Devonian volcanic rocks of the southern Chinese Altai, NW China: Petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis

Accepted Manuscript Devonian volcanic rocks of the southern Chinese Altai, NW China: petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis Xiaomei Ma, Keda Cai, Taiping Zhao, Zihe Bao, Xiangsong Wang, Ming Chen, M.M. Buslov PII: DOI: Reference:

S1367-9120(18)30138-X https://doi.org/10.1016/j.jseaes.2018.04.017 JAES 3471

To appear in:

Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

24 December 2017 26 March 2018 15 April 2018

Please cite this article as: Ma, X., Cai, K., Zhao, T., Bao, Z., Wang, X., Chen, M., Buslov, M.M., Devonian volcanic rocks of the southern Chinese Altai, NW China: petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis, Journal of Asian Earth Sciences (2018), doi: https://doi.org/10.1016/j.jseaes.2018.04.017

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Devonian volcanic rocks of the southern Chinese Altai, NW China: petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis Xiaomei Ma1,3,4, Keda Cai2*, Taiping Zhao1, Zihe Bao3,4 , Xiangsong Wang3,4, Ming Chen5, M.M. Buslov6 1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China 2. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China 3. University of Chinese Academy of Sciences, Beijing 100029, China 4. Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China 5. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China 6. Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, 630090 Novosibirsk, Russia

*

Corresponding author: Keda Cai School of Earth Sciences and Resources, China University of Geosciences, Beijing 29 Xuyuan Road, Haidian District, Beijing, P.R. China Mobile Phone: +86 15739538922 E-mail: [email protected] 1

Abstract Ridge–trench interaction is a common tectonic process of the present-day Pacific Rim accretionary orogenic belts, and this process may facilitate “slab-window” magmatism that can produce significant thermal anomalies and geochemically unusual magmatic events. However, ridge-trench interaction has rarely been well-documented in the ancient geologic record, leading to grossly underestimation of this process in tectonic syntheses of plate margins. The Chinese Altai was inferred to have undergone ridge subduction in the Devonian and a slab-window model is proposed to interpret its high-temperature metamorphism and geochemically unique magmatic rocks, which can serve as an excellent and unique place to refine the tectonic evolution associated with ridge subduction in an ancient accretionary orogeny. For this purpose, we carried out geochemical and geochronological studies on Devonian basaltic rocks in this region. Secondary ion mass spectrometry (SIMS) zircon U-Pb dating results yield an age of 376.2±2.4 Ma, suggesting an eruption at the time of Late Devonian. Geochemically, the samples in this study have variable SiO2 (43.3-58.3 wt.%), low K2O (0.02-0.07 wt.%) and total alkaline contents (2.16-5.41 wt.%), as well as Fe2O3T/MgO ratios, showing typical tholeiitic affinity. On the other hand, the basaltic rocks display MORB-like REE patterns ((La/Yb)N=0.90-2.57) and (Ga/Yb)N=0.97-1.28), and have moderate positive εNd(t) values (+4.4 to +5.4), which collectively suggest a derivation from a mixing source comprising MORB-like mantle of a mature back-arc basin and subordinate arc mantle wedge. These basaltic rocks are characterized by Low La/Yb (1.26-3.69), Dy/Yb (1.51-1.77) and Sm/Yb (0.83-1.32) 2

ratios, consistent with magmas derived from low degree (~10%) partial melting of the spinel lherzolite source at a quite shallow mantle depth. Considering the distinctive petrogenesis of the basaltic rocks in this region, the Late Devonian basalts in the southern Chinese Altai is suggested to have witnessed the propagating process of slab-window magmatism that was induced by ridge subduction in a nascent rifting stage of a back-arc basin.

Keywords: Chinese Altai; CAOB; Slab-window; Ridge subduction; Ridge-trench interaction

3

1. Introduction Accretionary orogenesis takes place at intraoceanic and/or continental margin convergent plate boundaries (Şengör et al., 1993; Cawood et al., 2009; Xiao et al., 2015), the process of which generally involves complicated subduction of oceanic plates and long-lived accretion of diverse tectonic terranes (Şengör et al., 1993; Windley et al., 2007; Cawood et al., 2009; Xiao et al., 2013, 2015). As a typical region of ongoing accretionary orogenesis, the present-day Pacific Rim is characterized by a common tectonic feature of ridge–trench interaction (Sisson et al., 2003; Windley et al., 2007; McCrory and Wilson, 2009), which has been demonstrated to have a strong impact on magmatic activity, metamorphism and mineralization at convergent plate margins (Cole and Basu, 1992; Haeussler et al., 1995; Sisson et al., 2003; Chadwick et al., 2009; McCrory and Wilson, 2009). In contrast, few knowledges regarding this common tectonic process has been obtained from ancient accretionary orogens, and this situation leads to the underestimate of this process in tectonic syntheses of plate margins in the ancient geologic record (Sisson et al., 2003). The Central Asian Orogenic Belt (CAOB), with an occurrence of vast area in the central and northern Asian territory (Fig. 1a), is regarded as one of the largest accretionary orogenic belts on Earth, the formation of which can be attributed to long-lived subduction of Paleo-Asian oceanic plates and accretion of numerous tectonic terranes, including ophiolites, island arcs, seamounts, accretionary prisms and micro-continental blocks (Şengör et al., 1993; 1996; Windley et al., 2002, 2007; Xiao 4

et al., 2004, 2009). Xiao et al. (2015) reviewed many aspects of research progress on the CAOB and attributed its tectonic framework to three major collage systems: Mongolian in the north, Tarim-North China in the south, and the intervening Kazakhstan orocline, and they further advocated the final amalgamation of the Kazakhstan and Mongolian collage systems along the Irtysh Shear Zone and the convergence of the Tarim and North China cratons along the South Tianshan-Solonker suture zone (Fig.1a) (Şengör et al., 1993; Şengör and Natal'in, 1996; Windley et al., 2007; Xiao et al., 2015). The region of Chinese Altai can be regarded as a Paleozoic continental margin of the Mongolian collage system that faced directly to the O’b-Zaisan oceanic realm (a portion of the Paleo-Asian oceanic plate) in the Paleozoic. It is mainly composed of variably deformed and metamorphosed sedimentary and volcanic rocks as well as granitoid intrusions (Zou et al., 1988; He et al., 1990; Qu and Zhang, 1991; He et al., 1994; Chen and Jahn, 2002; Windley et al., 2002; Wang et al., 2009a; Xiao et al., 2009; Cai et al., 2012b; Liu et al., 2012). Recently, according to new research advances on geochronology, geochemistry, metamorphism and petrology, several workers invoked oceanic ridge subduction process to account for the Devonian unique geological features in the Chinese Altai (Sun et al., 2009; Cai et al., 2010, 2011a, 2011b, 2011c, 2012a; Jiang et al., 2010; He et al., 2015). However, it has been a tough work to further define the geometrical evolution of such process, because the region has been subjected to extensive and complex deformation, associated with long distance displacement (Şengör et al., 1993; Şengör and Natal'in, 1996; Xiao et al., 5

2015). Fortunately, igneous rocks with diagnostic geochemical fingerprints can act as a petrologic probe to trace the spatial-temporal evolution of the ridge subdution, as best exemplified in Alaska, Baja California, and south Chile (Karsten et al., 1996; Benoit et al., 2002; Castillo, 2008; Chadwick et al., 2009; Cole and Stewart, 2009). In the current contribution, we studied the Devonian volcanic rocks in the south Chinese Altai where has been claimed for slab-window magmatism induced by ridge subduction in the Paleozoic (Windley et al., 2007; Sun et al., 2008; Cai et al., 2011a, 2012a; He et al., 2015), and our new findings together with previous associated studies, allow us to unravel source nature of magmas, petrogenesis and to refine the tectonic evolution during the period of ridge subduction in an ancient accretionary orogeny. 2. Geological background The CAOB covers an immense area extending southwards from the Siberian Craton to the North China and Tarim Cratons, and eastwards from the Ural Mountain to the Pacific coast (Fig. 1a), occurring as the largest Phanerozoic accretionary orogenic belt on Earth (Şengör et al., 1993;Şengör and Natal'in, 1996; Jahn et al., 2000a, 2000b; Xiao et al., 2004; Windley et al., 2007). The Altai Mountain extends from Russia through east Kazakhstan and north Xinjiang of China to western and southern Mongolian, and it is bounded by the Junggar to the south and the Sayan belt to the north (Fig. 1b). Its architecture includes a variety of tectonic units that are now sliced by large, mostly inactive strike–slip faults with very substantial and commonly poly-phase and poly-sense displacements in Late Paleozoic (Şengör and Natal'in, 6

1996; Buslov et al., 2003, 2004a, 2004b; Windley et al., 2007; Buslov, 2011). The Charysh–Terekta– Ulagan–Sayan suture-shear zone (CTUSs) is one of these inactive strike–slip faults, which separates the Altai-Mongolian terrane from the Gorny Altai terrane to the north and from West-Sayan terrane to the east, respectively (Buslov et al., 2001, 2003, 2004a, 2004b, 2013; Buslov, 2011). The Altai-Mongolian terrane is about 1000 km long and 250 km wide, include Mongolian Altai and southern Russian Altai (Zonenshain et al., 1990; Berzin et al., 1994; Buslov et al., 2001, 2003, 2013; Cai et al., 2014a, 2014b; Jiang et al., 2017). The sedimentary sequences of the Altai-Mongolian terrane are dominated by Middle Paleozoic rhythmically layered quartz-feldspathic and polymictic sandstones, siliceous shales, and phyllitic clay shales (Long et al., 2008; Jiang et al., 2017). Igneous rocks also have extensive outcrops in the Altay-Mongolian terrane, and show various lithology, chemical composition and mineralization (Wang et al., 2006; Yuan et al., 2007; Wang et al., 2009; Cai et al., 2010, 2011a, 2011c, 2012a, 2012b; Glorie et al., 2011; Kruk et al., 2011). As for metamorphic rocks, most of them near the faults zones, were formed in the Late Silurian–Devonian (garnet-kyanite and andalusite-cordierite metamorphic dome) and in the Late Devonian-Early Carboniferous (andalusite-cordierite metamorphic dome) (Kruk et al., 2011; Buslov et al., 2013; Kruk, 2015; Jiang et al., 2015). The Chinese Altai, in the northernmost Xinjiang Uygur Autonomous Region, as an important constitute of the Altai-Mongolian terrane, is situated on the middle segment of the mountain, which was ascribed to a portion of the Paleozoic continental 7

margin of the Mongolian collage system that faced directly to the O’b-Zaisan oceanic realm (Windley et al., 2007; Xiao et al., 2015). This region is dominated by variably deformed and metamorphosed Ordovician-Devonian sedimentary and volcanic rocks as well as granitoid intrusions (Zou et al., 1988; He et al., 1990, 1994; Chen and Jahn, 2002; Windley et al., 2002; Wang et al., 2006, 2009; Yuan et al., 2007; Sun et al.,2008; Xiao et al., 2009; Long et al., 2008, 2010; Cai et al., 2012b; Liu et al., 2012; Wang et al., 2014; Jiang et al., 2016). In term of these new research progresses on distinctive stratigraphy, metamorphism, deformation pattern and magmatism, the Chinese Altai is divided into four major fault-bounded tectonic domains, including Northern Altai Domain, Central Altai Domain, Qiongkuer Domain, and Southern Altai Domain (Windley et al., 2002; Xiao et al., 2004; Sun et al., 2008) (Fig. 1b). The Northern Altai Domain is mostly made up of Late Devonian to Early Carboniferous clastic sediments, limestone and minor Devonian andesite and dacite, as well as several granitic intrusions with Silurian to Early Devonian emplacement ages (Lou, 1997). The Central Altai Domain is composed predominantly of low-grade metasedimentary rocks of the Habahe Group and a large number of granitic batholiths. The Qiongkuer Domain comprises Late Silurian sedimentary rocks (Kulumuti Group), Early Devonian volcanic and pyroclastic rocks (Kangbutiebao Formation) and Mid-Devonian marine clastic rocks with minor pillow basalts (Altay Formation). Rocks in Qiongkuer Domain widely experienced high temperature metamorphism with local metamorphic grade up to granulite facies. Metamorphic rims of zircon grains from these high-grade rocks have ~390 Ma ages (Jiang et al., 2010). Granitic 8

batholiths were intruded at the period of 460-360 Ma (Cai et al., 2011a, 2011c). The Southern Altai Domain is restricted to the region between the Qiongkuer Domain and the Erqis fault, consisting of schist, paragneiss/orthogneiss, amphibolite, migmatite and metachert. The Qiongkuer Domain and the Southern Altai Domain constitute the south region of the Chinese Altai, and the study area is located on the west of the Qiongkuer Domain (Fig. 1b). It is noted that Kangbutiebao volcanic formation is the major sequence of the Qiongkuer Domain, and it bears many economic mineral deposits (Yang et al., 2017). Igneous zircon grains from metarhyolites of this formation yielded U-Pb ages of 412 to 400 Ma, which suggest that the siliceous volcanic rocks erupted in the Early Devonian (Chai et al., 2009; Liu et al., 2010). The outcrops of our study area include the Ashele Formation and the Qiye Formation (Fig. 2). The former is dominated by intermediate-acid volcanic rocks (mainly dacite and andesite) with a few basaltic lavas and sedimentary rocks, whereas, the latter, without precise isotopic data, unconformably rests on the former. Diverse volcanic rocks of the Ashele Formation were dated at 388.2 Ma, 387.0 Ma, 379.4 Ma, and 375 Ma (Wan et al., 2010; Yang et al., 2014), indicating the Ashele Formation to have been formed in the Middle-Late Devonian. These volcanic sequences in the Qiongkuer Domain record the tectonic evolution of the south Chinese Altai in the Devonian, and further study on the Qiye Formation volcanic rocks is apparently able to refine or replenish some detailed stories of the tectonic process. 3. Sample description 9

The Qiye Formation roughly includes three volcanic sequences: the lower mainly contain volcanic breccias, rhylites and tuffs; the middle primarily comprises volcanic breccias, tuffaceous sandstones and andesites; and the upper consists chiefly of tuffs, basalts and basaltic andesites. Our samples were collected from the upper sequence of the formation, and they are basaltic in composition. The outcrops of the basaltic rocks are massive, dark-gray to gray-green, and show porphyritic texture (Fig. 3a, c, e). In thin sections, phenocrysts (5%-10%) comprise plagioclase, pyroxene and olivine (Fig. 3b, d, f). Plagioclases generally appear as isolated euhedral to subhedral minerals and show 0.5-1 mm in length (Fig. 3b, d). The granular pyroxene and olivine generally show fractured appearances and has undergone post-magmatic alteration. The matrix is dominated by microlitic plagioclase and dark mineral. 4. Analytical methods 4.1 Zircon U-Pb dating One sample (ASL01) collected from Qiye Formation was analyzed for zircon U-Pb isotopic compositions in this study. After sample crushing, zircons were separated by standard heavy liquid and magnetic techniques. Crystal grains from the 251m non-magnetic fractions were hand-picked and mounted on adhesive tape, then enclosed in epoxy resin and polished to about half of their thickness. Cathodoluminescence (CL) images were obtained using a JXA-8100 Electron Probe Micro-analyzer with a Mono CL3 Cathodoluminescence System for high resolution imaging and spectroscopy at Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS), to investigate selected zircon internal structures and choose 10

potential target sites for U-Pb analyses. Secondary ion mass spectrometry (SIMS) zircon U–Pb dating analyses were performed on a Cameca IMS-1280HR ion microprobe at GIGCAS, following analytical procedures similar to Li et al. (2009). During the analysis, the O 2 primary ion beam with an intensity of ~10 nA was accelerated at -13kV. The ellipsoidal spot is about 20 μm × 30 μm in size. Positive secondary ions were extracted with a 10 kV potential. Calibration of Pb/U ratios is relative to the standard zircon Plešovice (337.13 Ma) (Sláma et al., 2008), which was analyzed once every four unknowns, based on an observed linear relationship between ln (206Pb/238U) and ln (238U16O2/238U). A secondary standard zircon Qinghu (Li et al., 2013) was analyzed as unknown to monitor the reliability of the whole procedure and yield a concordant age of 158.5±3.3 Ma, consistent with its recommended value. The data reduction was carried out using the Isoplot/Ex 3 software (Ludwing, 2003). SIMS zircon U-Pb isotopic data are presented in Table1. 4.2 Whole-rock major and trace element analyses Whole-rock major and trace elements were analyzed at GIGCAS. Major element oxides were determined by wavelength-dispersive X-ray fluorescence spectrometry (XRF) on fused glass beads using a Rigaku RIX 2000 X-ray fluorescence spectrometer (XRF). Calibration lines used in quantification were produced by bivariate regression of data from 36 reference materials encompassing a wide range of silicate compositions (Li et al., 2006), and analytical uncertainties are 1-5%. Bulk rock trace elements, including REEs, HFSEs and LILEs, were analyzed using Perkin-Elmer Sciex ELAN 6000 inductively-coupled plasma mass spectrometer 11

(ICP-MS) for nebulized sample solutions following the analytical procedures described by Liu et al. (1996) and Li (1997). Approximately 0.05g of powdered sample was decomposed in high-pressure Teflon bombs using an HF+HNO3 mixture for 7 days at ~100°C. An internal standard solution containing the single element Rh was used to monitor drift in mass response during counting. A suit of international and Chinese national rock standards were used for calibrating element concentrations of unknowns, consisting of BHVO-2, MRG-1, SY-4, G-2. GSR-1, GSR-2, GSR-3, and GSR-12. Analytical precision is generally better than ±5-10 %. The major and trace element results are presented in Table2. 4.3 Whole-rock Sr-Nd isotope analyses The whole-rock Sr-Nd isotopic compositions were measured on a Micromass IsoProbe MC-ICP-MS at the GIGCAS. Sample for the Sr and Nd isotopic analysis were dissolved in a mixture of HF-HClO4, and Sr and Nd were separated using a two-step ion exchange procedure. The 87Sr/86Sr and 143Nd/144Nd ratios were measured on a Micromass IsoProbe MC-ICP-MS. The detailed analytical procedures were described by Wei et al. (2002) and Liang et al. (2003). NBS987 and Shin Estu JNdi-1 were used as certified reference standard solutions for

87

Sr/86Sr and

143

Nd/144Nd

isotopes ratios, respectively. Multiple analyses of NBS987 yielded an average 87

Sr/86Sr ratio of 0.710247±17 (2σ) while the Shin Estu JNdi-1 standard yielded an

average

143

Nd/144Nd ratio of 0.512120±8 (2σ). The

87

Rb/86Sr and

147

Sm/144Nd ratios

were calculated from the Rb-Sr and Sm-Nd concentrations determined by whole-rock trace element analysis. The Sr and Nd isotopic compositions are listed in Table3. 12

5. Results 5.1 Zircon U-Pb geochronology Most of zircon grains from the basalt are irregular and subhedral minerals, and have short-prismatic shapes. The lengths of the zircon grains are generally from 30 μm to 100 μm and the width ranges from 30 μm to 50 μm. Ten zircon grains yield a wide ranges in U (221-906 ppm) and Th (151-959 ppm) contents, and the corresponding Th/U rations are in the range of 0.6 to 1.5 (Table 1). Their high Th/U ratios, together with CL images of oscillatory zoning, suggest an igneous origin (Belousova et al., 2002). All the analyses of the zircon grains give consistent 206

Pb/238U ages (370-378 Ma), showing a weighted mean age of 376.2±2.4 Ma

(MSWD=0.34) (Fig. 4). 5.2 Whole-rock major and trace element geochemistry Major and trace element contents of the basalts are presented in Table 2. Our samples display large variations in SiO2 contents (43.3-58.3 wt.%) and have low contents of K2O (0.02-0.06 wt.%) and TiO2 (0.60-1.27 wt.%). The total alkaline contents (Na2O+K2O) and the Na2O/K2O ratios are 2.16-5.41 wt.% and 62-218, respectively. All the samples plot the sub-alkaline and basaltic andesite field on the Nb/Y-Zr/Ti diagram (Fig. 5a). The basalts mostly fall within the typical tholeiite field on the SiO2-FeOT/MgO diagram (Fig. 5b). The basaltic rocks of the Qiye Formation exhibit consistent chondrite-normalized REE patterns, with negligible enrichment of LREE ((La/Yb) N= 0.90-2.57), flat HREE patterns ((Ga/Yb)N= 0.97-1.28), and weak Eu anomalies (Eu/Eu*=0.81-1.35) (Fig. 6a). 13

The primitive mantle-normalize trace elements diagrams show enrichment of large ion lithophile elements such as Ba, Th, U and depletion of high filed strength elements, such as Nb, Ta and Ti (Fig. 6b). 5.3 Whole-rock Sr-Nd isotopic composition Whole-rock Sr-Nd isotopic data are plotted in Fig. 8a. The initial 87Sr/86Sr values of the basaltic rocks range from 0.7058 to 0.7064, and the ε Nd(t) values vary from +4.4 to +5.3. The samples of the Qiye Formation have higher initial

87

Sr/86Sr values

and lower εNd(t) values relative to the depleted MORB mantle (DMM), which are similar to those of the mafic dykes emplaced in the Habahe area and the volcanic counterparts from the Ashele Formation (Fig. 7a) (Cai et al., 2010; Wu et al., 2015).

6. Discussion 6.1 Devonian “booming” magmatism in the Chinese Altai Although the Qiye volcanic formation was previously assigned to be a Middle-Late Devonian sequence, primarily according to the fact that the unconformity between it and the underlying Ashele volcanic formation that was definitely constrained to be the Early-Middle Devonian sequence by U-Pb zircon ages of 402-375 Ma (Wan et al., 2010; Yang et al., 2014), there has been, so far, no constraint from precise isotopic dating data. The zircon U-Pb dating result in this study allows us, for the first time, to define the eruption time of the upper sequence of the Qiye volcanic formation at 376.2 Ma, which quantitatively substantiates this formation to have formed in the Middle-Late Devonian. 14

Apart from the Ashele and Qiye formations, the Kangbutiebao and Altay formations are actually other two major Devonian volcanic strata in the Chinese Altai. The Kangbutiebao Formation is distributed in the Qiongkuer Domain and it is mainly composed of rhyolite, tuff and mafic volcanic rock. Zircon U-Pb dating and geochemical study suggested that the volcanic rocks of the Kangbutiebao Formation erupted at 412-400 Ma and they have typical subduction-related geochemical signatures (Chai et al., 2009; Liu et al., 2010). The Altay Formation consists mainly of marine clastic and volcanic rocks, which are extensively distributed in the Qiongkuer Domain of the south Chinese Altai (Fig. 1b). The total thickness of the Altay Formation is over 2000 m and its diagnostic fossils indicate the depositional time in the Middle to Late Devonian ( cf., Xiao et al., 1992; BGMRX, 1993; Windley et al., 2002). In the aspect of intrusive rocks, Cai et al. (2011a) have compiled the zircon U-Pb ages of the Chinese Altai granites and drew a conclusion that the intrusive volumes of granitic rocks culminated at 400 Ma, forming a number of huge granitic batholiths with some mafic-ultramafic bodies (Sun et al., 2008; Cai et al., 2012a; He et al., 2015). Therefore, the Devonian magmatic rocks are widely emplaced in the Chinese Altai, and they witnessed a “booming” igneous event during the magmatic and tectonic evolution of the region. In addition, it is noted that some igneous rocks with distinctive geochemical features were also generated during this period, such as boninites, adakites and MORB-like pillow basalts (cf., Xu et al., 2003; Niu et al., 2006a), which are most likely products of an unique geodynamic process (Cai et al., 15

2011a). 6.2 Petrogenesis 6.2.1 Estimate of the alteration effects It is necessary to estimate the alteration effects before applying the geochemical compositions to discuss petrogenesis of the volcanic rocks, since that the samples show relatively high LOI values (2.91-5.09 wt.%), low K2O contents, and commonly mineral alterations in thin sections (Fig. 3). In general, as a typical high field strength element (HFSE), zirconium (Zr) maintains immobile during the low-grade metasomatism and alteration, it thus can act as an alteration-independent index of geochemical variation for volcanic rocks (e.g., Polat and Hofmann, 2003). As for our samples, the dispersed distributions of the LILEs (e.g., K, Rb, Ba) on the plots of individual element versus Zr suggest obvious modifications of these elemental compositions. In contrast, consistent variations of those HFSEs (e.g., Nb, Ta, Ti, Hf ) indicate conservative behaviors similar to the immobility of Zr (Fig. 8). In addition, coherent REE patterns, spider diagrams and uniform isotopic compositions are likely robust evidence against strong influence of alteration on REE and isotopic compositions. Accordingly, these lines of evidence support that most data, including geochemical contents of HFSEs and REEs, and whole-rock Sr-Nd isotopic compositions, are reliable in discussing the petrogenesis and tectonic setting of the volcanic rocks. 6.2.2 Fractional crystallization and crustal contamination Experimental studies have documented that primary partial melts equilibrated 16

with their mantle source generally have Mg# of 73-81, Cr>1000 ppm and Ni>400 ppm (Wilson, 1989), which are apparently higher than 43-57 Mg#, 35.5-125.9 ppm Cr and 17.7-47.1 ppm Ni of the volcanic rocks of the Qiye Formation. These deficits in elemental concentrations may correspond to fractional crystallization of some minerals during the parental magma evolution, including olivine and pyroxene that are preferentially compatible with Mg, Fe, Cr and Ni (Fig. 9). With increasing SiO2, both TiO2 and Fe2O3T decrease obviously (Fig. 9), which indicates crystal fractionation of Fe-Ti oxide. It is noted that weak Eu anomalies argue against plagioclase as a significant fractional phase during magma evolution. Although the mantle-derived magmas are easily subjected to contamination by crustal materials in the process of emplacement and eruption, it is inferred to be a negligible process influencing the geochemical compositions of Qiye Formation volcanic rocks according to several lines of evidence as follows. On the one hand, our volcanic samples are characterized by very low K2O concentrations (average 0.03 wt.%), which differ significantly from these mafic magmas contaminated by crustal materials that are strongly enriched in K2O (Bulk continental crust, K2O =1.8 wt.%; Rudnick and Gao, 2003). On the other hand, the strikingly lower Th/Ce ratios (0.02-0.10) of the volcanic rocks relative to the crustal candidate (average continental crust, Th/Ce=0.15; Taylor and McLennan,1995) do not favor the possibility that the magma evolution could have been influenced by crustal contamination. Moreover, the homogeneous whole-rock Sr-Nd isotopic compositions do not support that the crustal contamination had strong influences on the magma evolution of the Qiye volcanic 17

rocks. 6.2.3 The nature of mantle source and magma generation Our basaltic samples are characterized by quite low K2O contents (0.02-0.06 wt.%) and obviously high Fe2O3T/MgO ratios (Fig. 5b), showing geochemical characteristic of tholeiitic rocks, which are distinguished from calc-alkaline rocks that are derived from partial melts of sub-arc mantle wedge ubiquitously with the contributions from slab-derived fluids and/or melts in a subduction-related tectonic setting (Haase et al., 2002; Hawkesworth et al., 1993; Stern, 2002; Sun and McDonough, 1989). In the study region, the Early-Middle Devonian Kangbutiebao volcanic formation actually occurs as a typical rock association comprising rhyolite, tuff and andesite as well as basaltic rocks, and these rocks generally exhibit subdcuction-related signatures in geochemical composition, such as high La/Yb ratios (3.14-4.36) and obviously negative Nb-Ta anomalies (Fig. 6b) (e.g., Chai et al., 2009; Chai et al., 2012; Cong et al., 2007; Liu et al., 2010). The petrologic and geochemical evidence suggests the genesis of Kangbutiebao Formation basaltic rocks involving diverse components from sub-arc mantle wedge and fluids and/or melts of subduction-related oceanic lithosphere (Cai et al., 2011b; Chai et al., 2012; Cong et al., 2007; Liu et al., 2012). In contrast, the Middle-Late Devonian Ashele and Qiye volcanic formations are dominated by mafic-intermediate tholeiitic volcanic components with less felsic volcanic rocks (e.g.,Niu et al., 2006; Xu et al., 2003), and they have lower La/Yb ratios (Fig. 10c) with moderately negative Nb-Ta anomalies (Fig. 6b) relative to the Kangbutiebao Formation basaltic rocks (Niu et al., 2006; Xu 18

et al., 2003). These features strongly argue for their derivations distinguishable from the volcanic rocks of the Kangbutiebao Formation. The lower contents of LREEs and LILEs for the Qiye basaltic rocks relative to the Kangbutiebao Formation basaltic rocks indicate less or no contribution from slab-derived fluids and/or melts, given these elements compatible strongly in hydrous agents in subduction zone magmatism (Haase et al., 2002; Hawkesworth et al., 1993; Stern, 2002; Sun and McDonough, 1989). The trace elemental patterns of the Qiye basaltic rocks resemble those of the Ashele Formation basalts and Kurti mafic igneous rocks in the region, which display flat to light rare earth element (REE)-depleted patterns and have variable depletions in high field-strength elements (HFSE) (Fig. 6a,b). Xu et al. (2003) attributed the unique geochemical signatures of the Kurti mafic rocks to their mantle sources that contain more mid-ocean ridge basalt (MORB) component and less arc component. However, it is noted that the Qiye basaltic rocks have slightly higher La/Yb and Th/Nb ratios than those of the Kurti and Ashele mafic rocks (Fig. 10b,c), implying that a little more amount of arc components were probably involved in the magma sources, but far less than the typical arc magmas (Haase et al., 2002; Hawkesworth et al., 1993; Stern, 2002; Sun and McDonough, 1989). As for the aspect of whole-rock Sr-Nd isotopic compositions, the Qiye basaltic rocks show relatively lower εNd (t) values, but higher initial 86Sr/87Sr ratios than those of the Kurti mafic igneous rocks (Fig. 7a, 10d), and the isotopic signatures of their mantle sources are similar to those of Kangbutiebao Formation basaltic rocks, showing a feature of a sub-arc mantle. Therefore, the Qiye basaltic rocks with 19

back-arc basaltic REE patterns have moderate positive εNd (t) values, which may result from the short time elapse for a depleted back arc mantle source. If the basaltic samples with the highest εNd (t) value of the Kurti mafic igneous rocks is taken as a mature back arc depleted mantle source (Xu et al., 2003), and the basalt of the Kangbutiebao Formation represents a typical sub-arc mantle wedge (Wan, 2009), our mixing calculation gives a estimate of roughly 20-30% typical sub-arc mantle wedge component in their magma source (Fig. 7b). The REEs and HFSEs of the Qiye basaltic rocks have preserved the nature of the mantle sources, so their abundances and ratios can be utilized to evaluate the composition and melting degree of the mantle. Basaltic melts are generally produced by partial melting of spinel- or garnet-bearing peridotite mantle, and they intake LREEs preferentially (Peters et al., 2008). In contrast, HREEs are strongly compatible in garnet, but are incompatible in spinel (McKenzie and O'nions, 1991). Thus, compared with partial melts derived from spinel-facies peridotite mantle, basaltic magmas originated from garnet-facies mantle source can be expected to have higher La/Yb ratios and significant depletion of HREEs relative to MREEs (Peters et al., 2008). The relatively low La/Yb ratios (1.26-3.69) and Dy/Yb ratios (1.51-1.77) of the Qiye basaltic rocks suggest that the partial melts have occurred within the spinel-facies peridotite source (Fig. 11a). Given that Sm and Yb have comparable partition coefficients during partial melting of a spinel lherzolite source, the Sm/Yb ratio is generally constant but the La/Sm ratio may decrease with the increase of melting degree (Aldanmaz et al., 2000). The variations of Sm/Yb and La/Sm ratios 20

can thus be used to assess the melting degree of the mantle source at ~10%, suggesting a quite shallow mantle melting zone (Fig. 11b). 6.3 Tectonic setting Devonian magmatism resulted in the generation of widespread igneous rocks, including extrusive and intrusive rocks in the southern Chinese Altai (Fig. 1b). However, these rocks with diverse geochemical characteristics have been attributed to the magmatic products in controversial tectonic settings, like active continental margin (eg., Chai et al., 2009, 2012b; Cong et al., 2007; Liu et al., 2010), back-arc rifting (eg., Xu et al., 2003), and ridge-trench interaction associated with slab-window (eg., Sun et al., 2008; Cai et al., 2010, 2011a, 2011b, 2011c, 2012a; Jiang et al., 2010; He et al., 2015). The Qiye basaltic samples have tholeiitic composition and flat chondrite-normalized REE patterns unlike those of the typical magmas in a normal continental margin, suggesting their parental magmas forming in a fluid-deficit tectonic setting. These tectonic settings may contain numerous sources with distinct geochemical signatures, such as depleted MORB mantle, enriched plume related mantle, subcontinental lithospheric mantle, and subduction component-enriched mantle (Sun and McDonough, 1989; Kerr et al., 2002; Pearce et al., 2005; Xu et al., 2005). Fig. 12a-b illustrates the variety of tectonic settings plotted by widely used tectonic discrimination diagrams based on various combinations of relatively immobile elements. The Qiye basaltic samples overlap the fields of the volcanic arc basalt and MORB, which is consistent with our interpretation that their parental magmas were derived from a mixing source comprising MORB-like mantle of a 21

mature back-arc basin and subordinate arc mantle wedge (Fig. 7a, b). The quite shallow mantle melting zone for generating the Qiye basaltic rocks suggests considerable upwelling of the MORB-like depleted mantle in a distinctive tectonic setting. The creation of oceanic lithosphere is driven by spreading of the mid-ocean ridge and its descent occurs at convergent boundaries, i.e., subduction zones. Wilson cycle delineated the lifespan of an oceanic plate, however, little is known about the detailed interaction between the spreading mid-ocean ridge and subduction zones during the consumption of an oceanic plate (cf., Thorkelson and Taylor, 1989; Thorkelson, 1996; Brown, 1998; Santosh and Kusky, 2010; Zhang et al., 2010). It is noted that the spreading oceanic ridge is characterized by the thinnest crust generated by decompression partial melting without additions of fluids at a quite shallow mantle depth (Keleman et al., 2004). When the spreading ocean ridge with the thinnest crust is dragged into a subduction zone, “slab window” beneath the overriding plate may form as the result of upwelling of the hot asthenosphere and the typical subdution-related arc magmatism will be replaced by MORB-type melts (Dickinson and Snyder, 1979; Thorkelson, 1996; Santosh and Kusky, 2010). Moreover, this outstanding tectonic process will supply abundant heat to the ambient mantle and overriding plate from the upwelling of asthenosphere, which may cause regional high temperature metamorphism and diverse magmatism with distinctive geochemical compositions (Lagabrielle et al., 1994; Karsten et al., 1996; Abratis, 1998; Benoit et al., 2002; Sisson et al., 2003; Cole and Stewart, 2009; Geng et al., 2009; Zhao et al., 22

2009; Jiang et al., 2010; Yin et al., 2010; Zhang et al., 2010). According to our new finding of this study and regional geologic facts, several lines of evidence enable us to draw a reliable conclusion that the Qiye basaltic rocks were “slab-window” magmatic products emplaced in a nascent realm of back-arc rifting during ridge-trench interactions when the spreading oceanic ridge was being subducted in the south Chinese Altai. (1) The Qiye basaltic rocks have tholeiitic compositions and show MORB-like REE patterns, implying derivation of their parental magmas dominated by decompression partial melting of a MORB-like depleted mantle source. (2) Numerous igneous rocks with distinctive geochemical signatures, including high-Mg andesites, adakitic rocks, and boninitic rocks, as well as MORB-type gabbros, were emplaced in the Chinese Altai during Devonian. The petrogenesis of these rocks require an exceptional heat source by upwelling of the hot asthenosphere (eg., Xu et al., 2003; Zhang et al., 2003; Niu et al., 2006a, 2006b; Cai et al., 2010; Wong et al., 2010). (3) Cai et al. (2011a) compiled the zircon U-Pb ages and Hf isotopic data of the igneous rocks in the Chinese Altai and they outlined a dramatic change of Hf isotope at ca. 400 Ma, i.e., both positive and negative εHf(t) (-18 to +15) prior to 400 Ma to all positive εHf(t) values (0 to +16) after that. This change suggests that juvenile materials became dominant in the magma source in the Late Devonian. (4) Devonian high temperature metamorphism has been documented by the P-T estimates of 720-800 ºC and 0.5-0.7 kbar (Zhuang, 1994; Li and Chen, 2004; Wei et 23

al., 2007; Zheng et al., 2007; Wang et al., 2009b; Jiang et al., 2010) (5) The present-day lower crust of the Chinese Altai has a thickness of over 30 km, which is revealed by seismic data (Wang et al., 2003), and the lower crustal component is composed by mafic granulite and/or mafic garnet-granulite (Jiang et al., 2016). These mafic constituents was attributed to the contributions from basaltic magmas of upwelling asthenosphere in the Devonian tectono-magmatic evolution (Wang et al., 2003; Wang et al., 2006; Yuan et al., 2007; Cai et al., 2010, 2011a).. Although there is no unique geological evidence for ridge-trench interactions (Sisson et al., 2003), the mentioned above facts are collectively able to consider as responses to spreading oceanic ridge subduction in the accretionary orogenic belts, such as in Japan, southern Alaska and Chile ( Maruyama, 1997; D'Orazio et al., 2001; Gorring et al., 2003; Cole and Stewart, 2009; Karsten et al., 1996; Benoit et al., 2002; Castillo, 2008; Chadwick et al., 2009) 6.4 Propagation of slab-window magmatism induced by ridge subduction Although all subduction zones of convergent plate boundaries should eventually interact with a spreading oceanic ridge, it has been a quite difficult work to assess the possible geometric configuration of the ridge-trench interactions, because all of them are characterized by four-dimensional processes (Sisson et al., 2003). In the present-day Pacific basin, there are several examples of active or recently extinct spreading oceanic ridges interacting with trenches, like in Japan, Alaska, Baja California, and south Chile ( Karsten et al., 1996; Maruyama, 1997; D'Orazio et al., 2001; Benoit et al., 2002; Gorring et al., 2003; Cole and Stewart, 2009; Castillo, 2008; 24

Chadwick et al., 2009). As for a specific case, the spreading oceanic ridge may be perpendicular to the subduction zone, and this case may cause strong compression of the overriding plate and gives rise to a roughly symmetrical slab-window, like in the south Chile (Murdie and Russo, 1999; Russo et al., 2010). In contrast, if the spreading oceanic ridge is parallel to the subduction zone, it will induce regional extension of the overriding plate, generating a rifting back arc basin, such as in the Baja California (McCrory et al., 2009; Lomize and Luchitskaya, 2012). The outstanding configuration of the Baja California occurs as a combination of magmatic belt and back-arc rifting basin, and compositions of the magmatic belt show an obvious shrift from calc-alkaline to tholeiitic, adakitic and high magnesium andesitic at ca. 12 Ma (Aguillo´n, 2001; Benoit et al., 2002; Wilson et al., 2005 Castillo, 2008). These comparable geological features have also been observed for the southern Chinese Altai in the Devonian (Xu et al., 2003; Niu et al., 2006a, 2006b; Cai et al., 2010, 2011a, 2011b, 2011c, 2012a), which inspires us to invoke the case of Baja California to interpret the tectonic evolution of the Devonian south Chinese Altai (Fig. 13a, b). Prior to 409 Ma, the Chinese Altai likely represents an active continental margin or a magmatic arc as the result of subduction of the Paleo-Asian oceanic plate (e.g., Şengör et al., 1993; Chen and Jahn, 2002; Windley et al., 2002; Xiao et al., 2004, 2008, 2009a, 2009b, 2010) and the long-lived subduction produced a large amount of magmatic rocks, including granitic and pyroclastic rocks (Wang et al., 2006; Briggs et al., 2007; Long et al., 2007; Yuan et al., 2007; Sun et al., 2008; Cai et al., 2011b; Wang et al., 2011). The clastic sedimentary rocks of the Habahe Group, mainly 25

consisting of arkoses and conglomerates, were deposited on the active margin (Long et al., 2008). In addition, Kangbutiebao Formation volcanic rocks erupted in a period of ca. 412 Ma to 406 Ma, and they are typical arc magmatic rocks that consist mainly of metasilicic pyroclastic rocks and minor mafic volcanic rocks (Chai et al., 2009; Liu et al., 2010). Approximately at 409 Ma, Keketuohai Alaskan-type mafic-ultramfic complex intruded the pyroclastic and sedimentary rocks, and arc magmatism became waning in the eastern region of the Chinese Altai, which may be caused by asthenosphere upwelling through the slab-window triggering extensive partial melting of the refractory lithosphere to give birth to the large number of mafic-ultramafic complexes and voluminous granitic batholiths (Fig. 13a) (Cai et al., 2012a). On the other hand, partial melting of oceanic crust produced Kalaxiangeer adakitic rocks of porphyry copper (Zhang et al., 2006; Xiang et al., 2009). As time went on, a marginal ribbon was almost split from the eastern region of the Chinese Altai, giving rise to a mature back-arc basin, which is indicated by the Kurti mafic igneous rocks (Xu et al., 2003). Whereas, in the western region of the Chinese Altai, the ~375 Ma Habahe mafic dykes with MORB-like signature suggest that the slab window probably expanded westward beneath the Habahe area (Cai et al., 2010; in present-day coordinates). However, in the adjacent Ashele area (50 km west of Habahe area) (Fig. 1b), the Qiye basaltic rocks have transitional geochemical compositions between arc magmas and back arc basaltic melts, which may suggest a propagating slab-window magmatism induced by ridge subduction in a nascent rifting 26

stage of the back-arc basin (Fig. 13b).

7. Conclusions (1) The basaltic rocks of the upper Qiye Formation have a U-Pb zircon age of 376.5±2.4 Ma. (2) The Qiye basaltic rocks have tholeiitic compositions and MORB-like REE patterns, which, together with their moderate positive εNd(t) (+4.4 to +5.4), suggest their derivation from a mixing source comprising MORB-like mantle of a mature back arc basin and subordinate arc mantle wedge. Such geochemical compositions can be interpreted by low degree (~10%) partial melting of the spinel lherzolite source at a quite shallow mantle depth. (3) The Qiye basaltic rocks with distinctive petrogenesis relate to a propagating slab-window magmatism induced by ridge subduction in a nascent rifting stage of the back-arc basin in the Chinese Altai.

Acknowledgments This study was financially supported by National Science Foundation of China (41622205), the Major Basic Research Project of the Ministry of Science and Technology of China (2014CB448000) and CAS President’s International Fellowship Initiative (PIFI) to M.M. Buslov. This work is a contribution to the Talent Awards to KDC from the China Government under the 1000 Talent Plan.

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References: Abratis, M., 1998. Geochemical variations in magmatic rocks from southern Costa Rica as a consequence of Cocos Ridge subduction and uplift of the Cordillera de Talamanca. Germany. Aguillónrobles, A., Calmus, T., Benoit, M., Bellon, H., Maury, R.C., Cotten, J., Bourgois, J., Michaud, F., 2001. Late Miocene adakites and Nb-enriched basalts from Vizcaino Peninsula, Mexico: Indicators of East Pacific Rise subduction below southern Baja California? Geology, 29(6): 531-534. Aldanmaz, E., Pearce, J.A., Thirlwall, M.F., Mitchell, J.G., 2000. Petrogenetic evolution of late Cenozoic, post-collision volcanism in western Anatolia, Turkey. Journal of Volcanology and Geothermal Research, 102(1–2): 67-95. Badarch, G., Cunningham, W.D., Windley, B.F., 2003. A new terrane subdivision for Mongolia: implications for the Phanerozoic crustal growth of Central Asia. Journal of Asian Earth Sciences, 21(1): 87-110. Belousova, E., Griffin, W., O'Reilly, S.Y., Fisher, N., 2002. Igneous zircon: trace element composition as an indicator of source rock type. Contributions to Mineralogy and Petrology, 143(5): 602-622. Benoit, M., Aguillon-Robles, A., Calmus, T., Maury, R.C., Bellon, H., Cotten, J., Bourgois, J., Michaud, F., 2002. Geochemical diversity of Late Miocene volcanism in southern Baja California, Mexico: Implication of mantle and crustal sources during the opening of an asthenospheric window. Journal of Geology, 110(6): 627-648. Berzin, N.A., Coleman, R.G., Dobretsov, N.L., Zonenshain, L.P., Xuchang, X., Chang, E.Z., 1994. Geodynamic map of the western part of the Paleoasian ocean. Russian Geology & Geophysics, 35(7): 5-22. BGMRX (Bureau of Geology andMineral Resources of Xinjiang Uygur Autonomous Region, 1993. Regional Geology of Xinjiang Uygur Autonomous Region. People's Republic of China, Ministry of Geology and Mineral Resources. Geological Memoirs, Series 1, No. 32. Geological Publishing House, Beijing, p. 206. in Chinese. Briggs, S.M., Yin, A., Manning, C.E., Chen, Z.L., Wang, X.F., Grove, M., 2007. Late Paleozoic tectonic history of the Ertix Fault in the Chinese Altai and its implications for the development of the Central Asian Orogenic System. Geological Society of America Bulletin, 119(7-8): 944-960. Brown, M., 1998. Ridge-trench interactions and high-T-low-P metamorphism, with particular reference to the Cretaceous evolution of the Japanese Islands. Geological Society London Special Publications, 138(1): 137-169. Buslov, M.M., Saphonova, I.Y., Watanabe, T., Obut, O.T., Fujiwara, Y., Iwata, K., Semakov, N.N., Sugai, Y., Smirnova, L.V., Kazansky, A.Y., 2001. Evolution of the Paleo-Asian Ocean (Altai-Sayan Region, Central Asia) and collision of possible Gondwana-derived terranes with the southern marginal part of the Siberian continent. Geosciences Journal, 5(3): 203-224. Buslov, M.M., Watanabe, T., Smirnova, L.V., Fujiwara, I., Iwata, K., Grave, I.D., Semakov, N.N., Travin, A.V., Kir'Yanova, A.P., Kokh, D.A., 2003. Role of strike-slip faults in Late Paleozoic-Early Mesozoic tectonics and geodynamics of the Altai-Sayan and East Kazakhstan folded zone. Geologiya I Geofizika, 44(1-2): 49-75. Buslov, M.M., Fujiwara, Y., Iwata, K., Semakov, N.N., 2004a. Late Paleozoic-Early Mesozoic Geodynamics of Central Asia. Gondwana Research, 7(3): 791-808. Buslov, M.M., Watanabe, T., Fujiwara, Y., Iwata, K., Smirnova, L.V., Safonova, I.Y., Semakov, N.N., 28

Kiryanova, A.P., 2004b. Late Paleozoic faults of the Altai region, Central Asia: tectonic pattern and model of formation. Journal of Asian Earth Sciences, 23(5): 655-671. Buslov, M.M., 2011. Tectonics and geodynamics of the Central Asian Foldbelt: the role of Late Paleozoic large-amplitude strike-slip faults. Russian Geology & Geophysics, 52(1): 52-71. Buslov, M.M., Geng, H., Travin, A.V., Otgonbaatar, D., Kulikova, A.V., Ming, C., Stijn, G., Semakov, N.N., Rubanova, E.S., Abildaeva, M.A., Voitishek, E.E., Trofimova, D.A., 2013. Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area. Russian Geology and Geophysics, 54(10): 1250-1271. Buslov, M.M., Cai, K.D., 2017. Tectonics and Geodynamics of the Altai-Junggar Orogen in the Vendian-Paleozoic: Implications for the Continental Evolution and Growth of the Central Asian Fold Belt. Geodynamics & Tectonophysics, 8(3): 421-427. Cai, K.D., Sun, M., Yuan, C., Zhao, G.C., Xiao, W.J., Long, X.P., Wu, F.Y., 2010. Geochronological and geochemical study of mafic dykes from the northwest Chinese Altai: Implications for petrogenesis and tectonic evolution. Gondwana Research, 18(4): 638-652. Cai, K.D., Sun, M., Yuan, C., Zhao, G., Xiao, W., Long, X., Wu, F., 2011a. Prolonged magmatism, juvenile nature and tectonic evolution of the Chinese Altai, NW China: Evidence from zircon U–Pb and Hf isotopic study of Paleozoic granitoids. Journal of Asian Earth Sciences, 42(5): 949-968. Cai, K.D., Sun, M., Yuan, C., Long, X.P., Xiao, W.J., 2011b. Geological framework and Paleozoic tectonic history of the Chinese Altai, NW China: a review. Russian Geology and Geophysics, 52(12): 1619-1633. Cai, K.D., Sun, M., Yuan, C., Zhao, G.C., Xiao, W.J., Long, X.P., Wu, F.Y., 2011c. Geochronology, petrogenesis and tectonic significance of peraluminous granites from the Chinese Altai, NW China. Lithos, 127(1-2): 261-281. Cai, K.D., Sun, M., Yuan, C., Zhao, G., Xiao, W., Long, X., 2012a. Keketuohai mafic–ultramafic complex in the Chinese Altai, NW China: Petrogenesis and geodynamic significance. Chemical Geology, 294-295: 26-41. Cai, K.D., Sun, M., Yuan, C., Xiao, W.J., Zhao, G.C., Long, X.P., Wu, F.Y., 2012b. Carboniferous mantle-derived felsic intrusion in the Chinese Altai, NW China: Implications for geodynamic change of the accretionary orogenic belt. Gondwana Research, 22(2): 681-698. Castillo, P.R., 2008. Origin of the adakite-high-Nb basalt association and its implications for postsubduction magmatism in Baja California, Mexico. Geological Society of America Bulletin, 120(3-4): 451-462. Cawood, P.A., Kröner, A., Collins, W.J., Kusky, T.M., Mooney, W.D., Windley, B.F., 2009. Accretionary orogens through Earth history. Geological Society, London, Special Publications, 318(1): 1-36. Chadwick, J., Perfit, M., Mcinnes, B., Kamenov, G., Plank, T., Jonasson, I., Chadwick, C., 2009. Arc lavas on both sides of a trench: Slab window effects at the Solomon Islands triple junction, SW Pacific. Earth & Planetary Science Letters, 279(3–4): 293-302. Chai, F.M., Mao, J., Dong, L., Yang, F., Liu, F., Geng, X., Zhang, Z., 2009. Geochronology of metarhyolites from the Kangbutiebao Formation in the Kelang basin, Altay Mountains, Xinjiang: Implications for the tectonic evolution and metallogeny. Gondwana Research, 16(2): 189-200. Chai, F.M., Yang, F.Q., Liu, F., Geng, X., Zhang, Z., Chen, B., 2012. Geochronology and genesis of the meta-felsic volcanic rocks in the Kangbutiebao Formation from the Maizi Basin at the southern margin of the Altay, Xinjiang. Dizhi Kexue/ Chinese Journal of Geology, 47(1): 221-239. 29

Chen, B., Jahn, B.M., 2002. Geochemical and isotopic studies of the sedimentary and granitic rocks of the Altai orogen of northwest China and their tectonic implications. Geological Magazine, 139(1): 1-13. Cole, R.B., Basu, A.R., 1992. Middle tertiary volcanism during ridge-trench interactions in Western california. Science, 258(5083): 793. Cole, R.B., Nelson, S.W., Layer, P.W., Oswald, P.J., 2006. Eocene volcanism above a depleted mantle slab window in southern Alaska. Geological Society of America Bulletin, 118(1-2): 140-158. Cole, R.B., Stewart, B.W., 2009. Continental margin volcanism at sites of spreading ridge subduction: Examples from southern Alaska and western California. Tectonophysics, 464(1): 118-136. Cong, F., Tang, H., Yuping, S.U., 2007. Geochemistry and tectonic setting of Devonian rhyolites in southern Altay, Xinjiang, northwest China. Geotectonica Et Metallogenia, 31(3): 359-364. D'Orazio, M., Agostini, S., Innocenti, F., Haller, M.J., Manetti, P., Mazzarini, F., 2001. Slab window-related magmatism from southernmost South America: the Late Miocene mafic volcanics from the Estancia Glencross Area (∼52°S, Argentina–Chile). Lithos, 57(2–3): 67-89. Dickinson, W.R., Snyder, W.S., 1979. Geometry of Subducted Slabs Related to San Andreas Transform. Journal of Geology, 87(6): 609-627. Geng, H.Y., Sun, M., Yuan, C., Xiao, W., Xian, W., Zhao, G., Zhang, L., Wong, K., Wu, F., 2009. Geochemical, Sr–Nd and zircon U–Pb–Hf isotopic studies of Late Carboniferous magmatism in the West Junggar, Xinjiang: implications for ridge subduction? Chemical Geology, 266(3): 364-389. Glorie, S., Grave, J.D., Buslov, M.M., Zhimulev, F.I., Izmer, A., Vandoorne, W., Ryabinin, A., Haute, P.V.D., Vanhaecke, F., Elburg, M.A., 2011. Formation and Palaeozoic evolution of the Gorny-Altai–Altai-Mongolia suture zone (South Siberia): Zircon U/Pb constraints on the igneous record. Gondwana Research, 20(2): 465-484. Gorring, M., Singer, B., Gowers, J., Kay, S.M., 2003. Plio–Pleistocene basalts from the Meseta del Lago Buenos Aires, Argentina: evidence for asthenosphere–lithosphere interactions during slab window magmatism. Chemical Geology, 193(3–4): 215-235. Gorring, M.L., Kay, S.M., 2001. Mantle Processes and Sources of Neogene Slab Window Magmas from Southern Patagonia, Argentina. Journal of Petrology, 42(6): 1067-1094. Haase, K.M., Worthington, T.J., Stoffers, P., Garbe-Schönberg, D., Wright, I., 2002. Mantle dynamics, element recycling, and magma genesis beneath the Kermadec Arc-Havre Trough. Geochemistry, Geophysics, Geosystems, 3(11): 1-22. Haeussler, P.J., Bradley, D., Goldfarb, R., Snee, L., Taylor, C., 1995. Link between ridge subduction and gold mineralization in southern Alaska. Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz, 56(5-6): 845-857. Hawkesworth, C.J., Gallagher, K., Hergt, J.M., McDermott, F., 1993. Mantle and Slab Contributions in ARC Magmas. Annual Review of Earth and Planetary Sciences, 21(1): 175-204. He, G.Q., Han, B., Yue, Y., Wang, J., 1990. Tectonic division and crustal evolution of Altay orogenic belt in China. Geoscience of Xinjiang, 2: 9-20. He, G.Q., Li, M., Liu, D., Zhou, N., 1994. Paleozoic crustal evolution and mineralization in Xinjiang of China. Xinjiang People’s Publishing House, Urumqi, 437. He, Y.L., Sun, M., Cai, K.D., Xiao, W.J., Zhao, G.C., Long, X.P., Li, P.F., 2015. Petrogenesis of the Devonian high-Mg rock association and its tectonic implication for the Chinese Altai orogenic belt, NW China. Journal of Asian Earth Sciences, 113: 61-74. 30

Hole, M.J., Rogers, G., Saunders, A.D., Storey, M., 1991. Relation between alkalic volcanism and slab-window formation. Geology, 19(6): 657-660. Jahn, B.M., Wu, F., Chen, B., 2000a. Granitoids_of_the_Central_Asian_Orogenic_Belt_and continental growth in the Phanerozoic. Earth Sciences Jahn, B.M., Wu, F., Chen, B., 2000b. Massive granitoid generation in Central Asia: Nd isotope evidence and implication for continental growth in the Phanerozoic. Episodes. Jiang, Y., Sun, M., Zhao, G., Yuan, C., Xiao, W., Xia, X., Long, X., Wu, F., 2010. The 390 Ma high-T metamorphic event in the Chinese Altai: A consequence of ridge-subduction? American Journal of Science, 310(10): 1421-1452. Jiang, Y.D., Stipska, P., Sun, M., Schulmann, K., Zhang, J., Wu, Q.H., Long, X.P., Yuan, C., Racek, M., Zhao, G.C., Xiao, W.J., 2015. Juxtaposition of Barrovian and migmatite domains in the Chinese Altai: a result of crustal thickening followed by doming of partially molten lower crust. Journal of Metamorphic Geology, 33(1): 45-70. Jiang, Y.D., Schulmann, K., Sun, M., Štípská, P., Guy, A., Janoušek, V., Lexa, O., Yuan, C., 2016. Anatexis of accretionary wedge, Pacific-type magmatism, and formation of vertically stratified continental crust in the Altai Orogenic Belt. Tectonics, 35(12): 3095-3118. Jiang, Y.D., Schulmann, K., Kröner, A., Sun, M., Lexa, O., Janoušek, V., Buriánek, D., Yuan, C., Hanžl, P., 2017. Neoproterozoic-Early Paleozoic Peri-Pacific Accretionary Evolution of the Mongolian Collage System: Insights From Geochemical and U-Pb Zircon Data From the Ordovician Sedimentary Wedge in the Mongolian Altai. Tectonics, 36(11): 2305-2331. Karsten, J.L., Klein, E.M., Sherman, S.B., 1996. Subduction zone geochemical characteristics in ocean ridge basalts from the southern Chile Ridge: Implications of modern ridge subduction systems for the Archean. Lithos, 37(2): 143-161. Kelemen, P.B., Hanghøj, K., Greene, A.R., 2004. One View of the Geochemistry of Subduction-Related Magmatic Arcs, with an Emphasis on Primitive Andesite and Lower Crust. Treatise on Geochemistry, 138: 1-70. Kerr, A.C., Tarney, J., Kempton, P.D., Spadea, P., Nivia, A., Marriner, G.F., Duncan, R.A., 2002. Pervasive mantle plume head heterogeneity: Evidence from the late Cretaceous Caribbean-Colombian oceanic plateau. Journal of Geophysical Research Solid Earth, 107(B7): ECV 2-1–ECV 2-13. Klein, E.M., Karsten, J.L., 1995. Ocean-ridge basalts with convergent-margin geochemical affinities from the Chile Ridge. Nature, 374(6517): 52-57. Kruk, N.N., Rudnev, S.N., Vladimirov, A.G., Shokalsky, S.P., Kovach, V.P., Serov, P.A., Volkova, N.I., 2011. Early–Middle Paleozoic granitoids in Gorny Altai, Russia: Implications for continental crust history and magma sources. Journal of Asian Earth Sciences, 42(5): 928-948. Kruk, N.N., 2015. Continental crust of Gorny Altai: stages of formation and evolution; indicative role of granitoids. Russian Geology & Geophysics, 56(8): 1097-1113. Lagabrielle, Y., Le Moigne, J., Maury, R., Cotten, J., Bourgois, J., 1994. Volcanic record of the subduction of an active spreading ridge, Taitao Peninsula (southern Chile). Geology, 22(6): 515-518. Li, H.Q., Chen, F.W., 2004. Isotopic geochronology of regional mineralization in Xinjiang, NW China:. Geological Publishing House, 19-58 pp. Li, X.H., 1997. Geochemistry of the Longsheng Ophiolite from the southern margin of Yangtze Craton, SE China. Geochemical Journal, 31(5): 323-337. Li, X.H., Li, Z.X., Wingate, M.T., Chung, S., Liu, Y., Lin, G., Li, W., 2006. Geochemistry of the 755Ma Mundine Well dyke swarm, northwestern Australia: part of a Neoproterozoic mantle 31

superplume beneath Rodinia? Precambrian Research, 146(1): 1-15. Li, X.H., Liu, Y., Li, Q., Guo, C.H., Chamberlain, K.R., 2009. Precise determination of Phanerozoic zircon Pb/Pb age by multicollector SIMS without external standardization. Geochemistry, Geophysics, Geosystems, 10(4). Li, X.H., Tang, G.Q., Gong, B., Yang, Y.H., Hou, K.J., Hu, Z.C., Li, Q., Liu, Y., Li, W., 2013. Qinghu zircon: A working reference for microbeam analysis of U-Pb age and Hf and O isotopes. Chinese Science Bulletin, 58(36): 4647-4654. Liang, X.R., Wei, G.J., Li, X.H., Liu, Y., 2003. Precise measurement of

143

Nd/144Nd and Sm/Nd ratios

using multiple-collectors inductively coupled plasma-mass spectrometer (MC-ICPMS). Geochimica, 32(1): 91-96. Liu, W., Liu, L., Liu, X., Shang, H., Zhou, G., 2010. Age of the Early Devonian Kangbutiebao Formation along the southern Altay Mountains and its northeastern extension. Acta Petrologica Sinica, 26(2): 387-400. Liu, W., Liu, X.j., Xiao, W.j., 2012. Massive granitoid production without massive continental crust growth in the Chinese Altay: Insight into the source rock of granitoids using integrated zirconU-Pb age, Hf-Nd-Sr isotopes and geochemistry. AmericanJournalofScience, 312(6): 629-684. Liu, Y., Liu, H.C., Li, X.H., 1996. Simultaneous and precise determination of 40 trace elements in rock samples using ICP-MS. Geochimica, 25(6): 552-558. Lomize, M.G., Luchitskaya, M.V., 2012. Subduction of spreading ridges as a factor in the evolution of continental margins. Geotectonics, 46(1): 47-68. Long, X.P., Sun, M., Yuan, C., Xiao, W.J., Lin, S., Wu, F., Xia, X., Cai, K., 2007. U–Pb and Hf isotopic study of zircons from metasedimentary rocks in the Chinese Altai: implications for Early Paleozoic tectonic evolution. Tectonics, 26(5). Long, X.P., Sun, M., Yuan, C., Xiao, W.J., Cai, K., 2008. Early Paleozoic sedimentary record of the Chinese Altai: Implications for its tectonic evolution. Sedimentary Geology, 208(3-4): 88-100. Long, X.P., Yuan, C., Sun, M., Xiao, W.J., Wang, Y.J., Cai, K.D., Xia, X.P., Xie, L.W., 2010. Detrital zircon ages and Hf isotopes of the early Paleozoic flysch sequence in the Chinese Altai, NW China: New constrains on depositional age, provenance and tectonic evolution. Tectonophysics, 480(1-4): 213-231. Lv, Z.H., Zhang, H., Tang, Y., Liu, Y.L., Zhang, X., 2018. Petrogenesis of syn-orogenic rare metal pegmatites in the Chinese Altai: evidences from geology, mineralogy, zircon U-Pb age and Hf isotope. Ore Geology Reviews. Lou, F.S., 1997. Characteristics of Late Caledonian granites in the Nuerte area, Altay. Jiangxi Geology, 11: 60-66. Ludwing, K., 2003. Isoplot/Ex version 3.00—A geochronology toolkit for Microsoft Excel. Berkeley Geochronol Center Spec Publ, 4: 1-70. Maruyama, S., 1997. Pacific‐type orogeny revisited: Miyashiro‐type orogeny proposed. Island Arc, 6(1): 91-120. McCrory, P.A., Wilson, D.S., 2009. Introduction to Special Issue on: Interpreting the tectonic evolution of Pacific Rim margins using plate kinematics and slab-window volcanism. Tectonophysics, 464(1-4): 3-9. McCrory, P.A., Wilson, D.S., Stanley, R.G., 2009. Continuing evolution of the Pacific–Juan de Fuca–North America slab window system—A trench–ridge–transform example from the 32

Pacific Rim. Tectonophysics, 464(1-4): 30-42. McKenzie, D., O'nions, R., 1991. Partial melt distributions from inversion of rare earth element concentrations. Journal of Petrology, 32(5): 1021-1091. McKenzie, D., Bickle, M., 1988. The volume and composition of melt generated by extension of the lithosphere. Journal of petrology, 29(3): 625-679. McKenzie, D., O'nions, R.K., 1991. Partial melt distributions from inversion of rare earth element concentrations. Journal of Petrology, 32(5): 1021-1091. Meschede, M., 1986. A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. Chemical Geology, 56(3): 207-218. Miyashiro, A., 1974. Volcanic rock series in island arcs and active continental margins, 274, 321-355 pp. Murdie, R.E., Russo, R.M., 1999. Seismic anisotropy in the region of the Chile margin triple junction. Journal of South American Earth Sciences, 12(3): 261-270. Niu, H.C., Sato, H., Zhang, H.X., Ito, J., Nagao, T., Yu, X.Y., Terada, K., Zhang, Q., 2006a. Juxtaposition of adakite, boninite, high-TiO2 and low-TiO2 basalts in the Devonian southern Altay, Xinjiang, NW China. Journal of Asian Earth Sciences, 28(4-6): 439-456. Niu, H.C., Yu, X.Y., Xu, J.F., 2006b. Late Paleozoic

Volcanism

and Associated Metallognesis in the

Altay Area, Xinjiang, China. Geological Publishing House, Beijing. Pearce, J.A., Stern, R.J., Bloomer, S.H., Fryer, P., 2005. Geochemical mapping of the Mariana arc-basin system: Implications for the nature and distribution of subduction components. Geochemistry Geophysics Geosystems, 6(7): 406-407. Pearce, J.A., Cann, J.R., 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth and Planetary Science Letters, 19(2): 290-300. Peters, T.J., Menzies, M., Thirlwall, M., Kyle, P.R., 2008. Zuni–Bandera volcanism, Rio Grande, USA — Melt formation in garnet- and spinel-facies mantle straddling the asthenosphere–lithosphere boundary. Lithos, 102(1-2): 295-315. Peng, X., LianChang, Z., HuaYing, W., XiaoJing, Z., ZhiGuang, C., Bo, W., 2009. Ages of the zircons from ore-bearing porphyries in II-III ore area of Kalaxianger porphyry copper ore belt in Qinghe, Xinjiang and its geological significance. Acta Petrologica Sinica, 25(6): 1474-1483. Polat, A., Hofmann, A., 2003. Alteration and geochemical patterns in the 3.7–3.8 Ga Isua greenstone belt, West Greenland. Precambrian Research, 126(3): 197-218. Qu, G.S., Zhang, J.J., 1991. Irtys structural zone [in Chinese]. Geoscience Xinjiang 3, 115–131. Reimink, J.R., Chacko, T., Stern, R.A., Heaman, L.M., 2014. Earth’s earliest evolved crust generated in an Iceland-like setting. Nature Geoscience, 7(7): 529-533. Rudnick, R.L., Gao, S., 2003. Composition of the Continental Crust. 1-51. Russo, R.M., Vandecar, J.C., Comte, D., Mocanu, V.I., Gallego, A., Murdie, R.E., 2010. Subduction of the Chile Ridge: Upper mantle structure and flow. Gsa Today: 4-10. Santosh, M., Kusky, T., 2010. Origin of paired high pressure-ultrahigh-temperature orogens: a ridge subduction and slab window model. Terra Nova, 22(1): 35-42. Şengör, A., Natal'In, B., Burtman, V., 1993. Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia. Nature, 364(6435): 299-307. Şengör, A.M.C., Natal'in, B.A., 1996. Paleotectonics of Asia: Fragments of a syn thesis. Shaw, J.E., Baker, J.A., Menzies, M.A., Thirlwall, M.F., Ibrahim, K.M., 2003. Petrogenesis of the Largest Intraplate Volcanic Field on the Arabian Plate (Jordan): a Mixed Lithosphere–Asthenosphere 33

Source Activated by Lithospheric Extension. Journal of Petrology, 44(9): 1657-1679. Sisson, V.B., Pavlis, T.L., Roeske, S.M., Thorkelson, D.J., 2003. Introduction: An overview of ridge-trench interactions in modern and ancient settings. In: Sisson, V.B., Roeske, S.M., Pavlis, T.L. (Eds.), Geology of a Transpressional Orogen Developed During Ridge–trench Interaction Along the North Pacific Margin: Geological society of America, special paper 371, pp. 1–18. Geology of , 371(1): 31-3. Sláma, J., Košler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S., Morris, G.A., Nasdala, L., Norberg, N., 2008. Plešovice zircon-a new natural reference material for U–Pb and Hf isotopic microanalysis. Chemical Geology, 249(1): 1-35. Stern, R.J., 2002. Subduction zones. Reviews of Geophysics, 40(4). Sun, M., Long, X.P., Cai, K.D., Jiang, Y.D., Wang, B.Y., Yuan, C., Zhao, G.C., Xiao, W.J., Wu, F.Y., 2009. Early Paleozoic ridge subduction in the Chinese Altai: Insight from the abrupt change in zircon Hf isotopic compositions. Science in China Series D: Earth Sciences, 52(9): 1345-1358. Sun, M., Yuan, C., Xiao, W.J., Long, X.P., Xia, X.P., Zhao, G.C., Lin, S.F., Wu, F.Y., Kröner, A., 2008. Zircon U–Pb and Hf isotopic study of gneissic rocks from the Chinese Altai: Progressive accretionary history in the early to middle Palaeozoic. Chemical Geology, 247(3-4): 352-383. Sun, S.S., McDonough, W.s., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society, London, Special Publications, 42(1): 313-345. Taylor, S.R., McLennan, S.M., 1995. The geochemical evolution of the continental crust. Reviews of Geophysics, 33(2): 241-265. Thorkelson, D.J., 1996. Subduction of diverging plates and the principles of slab window formation. Tectonophysics, 255(1-2): 47-63. Thorkelson, D.J., Taylor, R.P., 1989. Cordilleran slab windows. Geology, 17(9): 833-836. Wan, B., 2009. The formation of VMS deposits in the process of lateral accretion in the Southern Altai: geological, geochemical characteristics and mineralization. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing. Wan, B., Zhang, L.C., 2006. Sr-Nd-Pb isotope geochemistry and tectonic setting of Devonian polymetallic metallogenic belt on the Southern margin of Altaid, Xingjing. Acta Petrologica Sinica, 22(1): 145-152. Wan, B., Zhang, L.C., Xiang, P., 2010. The Ashele VMS-type Cu-Zn Deposit in Xinjiang, NW China Formed in a Rifted Arc Setting. Resource Geology, 60(2): 150-164. Wang, T., Hong, D.W., Jahn, B.M., Tong, Y., Wang, Y.B., Han, B.F., Wang, X.X., 2006. Timing, petrogenesis, and setting of Paleozoic synorogenic intrusions from the Altai Mountains, northwest China: Implications for the Tectonic evolution of an accretionary orogen. Journal of Geology, 114(6): 735-751. Wang, T., Jahn, B.M., Kovach, V.P., Tong, Y., Hong, D.W., Han, B.F., 2009. Nd–Sr isotopic mapping of the Chinese Altai and implications for continental growth in the Central Asian Orogenic Belt. Lithos, 110(1-4): 359-372. Wang, W., Wei, C.J., Wang, T., Lou, Y.X., Chu, H., 2009. Confirmation of pelitic granulite in the Altai orogen and its geological significance. Chinese Science Bulletin, 54(14): 2543-2548. Wang, Y.J., Yuan, C., Long, X.P., Sun, M., Xiao, W.J., Zhao, G.C., Cai, K.D., Jiang, Y.D., 2011. Geochemistry, zircon U–Pb ages and Hf isotopes of the Paleozoic volcanic rocks in the northwestern Chinese Altai: Petrogenesis and tectonic implications. Journal of Asian Earth Sciences, 42(5): 969-985. 34

Wang, Z.H., Sun, S., Li, J.L., Hou, Q.L., Qin, K.Z., Xiao, W.J., Hao, J., 2003. Paleozoic tectonic evolution of the northern Xinjiang, China: Geochemical and geochronological constraints from the ophiolites. Tectonics, 22(2): 9/1-9/15. Wei, C.J., Clarke, G., Tian, W., Qiu, L., 2007. Transition of metamorphic series from the Kyanite- to andalusite-types in the Altai orogen, Xinjiang, China: Evidence from petrography and calculated KMnFMASH and KFMASH phase relations. Lithos, 96(3): 353-374. Wei, G.J., Liang, X.R., Li, X.H., Liu, Y., 2002. Precise measurement of Sr isotopic composition of liquid and solid base using (LP) MC-ICPMS. Geochimica, 31(3): 295-305. Wilson, D.S., McCrory, P.A., Stanley, R.G., 2005. Implications of volcanism in coastal California for the Neogene deformation history of western North America. Tectonics, 24(3): 1-22. Wilson, M., 1989. Igneous Petrogenesis. Chapman and Hall, London, 466pp. Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, 20: 325-343 Windley, B.F., Alexeiev, D., Xiao, W.J., Kröner, A., Badarch, G., 2007. Tectonic models for accretion of the Central Asian Orogenic Belt. Journal of the Geological Society, 164(1): 31-47. Windley, B.F., Kröner, A., Guo, J., Qu, G., Li, Y., Zhang, C., 2002. Neoproterozoic to Paleozoic geology of the Altai orogen, NW China: new zircon age data and tectonic evolution. The Journal of geology, 110(6): 719-737. Wong, K., Sun, M., Zhao, G.C., Yuan, C., Xiao, W.J., 2010. Geochemical and geochronological studies of the Alegedayi Ophiolitic Complex and its implication for the evolution of the Chinese Altai. Gondwana Research, 18(2-3): 438-454. Wu, Y.F., Yang, F.Q., Liu, F., Geng, X., Li, Q., Zheng, J., 2015. Petrogenesis and tectonic settings of volcanic rocks of the Ashele Cu–Zn deposit in southern Altay, Xinjiang, Northwest China: Insights from zircon U–Pb geochronology, geochemistry and Sr–Nd isotopes. Journal of Asian Earth Sciences, 112: 60-73. Xiao, W.J., Windley, B.F., Sun, S., Li, J., Huang, B., Han, C., Yuan, C., Sun, M., Chen, H., 2015. A Tale of Amalgamation of Three Permo-Triassic Collage Systems in Central Asia: Oroclines, Sutures, and Terminal Accretion. Annual Review of Earth and Planetary Sciences, 43(1): 477-507. Xiao, W.J., Windley, B.F., Allen, M.B., Han, C., 2013. Paleozoic multiple accretionary and collisional tectonics of the Chinese Tianshan orogenic collage. Gondwana Research, 23(4): 1316-1341. Xiao, W.J., Huang, B.C., Han, C.M., Sun, S., Li, J.L., 2010. A review of the western part of the Altaids: A key to understanding the architecture of accretionary orogens. Gondwana Research, 18(2-3): 253-273. Xiao, W.J., Kroner, A., Windley, B.F., 2009a. Geodynamic evolution of Central Asia in the Paleozoic and Mesozoic. International Journal of Earth Sciences, 98(6): 1185-1188. Xiao, W.J., Windley, B.F., Yuan, C., Sun, M., Han, C.M., Lin, S.F., Chen, H.L., Yan, Q.R., Liu, D.Y., Qin, K.Z., Li, J.L., Sun, S., 2009b. Paleozoic Multiple Subduction-Accretion Processes of the Southern Altaids. American Journal of Science, 309(3): 221-270. Xiao, W.J., Pirajno, F., Seltmann, R., 2008. Geodynamics and metallogeny of the Altaid orogen. Journal of Asian Earth Sciences, 32(2-4): 77-81. Xiao, W.J., Windley, B.F., Badarch, G., Sun, S., Li, J., Qin, K., Wang, Z., 2004. Palaeozoic accretionary and convergent tectonics of the southern Altaids: implications for the growth of Central Asia. Journal of the Geological Society, 161: 339-342. Xiao, X.C., Tang, Y., Feng, Y., Zhu, B., Li, J., Zhao, M., 1992. Tectonic evolution of northern Xinjiang and 35

its adjacent regions. Geol. Publ. House, Beijing: 104-121. Xu, J.F., Castillo, P.R., Chen, F.R., Niu, H.C., Yu, X.Y., Zhen, Z.P., 2003. Geochemistry of late Paleozoic mafic igneous rocks from the Kuerti area, Xinjiang, northwest China: implications for backarc mantle evolution. Chemical Geology, 193(1): 137-154. Xu, Y.G., Ma, J.L., Frey, F.A., Feigenson, M.D., Liu, J.-F., 2005. Role of lithosphere–asthenosphere interaction in the genesis of Quaternary alkali and tholeiitic basalts from Datong, western North China Craton. Chemical Geology, 224(4): 247-271. Yang, F.Q., Geng, X.X., Wang, R., Zhang, Z.X., Guo, X.J., 2017. A synthesis of mineralization styles and geodynamic settings of the Paleozoic and Mesozoic metallic ore deposits in the Altay Mountains, NW China. Journal of Asian Earth Sciences. Yang, F.Q., Liu, F., Li, Q., Geng, X.X., 2014. In situ LA–MC–ICP–MS U–Pb geochronology of igneous rocks in the Ashele Basin, Altay orogenic belt, northwest China: Constraints on the timing of polymetallic copper mineralization. Journal of Asian Earth Sciences, 79: 477-496. Yin, J.Y., Yuan, C., Sun, M., Long, X.P., Zhao, G.C., Wong, K.P., Geng, H.Y., Cai, K.D., 2010. Late Carboniferous high-Mg dioritic dikes in Western Junggar, NW China: geochemical features, petrogenesis and tectonic implications. Gondwana Research, 17(1): 145-152. Yuan, C., Sun, M., Xiao, W.J., Li, X.H., Chen, H.L., Lin, S.F., Xia, X.P., Long, X.P., 2007. Accretionary orogenesis of the Chinese Altai: Insights from Paleozoic granitoids. Chemical Geology, 242(1-2): 22-39. Zhang, H.X., Niu, H.C., Terada, K., Yu, X.Y., Sato, H., Ito, J., 2003. Zircon SHRIMP U-Pb dating on plagiogranite from Kuerti ophiolite in Altay, North Xinjiang. Chinese Science Bulletin, 48(20): 2231-2235. Zhang, Z.M., Zhao, G.C., Santosh, M., Wang, J.L., Dong, X., Shen, K., 2010. Late Cretaceous charnockite with adakitic affinities from the Gangdese batholith, southeastern Tibet: Evidence for Neo-Tethyan mid-ocean ridge subduction? Gondwana Research, 17(4): 615-631. Zhang, Z., Yan, S., Chen, B., Zhou, G., He, Y., Chai, F., He, L., Wan, Y., 2006. SHRIMP zircon U-Pb dating for subduction-related granitic rocks in the northern part of east Jungaar, Xinjiang. Chinese Science Bulletin, 51(8): 952-962. Zhao, J.H., Zhou, M.F., 2007. Geochemistry of Neoproterozoic mafic intrusions in the Panzhihua district (Sichuan Province, SW China): Implications for subduction-related metasomatism in the upper mantle. Precambrian Research, 152(1-2): 27-47. Zhao, Z.H., Xiong, X.L., Wang, Q., Bai, Z.H., Qiao, Y.L., 2009. Late Paleozoic underplating in North Xinjiang: Evidence from shoshonites and adakites. Gondwana Research, 16(2): 216-226. Zheng, C.Q., Kato, T., Enami, M., Xu, X.C., 2007. CHIME monazite ages of metasediments from the Altai orogen in northwestern China: Devonian and Permian ages of metamorphism and their significance. Island Arc, 16(4): 598-604. Zhuang, Y.X., 1994. Tectonothermal evolution in space and time and orogenic process of Altaide, China:. Changchun, Jilin Scienti?c and Technical Press. Zou, T.R., Chao, H.Z., Wu, B.Q., 1988. Orogenic and Anorogenic Granitoids in the Altay Mountains of Xinjiang and Their Discrimination Criteria. Acta Geological Sinica, 2(1): 45-64.

Figure captions: Fig. 1 (a) Schematic tectonic map of the Central Asian Orogenic Belt (CAOB) (after 36

Şengör et al., 1993, 1996; Xiao et al., 2015); (b) Simplified regional geological map of the Chinese Altai (after He et al., 1990; Windley et al., 2002; and Cai et al., 2010). N=Northern Altai Domain; C=Central Altai Domain; Q=Qiongkuer Domain; S=Southern Altai Domain.

Fig. 2 Geological map and sampling location of the Ashele region in the Chinese Altai (modified after Habahe Geological Map at 1:200,000 scale).

Fig. 3 Field photos (a,c,e) and photomicrographs (b,d,f) under cross-polarized light of the Qiye basaltic rocks. Pl=plagioclase; Px=pyroxene; Ol=olivine

Fig. 4 U–Pb Concordia diagram for zircons separated from the Qiye basaltic samples in the Chinese Altai.

Fig. 5 (a) Zr/Ti versus Nb/Y diagram distinguishing subalkaline and alkaline basalts (Winchester and Floyd, 1977). (b) Fe2O3T/MgO versus SiO2 diagram distinguishing tholeiitic and calc-alkaline series (Miyashiro, 1974).

Fig. 6 (a) Chondrite-normalized REE patterns for the Qiye basaltic rocks. (b) Primitive mantle-normalized trace element spider diagram for the Qiye basaltic rocks. Normalizing values from Sun and McDonough, 1989. Date for the Ashele basalts from Wu et al., 2015,and Wan et al., 2010, and date for the Kangbutiebao 37

basalts from Wan, 2009 and the Kurti mafic rocks from Xu et al., 2003 .

Fig. 7 (a) Diagram of εNd(t)-(87Sr/86Sr)i for Qiye basaltic rocks. (b) A binary mixing model for magma generation of the Qiye basaltic rocks. The data of the MORB-type mafic dykes are from Cai et al., 2010, and the others are same as the Fig. 6.

Fig. 8 Variation diagram for trace elements versus Zr contents for Qiye basaltic rocks.

Fig. 9 Variation diagrams for major oxides versus SiO2 contents for the Qiye basaltic rocks.

Fig. 10 Diagram of La/Nd versus La (a), La/Nb versus Th/Nb (b), Nb/Yb versus La/Yb (c) and εNd(t) versus La/Yb (d). The data sources are same as the Fig. 6. Fig.11 (a) La/Yb versus Dy/Yb diagram for the Qiye basaltic rocks. The melting model and mode are after Shaw et al., 2003. Values of partition coefficient are from the compilation of McKenzie and O'Nions, 1991. (b) Sm/Yb versus La/Sm diagram for the Qiye basaltic rocks (after Zhao and Zhou, 2007). Melting curves for spinel lherzolite and garnet peridotite with both DMM and PM compositions are after Aldanmaz et al., 2000. Numbers along lines represent the degree of the partial melting.

38

Fig. 12 Tectonic discrimination diagram (a) Nb*2-Zr/4-Y (after Meschede, 1986) and (b) Ti/100-Zr-3*Y for the Qiye basaltic rocks (after Pearce and Cann, 1973).

Fig.13 A schematic model illustrates the Devonian tectonic evolution of the Chinese Altai. (a) The initial stage of ridge subduction produced normal calc-alkaline arcmagmas of the Kangbutiebao Formation and the Keketuohai Alaskan-type mafic-ultramafic complex in the eastern Chinese Altai. (b) The propagating ridge subduction and slab-window magmatism resulted in the emplacements of the Qiye basaltic rocks, MORB-like mafic dykes in the western Chinese Altai and the Kurti back-arc mafic igneous rocks in the eastern Chinese Altai.

39

Highlights 1. The Qiye basaltic rocks were erupted at 376.2±2.4 Ma. 2. They have transitional geochemical compositions between arc magmas and back arc basaltic melts. 3. They were derived from a mixing source comprising MORB-like mantle and subordinate mantle wedge. 4. The petrogenesis of them was related to slab-window magmatism induced by ridge subduction. 5. They were formed in a nascent back-arc rifting basin during ridge-trench interaction.

40

Table1 SIMS zircon U-Pb ages of the Qiye basaltic rocks in the southern Chinese Altai, NW China ASL

Element

Isotopic ratios

0

conte

1

nts T

U

T

h

207

Pb/206

h

207

Isotopic ages (Ma)

Pb/235

Pb

206

Pb/238

U

207

U

Pb/206

207

Pb

Pb/235

206

Pb/238

U

U

Val 1

Val 1

/ (p

ASL

U Val. 1σ

(p p

p

m

m

)

)

Val. 1σ

Val

0.0

9

0

5

9

4

5

1

5

5

4

6

3

-

8

8

7

1

8

6

1 ASL

0.

2.

0.4

0.0

2.

2

7

5

9

4

7

1

7

8

9

8

7

-

6

0

3

.

2.

0.0

σ

.

35

27

37

8

6

2

2

.

5

0

1

.

6

5

0.0

1

0.

0.4

17 22 0. 0

Val 1σ

.

95 90 1. 0

1σ

2.

σ

.

37

8. 8

1

.

3

7

41

36

37

8.

37

8

5

2

1

.

6

7

0

9

3

.

2

.

.

1

4

1

5

41

2 ASL

9

9

73 74 0.

0.0

6

9

5

7

5

3

1

9

5

4

3

3

-

2

7

7

2

9

0

2

3 ASL

0.

7

6

5

4

1

1

4

1

3

6

5

-

3

4

ASL

3.

0.0

6

17

37

7.

37

8

5

1

1

.

9

4

4

9

8

9

.

.

9

8

2.

40

50

5

1

9

9

37

9.

37

7.

0

4

9

0

.

.

.

8

9

8

8

5

5

1

4

6

1

4

6

4

7

3

-

9

1

0

5

9

0

5

1.

2.

2.

35

32

37

8.

37

8

6

1

5

.

5

3

8

0

8

.

8

.

.

2

5

5

6

5

1

5

4

6

1

3

5

3

9

8

0

.

.

-

3

2

5

3

9

7

4

9

15 25 0.

0.0

1.

0.4

2.

2.

0.0

0.0

2.

3

3

6

0.4

0.0

0.0

9

1.

0.4

18 28 0. 0

9

6 0.0

ASL

41

2

58 38 1. 0

2.

9

9

9

0.4

0.0

0.0

4

ASL

2.

25 34 0. 0

1.

0.4

2.

42

25

2

1

37

24

38

37

7.

37

8.

4

9

7

7.

37

1

7. 42

0

1

9

5

5

1

8

-

4

7 ASL

1

4

4

5

1

7

.

1

4

1

4

9

8

.

6

.

.

1

9

6

7

5

3

30 51 0.

0.0

9

5

5

6

3

1

9

3

7

-

8

0

7

8 ASL

0.

2.

15

5

2

7

9

1

6

3

1

7

9

3

76 86 0.

0.0

9

8

5

5

6

2

1

8

4

9

6

6

-

6

2

0

7

0.4

0.0

0.0

3

9 ASL

2.

36

0

9

7.

37

7.

7

8

1

0

.

.

.

2

4

2

9

37

13

38

7.

39

8.

6

1

9

.

8

3

0

2

8

.

3

.

.

7

2

3

3

5 0.0

7

8

5

5

4

2

1

9

4

8

9

5

-

8

1

8

4

9

1

2.

4

77 86 0. 0

2.

1

35

0.

0.4

2

6

5

0.

0.4

2.

0.0

2.

37

13

37

7.

37

8

6

1

6

.

7

1

7

0

8

.

1

.

.

2

3

3

7

0

43

Table 2

Whole-rock major (wt.%) and trace element (ppm) contents of the

Qiye basaltic rocks in the southern Chinese Altai, NW China sa

Si

Ti

Al

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

m

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

p

4

4

4

4

4

4

4

4

2

2

2

2

2

2

2

2

2

l

A

A

A

A

A

A

A

A

H

H

H

H

H

H

H

H

H

e

S

S

S

S

S

S

S

S

B

B

B

B

B

B

B

B

B

L

L

L

L

L

L

L

L

1

1

1

1

2

2

2

2

2

0

0

0

0

0

0

0

1

6

7

8

9

0

1

2

3

4

2

3

4

5

7

8

9

0

49

52

51

51

51

50

58

54

43 44 49 54 52 48 52 51 44

O

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

2

9

1

2

8

1

3

3

6

3

6

8

0

0

4

7

9

6

0

0

0

0

0

0

0

0

0

3

9

3

5

5

8

2

0

0.

0.

0.

0.

0.

0.

0.

0.

1.

1.

0.

0.

0.

0.

0.

0.

1.

O

9

8

9

8

7

8

7

7

1

2

9

9

9

6

8

7

1

2

3

6

7

5

6

4

3

9

6

7

9

0

9

0

8

6

1

18

18

18

15

18

19

15

17

20 20 17 16 15 19 16 16 19

2

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

O

1

2

9

8

7

0

1

0

7

0

8

5

9

4

5

3

1

44

3

5

0

5

5

5

5

0

5

11

10

11

9.

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1

/

3

5

7

0

3

9

2

7

2

3

8

8

5

2

4

0

6

29

28

26

38

20

21

51

44

51 61 45 65 40 20 42 32 46

R

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

E

9

5

5

2

9

9

4

3

5

9

2

8

1

2

6

3

2

(L

0.

Y b ) N

Y b ) N

Σ

54

δ

E

3

1

5

0

2

1

9

5

5

5

0

1

1

3

4

4

8

1.

1.

0.

0.

1.

1.

0.

0.

1.

1.

1.

0.

1.

1.

0.

1.

1.

E

0

0

9

9

4

3

8

9

0

0

0

8

0

1

9

3

0

u

5

3

3

8

6

1

5

7

3

0

0

1

2

4

4

5

6

Fe2O3T is total iron as Fe2O3; Mg#=100×Mg2+/(Mg2+ + Fe2+ + Fe3+); Eu/Eu* = 2× EuN/(SmN+GdN); Subscript N means Chondrite-normalized. Normalizing values are from Sun and McDonough (1989).

Table 3 Whole-rock Sr-Nd isotopic compositions of the Qiye basaltic rocks in the southern Chinese Altai, NW China Sa

A Rb Sr

87

87

R

S (2

S

N

147

143

S

(2

INd Is

ε

TD f

m

g (

(

b

r

σ

m

d

m

N

σ

(

r

N

M

S

p

e p

p

/

/

)

(

(

/

d

)

t

(

d

(

m

l

p

p

8

8

p

p

1

/

)

t

(

M

/

e

m

m

6

6

p

p

4

1

)

t

a

N

)

)

S

S

m

m

4

4

)

)

d

r

r

)

)

N

4

d

N

4 22

-

d C1

3 0.6 64

0.0

0.7 0.0 3.0 9.

0.1

0.5

0.0 0.5 0.

55

C1

C1

C1

2

7 3

H

6 2

0

0

0

2

5

0

B

8

7

0

1

5

7

6

0

1

3 0.6 40 2

7 8

H

6 3

2

0.0

4

9

1

0

1

7

.

9

0

7

4

2

0

2

0

4 9

.

1

8

0

3

5

0

1

5

0

7

8

1

0

6

5

8

0.7 0.0 3.5 11 0

0

0

4

6

0

B

9

0

0

1

1

0

7

0

9

3 4.4 46 2

7 3

H

6

3

0.0

7

.

0

0

8

0

2

0

2

0

3 4

.

5

8

0

4

6

0

1

6

0

2

0

8

1

8

5

3

0.7 0.0 3.3 12

0

B

5

9

0

1

5

5

9

6

3

1

0

0.1

0.5

0.0 0.5 0.

5 10

-

.

6

1

0

1

7

.

5

0

0

7

2

0

2

0

2 6

.

9

8

0

4

5

1

0

3

0

2

8

5

6

4

5

1

0.7 0.0 2.4 8. 0

-

1

5

7

5 13

0

7

7 8

0.0 0.5 0. 1

0

2

0.5 8

0

0.0

0

0.1 .

2

3 0.2 18

6

2

0

9

0.1 0

0.5 8

0.0 0.5 0. 1

0

1

4 18

-

7

5

.

56

0

H

6 1

4

6

0

B

3

3

0

2

4

9

2

8

8

1)

4

8

2

0

2

0

4 8

5

8

0

3

6

0

0

4

0

8

4

4

6

4

5

0

TDM= (1/λ)ln{1+[(143Nd/ 144

Nd)DM-

(143Nd/144Nd)S -((147Sm/144Nd)DM - (147Sm/144Nd)S]}; 2)

λ=6.54*10-6,

(147Sm/144Nd)C=0.1,

(147Sm/144Nd)DM=0.21357, (143Nd/144Nd)DM=0.513151, (147Sm/144Nd)CHUR=0.1967.

57

.