Late Paleozoic arc magmatism in the southern Yili Block

Lithos 278–281 (2017) 111–125

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Late Paleozoic arc magmatism in the southern Yili Block (NW China): Insights to the geodynamic evolution of the Balkhash – Yili continental margin, Central Asian Orogenic Belt Yuchuang Cao a, Bo Wang a,⁎, Bor-ming Jahn b, Dominique Cluzel c, Liangshu Shu a, Linglin Zhong a a b c

State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, 210023 Nanjing, China Department of Geological Sciences, National Taiwan University, 10617 Taipei Université de la Nouvelle-Calédonie, BP R4, 98851 Noumea Cedex, New Caledonia

a r t i c l e

i n f o

Article history: Received 6 October 2016 Accepted 30 January 2017 Available online 08 February 2017 Keywords: Late Paleozoic Kazakhstan microcontinent Yili Block Tianshan (Tien Shan) Junggar Ocean Continental magmatic arc

a b s t r a c t The Yili Block represents the easternmost segment of the Kazakhstan–Yili microcontinent. Late Paleozoic magmatic rocks are extensively exposed in the Yili Block and are essential in understanding the tectonic development of the SW Central Asia Orogenic Belt (CAOB). We conducted field investigations, zircon U–Pb dating, whole-rock geochemical and Sr–Nd isotopic studies on the magmatic rocks from the Wusun Range, southern Yili Block. The Late Paleozoic volcanic and plutonic rocks of the Wusun Range show geochemical features consistent with that of calc-alkaline series, and they have positive εNd(t) values (0.9 to 5.6), Neo- to Mesoproterozoic single-stage Nd model ages (0.80 ~ 1.33 Ga), and variable initial 87Sr/86Sr ratios (0.7041–0.7059), suggesting that these magmatic rocks are likely derived from partial melting of a moderately depleted mantle wedge with minor involvement of a Precambrian continental crust. These new data, combined with previously published results put constraints on the Late Paleozoic magmatic and geodynamic evolution of the Balkhash–Yili active continental margin. The Late Paleozoic arc magmatism initiated from ~386 Ma along the northern Yili Block, and migrated southward to have occurred since ~340 Ma along its southern margin. Subsequently, the arc-related magmatism moved back northward and terminated at 310 Ma in the south and at ~295 Ma in the north. The OIB-like geochemical features of some volcanic rocks indicate incipient marginal rifting occurred along the southern Yili Block during Late Carboniferous. Taking into account the regional structural and tectonic data, the Carboniferous Yili magmatic arc may be laterally correlated with the Balkhash–Yili active margin of the Kazakhstan microcontinent, which was likely resulted from the southward subduction of the Junggar – North Tianshan Ocean. © 2017 Elsevier B.V. All rights reserved.

1. Introduction The Central Asian Orogenic Belt (CAOB; Fig. 1A) is bounded by the Baltic Craton to the west, the Siberian Craton to the north and the Tarim – North China cratons to the south. It is a giant orogenic belt and was built by subduction of the Paleo-Asian Ocean (PAO) and collision of multiple island arcs, microcontinents, accretionary wedges, oceanic islands and seamounts during the Late Mesoproterozoic to Late Paleozoic period (Coleman, 1989; de Jong and Wijbrans, 2006; de Jong et al., 2009; Eizenhöfer et al., 2014; Jahn et al., 2000; Khain et al., 2002; Mossakovsky et al., 1993; Sengör and Natal′in, 1996a, 1996b; Şengör et al., 1993; Wilhem et al., 2012; Windley et al., 2007; Xiao et al., 2004a, 2004b, 2010; Zonenshain et al., 1990). The Kazakhstan ⁎ Corresponding author at: School of Earth Sciences and Engineering, Nanjing University, 163# Xianlin Avenue, Nanjing, 210023, P.R. China. E-mail addresses: [email protected], [email protected] (B. Wang).

http://dx.doi.org/10.1016/j.lithos.2017.01.023 0024-4937/© 2017 Elsevier B.V. All rights reserved.

microcontinent, located in the southwest CAOB (Fig. 1B), is a continental assemblage formed by Early Paleozoic through successive accretion and collision of various continental fragments, island arcs and accretionary wedges (Biske and Seltmann, 2010; Glorie et al., 2010; Mikolaichuk et al., 1997; Wang et al., 2011a, 2012; Zonenshain et al., 1990). Late Paleozoic magmatic rocks occur extensively in the Kazakhstan microcontinent, especially along the Balkhash–Yili Orocline (Fig. 1B; Alekseiev et al., 2009; Windley et al., 2007; Xiao et al., 2010). Understanding the petrogenesis and tectonic setting of these magmatic rocks is critical for reconstructing the geodynamic evolution of the Paleo-Asian Ocean as well as the accretionary tectonism of the CAOB. The wedge-shaped Yili Block in the western Chinese Tianshan is the easternmost part of the Kazakhstan microcontinent (Fig. 1B). Voluminous Late Paleozoic magmatic rocks occur along the northern and southern margins of the Yili Block (Fig. 1B). They have been studied by many workers during the last decades (An et al., 2013; Han et al., 2010; Jiang et al., 1995; Long et al., 2008; Liu et al., 1994; Qian et al.,

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Fig. 1. (A) Tectonic framework of the Eurasia showing the geographic location of the Central Asian Orogenic Belt (CAOB) and its adjacent tectonic units (modified from Jahn et al., 2000; Şengör et al., 1993). (B) Simplified geological map of the Paleozoic Kazakhstan microcontinent and the Tianshan Belt (modified after Choulet et al., 2011; Wang et al., 2008, 2010, 2011a; Windley et al., 2007). Abbreviations: SKNT = Stepnyak – Kyrgyz North Tianshan, IKMT = Ishim – Kyrgyzstan Middle Tianshan, BC = Boshchekul – Chingiz, BA = Baidaulet – Akbastau, NB = North Balkhash, BY = Balkhash – Yili, CY = Chu – Yili, JB = Junggar – Balkhash, ACNT = Aktau – Chinese North Tianshan, ZTS = Zharma – Tarbagatay – Saur, WJ = West Junggar, KM = Karamai, CNT = Chinese North Tianshan, BGD = Bogda, CCT = Chinese Central Tianshan. Numbers refer to the major faults: 1 = North Tianshan Fault, 2 = Sailimu-Jinghe Fault, 3 = Nalati-Enyl'Chek Fault, 4 = Nikolaev Line.

2006; Ru et al., 2012; Wang et al., 2006a, 2007a, 2007b, 2009; Xia et al., 2004, 2008; Zhu et al., 2005, 2009, 2010). However, their genesis and tectonic setting remain controversial and various hypotheses have been put forward, including (1) post-orogenic continental rift (Che et al., 1996; Jiang et al., 1995), (2) large igneous province probably related to a mantle plume (Xia et al., 2003, 2004), (3) back-arc or intracontinental extension (Chen et al., 2001; Li and Yang, 1997; Qian et al., 2006), and (4) continental arc (Charvet et al., 2007, 2011; Filippova et al., 2001; Han et al., 2010; Long et al., 2008; Wang et al., 2007a, 2007b, 2009; Windley et al., 2007; Yakubchuk, 2004; Zhu et al., 2005, 2009, 2010). Among these conflicting hypotheses, the continental arc setting is most widely accepted. Nevertheless, different authors linked the continental arc with distinct subduction systems. Some considered that the Yili continental arc resulted from northward subduction of the South Tianshan Ocean (STO) (e.g., Gao et al., 1998, 2009; Xiao et al., 2004a, 2008, 2013; Zhu et al., 2009, 2010), whereas others favor southward subduction of the Junggar - North Tianshan Ocean beneath the Kazakhstan–Yili Block (Allen et al., 1993; Charvet et al., 2007, 2011; Wang et al., 2006a, 2007a, 2008, 2010, 2011b). The competing models are mainly based on geochemical data of magmatic rocks and/or regional structural data. The following issues are also important for better understanding the Late Paleozoic tectonic – magmatic evolution of the Yili Block. (1) The overall spatial and temporal

distribution of magmatic rocks in the Yili Block: along its southern margin both Early and Late Paleozoic magmatic rocks were widely recognized, whereas, along its northern margin only Late Paleozoic magmatic rocks occur (Figs. 1B and 2A). (2) Differences of lithology and structure exist between the Early and Late Paleozoic magmatic rocks: the Early Paleozoic magmatic rocks along the southern Yili Block are mainly basic-intermediate with ductile deformation fabrics (Wang et al., 2007b, 2010); whereas, the Late Paleozoic magmatic rocks are predominantly intermediate-acid without ductile deformation features. (3) Suture zones exist on both southern and northern boundaries of the Yili Block: the southern suture zone is represented by the highpressure metamorphic belt and associated ophiolitic mélanges developed along the Nalati Fault (Fig. 1B; e.g., Gao and Klemd, 2003; Gao et al., 1998; Wang et al., 2010); the northern suture zone is characterized by the Bayingou ophiolitic mélange along the North Tianshan Fault (Fig. 1B; Han et al., 2010; Wang et al., 2006a; Wu and Liu, 1989; Xu et al., 2005a, 2006). The aim of this study is to further discuss the Late Paleozoic geodynamic evolution of the Yili Block, and its genetic links with the Junggar – North Tianshan and/or South Tianshan oceanic basins. Field investigations, zircon U–Pb geochronology, whole-rock geochemical and Sr–Nd isotopic analyses have been conducted on the Late Paleozoic magmatic rocks from the Wusun Range in southern Yili Block (Fig. 2A).

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Fig. 2. (A) Simplified geological map of the Wusun Range, southern Yili Block (modified from 1:200,000 scale geological maps K44-IV, K44-V, K44-X and K44-XI by XBGMR, 1977, 1979a, 1979b, 1995). (B) Cross-sections across the Wusun Range showing stratigraphic contact between the late Paleozoic magmatic rocks and the associated sedimentary rocks. The sampling locations are shown as well.

This article presents these new data and a synthesis of already published results in order to better constrain the tectonic and magmatic evolution of the Balkhash – Yili Orocline and the geodynamic processes that formed this segment of the CAOB. 2. Geological background As one of the major constituents of the southwest CAOB, the Kazakhstan microcontinent is composed of several continental blocks with Paleoproterozoic to Neoproterozoic basement and Phanerozoic volcanic and sedimentary sequences (Bazhenov et al., 2003; Berzin and Dobretsov, 1994; Biske and Seltmann, 2010; Collins et al., 2003; Kheraskova et al., 2003; Mossakovsky et al., 1993; Sengör and Natal′in, 1996b). The continental blocks include the Ishim – Kyrgyzstan Middle Tianshan (IKMT), Stepnyak – Kyrgyzstan North Tianshan (SKNT), Chu – Yili (CY), Chinese North Tianshan (CNT), and Balkhash – Yili (BY) (Fig. 1B; Alexeiev et al., 2011; Degtyarev, 1999,

2003; Filippova et al., 2001; Kröner et al., 2008; Windley et al., 2007). The Yili Block is the easternmost part of the Kazakhstan microcontinent and is a wedge-shaped area separating the Chinese North Tianshan (CNT in Fig. 1B) to the north and Chinese Central Tianshan (CCT in Fig. 1B) to the south (Charvet et al., 2007, 2011; Gao et al., 2009; Qian et al., 2009; Wang et al., 2008). The tectonic boundary between the Yili Block and the Chinese North Tianshan is the Bayingou – Motuoshalagou ophiolitic mélange, which formed by closure of the Junggar – North Tianshan Oceanic basin (Gao et al., 1998, 2009; Shu et al., 2000; Wang et al., 2006a; Wang et al., 2008; Wu and Liu, 1989; Xu et al., 2005a, 2006) and was thereafter reworked by the North Tianshan Fault (NTF) (Fig. 1B). The Yili Block continues westward to join the Chu – Yili (CY) and Kyrgyzstan North Tianshan units, which are separated from the Chinese Central Tianshan (CCT) and Kyrgyzstan Middle Tianshan (KMT) by the Nalati Fault (NF) and the Nikolaev Line (NL), respectively (Fig. 1B). The Nalati Fault reworked the Akyazi – Kekesu high-pressure metamorphic belt and the associated

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ophiolitic mélange (Gao et al., 1995, 1998; Tang et al., 1995), both have been laterally correlated with the Atbashy metamorphic complex and ophiolitic mélange zones in Kyrgyzstan (e.g., Alekseiev et al., 2007, 2009; Hegner et al., 2010; Loury et al., 2015, 2016), separating the Kyrgyzstan Middle Tianshan from the South Tianshan (Fig. 1B). The Yili Block is considered as a Precambrian microcontinent hosting Paleozoic volcanic arcs (Charvet et al., 2011; Gao et al., 1998, 2009; Wang et al., 2006a, 2007a, 2008). Its basement is composed of Proterozoic amphibolite facies metamorphic rocks exposed along its northern and southern margins (Chen et al., 1999; XBGMR, 1993), including the granitic gneiss (800–930 Ma zircon ages; Chen et al., 1999; Hu et al., 2000; Wang et al., 2014) from the Sayram Lake (Fig. 1B) and granulite facies gneiss (1609 ± 40 Ma zircon age; Li et al., 2009) from the Awulale area (Fig. 1B). The basement is overlain unconformably by thick Late Paleozoic volcanic and sedimentary sequences consisting of the Upper Devonian to Lower Carboniferous Dahalajunshan Formation (C1d), Upper Carboniferous Yishijilike Formation (C2y), and Lower Permian Wulang Formation (P1w) (XBGMR, 1993). The volcanic rocks crop out in the Borohoro Range, northern Nalati Range, Awulale Range, Dahalajunshan Mountain, and Wusun Range (Figs. 1B and 2A). They consist of trachyandesite, andesite, rhyolite, basalt and pyroclastic rocks, which have ages of 386–300 Ma (An et al., 2013, Long et al., 2008; Qian et al., 2006; Ru et al., 2012; Wang et al., 2006a, 2006b, 2007a, 2007b, 2011b; Zhu et al., 2005, 2009, 2010). The volcanism persisted until the Early Permian, with lithological and geochemical features indicating intraplate or post-collisional environment (B. Wang et al., 2006; Wang et al., 2009; Zhao et al., 2006, 2009); Subsequently, the Middle to Late Permian molasse deposition post-dated the Andean-type orogenesis in the Yili Block (Charvet et al., 2007, 2011; Zhu et al., 2005). Voluminous Devonian-Carboniferous subduction-related granitoids are also distributed in the Yili Block (Li et al., 2010; Zhu et al., 2011). The northern and southern boundaries of the Yili Block are defined by two suture zones which were respectively reworked by the North Tianshan Fault and the Nalati Fault (Fig. 1B). To the north, the Bayingou ophiolitic mélanges are composed of blocks of ultramafic rocks, gabbros, basalts, pillow basalts, radiolarian-bearing cherts, and turbidites included in a matrix of sheared serpentinites and/or basalts. The ages of the radiolarian cherts and gabbros indicate that the oceanic crust of the Junggar – North Tianshan Ocean existed at least since Late Devonian to Early Carboniferous times (e.g. Wang et al., 2006a, 2006b, 2008; Xiao et al., 1990; Xu et al., 2006), and the closure of the oceanic basin occurred prior to 300 Ma as dated by “stitching granite” crosscutting the mélange zone (Han et al., 2010). To the south, a high-pressure metamorphic belt extends east–west along the Kekesu – Akeyazi – Atbashy areas (Fig. 1B). It comprises greenschist, micaschist, blueschist, paragneiss and lenses of eclogite and marble (Gao and Klemd, 2003; Gao et al., 2000, 2009; Lin et al., 2009; Wang et al., 2010). The protoliths of meta-mafic rocks include island-arc basalts, NMORB, E-MORB, OIB and graywackes (Khristov and Khristova, 1978; Gao et al., 2000, 2011; Li and Zhang, 2004). Ophiolites are developed to the south of the high-pressure metamorphic belt along the Atbashy, Dzhanydzher, Kekesu and Qiongkushitai areas (Figs. 1B and 2A). Multi-method dating suggest that the peak highpressure metamorphism occurred during 345–320 Ma (Burtman, 2008; Gao and Klemd, 2003; Gao et al., 2009; Hegner et al., 2010; Su et al., 2010; Wang et al., 2010). Several Early Paleozoic suture zones have been identified within the Kazakhstan microcontinent (Alexeiev et al., 2011; Konopelko et al., 2012; Kröner et al., 2012; Qian et al., 2009; Wang et al., 2011b; Windley et al., 2007). They may extend eastward and could be concealed within the Yili Block. Thus, the Yili Block may be tentatively subdivided into Northern Yili and Southern Yili subunits along the supposed suture zones (dashed lines in Fig. 1B); however, their actual boundary is unknown due to the overlying Cenozoic sedimentary cover (Wang et al., 2014). The northern and southern parts of the Yili Block underwent different geological evolution during the Early

Paleozoic (Zhu et al., 2006a, 2011). A sequence of Cambrian to Silurian sedimentary rocks was deposited in the northern Yili Block; whereas, in the southern Yili Block only minor Early Paleozoic rocks occur, as represented by the Upper Silurian Bayinbulak Formation (S3b) and Akeyazi Formation (S3a) (XBGMR, 1993), and these rocks were ductilely deformed and metamorphosed.

3. Field geology and sampling Field investigations were conducted mainly in the Wusun Range, southern Yili Block (Fig. 2A), along two approximately N–S transects to the north of the Zhaosu and Tekes cities (Fig. 2B). Early Carboniferous (C1) and Late Carboniferous (C2) volcanic rocks are widespread (XBGMR, 1979b, 1995), Carboniferous volcanic and sedimentary sequences make up the Dahalajunshan (C1d), Akshake (C1a) and Yishijilike (C2y) formations (XBGMR, 1993). The Dahalajunshan Formation is characterized by intermediate-basic volcanic rocks and marine limestones, with dark-green basalts exhibiting pillow structure (Fig. 3A). The Akshake Formation contains shallow marine sedimentary rocks, including fine-grained limestones, bioclastic limestones with intercalation of fine sandstones at the bottom and conglomerates, silty-mudstones, tuffaceous sandstones and siltstones at the top. The Yishijilike Formation is characterized by minor thin limestones and a series of terrigenous red sandstones, calcareous sandstones with interlayered andesites, rhyolites (Fig. 3B, C), amygdaloidal basalts, tuffaceous conglomerates and pyroclastic rocks. Many shallow water fossils (e.g., Caninia sp., Siphonodendron sp., and Gigantoproductus sp.) have been documented in the Carboniferous sedimentary rocks (XBGMR, 1993). Early Carboniferous to Permian plutonic rocks are also welldeveloped in the Wusun Range (Fig. 2A). They occur as small plutons or dikes intruding the Late Paleozoic volcanic and sedimentary sequences (Fig. 3D, E). The granitoids are mainly medium to coarsegrained biotite and K-feldspar granites, some biotite granites contain mafic microgranular enclaves (Fig. 3F). Diabase dikes, occurring to the north of the Tekes City, crosscut the Carboniferous volcanic and sedimentary sequences of the Dahalajunshan and Yishijilike formations (Fig. 2A). The terrigenous sediments of the Upper Permian Tiemulike Formation (P2t) and Triassic to Jurassic lacustrine sediments unconformably overlie the Carboniferous volcanic and sedimentary rocks as well as the intrusive rocks. The Paleozoic and Mesozoic rocks thrust over the Cenozoic deposits (Fig. 2). Thin-section study indicates that most basaltic rocks display porphyritic textures with phenocrysts of plagioclase (15–25 vol.%) and clinopyroxene (5–10 vol.%), and a groundmass with glass, finegrained plagioclase, clinopyroxene and oxides (Fig. 3G). Some basalts have experienced slight to moderate hydrothermal alteration (chloritization), and others display vesicular and/or amygdaloidal structures. Basaltic andesites mainly occur in the northern Zhaosu section (Fig. 3B) and show a porphyritic texture. They contain phenocrysts of plagioclase (10–15 vol.%) and clinopyroxene (~ 5 vol.%). The groundmass is composed of glass, fine-grained plagioclase, clinopyroxene and minor Fe-oxides (Fig. 3H). Porphyritic rhyolites with typical flow structures (Fig. 3C) mainly crop out in the northern Tekes section. Their phenocrysts comprise K-feldspar (8–15 vol.%), quartz (15–20 vol.%) and biotite (3–5 vol.%). Note that the felsic groundmass also exhibits clear rhyolitic structure (Fig. 3I). Trachyandesite, dacite, and pyroclastic rocks also occur in the study area. These weakly chloritized volcanic rocks experienced gentle deformation characterized by folding and fracturing, and no ductile deformation fabrics and no regional metamorphic minerals can be recognized. Fourteen fresh volcanic rocks and three granitoids were selected from the Wusun Range for zircon U–Pb dating, and whole-rock geochemical and Sr–Nd isotopic analyses. The sampling localities are shown in Fig. 2.

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Fig. 3. Field and microscopic pictures of the Carboniferous magmatic rocks in the Wusun Range. (A) pillow-shaped basalt, (B) andesite and (C) rhyolite from the north of Tekes City; (D, E) Intrusive contact between the granites and the volcanic rocks, north of the Tekes City; (F) Contact between the biotite granite and K-feldspar granite, north of the Zhaosu City; (G) basalt (XJ502); (H) andesite (15T92); (I) rhyolite (XJ512). Abbreviations: cpx = clinopyroxene; pl = plagioclase; fds = k-feldspar; mt = magnetite.

4. Analytical methods

4.2. Whole-rock element and Sr–Nd isotope geochemistry

4.1. LA–ICP–MS zircon U–Pb dating

Whole-rock chemical compositions were analyzed at the Department of Geosciences, National Taiwan University (Taipei) using an X-ray fluorescence (XRF) spectrometry on fused-glass disks for major element oxides and an Agilent 7500 s quadrupole ICP–MS for trace elements. Detailed analytical procedures are described in Yang et al. (2005). Analytical errors are 0.5–3% for major elements and 0.7–5% for trace elements. Five representative samples were measured for Sr–Nd isotopic compositions by thermal ionization mass spectrometry (TIMS) at the Institute of Earth Sciences, Academia Sinica (Taipei). A 7–collector Finnigan MAT–262 mass spectrometer was used for mass analysis. Detailed procedures for sample dissolution, chemical separation and isotope analysis can be found in Jahn et al. (2009).

Zircon grains were extracted from crushed rock powders through heavy liquids and magnetic separation techniques. Colorless single zircon grains without fractures were handpicked under a binocular microscope and then mounted with epoxy resins and finally polished to half-section of zircon grains. Cathodoluminescence (CL) imaging was conducted at the State Key Laboratory of Continental Dynamics, Northwest University (Xi'an, China) using a Quanta 400 FEG scanning electron microscope equipped with a Gatan mini–CL detector (Mono CL3+). Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA– ICP–MS) analyses were carried out on an Agilent 7500 s Mass Spectrometer coupled with a New Wave 193 μm laser ablation system installed at the State Key Laboratory for Mineral Deposits Research (Nanjing University). Twice an internal zircon standard GJ (608 ± 1.5 Ma; Jackson et al., 2004) and once an external zircon standard MudTank (732 ± 5 Ma; Black and Gulson, 1978) were analyzed before and after every tenth analysis of unknown samples to track the instrumental stability and control the quality of analysis. Common Pb correction was carried out using the Microsoft Excel® embedded program ComPbCorr#3 15G (Andersen, 2002). ISOPLOT 3.1 (Ludwig, 2003) software was used to calculate ages and construct Concordia plots. Uncertainties are quoted at 1σ for individual analyses and at 2σ (with 95% confidence level) for weighted mean ages.

5. Results 5.1. Zircon U–Pb ages Rhyolite sample 15T56A was collected to the north of Tekes City (Fig. 2; GPS: N43°26′26″, E81°54′37″). Zircon crystals from this sample are euhedral to subhedral and are 90–200 μm long and 70–110 μm wide with length/width ratios of 1.5 to 3 (Fig. 4A). They have moderate to high concentration of Th (112–571 ppm) and U (152–601 ppm), and rather high 232Th/238U ratios (0.64–1.12) (Supplementary Table S1).

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Fig. 4. CL images of the dated zircons (A and C) and Concordia diagrams (B and D) of the LA–ICP–MS analytical results for the rhyolites in the Wusun Range. The black circles represent analytical locations of the laser beam.

Their cathodoluminescence (CL) images display concentric oscillatory zoning (Fig. 4A), suggesting a magmatic origin for the zircon grains (Corfu et al., 2003). Fifteen spot analyses consistently yielded tightgrouped concordant 206Pb/238U ages of 307 to 322 Ma, and a weighted average 206Pb/238U age of 316.1 ± 2.6 Ma (2σ, MSWD =0.99, Fig. 4B). This age is considered as the crystallization time of the rhyolite. Another rhyolite sample 15T94 was collected from the section to the north of Zhaosu City (Fig. 2; GPS: N43°30′03″, E81°07′01″). Zircon crystals separated from this sample are euhedral to subhedral, 80–170 μm long and 60–90 μm wide. Their Th and U contents are 58–662 ppm and 77–234 ppm, respectively, with 232Th/238U ratios varying from 0.66 to 2.83 (Table S1). Such ratios, together with the concentric oscillatory zoning in their CL images (Fig. 4C), suggest a magmatic origin of the zircon crystals (Corfu et al., 2003). Sixteen spot analyses also consistently yielded concordant ages, with a weighted average 206Pb/238U age of 333.5 ± 2.6 (2σ, MSWD =0.45, Fig. 4D). This age is calculated as the crystallization time of this rhyolite. 5.2. Whole-rock element geochemistry Whole-rock chemical analyses reveal that most of seventeen samples have LOI contents from 0.83 to 4.19 wt% except two samples (XJ516–2 and XJ538) showing LOI N 5 wt%. Alkali elements show high variations: K2O = 0.21–5.30 wt% and Na2O = 1.87–8.79 wt%. However, the variations in total alkalis (ALK = 4.09–8.13 wt%) and Na2O/K2O ratios (0.49–1.46) are much more restricted. Exceptionally, a few samples show very high ALK (N10 wt%) and Na2O/K2O ratios (N3)

(Supplementary Table S2). Most magmatic rocks have A/CNK (Al2O3/ (CaO + Na2O + K2O) mol.) values lower than 1, except a few with A/CNK of 1.05 to 2.2. Mg# values of these samples are generally lower than 0.58 showing a decreasing tendency with increasing SiO2 contents (Table S2). In a Zr/TiO2 versus Nb/Y diagram (Fig. 5A), all samples plot in the sub-alkaline field showing a continuous variation from basic, intermediate to acid series. On the AFM (alkali - total FeO - MgO mol.) diagram, most samples follow the line of the calc-alkaline series, and the ALK contents of the volcanic rocks increase linearly with the decrease of total FeO and MgO abundances (Fig. 5B). According to the trace element distribution patterns (Fig. 6C, D), the Carboniferous magmatic rocks of the Wusun Range can be subdivided into two groups. Group 1 is composed of basalts and minor andesites of the Lower Carboniferous Dahalajunshan Formation (C1d). These rocks are characterized by low LREE/HREE ratios (3.3–5.7) and low (La/Yb)N values (2.5–5.9); In addition, they show relatively flat Chondrite-normalized HREE patterns with slightly enriched LREE (Fig. 6A). Group 2 consists of the rhyolitic volcanic rocks belonging to the Lower Carboniferous Akeshake Formation (C1a; 334–316 Ma, zircon U–Pb ages) and granitic rocks. These felsic rocks are characterized by prominent REE fractionation (LREE/HREE = 4.50–9.75, (La/ Yb)N = 5.01–10.08) and variable negative Eu anomalies (0.02–0.89) (Table S2; Fig. 6B). On the N-MORB-normalized trace element spider diagrams (Pearce, 1982) (Fig. 6C, D), the felsic rocks of the Group 2 show more pronounced LILE enrichment (e.g., Rb, Th, Ba, K) and HFSE depletion (e.g., Nb, Ta, Ti) compared to the basaltic and andesitic rocks of the Group 1.

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Fig. 5. Geochemical plots for the Late Paleozoic volcanic rocks in the Wusun Range. (A) Zr/TiO2 versus Nb/Y diagram (Winchester and Floyd, 1976); (B) AFM diagram (Irvine and Baragar, 1971); (C) Th/Yb versus Nb/Yb diagram (Pearce and Peate, 1995); (D) Th–Hf/3–Ta ternary discrimination diagram (Wood, 1980); (E) Sr/Y versus Y (Defant and Drummond, 1990) and (F) (La/Yb)N versus (Yb)N (Martin, 1986) discrimination diagrams. The symbols in gray represent plots of the previously published geochemical data of volcanic rocks from the Yili Block, data sources are listed in Supplementary Table 6. Abbreviations: CAB = calc-alkaline basalt; E-MORB = enriched mid-ocean ridge basalt; IAT = island arc tholeiitic basalt; N-MORB = normal mid-ocean ridge basalt; WPA = within-plate alkaline basalt; WPT = within-plate tholeiitic basalt.

5.3. Whole-rock Sr-Nd isotopic compositions

6. Discussion

The Sr-Nd isotopic data of five representative samples are plotted in Fig. 7 along with the literature data of Qian et al. (2006) from the northern Zhaosu section (Fig. 2A). The age of rhyolite sample 15T94 (333 Ma) was used to calculate initial isotopic ratios of samples XJ495–3, XJ502, and 15T92; and the isotopic ratios of the samples 15T56A and 15T60 were back-calculated at 316 Ma. The Early Carboniferous volcanic rocks (Group 1) have initial 87Sr/86Sr ratios from 0.7046 to 0.7059, and positive εNd(t) values ranging from +3.4 to +4.4. The initial 87Sr/86Sr ratios and εNd(t) values of the Late Carboniferous samples (Group 2) are 0.7046 ~ 0.7048 and +1.6 ~ +3.2, respectively (Supplementary Table S3). Single-stage Nd depleted mantle model ages (TDM1 (Nd)) of the Early and Late Carboniferous rocks are 0.80–1.33 Ga and 0.79–0.86 Ga, respectively.

6.1. Tectonic setting of the Carboniferous magmatic rocks in the southern Yili Block A differentiated series of mafic to felsic calc-alkaline lavas and pyroclastic rocks occur in the southern Yili Block. They have near-zero to slightly positive εNd(t) values (− 0.2 to + 5.6), variable initial 87 Sr/86Sr values and Proterozoic single-stage Nd model values (Supplementary Table S4; Fig. 7). This indicates that they were likely derived from partial melting of a moderately depleted mantle wedge with involvement of Precambrian continental crust. Although they display a nearly linear differentiation trend on the Nb/Y – Zr/TiO2 diagram (Fig. 5A, B), their REE patterns (Fig. 6A, B) cannot be modeled easily with fractional crystallization from a single parental magma chamber.

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Fig. 6. (A, B) Chondrite-normalized REE distribution patterns and (C, D) N-MORB-normalized trace element spider diagrams of the magmatic rocks from the Wusun Range, southern Yili Block. Chondrite normalization values are from Sun and McDonough (1989), N-MORB values are from Pearce (1982). Chondrite normalized REE distribution patterns of Ocean Island Basalt (OIB), Normal Mid-Ocean Ridge Basalt (N-MORB) and Enriched Mid-Ocean Ridge Basalt (E-MORB) are shown for comparison.

Besides, the wide range of Zr/Nb ratios (4 ~ 55) also suggest distinct magma sources (Davidson, 1996). The depleted and flat HREEs patterns and elevated LREEs and LILEs contents combined with negative Nb, Ta and Ti anomalies (Fig. 6) suggest that the magmas source were most likely modified by slabderived fluids. The relatively high Ba/Th ratios (142 ~ 466; Table S4) of the basaltic samples also indicate the significant impact of the slabderived fluids (Devine, 1995). Thus, the Carboniferous magmatic rocks in the southern Yili Block likely formed in a supra-subduction zone. In the Th–Hf/3–Ta ternary discrimination diagram (Fig. 5D), all samples plot in the calc-alkaline volcanic arc field. In addition, the relatively low La/Yb ratios of these calc-alkaline volcanic rocks are indicative of a

continental arc setting (Fig. 6A–D), which agrees with the Th/Yb versus Nb/Yb diagram (Fig. 5C; Pearce and Peate, 1995). Moreover, in the Th– Hf/3–Ta ternary discrimination diagram (Wood, 1980), a dominant mixing trend between continent-based arc (low Hf/Th) and intraoceanic arc (high Hf/Th) end-members suggests variable involvement of continental crust (high Th) (Fig. 5D). Thus, a continental arc (active margin) setting is consistent with the available data and fits well with the conclusions of most previous authors (Charvet et al., 2007, 2011; Filippova et al., 2001; Gao et al., 1998, 2009; Han et al., 2010; Long et al., 2008; Wang et al., 2007a, 2007b, 2009; Windley et al., 2007; Yakubchuk, 2004; Zhu et al., 2005, 2006a, 2009). It is worth noting that some Carboniferous magmatic rocks from the Wusun Range less depleted in Ta (and Nb) define a weak mixing trend between continent-based arc and intraplate magmas on the Hf/3-Th-Ta ternary diagram (Figs. 5D and 6A–B). The significance of these features will be discussed in the following section together with the literature data. According to the regional geological maps and our own field observations, the Lower Carboniferous volcanic rocks mainly comprise basaltic and andesitic rocks with minor rhyolitic rocks, and they are associated with the limestones, indicating a marine environment. The upper Carboniferous rhyolites and andesites with subordinate basalts, are associated with shallow marine to terrestrial sediments. This suggests that they erupted in a shallow water to an subaerial environment. Such a transition from an Early Carboniferous marine to a Late Carboniferous terrestrial environment may records Late Carboniferous uplift and emersion of the southern margin of the Yili Block. 6.2. Time–space distribution of the Carboniferous magmatic rocks in the Yili Block

Fig. 7. εNd(t) versus initial 87Sr/86Sr diagram for Late Paleozoic magmatic rocks from the Yili Block. Our new data are plotted as open color symbols, and the literature data in gray symbols.

To gain a better understanding of the Late Paleozoic geodynamic evolution the Yili Block, we need the maximum information of age, geochemical and isotopic data of the Carboniferous magmatic rocks. For this reason, such data from the literature are compiled and given in Supplementary Tables S4-S6 and Figs. 7-9. The literature data and our

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Fig. 8. Map compilation of the Late Paleozoic magmatic rocks in the Yili Block. Age data are listed in Table S5. Numbers represent the major faults: 1 = North Tianshan Fault; 2 = Sailimu – Jinghe Fault; 3 = Nalati Fault; 4 = Nalati – Xinyuan Fault.

Fig. 9. Histograms showing the age distributions of the Late Paleozoic magmatic rocks from the northern Yili (A) and southern Yili (B) areas.

study suggest that Carboniferous continental arc rocks in the western Tianshan belt mainly occur between the North Tianshan Fault and the Nalati Fault (Fig. 8). Some Carboniferous volcanic rocks occur near the Bayingou ophiolites in the Chinese North Tianshan, but they belong to the North Tianshan accretionary wedge and were likely formed in oceanic island arc or forearc basin settings (Han et al., 2010; Wang et al., 2006a). Small amount of Carboniferous granitic rocks also occur in the Baluntai area of the Central Tianshan (to the SE of the Nalati Fault), but these rocks are considered to have formed in a post-collisional setting (Shi et al., 2007; Xu et al., 2005b, 2006). Moreover, Ordovician to Silurian subduction-related magmatic rocks were emplaced in the southern Yili margin (Gao et al., 2009, 2011), but these rocks were deformed and metamorphosed and should have resulted from earlier magmatic and tectonic events (Charvet et al., 2011; Wang et al., 2008, 2010; Zhong et al., 2017). Thus, in this study, we will focus only on the undeformed and unmetamorphosed Late Paleozoic magmatic rocks from the Yili Block (Fig. 8). Late Paleozoic magmatic rocks in the Yili Block were emplaced during the 386 to 300 Ma interval (Figs. 8 and 9). The Cenozoic Yili Basin covering the center of the Yili Block and the Nalati – Xinyuan Fault roughly divides the Yili Block into the northern Yili and the southern Yili subunits (Fig. 8). A dataset of forty-two high-quality zircon U–Pb ages (Table S4) shows that active margin magmatism started as early as at 386 Ma and continued to 300 Ma in northern Yili, whereas that in the southern Yili from 368 to 313 Ma (Fig. 9). The high-precision zircon U–Pb ages (Table S4) are sufficient to conclude that the arc magmatism initiated earlier and terminated later in the northern Yili with respect to the southern Yili. In order to re-assess the previously published geochemical and isotopic data of the literature, the magmatic rocks in the Yili Block are divided into four age groups on the basis of zircon U–Pb data (and more scarcely according to the stratigraphic age of the enclosing sediments) and geographic locations. The four groups include (1) Late Devonian to Early Carboniferous rocks of the northern Yili (NY–D3-C1), (2) Late Devonian to Early Carboniferous rocks of the southern Yili (SY–D3-C1),

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(3) Late Carboniferous rocks of the northern Yili (NY–C2), and (4) Late Carboniferous rocks of the southern Yili (SY–C2) (Fig. 10). In general, most volcanic rocks of these four groups show REE distribution patterns similar to the calc-alkaline series and plot in the field of arc magmatic rocks (Fig. 5B-F). Further, they are almost indistinguishable between different groups and between different lithologies of one single group. Despite such similarity, some basic and intermediate volcanic rocks of the group SY–C2 have more enriched LREE and depleted HREE abundances, resulting in their OIB or EMORB type REE patterns to some extent (Fig. 10D). Qian et al. (2006) considered that these volcanic rocks might have formed in a back-arc extensional setting. Actually, on the Nb/Yb–Th/Yb and Hf/3–Th–Ta diagrams, these volcanic rocks of the group SY–C2 plot in the field close to the MORB array (Fig. 5C, D), this indicates an increasing input of depleted mantle component. As pointed out above, there is a vague tendency for these rocks to form a mixing line between continental-arc and intraplate fields. Such phenomenon is not uncommon in mature active margins. Consistently Nd isotope data (Table S3) show a tendency towards more depleted and homogeneous sources through time. Isotopically, the magmatic rocks of the Yili Block have changing εNd(t) values and 87Sr/86Sr ratios with time, i.e., more positive εNd(t) values and a wider range of 87Sr/86Sr ratios in the younger magmatic rocks (Table S6; Fig. 7). In addition, the Early Carboniferous magmatic rocks from both the northern and southern Yili Block (group NY–D3-C1 and SY–D3-C1) have similar εNd(t) values and 87 Sr/86Sr ratios; However, the Late Carboniferous magmatic rocks of the southern Yili Block have obviously lower 87Sr/86Sr ratios with respect to the Late Carboniferous rocks from the northern Yili, although the εNd(t) values of the Late Carboniferous rocks in the entire Yili Block are comparable (Fig. 7). Such an obvious shift towards more radiogenic Sr at almost constant εNd(t) values in Late Carboniferous rocks of the northern Yili is probably meaningless in terms of source and more likely related to some alteration. All these geochemical and isotopic data suggest that at least part of the Late Carboniferous magmatic rocks from the southern Yili area were generated with more important input of mantle material (MORB

and/or OIB) and less involvement of the continental crust with respect to the Early Carboniferous magmatic rocks in the southern Yili and all Carboniferous rocks in the northern Yili. Taking into account the general calc-alkaline geochemical features and continental arc-type characteristics of these magmatic rocks, a marginal rifting setting due to back-arc extension is most likely for the Late Carboniferous magmatic rocks in the southern Yili Block. In such a marginal rifting environment, possible upwelling of the asthenospheric mantle and thinning of the continental crust would result in the aforementioned geochemical features of the Late Carboniferous magmatic rocks in the southern Yili Block. As mentioned before, from the Early to Late Carboniferous, a transition from marine to shallow marine or terrestrial environments occurred in the southern margin of the Yili Block, and it likely resulted from the uplifting and emersion of the continental crust, which is probably induced by the upwelling of the asthenosphere beneath the marginal rift. In addition to this possibility, the mid-Carboniferous (~ 340– 320 Ma; e.g. Charvet et al., 2007, 2011; Loury et al., 2015; Wang et al., 2010) collision between the Yili (or Kyrgyzstan Middle Tianshan) and the Central Tianshan – Tarim blocks is also an important cause for the uplifting and emersion of the southern Yili margin. 6.3. Geodynamic implications for the Late Paleozoic tectonic development of the SW CAOB The Carboniferous magmatic rocks were considered by a few workers to have formed in a continental rifting or with a mantle plume (Xia et al., 2004, 2012; Xu et al., 2006), but most others agree that a continental arc fits better with the available geological and geochemical data. However, no consensus has been reached regarding the geodynamic evolution of the continental arc. Conflicting models suggested subduction of the South Tianshan Ocean (Gao et al., 1998, 2009, 2011; Han et al., 2010, 2011; Xiao et al., 2004a, 2008; Zhu et al., 2005, 2006a, 2006b, 2010); or alternatively, subduction of the Junggar – North Tianshan Ocean (Charvet et al., 2007, 2011; Wang et al., 2006a, 2007a, 2007b, 2009). In the model of subduction of the South Tianshan Ocean or the Turkestan Ocean, the magmatic rocks are generally linked with the

Fig. 10. Chondrite-normalized REE patterns (Sun et al., 1989) of volcanic rocks from the Yili Block (compiled from the literature, see supplementary data, Table S6).

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high-pressure metamorphic complex and associated ophiolitic mélange along the Kekesu – Akeyazi – Atbashy belt. Consequently, a northward subduction of the South Tianshan (or Turkestan) Ocean is proposed (e.g., Gao et al., 1998, 2009; Han et al., 2011; Xiao et al., 2004a). However, some problems may be encountered. On one hand, the Carboniferous subduction-related magmatic rocks occur only along the southern Yili Block to the north of the Kekesu – Akeyazi high-pressure metamorphic and ophiolite belt; they are entirely lacking in the Kyrgyzstan Middle Tianshan to the north of the Atbashy high-pressure metamorphic and ophiolite belt (Loury et al., 2015, 2016). As shown in Fig. 1B, the Carboniferous magmatic rocks continue westward in the Kyrgyzstan North Tianshan and southern Kazakhstan, about 500 km apart from the Atbashy suture zone. In fact, these magmatic rocks form the southern part of the Balkhash – Yili Late Paleozoic active margin (Windley et al., 2007) and therefore are genetically unrelated to the subduction of the Turkestan Ocean. Thus, the absence of magmatic activity from the Givetian to Serpukhovian and Bashkirian in the western and southern margins of the Kazakhstan (Ishim-Kyrgyzstan Middle Tianshan; IKMT in Fig. 1) argues against a northward subduction of the Turkestan (or South Tianshan) Ocean at that time (Alekseiev et al., 2009; Cook et al., 2002). On the other hand, structural and kinematic analyses of the Kekesu – Akeyazi – Atbashy high-pressure metamorphic complex indicate an early deformation event characterized by top-to-the-north shearing (Charvet et al., 2011; Lin et al., 2009; Loury et al., 2016; Wang et al., 2008, 2010). Thus, they do not support a northward subduction of the South Tianshan (Turkestan) Ocean. In addition, the Late Carboniferous arc-type granodiorite (~ 313 Ma) intrudes the Kekesu high-pressure metamorphic belt (Wang et al., 2007b), thus excluding a possible link between the Late Carboniferous arc magmatism of the Yili Block and the suture zone of the South Tianshan Ocean. Note that Early Paleozoic intrusive rocks are widely distributed along the southern Yili Block and also along the southern margin of the Kyrgyzstan Middle Tianshan (Alekseiev et al., 2009). Their geochemical features indicate a magmatic arc setting, thus, some authors considered that these Early Paleozoic arc-related magmatic rocks formed during the early stage of northward subduction of the South Tianshan Ocean (Gao et al., 2009; Han et al., 2011), but others argue that they may be due to the subduction of the Kyrgyz Terskey Ocean that was located to the north of the Kyrgyzstan Middle Tianshan (Alexeiev et al., 2016; Charvet et al., 2011). The eastward continuation of the Terskey suture into the Yili Block cannot be determined with the available data. However, the Early Paleozoic arc-type intrusive rocks in the southern Yili Block were ductilely deformed and metamorphosed to upper-greenschist to amphibolite facies (Gao et al., 2009; Konopelko et al., 2012; Zhong et al., 2017), and are distinguished from the undeformed, unmetamorphosed Carboniferous magmatic rocks in the Yili Block. Therefore, they should have been generated and metamorphosed during another subduction/accretion event prior to the Carboniferous magmatism. In the second model, widespread Late Devonian to Late Carboniferous magmatic rocks in the curved Balkhash – Yili belt are interpreted as an Andean-type arc produced by the subduction of the Junggar – North Tianshan Ocean (Charvet et al., 2007, 2011; Han et al., 2010; Wang et al., 2006a, 2007a, 2009; Windley et al., 2007) beneath the Kazakhstan microcontinent that was amalgamated in the Late Silurian (Windley et al., 2007). The Chinese North Tianshan (CNT) and Junggar – Balkhash accretionary belts correspond to Late Paleozoic suture zones that were reworked and bent by the Permian post-orogenic strike-slip duplexing (Choulet et al., 2011; Levashova et al., 2003; Wang et al., 2006a, 2007b, 2014). As discussed above, our new and literature data indicate that the Late Carboniferous magmatic rocks in the southern Yili Block probably formed in a marginal rifting setting related to back-arc extension. Considering the coeval wide arc range on the northern Yili margin, such a back-arc extension event favors a southward subduction of the

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Junggar – North Tianshan Ocean. The progressive migration of Late Paleozoic magmatism from the north to the south and then backward to the north also indicates that the trench was located to the north of the Yili Block. This is proved by the existence of the contemporaneous subduction wedge on the nothern border of the Chinese North Tianshan (Fig. 1B). Initiation of the back-arc extension was likely induced by upwelling of the asthenosphere, which is also partially responsible for the uplift and emersion of the continental crust along the southern Yili Block. Such back-arc extension induced by the subduction system of the Junggar Ocean was likely counteracted by contemporaneous convergence along the southern margin of the Yili Block related to the Yili - Central Tianshan collision, consequently, a back-arc basin was not produced. In summary, a new schematic three-stage geodynamic model of the southward subduction of the Junggar – North Tianshan Ocean is proposed for the Late Paleozoic tectonic and magmatic evolution of the Balkhash – Yili continental arc (Fig. 11). (1) During the Late Devonian to Early Carboniferous (ca. 380–340 Ma), southward subduction of the Junggar – North Tianshan Ocean initiated the arc-type magmatism along the northern margin of the Yili – Kazakhstan microcontinent, and the spreading of the North Tianshan Oceanic basin formed part of the Bayingou ophiolites (Li and Du, 1994; Xiao et al., 1992; Xu et al., 2005a). (2) In the mid-Carboniferous (ca. 340–320 Ma), closure of the Paleo-Tianshan Ocean (or called South Tianshan Ocean) to the south induced collision between the Yili Block with the Central Tianshan – Tarim blocks. This is documented by the high-pressure metamorphic complex in the Kekesu – Akeyazi – Atbashy belt (Gao et al., 1995, 2000, 2009; Hegner et al., 2010; Lin et al., 2009; Loury et al., 2015, 2016; Su et al., 2010; Wang et al., 2008, 2010). This collisional orogeny partially induced the uplifting of the southern margin of the Yili Block as well as the transition from Early Carboniferous marine to Late Carboniferous shallow marine or terrigenous sedimentary environments. At the same time, advancing subduction of the Junggar – North Tianshan Ocean led to southward migration of arc magmatism to the southern Yili Block. (3) During the Late Carboniferous (ca. 320–300 Ma), arctype magmatism weakened in the southern Yili Block, and arc-type volcanic rocks with increasing input of mantle materials were likely generated in a marginal rifting setting, which corresponds to a retreating subduction and back-arc extension probably induced by rollback of the subducting slab of the Junggar – North Tianshan Ocean. The arc magmatism ceased at ~310 Ma in the southern Yili and migrated backward to the northern Yili Block where it finally terminated at ~ 300– 295 Ma due to the closure of the Junggar – North Tianshan Ocean (Han et al., 2010; Wang et al., 2009). 7. Conclusions Based on a detailed study of the geology, geochemistry and geochronology of the Carboniferous magmatic rocks from the Wusun Range, southern Yili Block, and a synthesis of previous results on the Late Devonian to Carboniferous magmatic rocks in the entire Yili Block, the following conclusions can be obtained. (1) Carboniferous magmatic rocks in the Wusun Range are composed of continuous basic - intermediate - acid volcanic series and coeval plutonic rocks. These rocks are undeformed and unmetamorphosed. The associated sedimentary sequences show a variation from Early Carboniferous marine to Late Carboniferous shallow water environments. Geochemical and isotopic data indicate that the Carboniferous magmatic rocks belong to the calc-alkaline series, and part of the Late Carboniferous rocks show OIB-like features. A continental arc setting is the most probable environment for the Carboniferous magmatic rocks, and the minor Late Carboniferous OIB-like volcanic rocks in the southern Yili Block likely formed during marginal rifting stage due to the back-arc extension.

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Fig. 11. New schematic model illustrating the Late Paleozoic tectonic and magmatic evolution of the Yili continental arc and its relation to the subduction of the Junggar – North Tianshan Ocean.

(2) Available geochemical and geochronological data indicate that the Late Devonian to Carboniferous arc-related magmatism moved progressively from the northern to the southern margin of the Yili Block between ~ 386 Ma and ~ 340 Ma, and then migrated back northward in the Late Carboniferous. The time– space distribution of the Late Paleozoic arc magmatism in the Yili Block support a southward subduction of the Junggar – North Tianshan Oceanic lithosphere. Late Paleozoic subductionrelated magmatic rocks forms a part of the Late Paleozoic active margin along the Kazakhstan - Balkhash Orocline. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.lithos.2017.01.023. Acknowledgments We appreciate Mr. B. Wu from Nanjing University for his kind helps in the LA–ICP–MS dating. Mr. F.L. Lin and Mr. W.Y. Hsu at the Institute of Earth Sciences, Academia Sinica (Taipei), and Ms. Y.C. Lin of National Taiwan University provided valuable assistance during whole-rock element and isotopic analyses. We thank three reviewers, Profs. J. Charvet, Y. Rolland and K. de Jong for their constructive and detailed comments and suggestions that helped a lot in improving our paper. This research was sponsored by the National Nature Science Foundation of China (41390445, 41222019, 41172197, 41311120069) and by the State Key Laboratory for Mineral Deposits Research (Nanjing Univ.) (ZZKT201603). Bor-ming Jahn acknowledged the support of the MOST (Taiwan) through research grants: MOST 104-2116-M-002-004

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