earth elements (HREEs) ((La/Yb)N

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= 4.06- 14.28) and show negative Eu anomalies (δEu = 0.20-0.53). The behaviors of Sr, Y,

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La, and Yb are analyzed in Figure 4C, 4D. Most of them plot within the fields of normal arc andesite-dacite-rhyolite rocks in these diagrams.

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Whole-rock Sr–Nd isotopic compositions of Pb-Zn mineralization-related igneous rocks are shown in Table. 2, A1 and A3, including our new and previously published data. The mineralization-related rocks have relatively high 143

Nd/144Nd

ratios

(0.512112–0.512339),

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Sr/86Sr ratios (0.716202–0.771800) and

corresponding

to

(87Sr/86Sr)i

ratios

of

0.708206–0.717307 and εNd(t) values of −5.79 to −9.42, respectively.

5.2 Zircons trace elements and magmatic oxygen fugacity Zircon trace elements compositions from the mineralization-related granites in the Narusongduo deposit are listed in Table. 3. They are characterized by negative Eu anomalies (δEu = 0.06-0.50) and positive Ce anomalies (δCe = 9.65-214.80). Based on a calibration

ACCEPTED MANUSCRIPT by Trail et al. (2011, 2012) and calculation methods presented by Qiu et al. (2013), mineralization-related granites in the Narusongduo deposit have higher fO2 values (ΔFMQ

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-0.8 – +6.9, average = +2.5, n = 19) (Figure 5).

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5.3 Syncollisional igneous rocks

A comprehensive regional geochemical and isotopic database for the magmatic rocks

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without mineralization in the Gangdese magmatic belt is given in Table. 1, A2, and A3, including our new and previously published results. Because most Pb–Zn mineralization

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occurred during 65–50 Ma (Table. 1; Wang et al., 2015; Fu et al., 2017), igneous rocks that formed in this period were selected, including plutonic and volcanic rocks. Although the

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geochemical and isotopic data are scattered, they have compositions typical of calc-alkaline

6. Discussion

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(Fe-depleting) differentiation trends.

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6.1 The genesis and evolution of syncollisional magmatism Accompanied with the collision of India with Asia, a distinct magmatic flare-up event occurred in the Gangdese magmatic belt, exposed as the voluminous Linzizong volcanic rocks and coeval intrusions of the Gangdese batholith (syncollisional magmas) (Chung et al., 2005; Mo et al., 2007; 2008; Ji et al., 2014; Zhu et al., 2015). The former shows heterogeneous compositions from basalt to rhyolite and the latter mainly consists of diorites and granites (Chung et al., 2005). It is difficult to obtain comprehensive information about the evolutionary process of syncollisional magmas from a single or few samples, however, a statistical assessment of a large number of samples may provide a useful tool in addressing

ACCEPTED MANUSCRIPT this issue. To explore the magmatic nature of syncollisional magmas, we combined volcanic and plutonic data from the Gangdese magmatic belt.

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For the genesis of syncollisional magmas in the Gangdese belt, the Sr–Nd isotopic

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compositions of most syncollisional igneous rocks indicate mixing between mantle-derived basaltic magmas and ancient crustal melts (Fig. 6). A case study in the Narusongduo area show similar zircon ɛHf values between the Paleocene intermediate volcanic rocks [ɛHf = -6.86

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to -1.75 (Zhou, 2017)] and highly evolved granites [ɛHf = -5.58 to 2.21 (Ji et al., 2012)] and

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both of them represent products at different evolutionary stages of a long-lived upper crustal magma reservoir (Zhou et al., 2017), thus the mixing processes more likely occurred in the

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lower crustal “hot zones” (Annen et al., 2006). The injection of mantle-derived hydrous

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magmas into lower crustal hot zones produces residual H2O-rich and crustal partial melts

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(Annen et al., 2006), and the mixing leads to diversity in isotopic compositions of the syncollisional magmas. However, maximal involvement of the crustal components into hot

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zones is no more than 40% (Fig. 6), and such a degree of mixing is unlikely for generating silicic magmas. Hence, fractional crystallization is a more likely fundamental mechanism by which syncollisional magmas evolve towards intermediate to silicic compositions. As shown in Figure. 7, syncollisional magmas display consistent compositional variations. Apart from the heterogeneity of magma sources and the degree of melting, crystal fractionation is an important factor contributing to the compositional evolution. Total iron (expressed as FeOT) content continuously decreases with progressive differentiation (Figure 7A), which indicates they are calc-alkalic series (Gill, 1981; Arculus, 2003). Elevated magmatic H2O and fO2 both play prominent roles in the development of calc-alkaline trends

ACCEPTED MANUSCRIPT in magmatic evolution through suppressing earlier plagioclase crystallization and other silicates relative to mafic phases, promoting early amphibole and magnetite crystallization

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(Sisson and Grove, 1993; MuÈntener et al., 2001; Berndt et al., 2005; Zimmer et al., 2010).

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Compared with the differentiation trend of dry MORs and hydrous arc magmas, the inverse correlation between SiO2 and FeOT for all volcanic and plutonic rocks studied here (Figure 7A) suggests that syncollisional magmas are hydrous, which is similar to the almost

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ubiquitously hydrated arc magmas (Plank et al., 2013). This concept can be quantified by the

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phosphorous systematics of magmas. Apatite saturation and the evolutionary trends of P2O5 in magmas are controlled by magmatic water contents (Lee and Bachmann, 2014). By

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comparing the evolutionary trends of syncollisional magmas with modeling of equilibrium

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crystallization for dry and hydrous parental basalts, we can roughly estimate that the primitive

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syncollisional magmas contain ∼4 wt.% H2O (Figure 8). This hydrous nature of syncollisional magmas is also consistent with the differentiation of Na2O in magmas (Figure

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7C), which remains constant but decreases sharply when the SiO2 content exceeds ∼72 wt.%. An important implication is that the voluminous crystal fractionation of plagioclase occurred at the latest stage of magmatic evolution. This phenomenon is consistent with elevated magmatic H2O contents, which can suppress the crystallization of plagioclase during the earlier stage of magmatic differentiation (Berndt et al., 2005; Loucks, 2014; Lu et al., 2015). 6.2 Ore-forming related magmatic processes All of the skarn Pb-Zn deposits are found sporadically in the Gangdese magmatic belt. Most mineralization-related plutons are high silica granites (> 70% wt.% SiO2) and a case study in the Narusongduo deposit show mineralization-related granites are oxidized (Figure.

ACCEPTED MANUSCRIPT 3A; Figure. 5). In the skarn Pb-Zn deposits, the skarn-forming fluids are dominantly magmatic (Baker et al., 2004; Samson et al., 2008; Williams-Jones et al., 2010), hence the

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parental magmas are likely hydrous. Mineralization-related granites display intensely negative

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Eu anomalies (avg Eun/Eun* = 0.33; Fig. 4B), suggesting extensive fractionation of plagioclase from the primitive magmas. One possible mechanism for the generation of highly evolved magmas is that they form by crystal-liquid separation from upper crustal crystal

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mushes (Bachmann and Bergantz, 2004; Lee and Morton, 2015; Bachmann and Huber, 2016),

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and a case study in the Narusongduo deposit also supports that the mineralization-related high silica granites are extracted from an upper crustal magma reservoir (Zhou et al., 2017). Thus,

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the intensely negative Eu anomalies of the mineralization-related porphyries are attributed to

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the crystal–liquid segregation process, because of the stabilization of plagioclase in the crystal

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mush. This concept can be quantified base on the evolution of sodium in magmatic processes (Figure. 7C), which indicates that the voluminous plagioclase crystallized when magmatic

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SiO2 content exceeded ∼72 wt.%. Unlike porphyry Cu deposits worldwide, which are associated with high Sr/Y magmas (also called adakites or adakitic rocks) (Richards, 2011; Chiaradia et al., 2012; Lu et al., 2015), skarn Pb-Zn deposits in the Gangdese magmatic belt are genetically related to normal arc magmas (Figure. 4C, D). Interpretations for the genesis of high Sr/Y magmas include slab melting, mantle-source, and lower crust melting (Castillo, 2012), however, alternative explanations have proposed that similar geochemical characteristics are developed in normal mafic magmas by stabilization of amphibole ±garnet or destabilization of plagioclase during intracrustal processes (Macpherson et al., 2006; Richards, 2011; Chiaradia et al., 2009a; Lu et

ACCEPTED MANUSCRIPT al., 2015; Chiaradia, 2015). In the Gangdese magmatic belt, syncollisional magmas display variably Sr/Y values (Figure. 9A). Despite the scatter of data points, an obvious phenomenon

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is that SiO2 contents of high Sr/Y magmatic rocks are dominatingly distributed in the ∼56-72

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wt.% range and the high silica (> 72 wt.%) rocks rarely have high Sr/Y values (Figure. 9A) suggesting decreasing Sr/Y values through the stabilization of plagioclase at a terminal stage of magmatic fractionation. Comparison between coeval barren quartz diorite and

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mineralization-related porphyries in the Narusongduo deposit also indicates that highly

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evolved magmas have lower Sr/Y values (Figure. 9B).

Most Pb-Zn mineralization-related porphyries have high molar proportions of Al2O3/

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(CaO+Na2O+K2O) ("A/CNK"), which is a critical index for identifying S-type granites

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(Chappell and White, 1992). Nevertheless, compared with the average composition of the

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upper continental crust (Al2O3 = 15.4 wt.%) (Figure. 3D) (Rudnick and Gao, 2003) and typical S-type granite (Al2O3 > 15 wt.%) within the Himalayan collisional belt (Zeng et al.,

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2011), mineralization-related porphyries have lower Al2O3 contents (avg 12.3 wt.%; Fig. 3D). Their high A/CNK values resulted from low CaO and Na2O contents (Fig. 3E, 3G), which are generated by the fractionation of apatite and plagioclase during magmatic evolution (Fig. 8, Fig. 7C). For fractionated granites, the behavior of P is an important index to distinguish Iand S-type granites, and P2O5 moves in opposite directions with fractional crystallization, decreasing in the I-type and increasing in the S-type granites (Chappell and White, 1992; Chappell, 1999). Continuous decreases of P2O5 with progressive differentiation (Fig. 8) and lower P2O5 abundances (avg 0.02 wt.%) in the mineralization-related granites indicate that they are I-type granites. This concept is also supported by the lack of aluminium-rich minerals

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mineralization-related intrusions.

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6.3 Controls on the temporal distribution of Pb-Zn deposits

Recent Hf isotopic mapping shows that most Pb-Zn deposits are located in the northern Gangdese magmatic belt with ancient continental basement (Fig. 1B), which made an

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important contribution to the genesis of the Pb-Zn deposits (Hou et al., 2015b). The Sr-Nd

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isotopic compositions of mineralization-related granites in this study indicate that parent mineralization-related magmas are products of mixing between mantle-derived hydrous

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magmas and ancient crustal melts (Fig. 6), coupled with a high degree of crystal

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fractionation within the intracrustal processes. Hence, the contribution from ancient

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continental basement is critical for the formation of Pb-Zn deposits, which controls the spatial distribution of Pb-Zn deposits within the northern Gangdese magmatic belt. It is also

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noteworthy that most magmatic-hydrothermal Pb-Zn deposits developed during the syncollisional period, and our results may provide insight to this topic. All geochemical characteristics indicate Pb-Zn mineralization-related magmas underwent highly evolved. Recent studies suggest that high silica granites can be derived by fractionation from a basaltic parent (Jagoutz et al., 2012; Lee and Bachmann, 2014; Lee and Morton, 2015) and they represent the residual <5% of melts relative to the parent. Additionally, this entire magmatic process can drives incompatible elements enriched ∼30-fold compared with the basaltic parent (Lee and Morton, 2015). As an incompatible element, Pb is continuously enriched throughout the magmatic differentiation (Nadeau et al.,

ACCEPTED MANUSCRIPT 2013), and its concentration predictably reaches a maximum in high silica granites. Therefore, unlike porphyry Cu deposits, which are rarely related to high silica granites (Hedenquist and

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Lowenstern, 1994), magmatic-hydrothermal Pb-Zn deposits are usually associated with high

highly

fractional

crystallization

may

play

magmatic-hydrothermal Pb-Zn deposits.

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silica granites (Megaw et al., 1988; Meinert et al., 2005). The above discussion suggests that an

important

role

in

generating

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During the past 120 Ma, three magmatic flare-up events developed within the Gangdese

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magmatic belt (Fig. 1C). However, significant lead–zinc mineralization mainly accompanied the magmatic event during the syncollisional period. As shown in Fig. 10, both Indian Ocean

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spreading and India-Eurasia convergence decelerated abruptly with the collision of India with

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Eurasia, from ∼200 mm/yr around 65 Ma to ∼50 mm/yr around 40 Ma (White and Lister,

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2012). By coincidence, most Pb-Zn deposits developed during this stage within the Gangdese magmatic belt. In this sharp deceleration period, the Gangdese magmatic belt was in a

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compressional environment (Hou and Cook, 2009), induced by the collision between the two continents. In compressional environments, magmas have low evacuation efficiency and long magma chamber lifespans (Chiaradia et al., 2009b; Lee et al., 2013), which are favorable for basaltic parents evolved to high silica granites through sufficient fractional crystallization. Fertile high-silicic magmas emplaced in the shallow crust, leading to the development of ore-forming magmatic-hydrothermal systems (Fig. 10). 7. Conclusions

The following three main conclusions can be summarized from the observations discussed in this study:

ACCEPTED MANUSCRIPT (1) The Sr–Nd isotopic compositions of most syncollisional magmas (87Sr/86Sr = 0.7034–0.7123, εNd(t) = −9.0 to +1.8) indicate a mixing origin between mantle-derived basaltic

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magmas and ancient crustal melts, and fractional crystallization is a fundamental mechanism

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by which syncollisional magmas evolve towards intermediate to silicic compositions. (2) Most mineralization-related plutons are high silica granites (76.14% wt.% SiO2 on

the evolution of syncollisional magmas.

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average) with highly evolved chemical signatures, and they represent the final products from

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(3) The spatial distribution of most Pb-Zn deposits within the northern Gangdese magmatic belt is attributed to the lithospheric architecture. Compressional environment and

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syncollisional period.

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its effects on magmatic evolution control these deposits mainly developed during the

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Acknowledgments

This study was funded by the National Key Research and Development Program of China “Deep Structure and Ore-forming Process of Main Mineralization System in Tibetan Orogen” (2016YFC0600306), the China Geological Survey (DD20179172), the National Natural

Science

Foundation of China (Nos

41403043, 41320104004), and the

IGCP/SIDA-600. We express our gratitude to Yongjun Lu and an anonymous reviewer for insightful and helpful reviews and to Nelson Eby for thoughtful suggestions and efficient editorial handling.

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Figure and Table Captions

Fig 1. (A) Geological sketch map of Tibetan Plateau (after Wang et al., 2014). BNS-Banggonghu-Nujiang suture; IYZS-Indus-Yarlung Zangbo suture. (B) Geological map of the central and eastern Gangdese magmatic belt in the Lhasa terrane showing distribution of skarn Pb-Zn deposits. The boundaries for old and juvenile crustal blocks are from Hou et al., 2015b. LG-Longgen; CGL-Chagele; SND-Sinongduo; NRSD-Narusongduo; ZX-Zexue; LL-Lunlang;

XGG-Xinggaguo;

LTG-Lietinggang;

LML-Longmala;

MYA-Mengyaa;

DZL-Dongzhongla; DZSD-Dongzhongsongduo; YGL-Yaguila. (C) India-Asia convergence rate, intensity of magmatism in the Gangdese magmatic belt during past 120Ma. Red and blue

ACCEPTED MANUSCRIPT lines represent the rate of Indian Ocean spreading (Cande et al., 2010, 2011) and India-Asia convergence (White and Lister, 2012), respectively. Gray zone represents the intensity of

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magmatism in the Gangdese magmatic belt. The data are from Ji et al. (2014). The boundaries

. Fig

2.

Photomicrographs

showing

the

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of three-stage collisional processes are from Hou and Cook (2009).

petrographic

characteristics

of

Pb-Zn

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mineralization-related porphyries from the Gangdese magmatic belt. (A) and (B)

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Mineralization-related granite porphyry from the Narusongduo deposit; biotite partly has been replaced by muscovite; (C) Mineralization-related porphyry from the Yaguila deposit. (D)

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Magnetite in granodioritic porphyry from the Leqingla deposit. Mineral abbreviations: Qtz =

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under reflected light.

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quartz, Bi = biotite, Mgt = magnetite. (A) to (C) are under cross-polarized light whereas (D) is

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Fig 3. Histogram of major elements for skarn Pb-Zn mineralization-related rocks from the Gangdese belt. UCC represents average composition of the upper continental crust (Rudnick and Gao, 2003).

Fig 4. (A) Primitive mantle-normalized trace element patterns, and (B) chondrite-normalized REE patterns for skarn Pb-Zn mineralization-related rocks. Normalization values are from Sun and McDonough (1989). Plots of Sr/Y versus Y (c) and La/Yb versus Yb (d) for skarn Pb-Zn mineralization-related rocks. Fields for adakitic rocks are from Richards and Kerrich (2007).

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Fig 5. A-B show oxidation state of the Naursongduo mineralization-related granites estimated

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from zircon Ce anomalies. Abbreviations: FMQ = fayalite-magnetite-quartz buffer curve, MH

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= hematite-magnetite buffer curve, IW = iron-wüstite buffer curve. In A, Buffer curves are from Trail et al. (2011); in B, buffer curves are from Ernst (1976).

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Fig 6. Plot of whole-rock (87Sr/86Sr)i vs. εNd(t) values for the syncollisional igneous rocks and

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Pb-Zn mineralization-related granites in the Gangdese magmatic belt. The data source for syncollisional igneous rocks are presented in Table A3, and mineralization-related granites are

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from Table 2 and Table A1. The compositions of end-members used for mixing calculations

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are: the mantle-derived basaltic magmas (represented by the Dazi basalt; Gao et al., 2008):

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(87Sr/86Sr)i = 0.7043, εNd(t) = +5.2, Sr = 291 ppm, Nd = 9.6 ppm; Ancient crustal partial melts (represented by a strongly peraluminous granites from the central Lhasa subterrane; 08DX17,

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Zhu et al., 2011): (87Sr/86Sr)i = 0.7402, εNd(t) = − 15.4, Sr = 131 ppm, Nd = 43.40 ppm;

Fig 7. A-D show FeOT (wt.%), MgO (wt.%), Na2O (wt.%), K2O (wt.%) versus SiO2 (wt.%) for the syncollisional igneous rocks and skarn Pb-Zn mineralization-related rocks. Total iron (expressed as FeO) and MgO contents continuously decrease with progressive differentiation indicating syncollisional magmas are calc-alkalic series and ferromagnesian minerals are fractionation phases throughout the magmatic evolution. Compared with the differentiation trend of dry, tholeiitic MOR and rift magmas, syncollisional magmas are similar to hydrous

ACCEPTED MANUSCRIPT arc magmas. Curves of MOR and arc magmas are modified from Keller et al. (2015). Na2O remains constant in the early stage and decrease sharply when SiO2 contents exceed ∼72

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wt.%, indicating plagioclase is the latest fractionation phase. K2O is highly incompatible. The

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location of all mineralization-related data on these plots indicates they underwent high degrees of evolution. The data sources for the syncollisional igneous rocks are presented in

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Table A2.

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Fig 8. Plots of P2O5 (wt.%) versus SiO2 for syncollisional igneous rocks. Model of residual melts formed by equilibrium crystallization of parental basalts is from Lee et al. (2014). Pink

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straight line in (A) is hypothetical mixing line for basalt with high silica endmembers.

Fig 9. (A) Plots of Sr/Y versus SiO2 for syncollisional magmas and mineralization-related

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rocks. It is noteworthy that SiO2 contents of adakitic rocks are dominantly distributed in ∼56-72 wt.% and high silica (> 72 wt.%) rocks rarely have adakitic affinity. (B) Plots of Sr/Y versus SiO2 for barren and mineralization-related rocks in the Narusongduo deposit. Fields for adakitic rocks from Richards and Kerrich (2007).

Fig 10. Schematic illustration of the formation of skarn Pb-Zn deposits in the Gangdese magmatic belt. Mantle-derived hydrous magmas were injected to the lower crust and generating a deep crustal hot zone where magmatic mixing between hydrous basaltic magmas

ACCEPTED MANUSCRIPT and crustal partial melts occurred. India-Asia convergence decelerated abruptly with the collision of India and Eurasia, from ∼200 mm/yr around 65 Ma to ∼50 mm/yr around 40 Ma.

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The Gangdese magmatic belt was in an intensely compressional environment, in which

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magmas have low evacuation efficiency and long magma chamber lifespan. These are favorable for primary magmas evolving to high silica granites through sufficient fractional crystallization in crustal magma reservoirs. Fertile high-silicic magmas emplaced in the

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shallow crust and led the development of ore-forming magmatic-hydrothermal systems.

Table 1. Summary of the geologic characteristics of the major magmatic-hydrothermal

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lead–zinc deposits in the Gangdese magmatic belt.

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Table 2. The whole-rock chemical and isotopic compositions of the igneous rocks in the

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Narusongduo deposit from the Gangdese magmatic belt.

Table 3. Zircon trace element compositions of the Narusongduo granites.

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Graphical abstract

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Data source

Duan et al.,2014

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Table 1. Summary of the geologic characteristics of the major magmatic-hydrothermal lead¨Czinc deposits in the Gangdese magmatic belt Longitud Latitude Metallic Tonnage/or Host Associated Deposits e(E) (N) comm. e Grade rock intrusion Alteration Age Type Middle Permia n limesto Granite Skarnizatio U-Pb: 61.4 ¡À Skar Longgen 86.2 30.3 Pb-Zn-Cu ne porphyry n 1.2Ma n Skarnizatio n, sericitizatio Middle n Permia chloritizatio U-Pb: 62.9 ¡À n n, 1Ma Pb + Zn limesto Granite epidotizatio Re-Os:62.3 ¡À Skar Chagele 86.23 30.28 Pb-Zn-Ag £¾1Mt ne porphyry n 1.4Ma n Middle Pb + Permia Zn: n Skarnizatio 11.25 limesto Granite n, Skar Sinongduo 88.6 29.98 Pb-Zn % ne porphyry silicification n Paleoce ne Skarnizatio crystal n, Pb: tuff, silicification 7.63% Middle , Brec Zn: Permia chloritizatio U-Pb: 62.5 ¡À cia 2.41% n n, 0.77Ma pipe, Pb + Zn £¾ Cu: limesto Granite epidotizatio Re-Os:58 ¡À skar Narusongduo 88.77 29.97 Pb-Zn 20Mt 0.22% ne porphyry n 0.66Ma n Pb: Cretace Skarnizatio 9.97% ous Biotite n U-Pb: 56.5 ¡À Skar Xingaguo 90.93 29.88 Pb-Zn Zn: siltston granite chloritizatio 1.3Ma n

Duan et al.,2015

Zheng et al., 2015

Ji et al., 2012; Ji et al., 2014

Wang et al., 2016

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n, silicification , carbonatiza tion, marbleizati on

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Mengyaa

92.02

92.12

Pb-Zn-Fe-C 30.2 u

30.22 Pb-Zn-Ag

Pb¨CZn: £¾10 Mt

Pb: 10.11 % Zn: 11.88 % Ag: 100g/t

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Upper Permia n limesto ne, slate

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90.98

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Pb-Zn-Cu-F 30.03 e

Pb + Zn £¾ 50.3Mt Fe: 14.4 Mt Cu: 0.32 Mt

Pb + Zn: 7.74% Fe: 55.27 % Cu: 1.07%

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9.33%

Upper Permia n limesto ne

Middle Permia n limesto ne

Granodiorite porphyry

Monzonitic granite

Granite porphyry

Skarnizatio n, epidotizatio n, chloritizatio n Skarnizatio n, silicification , chloritizatio n, sericitizatio n, epidotizatio n Skarnizatio n, silicification , chloritizatio n, sericitizatio n,

U-Pb: 62.85 ¡À 0.58Ma Re-Os:62.28 ¡À 0.66Ma

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Yang et al., 2014; Ma et al.,2015

U-Pb: 55.7¡À0.3Ma Ar-Ar: 53.0¡À 3.7Ma

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Ar-Ar: 54.8 ¡À 0.4Ma; Re¨COs:63.6M a

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92.72

30.18 Pb-Zn-Ag

30.22 Pb-Zn

Pb +Zn: £¾52 Mt

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Granite porphyry

Skarnizatio n, silicification , carbonatati on

Skar n

Quartz porphyry

Skarnizatio n, silicification , carbonatiza tion

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Lower Permia n limesto ne

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Pb-Zn-Cu-A 30.2 g

Pb: 9.28% Zn: 8.62% Cu:1.1 3% Ag: 142.29 g/t Pb: 2.55% Zn: 2.57% Ag: 43.7g/ t Pb: 4.0% Zn: 2.0% Ag: 64.3 g/t

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epidotizatio n

Lower Permia n limesto ne

U-Pb: 62.4 ¡À 0.6Ma

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Huang et al., 2012

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Table 2 The whole-rock chemical and isotopic compositions of the igneous rocks in the Narusongduo deposit from the Gangdese magmatic belt Sa NRII NRII NRII NRII NRII mp I09- I09- I09- I09- I09- ND1 ND113 ND402 ND449 ND003 ND003 le 1-1 1-2 1-3 1-4 1-5 24-1 -2 -1 -2 -1 -2 Lithol Gra Gran Gra Gra Gra Quartz Quartz Quartz Quartz Quartz Quartz ogy nite ite nite nite nite diorite diorite diorite diorite diorite diorite Lo ngi tud e(E 88.7 88.7 88.7 88.7 88.7 88.8 ) 8 8 8 8 8 7 88.87 88.87 88.87 88.87 88.87 Lat itu de( 29.9 29.9 29.9 29.9 29.9 29.9 N) 7 7 7 7 7 8 29.98 29.98 29.98 29.98 29.98 Withou Withou Withou Withou Withou Withou Mine t t t t t t raliza Pb-Z Pb-Z Pb-Z Pb-Z Pb-Z minera minera minera minera minera minera tion n n n n n lization lization lization lization lization lization Ag e (M a) 62.5 62.5 62.5 62.5 62.5 59.6 SiO 80.7 74.8 76.5 79.9 63.2 2 1 4 4 76.5 1 5 60.89 63.12 63.15 58.87 60.14 TiO 2 0.18 0.25 0.23 0.24 0.19 0.87 0.96 0.87 0.83 0.9 0.93 Al2 14.3 14.9 15.4 13.2 15.6 O3 9.92 1 2 6 3 8 16.68 15.37 15.78 16.67 16.71 TF e2 O3 1.99 1.76 0.66 0.36 0.44 4.97 5.29 5.06 4.7 7.22 6.64 Mn O 0.02 0.02 0.02 0.02 0.02 0.07 0.07 0.09 0.07 0.08 0.06 Mg O 0.35 0.38 0.38 0.38 0.37 2.63 2.93 2.66 2.43 3.02 3.05 Ca O 0.63 0.57 0.37 0.26 0.12 4.09 5.32 3.81 3.66 3.5 3.47 Na 2O 0.15 0.18 0.13 0.11 0.08 3.64 3.99 3.75 4.04 3.75 3.86 K2 O 3.09 4.22 4.38 4.22 3.37 3.65 2.54 3.89 3.54 1.35 1.39 P2 0.02 0.02 0.02 0.02 0.02 0.26 0.35 0.25 0.25 0.21 0.21

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3.14

2.3

2.41

2.17

0.81

0.95

1.12

1.49

4.37

3.44

149 11.4 1.9 1 32.5 14.6 8.9 222 0.7 23.8 18.2 3.1 60.6 1.9 10.7 10.2 1.2 2 13.6 3.4 0.9 8.7 5 3.2 2 26.2 42.1 4.2 12.9 2.1 0.2 1.7 0.3 1.6 0.3 1.1 0.2 1.3 0.2

192 16.5 1.2 0.8 6.7 25.7 12.9 320 1 27.9 26.8 4.4 89.1 2.9 16.4 6.4 0.9 1.7 22.6 1.6 1 2.9 8.2 3.7 2.5 36 60.5 6.1 19 2.8 0.3 2.6 0.4 2.4 0.5 1.6 0.3 2 0.3

213 18.3 1.3 0.3 37.9 20 12.6 250 1 23 26.7 4.4 91.3 2.9 15.4 5.4 0.8 1.4 16 1.2 1.3 1.8 8.1 3.7 2.7 30 53.3 5.3 16.9 2.6 0.3 2.3 0.4 2.3 0.5 1.5 0.3 2 0.3

211 11.1 0.1 0.2 2.8 30.2 14.4 189 1 11.4 19.5 3.9 91.6 2.9 17.2 6 1.2 1.8 17.3 1.3 0.7 2 11.5 4.2 2.7 29.6 52 5 16.3 2.5 0.2 2.3 0.4 2.3 0.5 1.6 0.3 2 0.3

180 11.3 0.5 0.1 4.3 12.6 12.4 273 0.9 10.6 20.2 3.5 87.5 2.6 14.4 8.4 0.8 1 15.3 1.4 0.9 2.8 6.3 3.7 2.2 31.8 53.9 5.4 16.5 2.5 0.3 2.2 0.4 2.1 0.4 1.4 0.3 1.8 0.3

155 664 14.1 22.2 49.8 77.3 10.7 613 1.02 24.5 29.3 3.78 13.7 0.47 17.3 19.7 2.68 9.82 105 41.5 1.15 0.7 11.9 1.92 0.67 53.9 102 11.8 43.6 6.85 1.41 5.47 0.83 3.48 0.61 1.86 0.24 1.43 0.2

60.8 799 15.4 24.6 13.4 84.1 7.01 566 0.48 15.8 8.05 1.39 14.8 0.37 11.4 9.31 1.29 9.7 107 60.9 1.09 0.67 5.66 0.76 0.34 38.6 73.5 8.81 34.6 5.6 1.45 3.93 0.58 2.73 0.44 1.11 0.14 0.87 0.15

161 658 14 22.5 35 171 11.6 576 0.97 53.9 33.8 5.53 19.9 0.84 18.5 18.6 1.78 9.63 103 48.3 1.31 2.42 8.99 2.55 0.78 58.1 112 12.9 47.3 7.49 1.34 5.85 0.82 3.8 0.66 1.76 0.33 1.72 0.25

123 692 13.1 17.9 31 72.1 9.15 571 0.76 20.2 23.2 2.15 17.8 0.88 14.3 16.7 1.93 8.69 92.8 32.8 1.79 0.33 8.86 1.43 0.57 46.7 88.8 10.4 38.7 6.09 1.38 4.57 0.68 3.06 0.5 1.51 0.17 1.45 0.21

64.4 517 16.7 5.94 7.21 59.2 10.2 199 0.87 18.8 11.8 1.28 65 2.55 29.2 46.1 2.01 14.7 134 8.58 0.43 0.86 7.87 1.29 0.89 41.6 77.5 9.44 37.1 6.59 1.55 5.32 0.99 4.92 0.97 2.53 0.44 2.58 0.32

83.5 642 16.9 5.68 9.17 60.9 11 231 0.87 31.8 12.8 1.45 73.2 2.74 33.3 42.3 1.66 16.6 142 8.65 0.83 1.34 5.11 1.59 1.34 47.1 83.7 10.6 40.9 7.48 1.65 6.8 1.13 5.75 1.15 2.98 0.51 3.07 0.37

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O5 LOI pp m Rb Sr Co Ni Cu Zn Nb Ba Ta Pb Th U Zr Hf Y Li Be Sc V Cr Mo Sb Cs W Tl La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

0.74 358

0.75 319

0.70 874

0.7080 21

0.71 229

0.71 366

0.71 224

0.70 817

0.7075 9

0.09 793 8

0.09 264 2

0.09 159 1

0.09 4973

0.51 214 7

0.51 211 7

0.51 211 2

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0.5123 72

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87 Sr/ 86 Sr (87 Sr/ 86 Sr)i 14 7S m/ 14 4N d 14 3N d/1 44 Nd ¦Å Nd (t)

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Table 3 Zircon trace element compositions of the Narusongduo granites Sa m lg( pl N S G H T ¦Ä ¦Ä T(¡ fO e La Ce Pr d m Eu d Tb Dy o Er m Yb Lu Ce Eu æ) 2) NS LD 35 45 21 29 12 61 13 13 26 14 65 -1 -3- 0. .7 0. 1. 6. 0. .6 .7 8. 6. 1. 9. 86 5. 5. 0. 8. 4. 01 27 9 19 94 38 38 8 5 98 45 29 78 .6 42 18 07 68 18 NS LD 24 24 10 13 27 62 63 12 76 60 -2 -3- 0. .7 0. 2. 4. .5 .3 5. 56 4. .5 5. 6. .8 0. 1. 0. 02 3 7 22 53 35 1 7 5 49 .9 24 7 38 12 6 27 56 22 NS LD 30 14 28 13 29 29 58 12 69 -1 -3- 0. .4 0. 1. 2. 0. .1 5. 70 .1 0. .3 6. .5 0. 0. 0. 3. 03 47 1 25 69 74 54 5 72 .8 7 39 5 56 2 81 24 58 02 NS 14 LD 75 15 17 79 40 15 70 15 86 27 31 74 -1 -3- 4. .8 2. .4 .7 1. .4 32 0. 6. 9. 4. .9 8. .4 0. 4. 5. 04 17 6 27 9 8 54 1 .3 46 51 58 62 8 68 3 1 09 23 NS LD 14 76 32 15 36 37 74 10 64 -1 -3- 1. 34 0. 2. 2. 0. .3 5. .9 .1 6. .2 3. .6 2. 0. 3. 6. 05 72 .2 55 98 79 49 1 84 2 7 42 4 04 7 1 18 45 43 NS LD 26 10 12 45 20 44 44 86 29 70 -1 -3- 3. 33 1. 7. 5. 0. .2 .5 1. .8 7. .7 6. .5 .3 0. 5. 7. 06 44 .5 33 47 9 61 2 9 29 7 18 9 5 9 4 11 22 52 NS LD 10 10 52 18 20 75 32 69 67 13 85 85 -3- 0. 1. 0. 5. .8 2. .7 .6 7. .2 6. .6 8. 1. .9 0. 3. -6. 07 14 15 38 31 9 17 6 5 23 5 12 2 01 37 6 3 79 47 NS 13 LD 13 11 18 83 30 35 13 63 14 90 27 68 72 -1 -3- 0. 9. 0. .7 .1 5. .4 .1 8. 8. 1. 0. .9 5. .2 0. 5. 3. 08 25 82 77 4 3 32 1 6 1 17 17 71 1 8 8 4 37 28 NS LD 11 74 32 16 37 39 80 21 59 -1 -3- 0. 21 0. 0. 1. 0. .9 5. .7 .7 2. .7 3. .1 4. 0. 0. 7. 09 33 .6 15 99 68 25 2 46 6 4 43 1 13 5 8 15 99 08 NS 2. 52 2. 14 14 0. 62 28 37 14 68 15 15 28 28 0. 79 -1

0. 51

1. 95

-0. 83

6. 93

2. 91

2. 92 1.

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0. 22

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40 .3 1

0. 92

0. 14

.7 9

.4 9

3. 64

7. 26

6. 36

4. 8

14 .7 5

3. 75

.0 5

56 .1 6

25 5. 54

55 .3 4

54 2. 89

10 5. 12

11 5. 95

47 .9 5

20 5. 53

44 .8 2

32 6. 84

33 .5

12 .4

3. 51

43 .0 7

13 .5 8

13 9. 83

8. 71

1. 1

40 .5 4

15 .6 3

18 7. 42

1. 7

2. 52

0. 46

13 .9 8

9. 97

22 .9 6

6. 3

7. 76

11 .6 5

2. 15

4. 3

71 .1

08

7. 29

3. 11

0. 31

69 8. 78

-1 2. 71

4. 15

0. 5

95 2. 06

-1 0. 98

0. 69

-1 5. 66

0. 67

88 .5 5

9. 65

71 .5 3

69 9. 51

13 3. 91

39 .1 3

0. 19

71 9. 81

0. 2

63 6. 03

-1 6. 52

2. 08

0. 18

90 8. 73

-1 0. 86

1. 53

0. 29

65 3. 39

-1 3. 77

4. 32

-6. 4

6. 01

-6. 28

3. 92

-1 3. 82

2. 74

32 .4 6

15 8. 2

36 .1 1

36 6. 75

74 .5

11 2. 72

35 .1 4

35 4. 31

11 3. 41

46 0. 27

95 .1 3

88 2. 01

15 9. 64

15 .0 8

25 .2 6

9. 8

12 1. 64

48 .8 1

22 8

51 .2 3

10 0. 99

17 5. 89

0. 5

40 .7

19 .0 1

25 7. 79

10 7. 54

21 6. 82

49 .8 3

0. 06

59 .3 9

68 2. 6

41 3. 62

14 .7 2

0. 09

90 7. 82 10 48 .7 7

12 .8 8

17 3. 57

14 7. 63

72 .9

0. 1

71 0. 44

10 0. 07

2. 41

1. 01

1. 33

7. 18

7. 72

6. 06

80 .9 2

5. 01

29 .2 8

35 .6 7

2. 56

14 5. 72

23 .8 1

52 .4

2. 06

6. 89

5. 19

0. 57

28 .0 4

43

44 1. 73

77 .8 7

5. 92

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1. 48

14 6. 17

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0. 58

98

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0. 27

19 .0 5

.8 2

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0. 31

75 .7 6

0. 27

.1 2

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LD -310 NS LD -311 NS LD -312 NS LD -313 NS LD -315 NS LD -316 NS LD -317 NS LD -318 NS LD -319 NS LD -320

11 5. 99

24 5. 81

51 4. 24 10 90 .7 3

23 5. 94

51 5. 8 11 37 .5 8 22 19 .7 7

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77 .9 1

76 7. 12

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Highlights ► Syncollisional magmatic rocks in the Gangdese magmatic belt were derived from mixing between mantle-derived basaltic magmas and ancient crustal melts. ► Pb-Zn mineralization-related plutons in the Gangdese belt are high silica and oxidized granites. ► Compressional environment and its effects on magmatic evolution control Pb-Zn deposits in the Gangdese belt mainly developed during the syncollisional period.