Origins of the meta-mafic rocks in the southern Dunhuang Block (NW China): Implication for tectonic framework of the southernmost Central Asian Orogenic Belt
Funding information: Henan Polytechnic University, Grant/Award Number: 760307/018; Ministry of Science and Technology of the People's Republic of China, Grant/Award Number: 2016YFC0600401; National Natural Science Foundation of China, Grant/Award Number: 41730215
Abstract
The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogenic collages in the world with prominent juvenile crust addition, where the southernmost margin of the CAOB located is one hot topic in the international studies. The Dunhuang Block located to the south of the Beishan Orogen is a key position for outlining the tectonic framework of the south margin of the CAOB. However, at present, the tectonic attribution of the Dunhuang Block is still controversial. In this paper, we focus on the origins and protoliths of the meta-mafic rocks from the Hongliuxia complex in the southern Dunhuang Block for determining the tectonic attribution of the Dunhuang Block. In the field, the meta-mafic rocks are mainly exposed as tectonic blocks within the metasedimentary rocks displaying the “block-in-matrix” fabrics or as tectonic slices juxtaposed by faults. Geochemically, the meta-mafic rocks could be divided into three groups based on the rare earth elements (REE) and trace elements: the group 1 samples are depleted in the LREE relative to HREE and show flat HREE patterns, similar to the mid-oceanic ridge basalt; the group 2 samples show flat REE patterns without obvious differentiation between the LREE and HREE, like the oceanic plateau basalt; the group 3 samples are enriched in LREE relative to LREE, and have negative Nb, Ta, and Ti anomalies, similar to the island arc basalt. Conclusively, the protoliths of the meta-mafic rocks dominantly belong to the oceanic plate components. They were metamorphosed during Early Silurian to Middle Devonian in different depths of the subduction zone documented in previous studies. So, we suggest the Hongliuxia complex is an exhumed Palaeozoic subduction–accretion complex (SAC) formed during the oceanic plate subduction. This result confirms the Palaeozoic subduction event occurred in the Dunhuang region and indicates that the Dunhuang Block is a Palaeozoic Orogen rather than a part of Precambrian continent block. Considering the regional geology context, we speculate the Dunhuang Orogen belongs to the southernmost margin of the CAOB.
1 INTRODUCTION
The Central Asian Orogenic Belt (CAOB) is the largest accretionary orogenic belt on Earth, formed by the long-lived subduction–accretion processes of the Palaeo-Asian Ocean (PAO) during the Neoproterozoic to latest Permian or Early Triassic (Şengör, Natal'in, & Burtman, 1993; Windley, Alexeiev, Xiao, Kröner, & Badarch, 2007; Xiao et al., 2015; Xiao, Windley, Hao, & Zhai, 2003). The location of the southernmost margin of the CAOB is a focus of many international studies due to its significance for understanding the tectonic framework of the southern CAOB and continental growth (Şengör & Natal'in, 1996; Windley et al., 2007; Xiao et al., 2015; Xu, Charvet, Chen, Zhao, & Shi, 2013). The Beishan Orogen in the southern part of the CAOB connects the Southern Tien Shan Suture to the west with the Solonker Suture to the east (Xiao et al., 2010). In recent years, many Palaeozoic high-pressure metamorphic rocks, magmatic arcs, and forearc accretion complexes have been identified in the Beishan Orogen, and they were considered as the products of the subduction of the PAO (Guo et al., 2012; Guo et al., 2014; Guo, Chung, Xiao, Hou, & Li, 2017; Liu, Chen, Jahn, Wu, & Liu, 2011; Qu et al., 2011; Song et al., 2013; Song, Xiao, Han, & Tian, 2014; Song, Xiao, Windley, Han, & Lei, 2016; Song, Xiao, Windley, Han, & Tian, 2015; Tian et al., 2015; Xiao et al., 2015). These research achievements support the idea that the Beishan Orogen represents the southernmost part of the CAOB in the middle portion of the huge E-W striking accretionary orogen. However, as an important tectonic unit located to the south of the Beishan Orogen, the Dunhuang Block is relatively poorly studied as yet. Particularly, its tectonic attribution is still controversial: (1) some researchers considered it as a fragment of Precambrian continent based on the Precambrian geochronological data (He, Zhang, Zong, & Dong, 2013; Long, Yuan, Sun, Kröner, & Zhao, 2014; Lu, Li, Zhang, & Niu, 2008; Mei et al., 1998; Wang et al., 2013; Wang et al., 2014; Zhang, Gong, & Yu, 2012; Zhang, Yu, Gong, Li, & Hou, 2013; Zhao et al., 2015; Zhao, Diwu, Sun, Zhu, & Wang, 2013; Zhao, Sun, Diwu, & Yan, 2015; Zong et al., 2013), while (2) others proposed it is a Palaeozoic Orogen on account of the identification of the Palaeozoic magmatic–metamorphic events (Shi et al., 2020; Shi, Hou, Wu, Wang, & Chen, 2017; Wang et al., 2017; Zhao et al., 2016). This controversy hampers our understanding of the tectonic framework of the southern CAOB and how it extends southward.
The subduction–accretion complexes (SAC) are formed during the subduction of the oceanic plates. Generally, they are characterized by the trench-vergent thrusts, out-of-sequence thrusts, duplexes, fault propagation folds, and “block-in-matrix” fabrics in structures (Anma et al., 2011; Chester & Moore, 2018; Muraoka & Ogawa, 2011). Their compositions predominantly include the rocks derived from the subducting oceanic plate, high-pressure metamorphic rocks, trench turbidites, and materials from the overriding plate (Frisch, Meschede, & Blakey, 2011). Nowadays, it is accepted that the exhumed SACs exposed on land could represent the locations of ancient convergent plate boundaries and document the key information about the consumption of oceanic plates and the formation of orogens (Cawood et al., 2009; Yan et al., 2018).
In the southern Dunhuang Block, many eclogite, granulite, and amphibolite are exposing in the Hongliuxia complex. They record the Silurian–Devonian “clockwise” metamorphism P–T–t paths (Wang et al., 2017; Wang et al., 2018; Wang, Chen, et al., 2017). They are mainly exposed as tectonic blocks within the metasedimentary rocks (metamorphosed trench turbidites), exhibiting the “block-in-matrix” fabric (Shi et al., 2018). This lithological occurrence is similar to that of the SACs (e.g., Anma et al., 2011; Chester & Moore, 2018; Muraoka & Ogawa, 2011; Yamamoto, Mukoyoshi, & Ogawa, 2005). However, the origins and protoliths of those meta-mafic rocks are poorly constrained, which makes the nature of the Hongliuxia complex still unclear. In this paper, we present field relationships and whole-rock geochemical data of the meta-mafic rocks in the Hongliuxia complex. These data allow us to throw light upon the nature of the Hongliuxia complex and provide evidence for understanding the tectonic attribution of the Dunhuang Block and the tectonic framework of the southern CAOB.
2 GEOLOGICAL BACKGROUND
The CAOB is located to the south of the Siberia and East European cratons (Figure 1a). It is the largest Phanerozoic accretionary orogen on Earth with a length of ~2,500 km in the E-W trending (Şengör et al., 1993). The Beishan Orogen is located in the southern part of the CAOB. It is composed of several discrete arc terranes, including the Shibanshan, Shuangyingshan, Mazongshan, Hanshan, and Queershan terranes, separated from south to north by the Liuyuan, Hongliuhe–Xichangjing, Shibanjing–Xiaohuangshan, and Hongshishan ophiolitic mélanges (Xiao et al., 2010). Tectonically, the Dunhaung Block is situated to the south of the Beishan Orogen, connecting the Tarim Craton westerly and Alxa Block (western North China Craton) easterly, respectively (Figure 1b). It is divided into several discrete massifs by Cenozoic ENE–WSW striking faults, including the Sanweishan Massif, Dongbatu–Mogutai Massif, Hongliuxia Massif, and Karatashtag–Duobagou Massif (Figure 1c).
Locality maps of regional geology and the study locale. (a) General overview of the (CAOB) and adjacent units (after Şengör et al., 1993; Xiao et al., 2009); (b) Tectonic location of the Dunhuang Block (after Yue, Liou, & Graham, 2001); and (c) Simplified geological map of the Dunhuang Block (after China Geological Survey, 2004); (d) Simplified geological map of Hongliuxia Massif in the southern Dunhuang Block (modified after Bureau of Geology and Mineral Resources of Gansu Province, 1966) [Colour figure can be viewed at wileyonlinelibrary.com]
The Dunhuang Block was traditionally considered as a fragment of the Precambrian continent block. The rocks exposed in this region consist of a series of metamorphic supracrustal rocks and sporadic Archean TTG gneisses (Bureau of Geology and Mineral Resources of Gansu Province, 1989). The Archean TTG gneisses were previously viewed as fragments of the basement of the Tarim Craton (Long et al., 2014; Lu et al., 2008; Mei et al., 1998; Wang et al., 2013; Wang et al., 2014; Zong et al., 2013) or North China Craton (Zhang et al., 2012; Zhang et al., 2013; Zhao et al., 2013; Zhao, Diwu, et al., 2015; Zhao, Sun, et al., 2015). The metamorphic supracrustal rocks comprise the metasedimentary rock, meta-mafic rock, metavolcanic rock, marble, and minor migmatite. Previously, they were all thought to be formed in the pre-Sinian (Bureau of Geology and Mineral Resources of Gansu Province, 1989). Recently, many meta-mafic rocks metamorphosed in the Early Silurian to Late Devonian are recognized in nearly almost areas of the Dunhuang region (He, Zhang, Zong, Xiang, & Klemd, 2014; Meng, Zhang, Xiang, Yu, & Li, 2011; Peng et al., 2014; Pham et al., 2018; Wang et al., 2016; Wang et al., 2018; Wang, Chen, et al., 2017; Wang, Wang, et al., 2017; Wang, Zhang, Chen, et al., 2018; Zhang et al., 2020; Zhao et al., 2016; Zhao et al., 2019; Zong et al., 2012). The similar Palaeozoic metamorphic events are also reported in the neighbouring Beishan Orogen, such as the ~465 Ma HP eclogites west of Liuyuan in Beishan (Liu et al., 2011; Qu et al., 2011).
Palaeozoic–Mesozoic magmatic rocks are also identified in the Dunhuang Block with ages ranging from Cambrian to Triassic. Amongst, the Early Palaeozoic magmatic rocks are considered to be formed in the continental arc environment (Gan, Li, Song, & Li, 2020; Zhao et al., 2017; Zhu et al., 2019).The Carboniferous granitoids are ascribed as the collisional intrusions formed by partial melting of the thickened lower crust (Bao et al., 2017; Wang et al., 2016a; Wang et al., 2016b; Zhang, Guo, Zou, Feng, & Li, 2009; Zhao, Sun, Diwu, et al., 2017; Zhu, Wang, Xu, Chen, & Li, 2014). Besides, the Early-Mesozoic magmatic rocks are also distributed in different locations of the Dunhuang Block, which is suggested to be formed by the delamination of thickened continental crust and asthenosphere upwelling in the extension setting (Feng et al., 2018; Wang, Guo, Yu, & Zhang, 2020). The similar Palaeozoic–Mesozoic magmatic rocks are widely identified in the adjacent Beishan–Tianshan Orogen: 438–397 Ma granitoids in Beishan (Liu et al., 2011; Zhang & Guo, 2008; Zhao, Guo, & Wang, 2007), ~ 370 Ma volcanic rocks in the Dundunshan arc, south of Beishan (Guo et al., 2014, 2017), Silurian and Late Devonion granitoids in the central Tianshan (Shi et al., 2007), and Permian–Triassic magmatism in Beishan–Tianshan Orogen (Chen, Shu, & Santosh, 2011; Li et al., 2012; Li, Wang, Wilde, & Tong, 2013; Mao et al., 2014).
The Hongliuxia Massif located in the southern Dunhuang Block (Figure 1d) is occupied by the metamorphic complex mainly consisting of the metasedimentary rocks, meta-mafic rocks and marbles. The metasedimentary rocks are intensely deformed and mostly experienced the greenschist-facies metamorphism (Wang, Wang, et al., 2017). Protoliths of some metasedimentary rocks were trench turbidites deposited after the Middle Devonian (Shi et al., 2018). They enclose the lenticular meta-mafic rocks exhibiting the “block-in-matrix” fabric (Shi et al., 2017). The meta-mafic rocks, including the eclogite, mafic granulite, amphibolite, were mostly metamorphosed in 440 ~ 390 Ma (Wang, Chen, et al., 2017; Wang, Wang, et al., 2017; Wang, Zhang, Chen, et al., 2018). Some of them were metamorphosed from the oceanic island basalt and island arc basalt (Wang et al., 2014; Wang, Wang, et al., 2017). They record metamorphic peak P–T conditions ranging from 830 °C and 24.2 kbar for eclogite to 735–744°C and 17.1–17.7 kbar for mafic granulites, or 652°C and 10.2 kbar for amphibolite (Wang, Chen, et al., 2017; Wang, Wang, et al., 2017; Wang, Zhang, Chen, et al., 2018). The contrast P–T conditions of the meta-mafic rocks and field relationship perhaps evidences the tectonic juxtaposition of the different kinds of rocks. Besides, some granitoid rocks formed in 430 ~ 400 Ma, 360 ~ 340 Ma, and 320 ~ 313 Ma were intruded in the Hongliuxia complex (Wang et al., 2014; Wang, Chen, et al., 2016; Wang, Chen, et al., 2017; Wang, Zhang, Chen, et al., 2018; Zhao, Sun, Diwu, et al., 2017).
3 FIELD RELATIONSHIP AND PETROGRAPHY
3.1 Field relationship
The meta-mafic rocks in the Hongliuxia complex mostly expose as tectonic blocks within the metasedimentary rocks showing the “block-in-matrix” fabric. They are also occurred as tectonic slices juxtaposed with other rocks. In the field, the imbricated thrusts control the distribution of the marble and amphibolite slices and juxtaposed them together (Figures 2a,b). The amphibolite slice could be observed thrusting over the metasandstone slice on the S-dipping fault (Figure 2c). The contact boundaries of different slices are predominantly occupied by ductile shear zones, in which the lineations and σ-type boudins are developed (Figure 2d,e).
Meta-mafic rocks exposed as the tectonic slices in the Hongliuxia complex. (a, b) Imbricated thrusts juxtaposed the marble and amphibolite slices together; (c) The amphibolite slice thrust over the metasandstone slice; (d) Lineations developed on the marble; (e) Ductile shear zone developed in the contact boundary between the metasandstone and mica–quartz schist slices [Colour figure can be viewed at wileyonlinelibrary.com]
The meta-mafic blocks are variable in size and show asymmetric boudin structure defined by competent blocks within ductile matrix. These occurrences reflect the layer-paralleled shearing and even rotation (Figure 3a,b). The eclogite and amphibolite with expose together (Figure 3c) resulting from tectonic juxtaposition of rocks metamorphosed in different depths. The metasedimentary rocks, as the matrix of the meta-mafic blocks, generally intensely deformed and developed tight fold and lineation (Figure 3d,e). The S-C fabric developed in the matrix (Figure 3f) indicates the non-coaxial deformation.
Field relationships between the meta-mafic blocks and matrix. (a) Amphibolite boudins in the metasandstone; (b) Lenticular granulite in the mica–quartz schist; (c) Eclogite and amphibolite blocks exposed in the same outcrop-scale view; (d) Inclined tight fold developed in the mica–quartz schist; (e) Lineation defined by the oriented biotite and elongated quartz; (f) Asymmetric overturned fold showing top-to-the-north shear sense [Colour figure can be viewed at wileyonlinelibrary.com]
3.2 Petrography
The meta-mafic rocks in the Hongliuxia complex mainly consist of the eclogite, granulite, and amphibolite. The primary mineral association of the protoliths of the meta-mafic rocks were changed and replaced by metamorphic minerals (Figure 4a). The granulite generally consists of the garnet, hornblende, plagioclase, quartz and rear clinopyroxene (Figure 4b). The amphibolite could be divided into the garnet-bearing amphibolite made up of the garnet, hornblende, plagioclase, and quartz (Figure 4c), and garnet-free amphibolite composed of the hornblende, plagioclase, and quartz (Figure 4d). The current petrographic characters of the meta-mafic rocks can provide limited information about their protoliths, except for their origination from mafic rocks.
Microphotographs showing mineral assemblages and textures of the meta-mafic rocks in the Hongliuxia complex. (a) Granulite, clinopyroxene replaced by garnet, quartz, and plagioclase; (b) Garnet porphyroblasts, hornblende, plagioclase, and quartz in granulite; (c) Garnet-bearing amphibolite comprising the garnet, hornblende, plagioclase, and quartz; (d) Garnet-free amphibolite with hornblende, plagioclase, and quartz. Abbreviations: Bt, biotite; Cpx, clinopyroxene; Grt, garnet; Hbl, hornblende; Pl, plagioclase; Qtz, quartz [Colour figure can be viewed at wileyonlinelibrary.com]
4 GEOCHEMISTRY OF THE META-MAFIC ROCKS
Twenty-seven meta-mafic rock samples were selected for the whole-rock major and trace element analyses in the Wuhan Sample Solution Analytical Technology Co. Ltd., Wuhan, China. The results are listed in Table A1.
The meta-mafic rocks sampled from the Hongliuxia complex experienced high-grade metamorphism. Generally, the immobile elements such as the high-field-strength elements (HFSE: Nb, Ta, Zr, Hf, Ti, Th, and Y), REE, and transition elements (V, Cr, Ni, and Sc) remain unaffected during the metamorphism (e.g., Barnes, Naldrett, & Gorton, 1985; Bédard, 1999; Jochum, Arndt, & Hofmann, 1991; Safonova et al., 2016). Contents of some immobile elements of the samples are slightly changed (Figure 5a–f).
Variation degree of immobile elements affected by the metamorphism for the meta-mafic rocks [Colour figure can be viewed at wileyonlinelibrary.com]
Based on the chondrite-normalized REE patterns, the meta-mafic rock samples could be divided into three groups. In the primitive mantle-normalized trace element diagrams, the three groups of samples also show distinct characteristics.
The group 1 samples are characterized by depletion in LREE relative to HREE [(La/Yb)N = 0.50 ~ 1.04]. They have the flat HREE patterns with total REE abundances of 34.20 ~ 61.93 ppm (Figure 6a). In the primitive mantle-normalized trace element diagrams, they are depleted in the Th, Nb, Ta with the slightly negative Ti anomaly (Figure 6d). These geochemical features are similar to those of the normal-type mid-ocean ridge basalt (N-MORB). The group 2 samples show flat chondrite-normalized REE patterns without obvious differentiation between the LREE and HREE [(La/Yb)N = 1.01 ~ 1.70] with total REE abundances of 33.48 ~ 101.13 ppm (Figure 6b). In the primitive mantle-normalized trace element diagrams, they show the flat patterns without significantly variable anomalies of Th, Nb, Ta, and Ti (Figure 6e). These geochemical features are similar to those of the transitional-type mid-ocean ridge basalt (T-MORB). The group 3 samples are enriched in LREE relative to HREE [(La/Yb)N = 1.88 ~ 5.16] with relative flat HREE patterns (Figure 6c). The total REE abundances are between 67.74 ~ 135.45 ppm. In the primitive mantle-normalized trace element diagrams, they show negative Nb, Ta, and Ti anomalies and higher Th abundance (Figure 6f). These geochemical features are similar to those of the island arc basalt (IAB).
Rare earth elements (REE) and trace elements compositions of the meta-mafic rocks. (a-c) Chondrite-normalized REE patterns of the meta-mafic rocks; (d-f) Primitive mantle-normalized trace element diagram of the meta-mafic rocks. Chondrite and primitive mantle values, N-MORB, E-MORB, and OIB values are from Sun and McDonough (1989). Izu island arc basalt represents the intra-oceanic island arc basalt (after Ishizuka et al., 2015), and Lesser Antilles island arc basalt represents the intra-oceanic island arc basalt developed on the thickened oceanic crust (after Xia & Li, 2019; Du Frane, Turner, Dosseto, & Soest, 2009) [Colour figure can be viewed at wileyonlinelibrary.com]
5 PROTOLITHS OF THE META-MAFIC ROCKS
5.1 Group 1 samples
The group 1 samples have geochemical composition of tholeiitic basalt (Figure 7). Their chondrite-normalized REE patterns and primitive mantle-normalized trace element diagrams show N-MORB affinity. So, it is speculated that the protoliths of the group 1 samples are the products of the partial melting of the depleted asthenosphere beneath the mid-ocean ridge. This interpretation is also supported by the plotting of immobile elements diagrams (Figure 8), in which most samples plot into the N-MORB field.
Immobile elements diagrams for tectonic setting. (a) Hf–Ta–Th diagram (after Wood, 1980), IAT: Island Arc Tholeiites, CAB: Calc-alkaline Arc Basalts, OIB: Oceanic Island Basalts, N-MORB: N-type MORB, E-MORB: E-type MORB, WPTB: Within-Plate Tholeiitic Basalts, WPAB: Within-Plate Alkaline Basalts; (b) Nb/Yb-Th/Yb diagram (after Pearce & Peate, 1995) [Colour figure can be viewed at wileyonlinelibrary.com]
5.2 Group 2 samples
The group 2 samples have geochemical composition of calc-alkaline basalt (Figure 7). They also have the transitional MORB-like REE patterns and flat primitive mantle-normalized trace element diagrams resembling the oceanic plateau basalts (e.g., Xia & Li, 2019). In immobile elements diagrams (Figure 8), most samples plot into the transitional MORB and within-plate basalt fields. Some samples plot into the “Volcanic Arc” array (Figure 8b), but the absence of negative Nb, Ta, Ti anomalies in the primitive mantle-normalized trace element diagrams may exclude their subduction-related origins. So, it is suggested that protoliths of group 2 samples are possible the components of the oceanic plateau formed in the within-oceanic plate setting.
5.3 Group 3 samples
The group 3 samples have geochemical composition of calc-alkaline basalt and basaltic andesite (Figure 7). Their chondrite-normalized REE patterns and primitive mantle-normalized trace element diagrams are very similar to those of the island arc basalts, except for the relative higher total REE abundances. In immobile elements diagrams, most samples plot into the “Volcanic Arc” array (Figure 8). Some samples are closely the E-MORB and within-plate tholeiitic basalt (WPTB) fields. These geochemical features probably reflect the effect of subduction process during their formation (Sun & McDonough, 1989). So, it is assumed that the protoliths of this group samples are generated by partial melting of the mantle wedge above the intra-oceanic subduction zone.
Conclusively, the protoliths of the meta-mafic rocks in the Hongliuxia complex include the tholeiitic basalt, calc-alkaline basalt, and basaltic andesite. They are formed in the different tectonic settings in the oceanic plate, including the mid-oceanic ridge, intra-oceanic subduction zone, and the oceanic plateau.
6 DISCUSSION
6.1 Nature of the Hongliuxia complex
In the subduction zone, the subducted materials experienced diachronous metamorphic evolutions would be exhumed facilitated by the corner-flow, buoyancy force, thrusting, and underplating in the interface of subducting and overriding plates (e.g., Cloos & Shreve, 1988a, 1988b; Ernst, 2006; Gerya, Stöckhert, & Perchuk, 2002; Guillot, Hattori, de Sigoyer, Nägler, & Auzende, 2001; Gurnis, Hall, & Lavier, 2004; Hashimoto & Kimura, 1999; Hermann, Müntener, & Scambelluri, 2000; Stöckhert & Gerya, 2005; Taira, 2001). The thrusting and underplating processes could result in the development of imbricated faults and duplexes. Meanwhile, the competent bodies enclosed in the relative soft matrix are expected to undergo boudinage, lenticularization even re-aggregation to form the pinch-and-swell structure or block-in-matrix fabric (e.g., Malatesta, Crispini, Federico, Capponi, & Scambelluri, 2012). This peculiar field structural features and lithological associations would be documented in the exhumed SACs on land (e.g., Anma et al., 2011; Chester & Moore, 2018; Kusky et al., 2013; Muraoka & Ogawa, 2011; Rowe, Moore, Remitti, & Scientists, 2013; Shervais & Choi, 2012; Yamamoto et al., 2005).
In this study, our new field structures data reveal that the Hongliuxia complex in the southern Dunhuang Block is characterized by the stack of tectonic slices, imbricated thrusts, ductile shear zones, asymmetric folds and “block-in-matrix” fabric. Furthermore, the meta-mafic rocks, exposed as slices and tectonic blocks, are mostly originated from the components of the oceanic plate (this study and Wang, Wang, et al., 2017; Wang et al., 2014). They mostly record “clockwise” P–T–t paths but heterogeneous peak metamorphic P–T conditions (Wang, Wang, et al., 2017), and are enclosed within the in situ trench turbidites exhibiting the block-in-matrix fabric (Shi et al., 2018). These facts indicate that they have experienced the tectonic process of subduction-metamorphism-exhumation. So, we suggest the Hongliuxia complex is an exhumed SAC on land, which developed during the oceanic plate subduction process originally.
6.2 Evolution of the Hongliuxia SAC
The SACs formed in the subduction zone generally have a long-lived evolutional history. Its beginning age will not be earlier than the subduction initiation. However, as the subduction initiation is still limited understood (Gurnis et al., 2004; Korenaga, 2013; Stern, 2004; Stern & Gerya, 2018; Wakita, Nakagawa, Sakata, Tanaka, & Oyama, 2018), this age is difficult to constrain. The termination age of the evolution of SACs will not be later than the end of oceanic plate subduction. But, as the continuous process from the oceanic plate subduction to continental collision would not record direct evidence to constrain the ending time of oceanic plate subduction (Li et al., 1999), it is difficult to constrain the termination age as well. Consequently, the timing of a SAC we can obtain in practices, in fact, is a time bucket between its real beginning and termination ages.
The earliest subduction metamorphism event happened at ca. 435 Ma in the Hongliuxia SAC (Wang, Zhang, Chen, et al., 2018), which indicates the subduction initiation predated the Early Silurian. This speculation is supported by the earliest arc-affinity magmatism that took place in ca. 440 Ma in the Sanweishan arc to the north of the Hongliuxia SAC (Shi et al., 2020; Wang, Wu, et al., 2016a; Zhang et al., 2009; Zhao et al., 2019; Zhao, Sun, Diwu, et al., 2017). Some of the trench turbidite matrices in the Hongliuxia SAC were deposited posterior to 389 Ma (Shi et al., 2018), which means that the oceanic plate subduction in the Hongliuxia area had not finished at Middle Devonian. This is also supported by the ca. 390 Ma subduction metamorphism reported in the Hongliuxia SAC (Wang, Wang, et al., 2017). Moreover, the 320 ~ 313 Ma granite veins folded with the amphibolite (Wang, Zhang, Chen, et al., 2018; Zhao, Sun, Diwu, et al., 2017), perhaps representing the syn-tectonic magmatism during the formation and deformation of amphibolite. Taking into account of above geochronological data, we suggest the Hongliuxia SAC was developing during Early Silurian to Late Carboniferous at least.
A possible evolutionary model of the Hongliuxia SAC is proposed in Figure 9. (a) Prior to 440 Ma, the oceanic plate subduction was initiated in the southern Dunhuang region; (b) During the subduction (440 ~ 310 Ma), the basalts, carbonates, and sediments, even the potential continental fragments and oceanic plateau on the sea floor were transported to the trench. The different rocks were subducted and metamorphosed in different depths or were docked in the SAC due to high buoyancy (such as the continental fragments). Some metamorphic rocks would be exhumed to the shallow level and juxtaposed with each other; (c) The oceanic basin could be closed after 310 Ma.
A possible evolutionary model of the Hongliuxia SAC in the southern Dunhuang Orogen [Colour figure can be viewed at wileyonlinelibrary.com]
6.3 Tectonic implication
The Beishan Orogen is traditionally considered as the southernmost part of the CAOB, which consists of several ophiolitic mélanges and arcs (Xiao et al., 2010). The southernmost unit of the Beishan Orogen is the Shibanshan terrain. Some researchers regarded the Shibanshan terrain is a continental arc along the northern margin of the Dunhuang Block formed by the southward subduction of the PAO (Xiao et al., 2010; Zuo, Zhang, He, & Zhang, 1991), which developed at least by the beginning of Late Cambrian to Early Ordovician (Tian & Xiao, 2019). And some other people considered it as a Mesoproterozoic microcontinent amalgamated in the Beishan Orogen (He, Klemd, Yan, & Zhang, 2018; He, Sun, Mao, Zong, & Zhang, 2015; He, Zong, Jiang, Xiang, & Zhang, 2014; Jiang, He, Zong, Zhang, & Zhao, 2013; Yuan et al., 2015). In both modes, the Dunhuang Block was viewed as a fragment of Precambrian continent, and the southern extension of the CAOB is terminated at the Shibanshan terrain.
However, in this study, the identification of the Hongliuxia SAC in the southern Dunhuang Block confirms the oceanic plate subduction event occurred in the Dunhuang region during the Palaeozoic. And this subduction event was possibly responsible for the generation of the long-lived (460 ~ 360 Ma) Palaeozoic Sanweishan accretionary arc in the northern Dunhuang Block (Shi et al., 2020). The spatial–temporal configuration of the Sanweishan arc and Hongliuxia SAC pictures an accretionary arc and forearc accretionary complex system in the Dunhuang region, indicating the Dunhuang Block is a Palaeozoic Orogen developed on the north-dipping subduction zone.
Besides, the rock association of granitic gneiss, clastic rocks, schists, marble, and migmatites in the southern part of the Shibanshan terrain (He et al., 2015; He, Zong, et al., 2014; Jiang et al., 2013; Xiao et al., 2010; Zuo et al., 1991) is very similar to the metamorphic complex in the Sanweishan area (northern Dunhuang Block) in terms of compositions and ages (Meng et al., 2011; Shi et al., 2020; Zhao, Sun, Ao, Zhang, & Zhu, 2017). In the Sanweishan area, the metamorphic complex displays the structure-rock association similar to the accretionary complex (Shi et al., 2020), such as the strongly folded arc-derived detritus metasedimentary rocks, turbidites exhibiting incomplete Bouma sequence and the “block-in-matrix” fabric. If so, the metamorphic complex in the southern Shibanshan and Sanweishan areas may constitute a broad accretionary wedge extending from north to south. The Dunhuang Orogen, then, may be the southernmost margin of the broad CAOB.
7 CONCLUSIONS
Field relationships between the meta-mafic rocks and metasedimentary matrix exhibit a similarity with the subduction–accretion complex (SAC).
Geochemistry of the meta-mafic rocks constrains their origination from the components of the oceanic plate.
Identification of the Palaeozoic SAC in the southern Dunhuang Block suggests its nature of orogen. And the Dunhuang Orogen is possible the southward extension of the CAOB.
ACKNOWLEDGEMENTS
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. This study was supported by the National key research and development plan – Major special project for exploration and mining of deep earth resources (Grant number 2016YFC0600401), the National Natural Science Foundation of China (Grant number 41730215), and the Doctor foundation of Henan Polytechnic University (760307/018). We thank the Wuhan Sample Solution Analytical Technology Co. Ltd., Wuhan, China for the whole-rock geochemical testing and analyses.
Table A1 Whole-rock major and trace element compositions of the metamafic rocks in the Hongliuxia Massif
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REFERENCES
Anma, R., Ogawa, Y., Moore, G. F., Kawamura, K., Sasaki, T., Kawakami, S., … Akaiwa, S. (2011). Structural profile and development of the accretionary complex in the Nankai Trough, southwest Japan: Results of submersible studies. Netherlands: Springer.
Bao, W. H., Long, X. P., Yuan, C., Sun, M., Zhao, G. C., Wang, Y. J., … Zhang, Y. Y. (2017). Paleozoic adakitic rocks in the northern Altyn Tagh, northwest China: Evidence for progressive crustal thickening beneath the Dunhuang Block. Lithos, 272-273, 1–15. https://doi.org/10.1016/j.lithos.2016.12.006.
Barnes, S. J., Naldrett, A. J., & Gorton, M. P. (1985). The origin of the fractionation of platinum-group elements in terrestrial magmas. Chemical Geology, 53(3–4), 303–323. https://doi.org/10.1016/0009-2541(85)90076-2.
Bédard, J. H. (1999). Petrogenesis of boninites from the Betts Cove ophiolite, Newfoundland, Canada: Identification of subducted source components. Journal of Petrology, 40(12), 1853–1889. https://doi.org/10.1093/petroj/40.12.1853.
Bureau of Geology and Mineral Resources of Gansu Province. (1966). Report of 1:200,000 Regional Geological Survey of Biegai (in Chinese with English abstract).
Bureau of Geology and Mineral Resources of Gansu Province. (1989). Regional Geology of Gansu Province. Beijing, Geological Publishing House: (in Chinese). Geological Publishing House.
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. https://doi.org/10.1144/SP318.1.
Chen, X. J., Shu, L. S., & Santosh, M. (2011). Late Paleozoic post-collisional magmatism in the Eastern Tianshan Belt, Northwest China: New insights from geochemistry, geochronology and petrology of bimodal volcanic rocks. Lithos, 127(3–4), 581–598. https://doi.org/10.1016/j.lithos.2011.06.008.
Chester, F. M., & Moore, J. C. (2018). Tectonostratigraphy and processes of frontal accretion with horst-graben subduction at the Japan Trench. Special Paper of the Geological Society of America, 534, 101–113. https://doi.org/10.1130/2018.2534(06).
Cloos, M., & Shreve, R. L. (1988a). Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 1. Background and description. Pure and Applied Geophysics, 128(3–4), 455–500. https://doi.org/10.1007/BF00874548.
Cloos, M., & Shreve, R. L. (1988b). Subduction-channel model of prism accretion, melange formation, sediment subduction, and subduction erosion at convergent plate margins: 2. Implications and discussion. Pure and Applied Geophysics, 128(3–4), 501–545. https://doi.org/10.1007/BF00874549.
Du Frane, S. A., Turner, S., Dosseto, A., & Soest, M. V. (2009). Reappraisal of fluid and sediment contributions to Lesser Antilles magmas. Chemical Geology, 265, 272–278. https://doi.org/10.1016/j.chemgeo.2009.03.030.
Feng, L., Lin, S., Davis, D. W., Staal, C. R. V., Song, C., Li, L., … Ren, S. (2018). Dunhuang Tectonic Belt in northwestern China as a part of the Central Asian Orogenic Belt: Structural and U-Pb geochronological evidence. Tectonophysics, 747-748(13), 281–297. https://doi.org/10.1016/j.tecto.2018.09.008.
Gan, B. P., Li, Z. X., Song, Z. C., & Li, J. Y. (2020). Middle Cambrian granites in the Dunhuang Block, NW China mark the early subduction of the southernmost Paleo-Asian Ocean. Lithos, 372, 105654. https://doi.org/10.1016/j.lithos.2020.105654.
Gerya, T. V., Stöckhert, B., & Perchuk, A. L. (2002). Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation. Tectonics, 21(6), 1–19. https://doi.org/10.1029/2002TC001406.
Guillot, S., Hattori, K. H., de Sigoyer, J., Nägler, T., & Auzende, A.-L. (2001). Evidence of hydration of the mantle wedge and its role in the exhumation of eclogites. Earth and Planetary Science Letters, 193(1–2), 115–127. https://doi.org/10.1016/S0012-821X(01)00490-3.
Guo, Q., Xiao, W., Hou, Q., Windley, B. F., Han, C., Tian, Z., & Song, D. (2014). Construction of Late Devonian Dundunshan arc in the Beishan orogen and its implication for tectonics of southern Central Asian Orogenic Belt. Lithos, 184-187, 361–378. https://doi.org/10.1016/j.lithos.2013.11.007.
Guo, Q., Xiao, W., Windley, B. F., Mao, Q., Han, C., Qu, J., … Yong, Y. (2012). Provenance and tectonic settings of Permian turbidites from the Beishan Mountains, NW China: Implications for the Late Paleozoic accretionary tectonics of the southern Altaids. Journal of Asian Earth Sciences, 49, 54–68. https://doi.org/10.1016/j.jseaes.2011.03.013.
Gurnis, M., Hall, C., & Lavier, L. (2004). Evolving force balance during incipient subduction. Geochemistry, Geophysics, Geosystems, 5(7), Q07001. https://doi.org/10.1029/2003GC000681.
Hashimoto, Y., & Kimura, G. (1999). Underplating process from melange formation to duplexing: Example from the Cretaceous Shimanto Belt, Kii Peninsula, southwest Japan. Tectonics, 18(1), 92–107. https://doi.org/10.1029/1998TC900014.
Hastie, A. R., Kerr, A. C., Pearce, J. A., & Mitchell, S. (2007). Classification of altered volcanic Island arc rocks using immobile trace elements: Development of the Th–Co discrimination diagram. Journal of Petrology, 48(12), 2341–2357. https://doi.org/10.1093/petrology/egm062.
He, Z. Y., Klemd, R., Yan, L. L., & Zhang, Z. M. (2018). The origin and crustal evolution of microcontinents in the Beishan orogen of the southern Central Asian Orogenic Belt. Earth-Science Reviews, 185, 1–14. https://doi.org/10.1016/j.earscirev.2018.05.012.
He, Z. Y., Sun, L. X., Mao, L. J., Zong, K. Q., & Zhang, Z. M. (2015). Zircon U-Pb and Hf isotopic study of gneiss and granodiorite from the southern Beishan orogenic collage: Mesoproterozoic magmatism and crustal growth. Chinese Science Bulletin, 60, 389–399. https://doi.org/10.1360/N972014-00898 (in Chinese).
He, Z. Y., Zhang, Z. M., Zong, K. Q., & Dong, X. (2013). Paleoproterozoic crustal evolution of the Tarim Craton: Constrained by zircon U–Pb and Hf isotopes of meta-igneous rocks from Korla and Dunhuang. Journal of Asian Earth Sciences, 78(12), 54–70. https://doi.org/10.1016/j.jseaes.2013.07.022.
He, Z. Y., Zhang, Z. M., Zong, K. Q., Xiang, H., & Klemd, R. (2014). Metamorphic P–T–t evolution of mafic HP granulites in the northeastern segment of the Tarim Craton (Dunhuang Block): Evidence for early Paleozoic continental subduction. Lithos, 196-197, 1–13. https://doi.org/10.1016/j.lithos.2014.02.020.
He, Z. Y., Zong, K. Q., Jiang, H. Y., Xiang, H., & Zhang, Z. M. (2014). Early Paleozoic tectonic evolution of the southern Beishan orogenic collage: Insights from the granitoids. Acta Petrologica Sinica, 30(8), 2324–2338 (in Chinese with English abstract).
Hermann, J., Müntener, O., & Scambelluri, M. (2000). The importance of serpentinite mylonites for subduction and exhumation of oceanic crust. Tectonophysics, 327(3–4), 225–238. https://doi.org/10.1016/S0040-1951(00)00171-2.
Jiang, H. Y., He, Z. Y., Zong, K. Q., Zhang, Z. M., & Zhao, Z. D. (2013). Zircon U-Pb dating and Hf isotopic studies on the Beishan complex in the southern Beishan orogenic belt. Acta Petrologica Sinica, 29(11), 3949–3967 (in Chinese with English abstract).
Jochum, K., Arndt, N., & Hofmann, A. (1991). Nb-Th-La in komatiites and basalts: Constraints on komatiite petrogenesis and mantle evolution. Earth and Planetary Science Letters, 107(2), 272–289. https://doi.org/10.1016/0012-821X(91)90076-T.
Korenaga, J. (2013). Initiation and evolution of plate tectonics on Earth: Theories and observations. Annual Review of Earth and Planetary Sciences, 41(1), 117–151. https://doi.org/10.1146/annurev-earth-050212-124208.
Kusky, T. M., Windley, B. F., Safonova, I., Wakita, K., Wakabayashi, J., Polat, A., & Santosh, M. (2013). Recognition of ocean plate stratigraphy in accretionary orogens through Earth history: A record of 3.8 billion years of sea floor spreading, subduction, and accretion. Gondwana Research, 24(2), 501–547. https://doi.org/10.1016/j.gr.2013.01.004.
Li, J. L., Sun, S., Hao, J., Chen, H. H., Hou, Q. L., Xiao, W. J., & Wu, J. M. (1999). Time limit of collision event of collision orogens. Acta Petrologica Sinica, 15(2), 315–320 (in Chinese with English abstract).
Li, S., Wang, T., Wilde, S. A., & Tong, Y. (2013). Evolution, source and tectonic significance of Early Mesozoic granitoid magmatism in the Central Asian Orogenic Belt (central segment). Earth-Science Reviews, 126, 206–234. https://doi.org/10.1016/j.earscirev.2013.06.001.
Liu, X., Chen, B., Jahn, B. M., Wu, G., & Liu, Y. (2011). Early Paleozoic (ca. 465 Ma) eclogites from Beishan (NW China) and their bearing on the tectonic evolution of the southern Central Asian Orogenic Belt. Journal of Asian Earth Sciences, 42(4), 715–731. https://doi.org/10.1016/j.jseaes.2010.10.017.
Long, X. P., Yuan, C., Sun, M., Kröner, A., & Zhao, G. C. (2014). New geochemical and combined zircon U–Pb and Lu–Hf isotopic data of orthogneisses in the northern Altyn Tagh, northern margin of the Tibetan plateau: Implication for Archean evolution of the Dunhuang Block and crust formation in NW China. Lithos, 200-201, 418–431. https://doi.org/10.1016/j.lithos.2014.05.008.
Lu, S. N., Li, H. K., Zhang, C. L., & Niu, G. H. (2008). Geological and geochronological evidence for the Precambrian evolution of the Tarim Craton and surrounding continental fragments. Precambrian Research, 160(1–2), 94–107. https://doi.org/10.1016/j.precamres.2007.04.025.
Malatesta, C., Crispini, L., Federico, L., Capponi, G., & Scambelluri, M. (2012). The exhumation of high pressure ophiolites (Voltri Massif, Western Alps): Insights from structural and petrologic data on metagabbro bodies. Tectonophysics, 568-569, 102–123. https://doi.org/10.1016/j.tecto.2011.08.024.
Mao, Q. G., Xiao, W. J., Fang, T. H., Windley, B. F., Sun, M., Ao, S. J., … Huang, X. K. (2014). Geochronology, geochemistry and petrogenesis of Early Permian alkaline magmatism in the Eastern Tianshan: implications for tectonics of the Southern Altaids. Lithos, 190-191(3), 37–51. https://doi.org/10.1016/j.lithos.2013.11.011.
Mei, H. L., Yu, H. F., Lu, S. N., Li, H. M., Lin, Y. X., & Li, Q. (1998). Archean tonalite in the Dunhuang, Gansu Province: Age from the U-Pb single zircon and Nd isotope. Process Precambrian Research, 21(2), 41–45 (in Chinese with English abstract).
Meng, F. C., Zhang, J. X., Xiang, Z. Q., Yu, S. Y., & Li, J. P. (2011). Evolution and formation of the Dunhuang Group in NE Tarim basin, NW China: Evidence from detrital-zircon geochronology and Hf isotope. Acta Petrologica Sinica, 27(1), 59–76. https://doi.org/10.1134/S002449021101007X (in Chinese with English abstract).
Muraoka, S., & Ogawa, Y. (2011). Recognition of trench-fill type accretionary prism: Thrust anticlines, duplexes and chaotic deposits of Pliocene-Pleistocene Chikura Group, Boso Peninsula, Japan. Geological Society of America Special Papers, 480, 233–247. https://doi.org/10.1130/2011.2480(11).
Pearce, J. A., & Peate, D. W. (1995). Tectonic implications of the composition of volcanic arc magmas. Annual Review of Earth and Planetary Sciences, 23(1), 251–285. https://doi.org/10.1146/annurev.ea.23.050195.001343.
Peng, T., Wang, H., Chen, H. X., Meng, J., Lu, J. S., Wang, G. D., & Wu, C. M. (2014). Preliminary report on the metamorphic evolution of the Guanyingou amphibolites, Dunhuang Metamorphic Complex, NW China. Acta Petrologica Sinica, 30(2), 503–511 (in Chinese with English abstract).
Pham, V. T., Wang, H. Y. C., Zhang, Q. W. L., Liu, J. H., Shi, M. Y., Li, Z. M. G., & Wu, C. M. (2018). Metamorphic evolution and geochronology of the Changshanzi area, Dunhuang Orogenic Belt, Northwest China. Acta Petrologica Sinica, 34(9), 2773–2792 (in Chinese with English abstract).
Qu, J. F., Xiao, W. J., Windley, B. F., Han, C. M., Mao, Q. G., Ao, S. J., & Zhang, J. E. (2011). Ordovician eclogites from the Chinese Beishan: implications for the tectonic evolution of the southern Altaids. Journal of Metamorphic Geology, 29(8), 803–820. https://doi.org/10.1111/j.1525-1314.2011.00942.x.
Rowe, C. D., Moore, J. C., Remitti, F., & Scientists, I. E. T. (2013). The thickness of subduction plate boundary faults from the seafloor into the seismogenic zone. Geology, 41(9), 991–994. https://doi.org/10.1130/G34556.1.
Safonova, I., Maruyama, S., Kojima, S., Komiya, T., Krivonogov, S., & Koshida, K. (2016). Recognizing OIB and MORB in accretionary complexes: A new approach based on ocean plate stratigraphy, petrology and geochemistry. Gondwana Research, 33, 92–114. https://doi.org/10.1016/j.gr.2015.06.013.
Şengör, A. M. C., & Natal'in, B. A. (1996). Turkic-type orogeny and its role in the making of the continental crust. Annual Review of Earth and Planetary Sciences, 24(1), 263–337. https://doi.org/10.1146/annurev.earth.24.1.263.
Şengör, A. M. C., Natal'in, B. A., & Burtman, V. S. (1993). Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia. Nature, 364(6435), 299–307. https://doi.org/10.1038/364299a0.
Shervais, J. W., & Choi, S. H. (2012). Subduction initiation along transform faults: The proto-Franciscan subduction zone. Lithosphere, 4(6), 484–496. https://doi.org/10.1130/L153.1.
Shi, M. Y., Hou, Q. L., Wu, C. M., Wang, H. Y. C., & Chen, H. X. (2017). An analysis of the characteristics of the rock-structure association of the Dunhuang orogenic belt and their implications for tectonic setting. Geological Bulletin of China, 36(2–3), 238–250 (in Chinese with English abstract).
Shi, M. Y., Hou, Q. L., Wu, C. M., Wang, H. Y. C., Cheng, N. N., Zhang, Q. W. L., & Pham, V. T. (2018). Sedimentology, geochemistry, geochronology, and tectonic implication of the matrix in Hongliuxia mélange, southern Dunhuang Orogenic Belt. Acta Petrologica Sinica, 34(7), 2099–2118 (in Chinese with English abstract).
Shi, M. Y., Hou, Q. L., Wu, C. M., Yan, Q. R., Wang, H. Y. C., Cheng, N. N., … Li, Z. M. G. (2020). Paleozoic Sanweishan arc in the northern Dunhuang region, NW China: The Dunhuang Block is a Phanerozoic orogen, not a Precambrian Block. Journal of Asian Earth Sciences, 194, 103954. https://doi.org/10.1016/j.jseaes.2019.103954.
Shi, Y. R., Liu, D. Y., Zhang, Q., Jian, P., Zhang, F. Q., & Miao, L. C. (2007). SHRIMP zircon U–Pb dating of the Gangou granitoids, Central Tianshan Mountains, Northwest China and tectonic significances. Chinese Science Bulletin, 52, 1507–1516. https://doi.org/10.1007/s11434-007-0204-2.
Song, D., Xiao, W., Han, C., Li, J., Qu, J., Guo, Q., … Wang, Z. (2013). Progressive accretionary tectonics of the Beishan orogenic collage, southern Altaids: Insights from zircon U-Pb and Hf isotopic data of high-grade complexes. Precambrian Research, 227, 368–388. https://doi.org/10.1016/j.precamres.2012.06.011.
Song, D., Xiao, W., Han, C., & Tian, Z. (2014). Polyphase deformation of a Paleozoic forearc–arc complex in the Beishan orogen, NW China. Tectonophysics, 632, 224–243. https://doi.org/10.1016/j.tecto.2014.06.030.
Song, D., Xiao, W., Windley, B. F., Han, C., & Lei, Y. (2016). Metamorphic complexes in accretionary orogens: Insights from the Beishan collage, southern Central Asian Orogenic Belt. Tectonophysics, 688, 135–147. https://doi.org/10.1016/j.tecto.2016.09.012.
Song, D. F., Xiao, W. J., Windley, B. F., Han, C. M., & Tian, Z. H. (2015). A Paleozoic Japan-type subduction-accretion system in the Beishan orogenic collage, southern Central Asian Orogenic Belt. Lithos, s, 224–225, 195–213. https://doi.org/10.1016/j.lithos.2015.03.005.
Stern, R. J. (2004). Subduction initiation: spontaneous and induced. Earth and Planetary Science Letters, 226(3–4), 275–292. https://doi.org/10.1016/j.epsl.2004.08.007.
Stöckhert, B., & Gerya, T. V. (2005). Pre-collisional high pressure metamorphism and nappe tectonics at active continental margins: A numerical simulation. Terra Nova, 17(2), 102–110. https://doi.org/10.1111/j.1365-3121.2004.00589.x.
Sun, S. S., & McDonough, W. F. (1989). Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society, London, Special Publications, 42(1), 313–345. https://doi.org/10.1144/GSL.SP.1989.042.01.19.
Tian, Z., Xiao, W., Sun, J., Windley, B. F., Glen, R., Han, C., … Ao, S. (2015). Triassic deformation of Permian Early Triassic arc-related sediments in the Beishan (NW China): Last pulse of the accretionary orogenesis in the southernmost Altaids. Tectonophysics, 662, 363–384. https://doi.org/10.1016/j.tecto.2015.01.009.
Tian, Z. H., & Xiao, W. J. (2019). An Andean-type arc transferred into a Japanese-type arc at final closure stage of the Palaeo-Asian Ocean in the southernmost of Altads. Geological Journal, 55, 1–21. https://doi.org/10.1002/gj.3700.
Wakita, K., Nakagawa, T., Sakata, M., Tanaka, N., & Oyama, N. (2018). Phanerozoic accretionary history of Japan and the western Pacific margin. Geological Magazine, 155, 1–17. https://doi.org/10.1017/S0016756818000742.
Wang, H. Y. C., Chen, H. X., Lu, J. S., Wang, G. D., Peng, T., Zhang, H. C. G., … Wu, C. M. (2016). Metamorphic evolution and SIMS U-Pb geochronology of the Qingshigou area, Dunhuang Block, NW China: Tectonic implications of the southernmost Central Asian orogenic belt. Lithosphere, 8(5), 463–479. https://doi.org/10.1130/L528.1.
Wang, H. Y. C., Chen, H. X., Zhang, Q. W. L., Shi, M. Y., Yan, Q. R., Hou, Q. L., … Wu, C. M. (2017). Tectonic mélange records the Silurian–Devonian subduction-metamorphic process of the southern Dunhuang terrane, southernmost Central Asian Orogenic Belt. Geology, 45(5), 427–430. https://doi.org/10.1130/G38834.1.
Wang, H. Y. C., Wang, J., Wang, G. D., Lu, J. S., Chen, H. X., Peng, T., … Hou, Q. L. (2017). Metamorphic evolution and geochronology of the Dunhuang orogenic belt in the Hongliuxia area, northwestern China. Journal of Asian Earth Sciences, 135, 51–69. https://doi.org/10.1016/j.jseaes.2016.12.014.
Wang, H. Y. C., Zhang, Q. W. L., Chen, H. X., Liu, J. H., Zhang, H. C. G., Pham, V. T., … Wu, C. M. (2018). Paleozoic subduction of the southern Dunhuang Orogenic Belt, northwest China: Metamorphism and geochronology of the Shuixiakou area. Geodinamica Acta, 30(1), 63–83. https://doi.org/10.1080/09853111.2018.1427407.
Wang, H. Y. C., Zhang, Q. W. L., Lu, J. S., Chen, H. X., Liu, J. H., Zhang, H. C. G., … Wu, C. M. (2018). Metamorphic evolution and geochronology of the tectonic mélange of the Dongbatu and Mogutai blocks, middle Dunhuang orogenic belt, northwestern China. Geosphere, 14(2), 883–906. https://doi.org/10.1130/GES01514.1.
Wang, N., Wu, C. L., Ma, C. Q., Lei, M., Guo, W. F., Zhang, X., & Chen, H. J. (2016a). Geochemistry, zircon U-Pb geochronology and Hf isotopic characteristics for granites in Sanweishan area, Dunhuang Block. Acta Geologica Sinica, 90(10), 2681–2705 (in Chinese with English abstract).
Wang, N., Wu, C. L., Ma, C. Q., Lei, M., Guo, W. F., Zhang, X., & Chen, H. J. (2016b). Geochemistry, zircon U-Pb geochronology and Hf isotopic characteristics for granites in southern Dunhuang Block. Acta Petrologica Sinica, 32(12), 3753–3780 (in Chinese with English abstract).
Wang, Z. D., Guo, Z. J., Yu, X. J., & Zhang, Y. Y. (2020). Zircon U–Pb dating, geochemical, and Sr–Nd isotopic characteristics of Duobagou trachyandesite from Dunhuang, NW China: Implications for crust–mantle interaction. Geological Journal, 55, 4493–4506. https://doi.org/10.1002/gj.3656.
Wang, Z. M., Han, C. M., Su, B. X., Sakyi, P. A., Malaviarachchi, S. P. K., Ao, S. J., & Wang, L. J. (2013). The metasedimentary rocks from the eastern margin of the Tarim Craton: petrology, geochemistry, zircon U–Pb dating, Hf isotopes and tectonic implications. Lithos, 179, 120–136. https://doi.org/10.1016/j.lithos.2013.08.010.
Wang, Z. M., Han, C. M., Xiao, W. J., Wan, B., Sakyi, P. A., Ao, S. J., … Song, D. F. (2014). Petrology and geochronology of Paleoproterozoic garnet-bearing amphibolites from the Dunhuang Block, Eastern Tarim Craton. Precambrian Research, 255, 163–180. https://doi.org/10.1016/j.precamres.2014.09.025.
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. https://doi.org/10.1016/0009-2541(77)90057-2.
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. https://doi.org/10.1144/0016-76492006-022.
Wood, D. A. (1980). The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary Volcanic Province. Earth and Planetary Science Letters, 50(1), 11–30. https://doi.org/10.1016/0012-821X(80)90116-8.
Xia, L. Q., & Li, X. M. (2019). Basalt geochemistry as a diagnostic indicator of tectonic setting. Gondwana Research, 65, 43–67. https://doi.org/10.1016/j.gr.2018.08.006.
Xiao, W. J., Mao, Q. G., Windley, B. F., Han, C. M., Qu, J. F., Zhang, J. E., … Lin, S. F. (2010). Paleozoic multiple accretionary and collisional processes of the Beishan orogenic collage. American Journal of ENCE, 310(10), 1553–1594. https://doi.org/10.2475/10.2010.12.
Xiao, W. J., Windley, B. F., Hao, J., & Zhai, M. G. (2003). Accretion leading to collision and the Permian Solonker Suture, Inner Mongolia, China: Termination of the central Asian orogenic belt. Tectonics, 22(6). 1069. https://doi.org/10.1029/2002TC001484.
Xiao, W. J., Windley, B. F., Huang, B. C., Han, C. M., Yuan, C., Chen, H. L., … Li, J. L. (2009). End-Permian to mid-Triassic termination of the accretionary processes of the southern Altaids: implications for the geodynamic evolution, Phanerozoic continental growth, and metallogeny of Central Asia. International Journal of Earth Sciences, 98(6), 1189–1217. https://doi.org/10.1007/s00531-008-0407-z.
Xiao, W. J., Windley, B. F., Sun, S., Li, J. L., Huang, B. C., Han, C. M., … Chen, H. L. (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. https://doi.org/10.1146/annurev-earth-060614-105254.
Xu, B., Charvet, J., Chen, Y., Zhao, P., & Shi, G. Z. (2013). Middle Paleozoic convergent orogenic belts in western Inner Mongolia (China): Framework; kinematics; geochronology and implications for tectonic evolution of the Central Asian Orogenic Belt. Gondwana Research, 23(4), 1342–1364. https://doi.org/10.1016/j.gr.2012.05.015.
Yan, Z., Wang, Z. Q., Fu, C. L., Niu, M. L., Ji, W. H., Li, R. S., … Mao, X. C. (2018). Characteristics and thematic geological mapping of Mélanges. Geological Bulletin of China, 37(2–3), 167–191 (in Chinese with English abstract).
Yuan, Y., Zong, K. Q., He, Z. Y., Klemd, R., Liu, Y. S., Hu, Z. C., … Zhang, Z. M. (2015). Geochemical and geochronological evidence for a former early Neoproterozoic microcontinent in the South Beishan Orogenic Belt, southernmost Central Asian Orogenic Belt. Precambrian Research, 266, 409–424. https://doi.org/10.1016/j.precamres.2015.05.034.
Yue, Y. J., Liou, J. G., & Graham, S. A. (2001). Tectonic correlation of Beishan and Inner Mongolia orogens and its implications for the palinspastic reconstruction of north China. Memoirs-Geological Society of America, 194, 101–116.
Zhang, J. X., Gong, J. H., & Yu, S. Y. (2012). c. 1.85 Ga HP granulite-facies metamorphism in the Dunhuang Block of the Tarim Craton, NW China: Evidence from U–Pb zircon dating of mafic granulites. Journal of the Geological Society, 169(5), 511–514. https://doi.org/10.1144/0016-76492011-158.
Zhang, J. X., Yu, S. Y., Gong, J. H., Li, H. K., & Hou, K. J. (2013). The latest Neoarchean–Paleoproterozoic evolution of the Dunhuang Block, eastern Tarim craton, northwestern China: Evidence from zircon U–Pb dating and Hf isotopic analyses. Precambrian Research, 226, 21–42. https://doi.org/10.1016/j.precamres.2012.11.014.
Zhang, Q. W. L., Wang, H. Y. C., Liu, J. H., Shi, M. Y., Chen, Y. C., Li, Z. M., & Wu, C. M. (2020). Diverse subduction and exhumation of tectono-metamorphic slices in the Kalatashitage area, western Paleozoic Dunhuang Orogenic Belt, northwestern China. Lithos, 360-361, 105434. https://doi.org/10.1016/j.lithos.2020.105434.
Zhang, Y., & Guo, Z. (2008). Accurate constraint on formation and emplacement age of Hongliuhe ophiolite, boundary region between Xinjiang and Gansu Provinces and its tectonic implications. Acta Petrologica Sinica, 24, 803–809 (in Chinese with English abstract).
Zhang, Z. C., Guo, Z. J., Zou, G. Q., Feng, Z. S., & Li, H. F. (2009). Geochemical characteristics and SHRIMP U-Pb age of zircons from the Danghe reservoir TTG in Dunhuang, Gansu Province, and its significations. Acta Petrologica Sinica, 25(3), 495–505 (in Chinese with English abstract).
Zhao, Y., Ao, W. H., Yan, J. H., Zhai, M. G., Zhang, H., Wang, Q., & Sun, Y. (2019). Paleozoic tectonothermal event in Mt. Dongbatu, Dunhuang terrane, southernmost Central Asian Orogenic Belt (CAOB): Implications for petrogenesis and geological evolution. Lithos, 326-327, 491–512. https://doi.org/10.1016/j.lithos.2018.12.037.
Zhao, Y., Diwu, C. R., Ao, W. H., Wang, H. L., Zhu, T., & Sun, Y. (2015). Ca. 3.06 Ga granodioritic gneiss in Dunhuang Block. Chinese Science Bulletin, 60(1), 75–87. https://doi.org/10.1360/N972014-00382 (in Chinese).
Zhao, Y., Diwu, C. R., Sun, Y., Zhu, T., & Wang, H. L. (2013). Zircon geochronology and Lu-Hf isotope compositions for Precambrian rocks of the Dunhuang complex in Shuixiakou area, Gansu Province. Acta Petrologica Sinica, 29(5), 1698–1712 (in Chinese with English abstract).
Zhao, Y., Sun, Y., Ao, W., Zhang, H., & Zhu, T. (2017). Depositional age, provenance and tectonic significance of Precambrian metasedimentary rocks from the Dunhuang Complex, NW China: Evidence from field investigation, zircon U–Pb geochronology and whole–rock geochemistry. Precambrian Research, 326(15), 272–294. https://doi.org/10.1016/j.precamres.2017.12.032.
Zhao, Y., Sun, Y., Diwu, C., & Yan, J. (2015). The Archean-Paleoproterozoic crustal evolution in the Dunhuang region, NW China: Constraints from zircon U–Pb geochronology and in situ Hf isotopes. Precambrian Research, 271, 83–97. https://doi.org/10.1016/j.precamres.2015.10.002.
Zhao, Y., Sun, Y., Diwu, C. R., Guo, A. L., Ao, W. H., & Zhu, T. (2016). The Dunhuang Block is a Paleozoic orogenic belt and part of the Central Asian Orogenic Belt (CAOB), NW China. Gondwana Research, 30, 207–223. https://doi.org/10.1016/j.gr.2015.08.012.
Zhao, Y., Sun, Y., Diwu, C. R., Zhu, T., Ao, W. H., Zhang, H., & Yan, J. H. (2017). Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt. Journal of Asian Earth Sciences, 138, 562–587. https://doi.org/10.1016/j.jseaes.2017.02.037.
Zhao, Z. H., Guo, Z. J., & Wang, Y. (2007). Geochronology, geochemical characteristics and tectonic implications of the granitoids from Liuyuan area, Beishan, Gansu Province, Northwest China. Acta Petrologica Sinica, 23(8), 1847–1860 (in Chinese with English abstract).
Zhu, T., Wang, H. L., Xu, X. Y., Chen, J. L., & Li, P. (2014). Discovery of adakitic rocks in south margin of Dunhuang Block and its geological significance. Acta Petrologica Sinica, 30(2), 491–502. https://doi.org/10.1111/jmg.12069 (in Chinese with English abstract).
Zong, K. Q., Liu, Y. S., Zhang, Z. M., He, Z. Y., Hu, Z. C., Guo, J. L., & Chen, K. (2013). The generation and evolution of Archean continental crust in the Dunhuang Block, northeastern Tarim craton, northwestern China. Precambrian Research, 235(34), 251–263. https://doi.org/10.1016/j.precamres.2013.07.002.
Zong, K. Q., Zhang, Z. M., He, Z. Y., Hu, Z. C., Santosh, M., Liu, Y. S., & Wang, W. (2012). Early Palaeozoic high-pressure granulites from the Dunhuang Block, northeastern Tarim Craton: Constraints on continental collision in the southern Central Asian Orogenic Belt. Journal of Metamorphic Geology, 30(8), 753–768. https://doi.org/10.1111/j.1525-1314.2012.00997.x.
Zuo, G. C., Zhang, S. L., He, G. Q., & Zhang, Y. (1991). Plate tectonic characteristics during the early paleozoic in Beishan near the Sino-Mongolian border region, China. Tectonophysics, 188(3–4), 385–392. https://doi.org/10.1016/0040-1951(91)90466-6.
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