Early Paleozoic tectonic evolution of the North Qinling Orogenic Belt in Central China: Insights on continental deep subduction and multiphase exhumation

Earth-Science Reviews 159 (2016) 58–81

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Invited review

Early Paleozoic tectonic evolution of the North Qinling Orogenic Belt in Central China: Insights on continental deep subduction and multiphase exhumation Liang Liu a,⁎, Xiaoying Liao a, Yawei Wang a, Chao Wang a, M. Santosh b,c, Min Yang a, Chengli Zhang a, Danling Chen a a b c

State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China Centre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia School of Earth Sciences and Resources, China University of Geosciences Beijing, No. 29, Xueyuan Road, Haidian District, Beijing 100083, China

a r t i c l e

i n f o

Article history: Received 18 September 2015 Received in revised form 24 May 2016 Accepted 24 May 2016 Available online 26 May 2016 Keywords: North Qinling orogenic belt HP-UHP metamorphism Deep continental subduction and exhumation Ophiolite mélange Early Paleozoic

a b s t r a c t The North Qinling orogenic belt is an important component of Qinling composite orogen in Central China. Highpressure and ultra-high pressure (HP-UHP) rocks occur as lenses or layers surrounded by gneissic rocks in the northern, central, and southern Qinling Complex of the North Qinling belt, considered to have formed through deep continental subduction. The magmatic protoliths of the HP-UHP metamorphic rocks show formation ages (ca. 800 Ma), geochemical characteristics, and Pb-Nd isotopic compositions similar to those of the Neoproterozoic igneous rocks of the South Qinling belt. Continental materials of the South Qinling belt were dragged down to mantle depths by the Shangdan oceanic crust subducted and subjected to HP-UHP metamorphism at ca. 500 Ma. The Erlangping (and Kuanping) backarc basin formed in response to subduction of the Shangdan ocean and might have developed into a limited small ocean basin at ca. 500 Ma. The HP-UHP rocks yielded retrograde metamorphic ages of ca. 470–450 Ma and ca. 420–400 Ma. These ages are identical to the age of magmatic events in the North Qinling HP-UHP belt at ~500 Ma, ~450 Ma and ~420 Ma, related to deep subduction/collision, slab-breakoff and crustal thinning during post-collisional extension. The dominant ca. 500–400 Ma ages of detrital zircons from the Liuling Group of the South Qinling belt match well with those from the three stages of magmatic rocks and HP-UHP rocks in the Qinling Complex. This correlation suggests that the magmatic rocks and HP-UHP metamorphic rocks in the North Qinling belt initially exhumed to the surface, eroded and were then deposited in the Liuling basin in a post-orogenic extensional setting during middle to late Devonian. New evidence suggests that the Qinling Complex is a tectonic complex rather than a uniform stratigraphic unit or a microcontinent as previously believed, and is mainly composed of the exhumed HP-UHP metamorphic rocks, deep subduction- exhumation-related magmatic rocks and the early Neoproterozoic granites together with the host rocks from the over-riding plate at an active continental margin. The early Paleozoic tectonic history of the NQB includes oceanic slab subduction and formation of arc, backarc spreading, continental deep subduction, arc-continent collision, break off, and multi-stage exhumation of the deep subducted slab, as well as extension and thinning and associated erosion and deposition. © 2016 Elsevier B.V. All rights reserved.

Contents 1. 2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Geological background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 2.1. Southern margin of NCB (S-NCB). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

⁎ Corresponding author. E-mail address: [email protected] (L. Liu).

http://dx.doi.org/10.1016/j.earscirev.2016.05.005 0012-8252/© 2016 Elsevier B.V. All rights reserved.

L. Liu et al. / Earth-Science Reviews 159 (2016) 58–81

2.2.

North Qinling belt (NQB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1. Kuanping Complex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2. Erlangping Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3. Qinling Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4. Shangdan suture zone (SDSZ) . . . . . . . . . . . . . . . . . . . . . . . . 2.3. South Qinling belt (SQB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Northern margin of SCB (N-SCB) . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Distribution, age and nature of the HP-UHP metamorphic rocks . . . . . . . . . . . . . . . . 3.1. Distribution and metamorphic P–T condition of HP-UHP rocks . . . . . . . . . . . . . 3.1.1. Guanpo-Shanghuaishu areas . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2. Qingyouhe area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3. Zhaigen area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4. Songshugou area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5. Northern Xixia area . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Ages of the HP-UHP metamorphic rocks . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Protolith ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2. HP-UHP metamorphic ages . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3. Retrograde metamorphic ages . . . . . . . . . . . . . . . . . . . . . . . 3.3. Continental origin of HP-UHP metamorphic rocks . . . . . . . . . . . . . . . . . . . 4. The Shangdan and Erlangping ophiolitic mélanges . . . . . . . . . . . . . . . . . . . . . . 4.1. The Shangdan ophiolitic mélange . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. The Erlangping ophiolitic mélange . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Early Paleozoic magmatic events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Provenance and source of Paleozoic sedimentary rocks . . . . . . . . . . . . . . . . . . . . 6.1. Data on detrital zircons from middle–upper Devonian Liuling group . . . . . . . . . . 6.2. Data on detrital zircons from the Kuanping and Erlangping complexes . . . . . . . . . 7. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1. Tectonic implications of HP-UHP rocks . . . . . . . . . . . . . . . . . . . . . . . . 7.2. Shangdan oceanic lithosphere dragged the continental crust underwent deep subduction . 7.3. Erlangping and Kuanping back-arc basin . . . . . . . . . . . . . . . . . . . . . . . 7.4. Deep subduction of SQB Neoproterozoic continental crust . . . . . . . . . . . . . . . 7.5. The components of the Qinling Complex . . . . . . . . . . . . . . . . . . . . . . . 7.6. Magmatism related to HP-UHP exhumation . . . . . . . . . . . . . . . . . . . . . 7.7. Post-orogenic uplift, erosion and deposition . . . . . . . . . . . . . . . . . . . . . 8. Early Paleozoic tectonic evolution of NQB . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Subduction zones are characterized by accretionary prisms, and a subduction hinge that can migrate (Garfunkel et al., 1986). The kinematics of subduction zones provide important clues for geodynamic settings (Doglioni et al., 2007). For example, low slab dips correlate well with compression in advancing continental upper plates, whereas steep dips are often associated with extension in retreating oceanic upper plates, with accompanying slab retreat or slab rollback generating backarc spreading (e.g., Doglioni et al., 1999, 2007; Waschbusch and Beaumont, 1996; Heuret and Lallemand, 2005; Lallemand et al., 2005; Lucente and Margheriti, 2008). Furthermore, recent studies suggest that successive subduction of oceanic lithosphere drags the continental crust continuously deep beneath the overriding continent plate (Rubatto et al., 1998; Rubatto and Hermann, 2001; Ye et al., 2000; O'Brien, 2001; Rosenbaum and Lister, 2005; Song et al., 2006; Zheng et al., 2015, 2009). Eventually, the subducted oceanic lithosphere and the continental crust that is dragged down will breakoff (Davies and Blanckenburg, 1995; Chemenda et al., 1995). This is followed by tectonic uplift or exhumation during the extensional collapse of orogen (e.g., Song et al., 2014). Thus, mountain building could involve a number of processes including initial subduction of oceanic lithosphere, backarc spreading, subduction–collision of continental crust and slab breakoff. The Qinling orogenic belt lies between the South China block (SCB) and the North China block (NCB). It is located in a key tectonic position in Central China linking the Tongbai and Dabie Mountains in the east and the Qilian and Kunlun Mountains in the west, and is designated as the Central China Orogen (Fig. 1a). This orogenic belt is not only an important target to decipher the tectonic evolution of China and eastern

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Asia, but is also an ideal laboratory to study orogenic processes and the geodynamics of subduction and collision (e.g. Mattauer et al., 1985; Xu et al., 1986; Ren, 1991; Huang and Wu, 1992; Kroner et al., 1993; You et al., 1993; Zhang et al., 1995, 2001; Zhang et al., 1996; Xue et al., 1996; Gao et al., 1996; Zhai et al., 1998; Zhu et al., 1998; Meng and Zhang, 1999; Ratschbacher et al., 2003; Lu et al., 2009; Dong et al., 2011a; Wu and Zheng, 2013; Bader et al., 2013; Zhang et al., 2015; Dong and Santosh, 2016). Most workers regard the Qinling orogenic belt as a composite orogen that experienced multiple stages of tectonic evolution, resulting in the final early Mesozoic collision between the South China block and the North China block along the Central Mianlue suture zone and the Eastern Dabie-Sulu ultra-highpressure orogen (Zhang et al., 1995, 2001; Meng and Zhang, 2000; Dong et al., 2011a; Wu and Zheng, 2013). However, its early Palaeozoic tectonic evolution, including the location and timing of main sutures, subduction polarity, and tectonic history remain controversial (Xue et al., 1996; Meng and Zhang, 2000; Faure et al., 2001; Ratschbacher et al., 2006, 2003; Dong et al., 2011a, b, 2013; H. Wang et al., 2011; Wu and Zheng, 2013; Bader et al., 2013; Zhang et al., 2015). Extensive studies have been carried out on the geology and geochemistry of the Qinling orogenic belt, particularly the increasing new recognition of early Paleozoic high pressure-ultra high-pressure (HP-UHP) rocks in recent decades. Importantly, diamond inclusions were reported from gneiss (Yang et al., 2003), eclogites and amphibolites (Yang et al., 2005; Wang et al., 2014) and coesite inclusions from retrograde eclogite (Gong et al., 2016), confirming UHP metamorphism in the North Qinling belt. In this paper, we present an overview of HP-UHP metamorphic rocks in the North Qinling belt (NQB), and integrate new studies on Palaeozoic ophiolites, magmatic rocks and detrital zircon data of

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Fig. 1. Simplified geological map of China (a). Sketch map showing the tectonic division of the Qinling and the location of the study area (b). Modified after Dong and Santosh (2016).

sedimentary units, to evaluate the formation mechanism of North Qinling belt HP-UHP rocks. We also reconstruct the tectonic history of North Qinling belt during the early Paleozoic, and the processes of subduction/exhumation dynamics. 2. Geological background From north to south, the Qinling orogenic belt can be divided into four units: southern margin of NCB (S-NCB), NQB, South Qinling belt (SQB), and northern margin of SCB (N-SCB) (Zhang et al., 1995, 2001; Meng and Zhang, 2000; Dong et al., 2011a) (Fig. 1b). These units are separated by thrust faults or ductile shear zones. The major units in the Qinling region (parts of the Qinling orogen located in the western side of Nanyang basin) from north to south are described in the following subsections.

and a few ca. 900 Ma and 830 Ma old mafic sills and dykes have also been identified in the S-NCB (Liu et al., 2005; X.L. Wang et al., 2011; Peng et al., 2011). Based on these, Zhai et al. (2014) proposed Meso– Neoproterozoic multistage rifting events developed in the southern margin of NCB. The Sinian (Ediacaran)–Ordovician strata from S-NCB include platform carbonates, shales, and sandstones (Mattauer et al., 1985; Gao et al., 1995; Zhang et al., 1995, 2001). The regional absence of upper Ordovician (or middle-upper Ordovician)–Devonian (even Carboniferous– lower Permian) strata (Gao et al., 1995; Zhou et al., 2002) and the local unconformable contact between the Permian terrestrial sandy gravel stratum and the Kuanping Group (Xu et al., 1986) or Taowan Group (Zhou et al., 2002) suggest tectonic uplift during middle–late early Paleozoic (Zhou et al., 2002; Ratschbacher et al., 2003). Thus, the S-NCB was possibly involved in the Paleozoic collisional orogenesis (Zhang et al., 2001; Zhou et al., 2002; Dong et al., 2011a).

2.1. Southern margin of NCB (S-NCB) 2.2. North Qinling belt (NQB) The S-NCB is separated from NQB by the Luonan-Luanchuan fault in the south (Fig. 1b). It mainly consists of amphibolite-facies Archean– Paleoproterozoic basement complexes (e.g., Taihua and Dengfeng Groups) that are unconformably overlain by the Paleo-Mesoproterozoic volcanics of the Xiong'er Group and the Paleo-Neoproterozoic sedimentary rocks and Sinian (Ediacaran)–Mesozoic sedimentary sequences (Gao et al., 1996; Zhang et al., 2001; Dong et al., 2011a; Zhu et al., 2011). The Xiong'er Group mainly consists of low-grade meta-volcanic rocks, which is dominated by basaltic andesite and andesite with minor dacite and rhyolite, the eruption ages of these rocks are mainly around 1.80–1.75 Ga (Zhao et al., 2004a, 2001; He et al., 2009; Cui et al., 2011; Peng et al., 2011). He et al. (2009) and Ren et al. (2000) recently reported zircon U-Pb ages of ~ 1.45 and 1.65 Ga from the volcanic rock of the Jidanping Formation in the Xiong'er Group. Thus, the Xiong'er rocks represent multistage eruptions spread over Paleo-Mesoproterozoic (Zhao et al., 2009). Furthermore, several 1.75–1.62 Ga alkaline rock/alkaline granite and rapakivi granite suites (Lu et al., 2003; Bao et al., 2009; Zhao et al., 2004b)

The NQB is located between the Luonan-Luanchuan-Fangcheng fault to the north and the Shandan fault to the south (Fig. 1b). From north to south, this belt is composed of the Kuanping, Erlangping, and Qinling Complexes and Shangdan suture zone (Zhang et al., 2001) (Fig. 2). 2.2.1. Kuanping Complex The Kuanping Complex (previously referred to as the Kuanping Group) is located in the northernmost part of NQB and is separated from the Erlangping Complex in the south by the east-west trending Waxuezi-Qiaoduan fault (Fig. 2) (Zhang et al., 2001). The Kuanping Complex, which is mainly composed of terrigenous clastic rocks, meta-volcanics and marbles, underwent greenschist to low grade amphibolite-facies metamorphism (Xiao et al., 1988; SBGMR, 1989; Lin et al., 1990; Zhang et al., 1991; Liu et al., 1993). The Sm-Nd isochron ages ranging from 986 ± 169 Ma to 1153 ± 28 Ma from meta-volcanics reported in previous studies suggest that the Kuanping Complex is of Meso–Neoproterozoic age (Zhang et al., 1991, Zhang et al., 1994).

L. Liu et al. / Earth-Science Reviews 159 (2016) 58–81

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Fig. 2. Simplified geological map of the North Qinling Orogenic Belt. Modified after Dong et al. (2013).

However, Z.Q. Wang et al. (2009) documented early to middle Ordovician fossils (e.g., acritarchs, chitinozoans and scolecodont) in sedimentary rocks of the Kuangping Complex. New detrital zircons from the

sedimentary rocks of Kuanping Complex sampled from the Shangzhou area (Fig. 3a) show the youngest ages of 500–530 Ma (Lu et al., 2009; Diwu et al., 2010; Zhu et al., 2011; Shi et al., 2013; Gao et al., 2015).

Fig. 3. Simplified geological map of the Kuanping complex in Beikuanping-Banqiao area, Shanzhou County (a) (modified after Liu et al., 1993 and Lu et al., 2006). Simplified geological map of the Erlangping complex in Xixia County (b) (modified after Liu et al., 1989; Liu et al., 1993 and Sun, Lu, et al., 1996).

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Thus, the sedimentary rock unit formed during early–middle Ordovician (Lu et al., 2009, 2006; Shi et al., 2013). In the Banqiao and Sichakou sections around the Luonan and Shangxian areas (Fig. 3a), banded marble and meta-volcanic rocks occur together, with minor terrigenous sediments seen as interlays in the volcanic rocks (Lu et al., 2009). The U–Pb SHRIMP analysis on zircons from the meta-volcanic rocks and sandstone samples show identical young ages of ca. 500 Ma together with age peaks of 0.8–1.0 Ga, 1.4–1.6 Ga and 1.8–2.0 Ga (Lu et al., 2009), indicating that the volcanic rocks have captured zircons from a source similar to that of the sedimentary rocks. Thus, the meta-volcanic rocks from Kuanping Complex might have formed simultaneously or slightly later than the sedimentary rocks. Recent studies show that the protoliths of both greenschists and amphibolites from the western part of the Kuanping Complex at the Huxian and Meixian areas are of N-MORB affinity with zircon LA-ICPMS ages of 943 ± 6 Ma and 1445 ± 60 Ma, respectively (Diwu et al., 2010; Dong et al., 2015). These have been interpreted as the relics of an early Neoproterozoic or Mesoproterozoic ophiolite (Diwu et al., 2010; Dong et al., 2014). Therefore, the previously designated “Kuanping Group” should be a complex, which includes material derived from different ages and lithology. Furthermore, the Neoproterozoic or Mesoproterozoic volcanic rocks (referred to here as the “Meihu ophiolite”) should be separated from the Kuanping Complex.

2.2.2. Erlangping Complex The Erlangping Complex (previously referred to Erlangping Group) is separated from the Kuanping Complex to the north by the Waxuezi–Qiaoduan fault and from the Qinling Complex to the south by the Zhuyangguan–Xiaguan fault (Fig. 2). Three tectonic units can be identified within the Erlangping Complex in the Erlangping area (Fig. 3b). From north to south, these units include the northern clastic rock unit, central ophiolite unit (Erlangping ophiolite mélange), and southern meta-clastic rock unit. These units are separated by ductile shear zones (Liu et al., 1989, 1993; Sun, Lu, et al., 1996; Li et al., 1998; Zhang, 2006). The Devonian–Carboniferous palynological fossils in the clastic rocks suggest that the northern clastic rock unit formed during Devonian–Carboniferous (Pei et al., 1995). Therefore, this unit should be excluded from Erlangping Complex. The central ophiolite unit (Erlangping ophiolite mélange, Sun, Lu, et al., 1996) is mainly composed of basalts with minor chert, marble, and sandstone. To the west (Shangluo, Huxian and Meixian areas), this ophiolite unit is characterized by the occurrence of E-MORB and subduction-related basalts, andesites, and rhyolites (Zhang et al., 2001; Dong et al., 2011b). Wang et al. (1995) reported early–middle Ordovician radiolarians and conodonts from the chert in the Erlangping area. Recently, pillow lavas, gabbro and diabase from the ophiolite unit yielded zircon U-Pb ages of 463–474 Ma (Lu et al., 2003; Q.R. Yan et al., 2007; Zhao et al., 2012). The Manziying granite, which intruded into the ophiolite, gave a zircon U-Pb age of 459.5 ± 0.9 Ma (Guo et al., 2010). Therefore, it can be inferred that the volcanic rocks of the Erlangping ophiolite unit formed in early-middle Ordovician. The southern meta-clastic rock unit consists of low-amphibolite facies mica- quartz schist, meta-quartzose arkose, and meta-siltstone with volcanic intervals (Liu et al., 1989, 1993). The protoliths of the meta-clastic rock show features of low maturity of greywacke and lithic arenite, which formed at an active continental margin (Liu et al., 1993; Li et al., 1998). Recently, Yang et al. (2016) reported the youngest detrital zircon age of ca. 500 Ma from the meta-clastic rocks. Moreover, granodiorites intruded into the clastic unit of Erlangping Complex and yield U-Pb zircon ages of 480–475 Ma (Sun, Lu, et al., 1996; Wang et al., 2012) in the Xizhuanghe areas. Therefore, the southern meta-clastic rock unit must have formed during late Cambrian–early Ordovician at ca. 500–480 Ma and is possibly slightly older than the formation age of the volcanic rocks in the central ophiolite unit.

2.2.3. Qinling Complex The Qinling Complex, located between the Shangdan fault to the south and the Zhuyangguan–Xiaguan fault to the north (Fig. 2), is a medium- to high-grade metamorphic complex composed of gneisses, schists, amphibolites, marble, calc-silicate rocks (You et al., 1991). These rocks are mainly exposed at the boundary of Shanxi and Henan Provinces and occur discontinuously to the east and west. Extensive deformation and anatexis are widespread in the Qinling Complex. The HPUHP metamorphic rocks occur as lenses, blocks, or layers within gneisses. The sedimentary protoliths in the Qinling Complex are previously considered to have been deposited during the Paleoproterozoic (SBGMR, 1989; You et al., 1991; Zhang et al., 1994, 1995, 2001). However, rocks older than the early Neoproterozoic have not yet been discovered in this complex, and recent age data suggest that this complex was mainly formed during the late Mesoproterozoic–early Neoproterozoic (Yang et al., 2003; Lu et al., 2009; Yang et al., 2010; Diwu et al., 2014) or the early Neoproterozoic (Shi et al., 2009; Wan et al., 2011). Furthermore, early Neoproterozoic granites (979–911 Ma) (e.g. Dehe, Zhaigen, and Niujiaoshan granitic plutons; Lu et al., 2003; Chen et al., 2004a; Zhang et al., 2004; X.X. Wang et al., 2013) and Paleozoic granites (ca. 500, 450, and 420–400 Ma; T. Wang et al., 2009; X.X. Wang et al., 2013; Zhang et al., 2013) are represented in this complex. 2.2.4. Shangdan suture zone (SDSZ) The Shangdan suture zone (SDSZ), which separates the Qinling Complex and SQB, was produced by the subduction of the Shangdan Ocean (Fig. 2). It is marked by a discontinuously exposed tectonic mélange, which is mainly composed of ophiolitic assemblages, and subduction-related volcanic and sedimentary rocks. These rocks, collectively known as the Danfeng Complex, underwent greenschist to lower amphibolite facies metamorphism. From west to east, ophiolites with mainly ultramafic rocks, gabbros, basalts, diabasic dikes, pillow lavas, and radiolarian cherts are exposed in the Guanzizhen, Tangzang, Yanwan-Yinggezui, Heihe, and Danfeng areas (Meng and Zhang, 2000; Pei et al., 2005, 2006; Dong et al., 2011b; Li et al., 2015). These mafic rocks have geochemical characteristics of N-MORB, E-MORB, boninite and island arc basalt, which mainly formed during 534–500 Ma (Dong et al., 2011b; Li et al., 2015, 2012a). Cambrian–Ordovician radiolarians and conodonts were documented from the recrystallized limestone (Liziyuan Group) in the western part of the Danfeng Complex (Ding et al., 2004) and from the chert in the interlayers of the volcanic rocks (Guojiagou area of Dangfeng County) at the central part of the Danfeng Complex (Cui et al., 1995). 2.3. South Qinling belt (SQB) The SQB is located between the Shangdan zone in the north and the Mianlue zone in the south (Fig. 1b), and consists of crystalline basement and sedimentary cover. The basement comprises several Precambrian complexes metamorphosed under greenschist- to amphibolite-facies conditions. The sedimentary cover contains Sinian (Ediacaran) carbonate rocks, Cambrian–Ordovician limestones, Silurian shales, Devonian– Carboniferous clastic rocks, and a few upper Paleozoic–lower Triassic clastic sedimentary rocks (Zhang et al., 2001). The basement rock units in SQB mainly include the Douling and Xiaomoling Complexes (Zhang, 1988; Zhang et al., 2001) and the Wudangshan and Yaolinghe Groups (Fig. 4). These units are in contact through faults, and their local boundaries are unclear. Furthermore, a few lower Paleozoic alkali volcanic rocks (Huang, 1993), carbonatite-syenite complexes (440 Ma, Xu et al., 2008), and mafic dykes (433–435 Ma, Zhang et al., 2007; Dong et al., 2013) are developed in the SQB. The Douling Complex is composed of biotite gneiss and schist with subordinate hornblende gneiss, marble, and basalt. The protolith age of the Douling Complex was interpreted as early–middle Neoproterozoic (808–737 Ma) (Lu et al., 2009). However, Hu et al. (2013) reported a few felsic gneisses from the Douling Complex

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Fig. 4. Tectonic sketch maps of the South Qinling Belt showing the distribution of main basement rocks in South Qinling Belt. Modified after Dong and Santosh (2016).

formed at ca. 2.5 Ga, indicating that different age populations occur in the Douling Complex. The Wudangshan (or Yunxi) and Yaolinghe Groups are composed of greenschist facies metamorphosed volcanicsedimentary rocks intruded by mafic dykes (Xia et al., 2008). The rhyolite and tuff from the Wudangshan Group yielded zircon U-Pb ages in the range of 833–750 Ma (Ling et al., 2007; Xia et al., 2008). The volcanic rocks from the Yaolinghe Group show zircon U-Pb ages of 810–680 Ma (Li et al., 2003; Ling et al., 2007). The Xiaomoling Complex consists of mafic volcanic rock, gabbro, diorite, and granite, showing zircon U-Pb ages of 743–680 Ma (Niu et al., 2006). These data suggest that these units formed during middle-late Neoproterozoic, which is consistent with the Neoproterozoic volcanic events (845–746 Ma) of the N-SCB related to the breakup of the supercontinent Rodinia (Wang, 2000; Wang et al., 2003, 2001; Li et al., 2008). The sedimentary cover units can be divided into Sinian (Ediacaran)– early Paleozoic and late Paleozoic–middle Triassic sedimentary units (Zhang et al., 2001). Sinian carbonate and the Cambrian–middle Ordovician strata are extensively developed in the SQB and SCB, suggesting that SQB and SCB were connected during this time (Zhang et al., 2001). The early Paleozoic sedimentary unit, bounded by the Shangdan fault (SDF) to the north and the Maanqiao-Mianyuzui shear zone to the south, is named by the sedimentary wedge (Yu and Meng, 1995; Dong

et al., 2013) (Fig. 2). This unit is mainly composed of metamorphosed clastic and carbonate rocks (Yu and Meng, 1995; Dong et al., 2013 and references therein). These rocks mainly include mica-schist, and biotite-quartzite with a few lenticular calcite marbles in the Shangnan– Danfeng area. In the Shaliangzi and Hubaohe sections, the occurrence of conglomerate, sandstone, and carbonate sequences have been recorded from bottom to top (Meng et al., 1994; Dong et al., 2013). The formation of the sedimentary wedge was previously believed to have occurred during Devonian. However, based on the detrital zircon age data from sedimentary rocks and the age of the mafic dykes that intruded into the sediment, Dong et al. (2013) recent studies suggested that the sedimentary wedge formed at 455–435 Ma (late Ordovician–early Silurian). However, controversy surrounds the existence of the tectonic setting of the sedimentary wedge and the models proposed include post-orogenic molasse (Mattauer et al., 1985; Xu et al., 1986) and fore-arc sedimentary prism (Meng, 1994; Meng et al., 1994, 1997; Yu and Meng, 1995; Dong et al., 2013). Based on the characteristics of the depositional system, the Devonian sediments of the SQB can be sub-divided into the northern and southern domains separated by the Fengzhen–Shanyang fault (Fig. 2). The northern domain is composed of upper–middle Devonian sediments, termed as the Liuling Group, composed of greenschist facies metamorphic gray-green sandstone,

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siltstone, slate, and minor conglomerates. The southern domain is dominantly composed of deep water carbonate and siliceous clasts turbidite (Zhang et al., 2001; Zhou et al., 2002). The Liuling Group unconformably overlies Cambrian–Ordovician limestones, indicating that the Devonian sedimentary basin developed on an uplifted continent (Zhang et al., 2001; Zhou et al., 2002), whereas the southern domain conformably overlies continuous lower–middle Devonian limestones.

(Li et al., 1999; Wang, 2000; Wang et al., 2003, 2008, 2001; Yan et al., 2003; Ling et al., 2006; Xia et al., 2008; Zhao and Zhou, 2008, 2009; Zhao et al., 2010).

2.4. Northern margin of SCB (N-SCB)

The Guanpo eclogites (Hu et al., 1994, 1995) and Songshugou HP granulites (Liu and Zhou, 1994; Liu et al., 1996) were initially discovered in the northern and southern Qinling Complex, followed by the finding of micro-diamonds in zircons from the eclogite and their country gneiss from the Guanpo area (Yang et al., 2002). Recently, HP-UHP rocks were also discovered in Shuanghuaishu, Qingyouhe, Songshugou, Zhaigen, and northern Xixia areas in the northern, central, and southern Qinling Complex (Fig. 2).

The N-SCB is close to SQB and is located in the southern part of the Mianlue– Bashanhu–Fangxian–Xiangguang fault (Fig. 1b). The region comprises an Archean basement (represented by the Kongling and Houhe Groups) that is composed of tonalite–trondhjemite–granodiorite (TTG) gneisses, amphibolites, and metapelites (khondalites) metamorphosed under amphibolite to granulite-facies conditions (Gao and Zhang, 1990; Ling et al., 1997). In addition, imprints of Neoproterozoic tectono-magmatic activities are widely distributed in N-SCB (i.e., Hannan, Bikou, and Xixiang Groups and Huangling areas). These Neoproterozoic rocks mainly include gabbros, volcanic tuff, TTG gneisses, and alkali granites with ages in the range of 679–845 Ma

3. Distribution, age and nature of the HP-UHP metamorphic rocks 3.1. Distribution and metamorphic P–T condition of HP-UHP rocks

3.1.1. Guanpo-Shanghuaishu areas Eclogites or garnet amphibolites occur as lenses or layers within gneissic rocks (Fig. 5a) in the Guanpo and Shuanghuaishu areas of the northernmost Qinling Complex. These rocks range in size from less

Fig. 5. Field photographs of HP-UHP rocks from Qinling Complex showing the relationship between HP-UHP rocks and their country rocks. (a) Occurrence of eclogites as lenses within gneissic rocks in the Guanpo and Shuanghuaishu areas of the northernmost Qinling Complex. (b) Decreaes in the modal content of garnet from the core to the rim of individual eclogite lenses/(c–d) Two types of HP/UHP rocks include retrograde eclogites and amphibolites in the Qingyouhe area in the central Qinling Complex. (c) Retrograde eclogites occurring as lenses in the surrounding gneissic rocks. (d) Amphibolites seen parallel to the regional foliation in the gneisses. (e) The mafic HP granulite occurring as lenses in the amphibolite. (f) Felsic HP granulite forming interlayers in the felsic gneiss in the Songshugou area in the Southern Qinling Complex; (g-i) Garnet pyroxenite and retrograde eclogite occurring as lenses surrounded by garnet-bearing biotite-gneisses in the Zhaigen area, in the central part of the Qinling Complex. (h) Garnet amphibolite occurring as lenses in the garnet-bearing gneisses in Northern Xixia area, in the southern part of the Qinling Complex.

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than 10 m to several tens of meters or occur as boudins extending for hundreds of meters. The surrounding rocks are mainly composed of garnet-phengite schist, garnet-bearing phengite-albite schist, and garnet-bearing phengite-schist. In a few outcrops, fresh eclogite is preserved in the center of the lens and shows gradual transformation to garnet amphibolite or amphibolite towards the margins (Fig. 5b). Three metamorphic assemblages have been identified in the Guanpo eclogite: peak eclogite-facies metamorphic mineral assemblage of garnet + omphacite + phengite + quartz, early upper amphibolite facies retrograde metamorphic mineral assemblage of garnet + amphibole + plagioclase + biotite + quartz, and late lower amphibolite facies retrograde assemblage of amphibole + plagioclase + quartz (Hu et al., 1995; Yang et al., 2002; Zhang et al., 2009; Cheng et al., 2012). Micro-diamonds are identified as inclusions in zircons from both eclogites and country rock gneisses in this area, indicating that the rocks had experienced UHP stage at N3.5 GPa (Yang et al., 2003, 2002). The P–T condition of eclogite-facies metamorphism (T = 680– 770 °C, P = 2.25–2.65 GPa) was obtained by conventional Grt-Cpx thermometry and a Grt-Cpx-Phe geobarometer (Zhang et al., 2009). P–T pseudosection calculation shows that the metamorphic P–T conditions for eclogite-facies metamorphism are limited in the range of 2.6– 2.8 GPa and 660–710 °C (Cheng et al., 2012). The discrepancy between the consistent P–T estimates and the petrographic (diamond) evidence may be due to the present garnet–omphacite–phengite–quartz assemblage reflects a re-equilibrated period after UHP events. These mineral assemblages and their thermobarometric estimates define a clockwise P–T path involving near-isothermal decompression and cooling following the metamorphism peak (Fig. 6).

3.1.2. Qingyouhe area Two types of HP/UHP rocks occur in the Qingyouhe area in the central Qinling Complex: (1) retrograde eclogites and (2) amphibolites. The retrograde eclogites occur as lenses in the surrounding gneissic rocks (Fig. 5c) and are parallel to the regional foliation in the gneisses. The modal content of garnet decreases from the core to the rim of individual lenses. Gradual retrogression of the eclogites has generated amphibolites towards the margins of the lenses. The retrograde eclogites are characterized by eclogite-facies assemblage of garnet + omphacite + phengite + quartz, upper amphibolitefacies assemblage of garnet + amphibole + biotite + plagioclase + quartz, and lower amphibolite-facies assemblage of amphibole + plagioclase + epidote + quartz (Cheng et al., 2011; Liu et al., 2013). Cheng et al. (2011) estimated P–T conditions of 630–720 °C, 2.5–3.0 GPa and 1.4 ± 0.3 GP, 696 ± 56 °C representing eclogite-facies and subsequent amphibolite-facies metamorphism, respectively. These mineral assemblage and P–T estimates define a nearly isothermal decompression, clockwise, P–T path (Fig. 6). Amphibolites, occurring as dikes (Fig. 5d), are widely distributed in the Qinyouhe area. They are mainly composed of amphibole and plagioclase with minor quartz, biotite, and opaque minerals, and no relic UHP or HP mineral assemblages observed in the present assemblage. Wang et al. (2014) discovered diamond inclusion in metamorphic zircon from an amphibolite sample. Furthermore, the REE patterns show flat HREE patterns, and slight to insignificant positive or negative Eu anomalies, suggesting that the zircon crystals grew under eclogite-facies condition (Wang et al., 2014; Wang et al., 2016). In addition, Gong et al. (2016) recently discovered coesite inclusion in metamorphic zircon from an amphibolite sample in the west of Qingyouhe area. These studies indicate that the present amphibolite facies metamorphic rocks in the Qinling Complex might have undergone former HP-UHP metamorphism. However, evidence for HP-UHP eclogite-facies mineral assemblage had been mostly obliterated during the later retrograde metamorphic overprint. It is therefore possible that the HP-UHP rocks are volumetrically more abundant in the Qinling Complex than previously recognized.

Fig. 6. Summary of published P–T paths. The P–T conditions of ultrahigh-pressure metamorphism were defined by the presence of diamond in metamorphic zircons. GS, greenschist facies; AM, amphibolite facies; EA, epidote-amphibolite facies; Lw-Ec, lawsonite-eclogite facies; Ec, eclogite facies; Amp-Ec, amphibolite-eclogite facies; Ep-Ec, epidote-eclogite facies; HGR, high-pressure granulite facies; GR, granulite facies. P–T path 1 is cited from Hu et al. (1995) for the summary of eclogite in the northern segment of NQB. P–T path 2 is cited from Zhang et al. (2009) for the Guanpo eclogite. P– T path 3 is cited from Wang et al. (2014) and Cheng et al. (2011) for the diamondbearing UHP amphibolite and retrograde eclogite from the Qinyouhe area. P–T path 4 is cited from Liao et al. (2016) for the retrograde eclogite from the Zhaigen area. Fields of metamorphic facies and subfacies are after Liou et al. (2009).

3.1.3. Zhaigen area In the Zhaigen area, the central part of the Qinling Complex, garnet pyroxenite and retrograde eclogite occur as lenses surrounded by garnet-bearing biotite-gneisses (Fig. 5g and i) (Liu et al., 2013; Liao et al., 2016). Relic omphacite inclusions preserve in the garnet grains from retrograde eclogite, but matrix omphacite has been replaced by clinopyroxene and sodic plagioclase symplectite. Based on the microstructures, relations between mineral phases, and mineral composition, the following five metamorphic stages and mineral assemblages have been recognized: (1) prograde stage, which is recorded by the inner cores of garnets, together with mineral inclusions of clinopyroxene + amphibole + plagioclase ± quartz ± rutile; (2) eclogite-facies stage, recorded by garnet cores + relic omphacite (with a high jadeite content up to 31%) + rutile + quartz; (3) high-pressure granulite-facies stage represented by clinopyroxene + plagioclase symplectite after omphacite in the matrix; (4) medium-pressure granulite-facies stage, characterized by the growth of plagioclase + orthopyroxene coronas around garnet; and (5) retrogressive amphibolite-facies stage, which is represented by amphibole + plagioclase kelyphitic rims around garnet cores. The mineral assemblages and P–T pseudosection calculation define a clockwise P–T path (Fig. 6) involving a slight temperature increase and decompression from eclogite-facies to granulite-facies

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conditions and subsequently both temperature and pressure decrease to amphibolite-facies conditions (Liao et al., 2016). 3.1.4. Songshugou area The Songshugou area is located in the southern Qinling Complex, where previous studies identified both mafic and felsic HP granulites (Liu and Zhou, 1994; Liu et al., 1996). The mafic HP granulite is exposed as lenses in the amphibolite occurring in contact with the Songshugou ultramafic rocks (Fig. 5e), whereas the felsic HP granulite forms interlayers in the felsic gneiss of the Qinling Complex (Fig. 5f). Zhang (1999) reported eclogite-facies metamorphism of the garnet-clinopyroxene-amphibole rocks in this area as inferred from clinopyroxene and plagioclase symplectites and from their reconstructed omphacite compositions (Jd17–35). Recently, Chen et al. (2015) found relic omphacite grains from garnet amphibolite, which represents a retrograde eclogite and the peak pressure higher than previous studies in Songshugou. In retrograde eclogite, the prograde assemblage is indicated by inclusions within garnet cores, represented by the assemblage of hornblende + plagioclase + quartz ± titanite. The representative peak assemblage is garnet + omphacite + rutile + quartz. The post-peak decompressional assemblage occurs as clinopyroxene + amphibole + plagioclase coronas or symplectites surrounding the peak minerals. The later cooling assemblage includes amphibole + plagioclase + epidote + ilmenite + quartz. These assemblages indicate four stages of a clockwise P–T path. Liu et al. (2003, 2013) discovered abundant oriented rutile + quartz + apatite needles in garnet from the Songshugou felsic granulite, suggesting Si supersaturation in the garnet before exsolution and suggesting that this rock experienced UHP metamorphism. Therefore, the existing estimates of the peak pressure of the mafic and felsic HP granulites in the Songshugou area need to be revised taking into consideration eclogite-facies or UHP conditions. 3.1.5. Northern Xixia area The northern Xixia area is located in the southern part of the Qinling Complex. Garnet amphibolite occurs as lenses in the garnet-bearing gneisses in this area (Fig. 5h). The modal content of garnet in the garnet amphibolite lens shows decrease from the core to the margin. This feature is similar to those of other field occurrences mentioned previously, such as those in Qingyouhe and Zhaigen retrograde eclogites. The garnet amphibolite consists of garnet, amphibole, plagioclase, biotite, together with minor ilmenite and zircon. The early mineral assemblage and metamorphic stages are difficult to constrain because of the intense retrograde amphibolite-facies metamorphism. 3.2. Ages of the HP-UHP metamorphic rocks Considerable progress has been made recently in dating HP-UHP metamorphic rocks through the development of modern high precision analytical techniques including LA-ICPMS/SIMS/SHRIMP zircon and titanite U-Pb dating and garnet + whole rock Lu-Hf isochron dating, contributing to an enhanced dataset of the protolith ages, timing of HP-UHP metamorphism and retrograde metamorphism in the Qinling Belt (Table 1). 3.2.1. Protolith ages Chen and Liu (2011) and H. Wang et al. (2011) reported zircon U-Pb ages of 791 ± 6 Ma, 796 ± 13 Ma, and 814 ± 45 Ma from eclogites in the Guanpo and Shuanghuaishu areas through LA-ICPMS and SIMS techniques. Similar U-Pb ages of 798 ± 23 Ma and 799 ± 94 Ma were also determined from magmatic zircon cores obtained from two eclogites sampled from the Gaunpo areas (H. Wang et al., 2013). All the results above were obtained from the magmatic cores of zircon grains in these rocks, which are characterized by oscillatory or weak zoning, high Th/U, pronounced Eu anomalies and steep HREE patterns, interpreted as the formation ages of the protoliths (Table 1). Wang et al. (2016) suggested that the Qingyouhe amphibolite (interpreted as a

retrograde eclogite facies rock) has a protolith age of 774 ± 13 Ma. The ages of the protolith of the retrograde eclogite (also term as garnet amphibolites) in Songshugou area are 787 ± 16 Ma, 729 ± 24 Ma, and 796 ± 16 Ma (Li et al., 2012b; Qian et al., 2013; Chen et al., 2015). Moreover, Liao et al. (2016) obtained the protolith age of 786 ± 10 Ma by LAICPMS method from a retrograde eclogite sample in the Zhaigen area. The age of the protolith of the garnet amphibolites in the northern Xixia area is 843 ± 7 Ma (Liu et al., 2013). Therefore, these data suggest that the HP-UHP rocks from the different areas in NQB may have similar magmatic protolith ages of ca. 800 Ma. 3.2.2. HP-UHP metamorphic ages As shown in Table 1, the zircon U-Pb ages of 511–484 Ma, 493– 490 Ma, 506–484 Ma, 501–495 Ma, and 503–488 Ma were obtained by different methods from the HP-UHP metamorphic rocks from the Guanpo-Shuanghuaishu, Qingyouhe, Songshugou, Zhaigen, and northern Xixia areas, respectively. These zircon domains show no zoning or weak zoning, very low Th/U and 176Lu/177Hf ratios, insignificant Eu anomalies and flat HREE patterns, suggesting that they formed under eclogite-facies metamorphic conditions (Rubatto, 2002; Rubatto and Hermann, 2003). Most of them contain mineral inclusions of garnet, omphacite, rutile and/or phengite (Yang et al., 2003; H. Wang et al., 2011, 2013; Chen et al., 2015; Liao et al., 2016). A few zircon grains contain mineral inclusions of coesite (Gong et al., 2016) and diamond (Yang et al., 2003; Wang et al., 2014). These mineral assemblages suggest that they formed under HP-UHP eclogite-facies metamorphic condition. Therefore, the HP-UHP metamorphism is constrained at ca. 500 Ma. Obviously, the range in the UHP-HP metamorphic ages in Shuanghuaishu, Guanpo, Qingyouhe and Zhaigen areas (511–484 Ma) are nearly identical to that of the Songshugou area (506–484 Ma). This indicates that the HP-UHP rocks in the NQB experienced the same tectonic event. Recently, Wang et al. (2014) presented a comprehensive compilation of the zircon U–Pb ages of the NQB HP-UHP rocks applying statistical methods. The age data histograms of all zircon analyses show a peak at ca. 500 Ma cumulated from metamorphic ages of Songshugou HP-UHP rock, whereas a peak at 490 Ma cumulated from metamorphic ages of other areas. Considering the mean differences of ca. 10 Ma, they proposed that the Songshugou HP-UHP rock formed during a different event compared with the HP-UHP rocks from other areas. However, we consider this interpretation as unrealistic. Furthermore, the statistical method of Wang et al. (2014) did not take into account the error ranges of the different age data and dating methods (e.g., SHRIMP, LA-ICP-MS, SIMS, mineral-whole rock Lu-Hf). 3.2.3. Retrograde metamorphic ages New zircon U-Pb ages suggest that the HP-UHP rocks from Qingyouhe, Songshugou, Zhaigen, and northern Xixia areas record similar two retrograde ages of ca. 470–450 Ma and ca. 420–400 Ma (Table 1). Most of these two distinct retrograde metamorphic age groups were obtained from different domains within individual zircon grains. Compared with the HP-UHP metamorphic zircon domains, the retrograde domains are characterized by moderately steep HREE patterns with higher (Yb/Gd)N ratios and slightly negative Eu anomalies, and contain mineral inclusions of garnet, plagioclase, amphibolite and clinopyroxene (Liao et al., 2016; Gong et al., 2016). These features indicate that new zircon grew during plagioclase crystallization when garnet began to decompose during exhumation (Rubatto, 2002). The earlier retrograde metamorphic ages are similar to the titanite U-Pb age of ca. 470 Ma for eclogite in Guanpo (Bader et al., 2013) and that of garnet pyroxenite in Songshugou (Li et al., 2014). Age for the subsequent retrograde metamorphism is also supported by hornblende Ar40/Ar39 age of 420 ± 30 Ma from a Guanpo eclogite (Ratschbacher et al., 2003), whole rock-garnet-amphibole Sm-Nd and Lu-Hf isochron ages of 400 ± 8 Ma and 416 ± 5 Ma for a Qinyouhe retrograde eclogite (Cheng et al., 2011), and a titanite U-Pb age of 420 Ma for Songshugou garnet amphibolite (Li et al., 2014). Taking into account the above-

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Table 1 Geochronological data of zircons for HP/UHP rocks in different areas from the North Qinling Belt. Location

Sample

Guanpo Guanpo Guanpo Guanpo Guanpo Guanpo Guanpo Guanpo Guanpo Guanpo Shuanghuaishu Shuanghuaishu Shuanghuaishu Shuanghuaishu Shuanghuaishu Shuanghuaishu Qinyouhe Qinyouhe Qinyouhe Qinyouhe Qinyouhe Qinyouhe Zhaigen Zhaigen Shewei Xixia Xixia Xixia Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Songshugou Song shugou Songshugou

Felsic gneiss Felsic gneiss, diamond bearing Gneiss Eclogite Eclogite Eclogite Eclogite Eclogite Eclogite Paragniess Eclogite Eclogite Eclogite Eclogite Eclogite Eclogite Retrograde eclogite Retrograde eclogite Retrograde eclogite Retrograded eclogite Plagioclase amphbolite, diamond bearing Plagioclase amphbolite (retrograded eclogite) Retrograded eclogite Retrograded eclogite Two pyroxene granulite Garnet amphibolite Plagioclase amphibolite Plagioclase amphibolite Retrograde eclogite Retrograde eclogite Garnet pyroxenite Garnet pyroxenite Garnet pyroxenite/amphibolite Basic granulite Basic granulite Felsic granulite Felsic granulite Felsic gneiss Garnet amphibolite Garnet amphibolite Garnet amphibolite Garnet pyroxenite Garnet amphibolite Garnet amphibolite Garnet amphibolite

Protolith age (Ma)

791 ± 6

Peak metamorphic age (Ma)

Retro-metamorphic age (Ma)

511 ± 35 507 ± 37 508 ± 12 493 ± 170 505 ± 12 502 ± 11 501 ± 9

799 ± 94 471 470 796 ± 13 814 ± 45

798 ± 23

774 ± 13 786 ± 10 774 ± 9

489 ± 6 484 ± 5 490 ± 6 494 ± 3 490 ± 4 490 ± 12 490 ± 4

490 ± 6 490 ± 6 493 ± 5 497 ± 2 501 ± 9

843 ± 7

503 ± 5 502 ± 11, 501 ± 3 491 ± 14, 488 ± 13

796 ± 16

500 ± 8 501 ± 10 494 ± 9

473 ± 4 414 ± 1 400 ± 8 453 ± 9 448 ± 4 Ma 461 ± 5, 425 ± 3 471 ± 8 440 ± 2, 426 ± 1 452 ± 5, 400 ± 3 448 ± 7, 422 ± 3 448 ± 7.4, 425 ± 3 420 ± 30

~470 485 ± 3 504 ± 7 506 ± 3 497 ± 8

787 ± 16 729 ± 24 750–840 760–800

448 ± 4421 ± 2 413 ± 20

500 ± 10 484 ± 4 496 ± 9 484 ± 4 490 ± 9 491 ± 2 492 ± 2

mentioned zircon U-Pb, titanite U-Pb, hornblende Ar40/Ar39 and Sm-Nd and Lu-Hf isochron ages, we infer that the HP-UHP rocks from different areas of NQB witnessed the same two stages of retrograde metamorphism at ca. 470–450 Ma and ca. 420–400 Ma during exhumation. 3.3. Continental origin of HP-UHP metamorphic rocks Understanding the nature of protoliths of the HP-UHP rocks (oceanic versus continental crust (Chopin, 2003; Carswell, 1990; Maruyama et al., 1996; Ernst, 2001, 2006; Gilotti et al., 2014; Liu et al., 2015; Xu et al., 2015) is significant to trace the formation mechanism and tectonic history of the NQB. Based on the E-MORB- or OIB-like patterns of trace element distribution of the eclogites in the NQB (Hu et al., 1997; Zhang et al., 2003), Dong et al. (2011b) suggested that the eclogites are of oceanic crust origin and formed by the southward subduction of the Erlangping back-arc basin beneath the Qinling island arc. However, several lines of evidence offer alternative possibilities (e.g., Chen and Liu, 2011; H. Wang et al., 2013). Firstly, the protoliths of the NQB eclogites formed during mid-Neoproterozoic (ca. 800 Ma), whereas the Erlangping basaltic rocks formed during early Paleozoic. Secondly, there are systematic geochemical distinctions between the Erlangping basaltic rocks and the NQB eclogites (details in H. Wang et al., 2013). In order to ascertain the origin of the magmatic protoliths of the HP-

418 ± 5

468 ± 6 463 ± 2

Method and mineral

Reference

SHRIMP U/Pb zrn SHRIMP U/Pb zrn LA-ICPMS U/Pb zrn SHRIMP U/Pb zrn LA-ICPMS U/Pb zrn LA-ICP-MS U/Pb zrn SIMS U/Pb zrn LA-ICPMS U/Pb zrn U-Pb titanite 40 Ar-39Ar Phegite LA-ICPMS U/Pb zrn SIMS U/Pb zrn LA-ICPMS U/Pb zrn Lu-Hf Grt SIMS U/Pb zrn LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn Grt-Amp Lu-Hf Grt-Amp Sm-Nd LA-ICPMS U/Pb zrn SIMS U/Pb zrn LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn SHRIMP U/Pb zrn LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn SHRIMP U/Pb zrn Hornblend Ar-Ar LA-ICPMS U/Pb zrn SHRIMP U/Pb zrn LA-ICPMS U/Pb zrn SIMS U/Pb titanite LA-ICPMS U/Pb zrn SHRIMP LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn SIMS U/Pb Titanite LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn LA-ICPMS U/Pb zrn SIMS U/Pb zrn SIMS U/Pb zrn SIMS U/Pb zrn

Yang et al. (2003) Yang et al. (2003) Liu et al. (2003) Yang et al. (2005) Liu et al. (2010) Chen and Liu (2011) Cheng et al. (2012) H. Wang et al. (2013) Bader et al. (2013) Bader et al. (2013) H. Wang et al. (2011) H. Wang et al. (2011) H. Wang et al. (2011) Cheng et al. (2012) Cheng et al. (2012) H. Wang et al. (2013) Cheng et al. (2011) Cheng et al. (2011) Cheng et al. (2011) Liu et al. (2013) Wang et al. (2014) Wang et al. (2016) Liao et al. (2016) Liao et al. (2016) Zhang et al. (2011) Liu et al. (2013) Wang (2015) Wang (2015) Ratschbacher et al. (2003) Chen et al. (2015) Su et al. (2004) Li et al. (2014) Li et al. (2014) Chen et al. (2004b) Zhang et al. (2011) Zhang et al. (2011) Liu et al. (2013) Li et al. (2014) Liu et al. (2010) Li et al. (2012b) Qian et al. (2013) Li et al. (2014) Yu et al. (2016) Yu et al. (2016) Yu et al. (2016)

UHP rocks, we attempt to integrate their geochemical features, lithologic associations and regional correlations below. The geochemical data on the eclogites (retrograde eclogites) and garnet amphibolites samples from Guanpo, Qinyouhe and Songshugou areas show E-MORB like trace element features in Hf-Th-Ta diagram of Pearce (1982) (Fig. 7a) and high positive whole-rock εNd(t) (2.81–5.53) and zircon εHf(t) (10.5– 11.9) values (Cheng et al., 2012; H. Wang et al., 2013). In the Zr-Zr/Y, Ta/Yb-Th/Yb, and Ti-Zr diagram of Pearce (1982) and Hf–Th–Ta diagram of Wood (1980), these rocks all fall in the overlapping area of EMORB and continental tholeiites (Fig. 7b–d). It was assumed that the protoliths of these eclogites were of oceanic crust origin based on their E-MORB-like trace element features, although such features are also displayed by volcanic rocks developed in the continental rift setting, such as tholeiitic and subalkaline tholeiitic basalts in the Siberian Platform (Fig. 8). Nevertheless, field relationships show that the NQB eclogites (retrograde eclogites) occur as blocks and boudins embedded within continental crustal gneiss (Fig. 5). The protolith age of NQB eclogites and their country rocks (ca. 800 Ma) is ca. 250–300 Ma older than the age of HP-UHP metamorphism (ca. 500 Ma), suggesting that the eclogite protoliths were emplaced in continental crust prior to their deep subduction. Furthermore, the protoliths of the diamondbearing gneiss (country rock of eclogites) in the Guanpo and the UHP felsic gneiss in Songshugou area are typical continental sediments (Liu

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Fig. 7. Tectonic discriminant diagrams for the eclogites and retrograde eclogites from Qinling Complex. (a) Hf-Th-Ta (Wood, 1980), A: N-MORB; B: E-MORB and within-plate tholeiites; C: alkaline within-plate basalts; D1: island-arc tholeiites; D2: calc-alkaline basalts. (b) Zr vs Zr/Y diagram (Pearce, 1982), WPB: Within Plate Basalts; MORB: Mid Ocean Ridge Basalts; IAB: Island Arc Basalts. (c) Ta/Yb-Th/Yb (Pearce, 1982), IAT: Island Arc Tholeiites; ICA: Island Arc Calc-alkaline Basalts; SHO: Island Arc Shoshonites; TH: Tholeiite series; TR: Transitional series; ALK: Alkaline series; (d) Zr-Ti (Pearce, 1982), WPB: Within Plate Basalts; MORB: Mid Ocean Ridge Basalts; IAB: Island Arc Basalts. The data of the Qinyouhe amphibolite is from Wang et al. (2016), the data of Guangpo eclogite are from Chen and Liu (2011) and H. Wang et al. (2013), the data of Songshugou HP garnet pyroxenite is from Liu et al. (1996).

et al., 2003, 1996; Yang et al., 2002). Therefore, we infer that the HPUHP metamorphic rocks in the NQB are products of deep continental subduction. 4. The Shangdan and Erlangping ophiolitic mélanges Two ophiolitic mélanges are exposed along both sides of the Qinling Complex. These two are traditionally designated as the Shangdan ophiolitic mélange in the south and Erlangping ophiolite mélange in the north (Fig. 2). Extensive studies on the geology, geochemistry and geochronology of the two ophiolitic mélanges in last decades provide constraint on the evolution of two ophiolitic mélanges. 4.1. The Shangdan ophiolitic mélange The Shangdan ophiolitic mélange is predominantly composed of ultramafic and mafic rocks, and the mafic rocks can be divided into three geochemical groups: (1) MORB-like type (Pei et al., 2004; Li et al., 2007, 2015, 2012a; Chen et al., 2008; Dong et al., 2011b); (2) boninite-like type (Pei et al., 2006; Li et al., 2015, 2012a); and (3) island-arc type (Zhang et al., 1994; Pei et al., 2005; Li et al., 2007, 2015; Lu et al.,

2009; Dong et al., 2011b). The mafic rocks with N- and E-MORB affinity are characterized by depletion or slight enrichment of LREE without fractionation of high field strength elements (HFSE) and no negative Nb-Ta anomaly, suggesting that they represent remnants of the oceanic lithospheric crust of the Shangdan Ocean, which separated the North China and South China blocks (Dong et al., 2011b; Li et al., 2015). The formation age of the ophiolitic suite has been well constrained to range from 534 ± 9 Ma to 517.8 ± 2.8 Ma, except for few unreliable age data affected by apparent Pb loss such as the 471 ± 1.4 Ma age reported by Yang et al. (2006) from the gabbro of Guanzizhen ophiolite and the 483 ± 13 Ma age reported by Chen et al. (2008) from the basalt of Yanwan-Yinggezui ophiolite. Boninite and boninite-like rocks have been recorded from the Liziyuan meta-volcanic units in Tianshui (Pei et al., 2006) and the Yinggezui ophiolite in the Taibai area (Li et al., 2015, 2012a). These boninite-like rocks from the Yinggezui ophiolite display low TiO2 (0.09 wt. %–0.41 wt. %) and FeO* (4.3 wt.%–10.25 wt.%) contents, low Ti/V ratios and total REEs, and high MgO values (7.48 wt.%–14.1 wt.%), together with high Cr (303–1495 ppm) and Ni (102–383 ppm) values, indicating their primitive magma character (Li et al., 2015). Li et al. (2012a) reported ages of 523.8 ± 1.3 Ma and 474 ± 1.4 Ma from the

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Fig. 8. Primitive mantle-normalized trace element abundance patterns (a) and chondrite normalized rare-earth element diagrams (b) for the eclogites and retrograde eclogites from Qinling Complex (comparing with Siberia Platform Within-Plate magmatism Almukhamedov et al., 2004). Primitive mantle values from (Sun and McDonough, 1989).

boninite-like rocks (their sample numbers 08Y-1042 and 08Y-1031) and proposed two stages of boninite-like magmatism in the Shangdan ophiolitic mélange. We re-examined their data (see Table 4 in Li et al. (2012a) and age computations (Fig. 10d in Li et al. (2012a)) of the sample 08Y-1031 and found some discrepancies as follows. (1) The age of 474 ± 1.4 Ma computed from 28 data points out of 33 analyses exclude three concordant older ages (206Pb/238U ages of 556 ± 4 Ma, 526 ± 4 Ma and 511 ± 4 Ma) and two younger ages. (2) All the 207 Pb/ 235 U ages from the 28 data are older than their 206Pb/ 238 U age by about 10 Ma, and these zircons are dark in CL images (Fig. 10c in Li et al., 2012a), indicating Pb loss. Thus, the age of 474 ± 1.4 Ma is rather unreliable. Our recalculated age (including three old age data) from the dataset of Li et al. (2012a) show an upper intercept age of 519 ± 19 Ma (Fig. 9). This age is identical to the two concordant age data (526 ± 4 Ma and 511 ± 4 Ma), which were discarded by Li et al. (2012a), as well as with the age of 523.8 ± 1.3 Ma from another sample of Li et al. (2012a) within error. Thus, we interpret the age of 519 ± 19 Ma as a reliable estimate. This indicates that there is only one stage of boninitic magmatism at ca.

520 Ma. The boninite and boninite-like rocks form through asthenospheric upwelling and lithospheric extension during subduction initiation in a forearc setting (Crawford et al., 1989; Zhang, 1990; Zhang and Zhou, 2001; Dilek and Furnes, 2009, 2011; Dilek and Thy, 2009; Pearce and Robinson, 2010). Thus, the initial subduction of Shangdan ocean might have commenced at ca. 520 Ma. Island-arc type mafic rocks are widely distributed around Guanzizhen in Tianshui (Pei et al., 2005), Yanwan-Yinggezui in Taibai (Chen et al., 2008; Li et al., 2012a), Xiaowangjian and Heihe in Huxian (Dong et al., 2011b) and Guojiagou areas in Danfeng (Zhang et al., 1994; Lu et al., 2009). They show high MgO contents and follow differentiation trends typically displayed by calc-alkaline magmas. They are characterized by enrichment of LREE and Th, with a strong depletion of Nb and Ta. The formation age of the arc volcanic rocks can be constrained as 507 ± 3.0 to 499.8 ± 4.0 Ma, as obtained from the arc-related gabbros in the Guanzizhen area (Pei et al., 2005) and from the pillow basalt in the Guojiagou area of Danfeng County (Lu et al., 2009). This suggests that the Shangdan oceanic lithosphere continued subduction at ca. 500 Ma.

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Fig. 9. Zircon U–Pb concordia age plots for the Yinggezui gabbro (data-point error ellipses are 1σ), replotted and recalculated from Li et al. (2012a).

4.2. The Erlangping ophiolitic mélange The Erlangping ophiolitic mélange is predominantly composed of mafic rocks, minor ultramafic and/or andesite, and the mafic rocks can be divided into two geochemical groups: (1) MORB-like type (Sun, Lu, et al., 1996) and (2) island-arc type (Xue et al., 1996; Sun, Li, et al., 1996; Lu et al., 2009; Dong et al., 2011b). The mafic rocks with MORB affinity, characterized by low K tholeiite basalt with flat or slightly enriched LREE pattern, without fractionation of HFSE and no negative Nb-Ta anomaly (Sun, Lu, et al., 1996; Lu et al., 2009), may represent remnants of the oceanic lithospheric crust of the Erlangping Ocean, possibly within a back-arc basin setting (Sun, Lu, et al., 1996; Zhang and Zhou, 2001; Dong et al., 2011b). Despite the timing of opening of Erlangping Ocean is difficult to determine, based on the regional geology (see details in Section 2.2.2), we infer that the timing of Erlangping back-arc basin transformation to small ocean accompanied by limited extension occurred at ca. 500 Ma. Island-arc mafic rocks include the metabasalt and pillow basalt from the Caoliangyi and Wantan areas. These rocks exhibit high MgO and LREE contents, showing characteristics of calc-alkaline basalt, and a strong depletion of Nb and Ta (Sun, Li, et al., 1996; Lu et al., 2009; Dong et al., 2011b). They may represent arc magma generation associated with the subduction of Erlangping ocean (Sun, Li, et al., 1996; Lu et al., 2009). These arc volcanic rocks formed at ca. 463– 474 Ma (Lu et al., 2003; Yan et al., 2007a; Zhao et al., 2012), which is consistent with the age of early-middle Ordovician radiolarians within cherts of the Erlangping arc volcanic rocks in Wantan area (Wang et al., 1995). Additionally, the sedimentary unit in the Erlangping area was intruded by the Xizhuanghe granodiorite at 480 ± 7 Ma–475 ± 3 Ma (Sun, Lu, et al., 1996; Wang et al., 2012) similar to the volcanic unit of the Nanzhao area, which were intruded by the Banshanping quartz diorite at 486 ± 6.8 Ma (Lei, 2010). Some workers interpreted them as magmatism associated with the subduction of Erlangping ocean (Xue et al., 1996; Dong et al., 2011b; Wu and Zheng, 2013). If this interpretation is correct, the oldest age (486 Ma) of the magmatic plutons and the 474–463 Ma ages of

arc volcanic rocks indicate that the subduction of the Erlangping ocean occurred during ca. 486 Ma to 463 Ma. The Manziying granite of 459.5 ± 0.9 Ma intrude into the Erlangping ophiolite (Guo et al., 2010), which may mean the closure of the Erlangping ocean occurring earlier than ca. 460 Ma. In summary, the formation age of Shangdan Ocean represented by Shangdan ophiolite (534–518 Ma) is probably older than the formation age of Erlangping Ocean (ca. 500 Ma), and the timing of Shangdan oceanic subduction (ca. 520–500 Ma) is also obviously earlier than that of Erlangping oceanic subduction (ca. 486–463 Ma). 5. Early Paleozoic magmatic events Early Paleozoic granites are widely represented in the Qinling Complex (Fig. 2). Previous studies suggested that these early Paleozoic granites stem from arc magmatism associated with the northwards subduction of Shangdan ocean (e.g., Zhang et al., 2001; Ratschbacher et al., 2003; Dong et al., 2011b). The early Paleozoic granitic magmatism can be divided into three stages of ca. 500 Ma, 452 Ma, and 420–400 Ma from new zircon U-Pb age data (Zhang et al., 2013; X.X. Wang et al., 2013 and references therein). Among these, the magmatism at ca. 450 Ma is the strongest, whereas those at ca. 500 Ma and 420–400 Ma are relatively weak (Fig. 10). The first-stage (ca. 500 Ma) granitoids showing strong gneissic structure possess high contents of SiO2 (71.01%–71.62%), K2O + Na2O (8.14%– 8.43%), Al2 O 3 (15.41%–15.73%) and low CaO (1.56%–1.91%), MgO (0.48%–0.73%; Mg# = 43.19–48.01). Their A/CNK values range from 1.05 to 1.09. They are characterized by high LREE and LILE, moderate negative Eu anomalies, low concentration of HFSE and depletion of Nb, Ta, Sr, Ti and P. The initial 87Sr/86Sr ratios are very high, ranging from 0.72123 to 0.72710. It is likely that the plutons originated mainly from partial melting of crustal rocks (Zhang et al., 2013; X.X. Wang et al., 2013) during the crustal collision between SQB and the S-NCB (Zhang et al., 2013). The second-stage (ca. 450 Ma) granitoids with weak gneissic structure are composed mainly of I-type granodiorites, monzogranites and minor garnet-bearing mica granites. Most of the

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pluton of Fiambala, northwestern Argentina, Dcbari, 1994). Therefore, integrated with the regional geology, especially the formation age of gabbros (460–420 Ma) is obviously later than HP-UHP metamorphic age. Liu et al. (2008, 2012) proposed that the Sifangtai and Lajishan gabbros were produced during slab breakoff or delamination after the closure of the Shandan Ocean. Moreover, integrating SIMS and LAICPMS zircon geochronology and zircon Hf–O isotope studies, Zhang et al. (2015) proposed that the Fushui gabbro represents typical synsubduction mafic magmatism at 490–480 Ma. 6. Provenance and source of Paleozoic sedimentary rocks Paleozoic sedimentary rocks from the Liuling Group, Kuangping Complex and Erlangping Complex provide important information to constrain the tectonic evolution of the Qinling orogenic belt. 6.1. Data on detrital zircons from middle–upper Devonian Liuling group Fig. 10. Histograms of zircon apparent 206Pb/238U ages of early Paleozoic granites from North Qinling belt. Data from Zhang et al. (2013).

monzogranite and granodiorite are enriched in LILEs and depleted in HFSEs with pronounced negative spikes of Nb, Ta, Ti and P. The εNd(t) values vary from − 6.26 to 0.21. The zircon εHf(t) values range from − 11.7 to 8, suggesting a mixed source from mantle and crust materials. These features indicate that they probably were generated in a post-collisional setting (Zhang et al., 2013). The thirdstage (ca. 420 ~ 400 Ma) granitoids appears as small veins or dykes that intruded the Qinling Complex. These granitoids show strong differentiation and high K contents, which is interpreted as the product from high differentiation of crust-derived magma in an extensional setting (Zhang et al., 2013). These three stages of early Paleozoic granitoids can be temporally correlated with HP-UHP metamorphism at ca. 500 Ma and two stages of retrograde metamorphisms at ca. 470–450 Ma and ca. 420–400 Ma, respectively. A few early Paleozoic gabbros or gabbro suites, together with minor ultramafic rocks, intruded into the Danfeng Complex or Qinling Complex discontinuously along the northern part of the SDS zone. The available ages show 460 ± 29 Ma for the Sifangtai gabbro suite (Liu et al., 2012), 422 ± 7 Ma for the Lajimiao gabbro (Liu et al., 2009), and 480– 501 Ma for the Fushui gabbro suite (Li et al., 2006; Su et al., 2004; Zhang et al., 2015). The ages are identical with those of the three stages of granitic magmatism. In previous studies, some workers interpreted these gabbros or gabbro suites to have formed in an arc setting and considered them to represent parts of the Shangdan ophiolite mélange (Zhang and An, 1990; Li et al., 1993; Dong et al., 2011a, b). However, Zhang and Zhou (2001) and Liu et al. (2008, 2012) argued that the Sifangtai and Lajishan gabbros do not possess the characteristic of ophiolite and arc magmatism based on the following lines of evidence. 1) Geochemistry of the general gabbro body used to discriminate the tectonic setting as basalt is not reasonable because gabbro is the cumulate product of crystallization differentiation, rather a primitive magma. 2) In the outcrops, the Sifangtai and Lajimiao gabbros intrude the metabasalt of the Shangdan ophiolite mélange, representing young magma intrusions. Furthermore, the presence of diorite enclaves in the Sifangtai pluton is not consistent with an ophiolite assemblage. 3) Geochemically, gabbros in ophiolite assemblage have low REE content and La concentration (0.6–2 normalized to chondrite) and negative LREE (Kay and Senechal, 1976; Coleman, 1977; Pallister and Knight, 1981; Lapierre et al., 1992). Additionally, the gabbros from the Sifangtai and Lajimiao plutons have high REE content and show enrichment in La (4–45 times when normalized to chondrite). The Sifangtai gabbro shows negative Rb and Th anomaly (see Liu et al., 2008 in Fig. 10) in the MORB-normalized diagram, which is different from typical arc gabbro (e.g. gabbro

Extensive studies have been carried out on the Liuling Group to investigate the tectonic evolution of the Qinling orogenic belt (Mattauer et al., 1985; Xu et al., 1986; Meng, 1994; Meng et al., 1994, 1997; Gao et al., 1995; Yu and Meng, 1995). However, debates continue on the tectonic setting of the Liuling Group with respect to whether it was: 1) a forearc sedimentary basin (Meng et al., 1995; Mei et al., 1999); 2) a remnant ocean basin (Zhang et al., 2001); 3) an active continental margin (Z. Yan et al., 2007); 4) chasmic basin (Zhou et al., 2002); or 5) a marine foreland basin after the closure of Shangdan Ocean (Dong et al., 2013). Detrital zircon grains from the metasedimentary rocks from the middle-upper Devonian Liuling Group yielded five prominent time intervals at ca. 400–500 Ma, ca. 700–850 Ma, ca. 900–950 Ma, ca. 1.2– 2.0 Ga, and ca. 2.2–3.0 Ga, with maximum density around ca. 400– 500 Ma, 750–844 Ma, ca. 930 Ma, ca. 1.75 Ga, and ca. 2.5 Ga (Fig. 11a) (Duan, 2010; Dong et al., 2013; Liao et al., in preparation). CL images for detrital zircons with ages of ca. 400–500 Ma show two types of internal structures, clear oscillatory zoning is typical of grains of igneous (Th/U ratio, 0.20–1.14) and homogeneous core-rim structure is characteristic of metamorphic (Th/U ratio, 0.04–0.14) grains (Liao et al., unpublished data). As mentioned above, there are three stages (ca. 500 Ma, 450 Ma, and 420–400 Ma) of early Paleozoic magmatism and HP-UHP peak (ca. 500 Ma) and retrograde metamorphism (470– 450 Ma and 420–400 Ma) in the NQB. Age spectra of detrital zircon grains in the range from 500 Ma to 400 Ma show three peaks at ca. 497 Ma, ca. 451 Ma and ca. 420 Ma, which is an excellent match to the three age peaks of early Paleozoic magmatic rocks (Fig. 10) and metamorphic ages of HP-UHP rocks in the North Qinling belt. Thus, the provenance of the predominant zircon population with ages from 500 to 400 Ma should be attributed to the NQB. The Neoproterozoic igneous rocks with zircon U–Pb ages of ca. 780–685 Ma (Niu et al., 2006; Ling et al., 2010, 2008) from SQB might have provided the source of the ca. 750–850 Ma age population. The ca. 950 Ma populations might have been sourced from the NQB, which is the only region that have Neoproterozoic granitic rocks with ages of ca. 900–1000 Ma (Chen et al., 2004a; Wang et al., 1998, 2005; X.X. Wang et al., 2013; C.L. Zhang et al., 2004; Liu et al., 2006; Pei et al., 2007). Detrital zircon population ages of ca. 1.5 to 1.7 Ga were possibly sourced from the Xiong'er Group along the S-NCB (He et al., 2009; Cui et al., 2011; Peng et al., 2011), whereas the ca. 2.5–2.7 Ga derived from both the NCB and SCB (Dong et al., 2013). All the above interpretations suggest that the detritus for the Liuling Group was dominated by both NQB and SQB. Notably, detrital zircons with ages of ca. 400–500 Ma from the Liuling Group show magmatic and metamorphic sources from early Paleozoic magmatic rocks and HP-UHP metamorphic rocks in the North Qinling, indicating that these magmatic rocks and HP-UHP metamorphic rocks in NQB initially exhumed to the surface,

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Fig. 11. Zircon U–Pb age spectra for sediments from the Liuling Group (a), the Erlangping (b) and Kuanping (c) Complex. The data of Liuling sediments are from Duan (2010); Dong et al. (2013); Liao et al. (in preparation); The data of Kuanping complex are from Lu et al. (2003); Diwu et al. (2010); Zhu et al. (2011); Shi et al. (2013); the data of Erlangping complex are from Yang et al. (2016).

underwent erosion, and the detritus was deposited in the Liuling basin after ca. 400 Ma. 6.2. Data on detrital zircons from the Kuanping and Erlangping complexes The tectonic setting of the sedimentary units from the Kuanping and Erlangping Complexes remained controversial for a long time. The Kuanping Complex had been interpreted as an early

Neoproterozoic rift basin (Gao et al., 1991; Zhang et al., 2001) or small ocean basin (Zhang et al., 1991; Zhang et al., 1994), late Neoproterozoic – early Paleozoic within-plate extensional basin (Yan et al., 2008; Shi et al., 2013), or early Paleozoic back-arc basin of the Erlangping arc volcanic belt (Lu et al., 2009). The Erlangping Complex was interpreted as an early Paleozoic backarc basin related to the northward subduction of Shangdan Ocean (Li et al., 1998; Dong et al., 2011b).

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Fig. 11b and c shows a summary of the detrital zircon datasets for the Kuangping and Erlangping Complexes (Lu et al., 2009; Diwu et al., 2010; Zhu et al., 2011; Shi et al., 2013; Gao et al., 2015; Yang et al., 2016). The data from Kuangping and Erlangping exhibit an essentially similar distribution in detrital zircon populations, with three dominant age peaks at ca. 0.9–1.0 Ga, ca. 1.6–1.75 Ga and ca. 2.5–2.7 Ga and four subordinate peaks at ca. 550–600 Ma, 750–850 Ma, 1.35–1.48 Ga and 3.0– 3.4 Ga. The youngest age of detrital zircons from the Kuangping and Erlangping Complexes is about ca. 500 Ma. Combined with the earlymiddle Ordovician fossils identified from sedimentary rocks of the Kuanping Complex (Wang et al., 2009) and ca. 480 Ma (Sun, Lu, et al., 1996) granodiorite intruded into the sedimentary units of the Erlangping Complex, the sedimentary units of the Kuangping and Erlangping Complexes are constrained to have been deposited simultaneously during late Cambrian–middle Ordovician. Detrital zircons with the age range of ca. 0.9–1.0 Ga were derived from the Qinling Complex in the south (Lu et al., 2009; Shi et al., 2013, 2009; Diwu et al., 2010; Zhu et al., 2011) because the Qinling Complex is the only region that exposes magmatic rocks with ages of ca. 900– 1000 Ma. Detrital zircon populations of ca. 1.35–1.48 Ga and 1.6– 1.75 Ga fit with the reported ages for Xiong'er volcanic rock (Ren et al., 2000; Zhao et al., 2004a, 2001; He et al., 2009; Cui et al., 2011; Peng et al., 2011). Detrital zircon population ages of ca. 2.5–2.7 Ga and ca. 3.0–3.4 Ga could have been sourced from the Archean rocks of the NCB and SCB. In addition, there are some detrital zircons with ages in the range of 750 and 850 Ma in the Kuangping and Erlangping Complexes, these ages are restricted to the igneous rocks of the SQB and N-SCB. All the above interpretations suggest that the detritus for the Kuanping and Erlangping sedimentary units were dominated by both Qinling Complex and S-NCB. The similarity in depositional age and source of the sedimentary rocks from the associated Erlangping and Kuanping Complex suggest that they formed coevally in a similar or same tectonic setting during late Cambrian – middle Ordovician times.

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Ordovician and early Permian in S-NCB and the local unconformity between late Ordovician and middle Devonian in SQB (Gao et al., 1995; Zhang et al., 2001; Zhou et al., 2002; Dong et al., 2013, 2015).

7.2. Shangdan oceanic lithosphere dragged the continental crust underwent deep subduction As mentioned above, two ophiolitic mélanges are exposed along both sides of the Qinling Complex. However, which oceanic lithosphere represented by the ophiolitic mélanges had dragged the Neoproterozoic continental crust to mantle depth in order to generate the HP-UHP metamorphism remains controversial (Dong et al., 2011b; H. Wang et al., 2011; Bader et al., 2013; Wu and Zheng, 2013; Liu et al., 2013; Zhang et al., 2015). New geochemical, geochronological and regional geological evidences (see details in Section 4) indicate that (1) the formation of the small Erlangping ocean might have taken place at ca. 500 Ma, later than the formation age (534–518 Ma) of the Shangdan ophiolite; (2) the boninite-like rocks and arc volcanic rocks (ca. 520– 500 Ma) formed by subduction of Shangdan ocean slightly earlier than the arc magmatic and volcanic rocks (ca. 486–463 Ma) produced by subduction of Erlangping ocean; (3) obviously, the subduction timing of Shangdan ocean is earlier or coeval with the HP-UHP metamorphic age (ca. 500 Ma) in the NQB, whereas the subduction timing of Erlangping ocean is about 20 Ma later than the HP-UHP metamorphic age of the HP-UHP rocks in the NQB. Consequently, continental materials were dragged down by the Shangdan oceanic lithosphere and underwent deep subduction leading to widespread HP-UHP metamorphism in the NQB. Additionally, the distribution of early Paleozoic granitoids restricted to the NQB and the lack of the Early Paleozoic calcalkaline magmatism in the S-NCB, all suggest that the Shangdan ocean was subducted to the north and the Erlangping ocean was subducted to the south.

7. Discussion 7.3. Erlangping and Kuanping back-arc basin 7.1. Tectonic implications of HP-UHP rocks High-pressure/ultra high-pressure (HP-UHP) metamorphic rocks within orogenic belts record dynamic earth processes of subduction and exhumation of both oceanic and continental lithospheric material. They mark paleo-subduction zones of convergent plate boundaries, and provide important information on the subduction of oceanic lithosphere, arc activity, back-arc spreading, continental subduction/collision, breakoff and tectonic uplift or exhumation during the extensional collapse of orogen (Carswell, 1990; Davies and Blanckenburg, 1995; Chemenda et al., 1995; Maruyama et al., 1996; Rubatto et al., 1998; Rubatto and Hermann, 2001; Ye et al., 2000; O'Brien, 2001; Chopin, 2003; Rosenbaum and Lister, 2005; Ernst, 2001, 2006; Zheng et al., 2015, 2009; Liou et al., 2009; Song et al., 2014, 2006; Gilotti et al., 2014; Liu et al., 2015; Xu et al., 2015). As mentioned in Section 3, the HP-UHP metamorphic rocks in the NQB were produced by deep continental subduction, and show almost identical protolith ages of ca. 800 Ma, HP-UHP metamorphic age of ca.500 Ma, and retrograde metamorphic ages of 470–450 Ma and 420–400 Ma, as well as clockwise P–T paths (Fig. 6). They present crucial constraints on the origins of the early Paleozoic ophiolites, magmatic rocks and sedimentary basins of Qinling Orogen, and on the relationships between the ophiolites, magmatic rocks and sedimentary basins of the Early Paleozoic Qinling orogen. The HP-UHP metamorphic ages suggest that the oceanic basin closed at ca. 500 Ma, and the subducted continent slab was dragged down. The retrograde metamorphic ages imply that the previously subducted continental slab experienced two episodes of exhumation at ca. 470–450 Ma and ca. 420– 400 Ma after deep subduction and HP-UHP metamorphism, which is consistent with the regional unconformity between middle-late

Geological observation, fossils records and the new detrital zircon age data (Fig. 11 b and c) lead to the following suggestions. 1) The Erlangping Complex was mainly composed of sedimentary and volcanic units. The sedimentary unit formed during late Cambrian–middle Ordovician (ca. 500–480 Ma), and is possibly slightly older than the formation age of the volcanic rocks (ca. 500–460 Ma) in the ophiolite unit. 2) The provenance of the sedimentary units from the Erlangping Complex was dominated by both Qinling Complex and S-NCB. 3) The formation age (ca. 500–480 Ma) of the Erlangping sedimentary unit was later than the formation time (ca. 520–500 Ma) of arc rocks in the Shangdan ophiolitic mélange, which was produced by the northward subduction of the Shangdan ocean. Thus, we suggest that the “Erlangping ocean” represented by the Erlangping ophiolite unit (basalt with an MORB geochemical signature) was developed in an initial Erlangping back-arc basin related to the northward subduction of Shangdan Ocean during early Paleozoic. This interpretation is consistent with that of the Li et al. (1998); Zhang et al. (2001) and Dong et al. (2011b), and similar in the generation of backarc spreading in deep subduction zone (e.g., Doglioni et al., 2007). The sedimentary units of the Kuangping Complex have a similar depositional age and source of the sedimentary unit as those of the Erlangping Complex (Fig. 11 b and c), which indicates that they formed simultaneously in a similar or the same back-arc setting during late Cambrian–middle Ordovician. In addition, there are some detrital zircons with ages in the range of 600–840 Ma in the sedimentary rocks of the Kuangping and Erlangping Complexes, these ages are restricted to the igneous rocks of the SQB and N-SCB. This indicates that the Shangdan ocean, which separated the NQB and SQB, might have closed during the deposition of the sedimentary rocks (ca. 500–480 Ma) of the Kuangping and Erlangping Complexes.

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7.4. Deep subduction of SQB Neoproterozoic continental crust Widespread Neoproterozoic magmatism (ca. 680–850 Ma) in the SQB (or N-SCB) could be considered as an exclusive feature for distinguishing the SQB (or N-SCB) from the NCB (e.g. Li et al., 2003; Ling et al., 2008) with only minor Neoproterozoic mafic sills and dykes (ca. 900–830 Ma) (Liu et al., 2005; X.L. Wang et al., 2011). The NQB eclogites have Neoproterozoic protolith ages of ca. 800 Ma and their geochemical features are similar to continental tholeiitic basalts (Figs. 7 and 8). In this regard, the NQB eclogites should have a tectonic affinity to the SQB and N-SCB. The available reports together with our unpublished data also suggest that the NQB HP-UHP rocks possess a Pb isotopic composition similar to that of Neoproterozoic volcanic rocks in SQB and N-SCB, but is distinct from that of the NCB (Fig. 12). In the εNd (t) versus TDMI diagram (Fig. 13), the magmatic protoliths

of the NQB HP-UHP rocks are identical to those of Neoproterozoic basalts (Yaolinghe and Tiechuanshan) in SQB. Therefore, the protoliths of the NQB HP-UHP rocks are inferred to have a tectonic affinity with the SQB. As indicated above, continental subduction will take place only with prior oceanic subduction. We propose, therefore, that HPUHP rocks formed by the deep subduction of SQB dragged down by the Shangdan oceanic lithosphere. 7.5. The components of the Qinling Complex Based on the widespread distribution of the HP-UHP metamorphic rocks in the Qinling Complex, some workers suggested that the entire Qinling Complex (or as a microcontinent) underwent deep continental subduction (e.g. Zhang et al., 2015), whereas others proposed that part of the Qinling Complex experienced HP-UHP metamorphism in early

Fig. 12. 207Pb/204Pb vs. 206Pb/204Pb (a) and 208Pb/204Pb vs. 206Pb/204Pb (b) diagram for the HP-UHP rocks from Qinling Complex. SNCB: southern margin of the North China Block; NQB: north Qinling belt; WN-SCB + WSQ: weat segment of the northern margin of the South China Block and west segment of the South Qinling belt; EN-SCB + ESQ: east segment of the northern margin of the South China Block and east segment of the South Qinling belt (Zhang et al., 2002); The data of Guanpo and Shuanghuaishu eclogite are from H. Wang et al. (2013); the data of Qingyouhe amphibolite and retrograde eclogite, Zhaigen retrograde eclogite, Songshugou UHP felsic gneiss and North Xixia felsic gneiss data are our unpublished data.

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early Neoproterozoic granitic plutons with highly degree of deformation in the NQB (e.g., Dehe and Fangzhuang granites, Fig. 14). These features indicate that only part of the pre-early Paleozoic rocks of the Qinling Complex experienced deep subduction. Thus, we propose that the Qinling Complex is a tectonic complex rather than a uniform stratigraphic unit or a microcontinent as previously believed, and is mainly composed of exhumed HP-UHP metamorphic rocks, produced by the deep subduction of SQB dragged down by the northward subduction of the Shangdan ocean, deep continental slab exhumation- related magmatic rocks and the early Neoproterozoic granites and associated host rocks from the overriding plate at an active continental margin. 7.6. Magmatism related to HP-UHP exhumation

Fig. 13. TDM1 vs. εNd (t) diagram for Neoproterozoic basic rocks from the Qinling Complex. The data are from Ling et al. (2002, 2003), H. Wang et al. (2013) and Wang (2015).

Paleozoic (e.g. Liu et al., 2013). As suggested in Section 6, detrital zircons in the sedimentary rocks of Erlangping and Kuanping Complexes show ages of 0.9–1.0 Ga, which was sourced from the early Neoproterozoic granites of the Qinling Complex. This suggests that the early Neoproterozoic granites in the Qinling Complex were exhumed, eroded and the detritus accumulated in the Erlangping and Kuanping sedimentary basin during ca. 500–480 Ma, and were not subjected to the early Paleozoic deep continental subduction (ca. 500 Ma). This interpretation is also supported by the occurrence of typical igneous structures in some

The retrograde ages and clockwise P–T paths imply that NQB HPUHP metamorphic rocks experienced two episodes of exhumation at ca. 470–450 and ca. 420–400 Ma after deep subduction and HP-UHP metamorphism. As described above, the magmatism of ca. 450 Ma is strongest in the North Qinling belt (Fig. 10), and is coeval with the early stage of retrograde metamorphism. The ca. 450 Ma granitoids are enriched in LILEs and depleted in HFSEs with pronounced negative spikes of Nb, Ta, Ti and P. The εNd(t) values vary from −6.26 to 0.21. The zircon εHf(t) values are from −11.7 to 8. The coeval gabbros display a high Na2O (2.29%–2.81%), FeOT (6.53%–7.60%) and MgO (9.12%– 9.74%) and show a flat REE pattern, relative enrichment of LILEs and evidently positive Pb anomaly and depletion of Nb and Ta. They have low (87Sr/86Sr)i ratios of 0.70353 to 0.70434 and positive εNd(t) values of 3.98 to 4.10. The zircon εHf(t) values are variable from −23.7 to 9.6 (details in Zhang et al., 2013). Therefore, the ca. 450 Ma magmatism was possibly derived from the partial melting of different sources in the crust at different depths through mantle-crust interaction following slab break-off (e.g., Von Raumer et al., 2013). The ca. 420–400 Ma of

Fig. 14. Field photographs of Fangzhuang and Dehei granite gneiss (a-b) from Qinling Complex and their photomicrographs (c–d). Qtz, quartz; Pl, plagioclase; Kfs, potassium feldspar; Bi, biotite.

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Fig. 15. Schematic cartoons showing the tectonic evolution of North Qinling belt. See text for explanation.

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granitoids are coeval to the later stage of retrograde metamorphic age, which show strong differentiation and high K contents, interpreted as the product of partial melting of continental crust in a post-collision extensional tectonic setting (T. Wang et al., 2009; X.X. Wang et al., 2013; Zhang et al., 2013). 7.7. Post-orogenic uplift, erosion and deposition The exhumation of ancient orogens leads to erosion and deposition of detritus into sedimentary basin. The detrital zircon grains from Liuling Group show ages in the range 500 Ma to 400 Ma and carry grains of both magmatic and metamorphic origin with three age peaks at ca. 500 Ma, ca. 450 Ma and ca. 420 Ma (Fig. 11a). These age peaks show a remarkable correlation with the timing of magmatism related to subduction/collision, slab breakoff and postcollision extension, as well as with the HP-UHP metamorphism and two stages of retrograde events in the NQB. A possible interpretation or the magmatic rocks and HP-UHP units in NQB is that these were initially exhumed to the surface, underwent erosion, and were then deposited in the Liuling basin after ca. 400 Ma. In addition, the provenance of detrital zircons from the Liuling sediments show sources from both the NQB and the Neoproterozoic basement rocks in SQB. Thus, combined with regional geology, we propose that the tectonic setting of the Middle to Upper Devonian Liuling Group might represent a post-orogenic extensional basin. 8. Early Paleozoic tectonic evolution of NQB Diwu et al. (2010) and Dong et al. (2014) reported N-MORB features from the relics of the early Neoproterozoic or Mesoproterozoic ophiolite in the western part of the Kuanping Complex in Huxian and Meixian areas with zircon U-Pb ages of 943 ± 6 Ma and 1445 ± 60 Ma, probably representing the formation time of the so-called “Meihu Ocean”. The oceanic lithosphere possibly subducted towards the south beneath SQB or N-SCB at ca. 1000 Ma (Diwu et al., 2010; Dong et al., 2014). During ca. 979–711 Ma, the exhaustion of the “Meihu oceanic crust” led to the collision between SQB or N-SCB and S-NCB, followed by syn-collisional (980–910 Ma), post-collisional (895–815 Ma) and extensional setting (760–710 Ma) and resulting in the development of numerous early Neoproterozoic granitic intrusions in Qinling Orogen, in response to the assembly and breakup of the Rodinia supercontinent (Lu et al., 2003; Chen et al., 2004a; Zhang et al., 2004; T. Wang et al., 2009; X.X. Wang et al., 2013; Dong et al., 2015). After ca. 710 Ma, the extension tectonics was succeeded by rift-related igneous rocks (Niu et al., 2006; Ling et al., 2010, 2008; X.X. Wang et al., 2013), and the Shangdan Ocean opened along the S-NCB after 600 Ma (Dong et al., 2015). Subsequently, the NQB witnessed its early Paleozoic tectonic evolution. We present the following (Fig. 15) new insights into the formation and tectonic evolution of NQB during early Paleozoic. 1) Formation of the Shangdan Ocean during ca. 600–534 Ma (Fig. 15a). 2) During ca. 524–500 Ma, the northward subduction of the Shangdan Ocean beneath the southern margin of the NCB produced arc volcanic rocks (Qinling arc), leading to the formation of the Erlangping and Kuanping back-arc basin, which received the detritus from both the early Neoproterozoic granites of the Qinling arc in the south and the Xiong'er volcanic rock of the S-NCB in the north (Fig. 15b). At the last part of this stage (ca. 500 Ma) following the development of the Erlangping and Kuanping back-arc basins, rift-related volcanic rocks formed (Fig. 15c). 3) During ca. 500–485 Ma (Fig. 15d), the SQB was dragged by the northward subduction of the Shangdan ocean, underwent continental deep subduction, and collision between SQB and Qinling arc resulted in the closure of the Shangdan ocean, and in the production of HP-UHP rocks and syn-subduction magmatism in NQB.

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Meanwhile, the Erlangping back-arc basin might have developed into a small oceanic basin. 4) During ca. 485–460 Ma, the southward subduction of the Erlangping oceanic basin produced the arc magmatic and volcanic rocks (Fig. 15e) and the Erlangping oceanic basin was closed at ca. 460 Ma (Fig. 15f). At ca. 470–450 Ma, following the breakoff of the deep subducted continental plate of the SQB, which was dragged down by the Shangdan oceanic lithosphere, the first stage exhumation of the HP-UHP rocks occurred with upper amphibolite facies retrograde metamorphism at ca. 470–450 Ma in the subduction channel (Fig. 15e-f). After break off of the deep subducted slab of the SQB, asthenospheric upwelling at the base of metasomatized continental lithosphere resulted in extensive magmatic activity (ca. 450 Ma) and further exhumation of the HP-UHP rocks, which were locally overprinted by granulite-facies retrograde metamorphism in the NQB (Fig. 15f). During this period, the former subduction channel might have been destroyed by the rising asthenosphere, and the exhumed HP-UHP rocks were dismembered by the intrusion of magmatic plutons resulting the distribution of the former in the northern, central, and southern parts of the Qinling Complex. 5) After ca. 440 Ma (Fig. 15g), the NQB underwent extension and thinning. With progressive sinking of the slab, further uplift and the deep return flow developed maintaining high temperature at the base of the lithosphere, and allowing the late stage exhumation of HP-UHP metamorphic rocks, followed by minor magmatism at ca. 420– 400 Ma. Also, a few early Paleozoic alkaline volcanic rocks (Huang, 1993), carbonatite-syenite complexes (440 Ma), and mafic dykes (433–435 Ma) developed in the SQB. During middle to upper Devonian, post-orogenic extension resulted in the formation of isolated basins (e.g. Liuling Group of the SQB).

Acknowledgments This work is supported by Major State Basic Research Development Projects (2015CB856103), National Natural Science Foundation of China (Grant Nos. 41430209, 41421002 and 41572049), Innovative Research Team in University (Grant IRT1281) and MOST Special Fund from the State Key Laboratory of Continental Dynamics. We thank Carlo Doglioni (Editor-in-Chief) and Prof. Leonardo Casini and another anonymous reviewer for their constructive comments and suggestions that significantly improved the quality of the manuscript. References Almukhamedov, A.I., Medvedev, A.Y., Zolotukhin, V.V., 2004. Chemical evolution of the Permian–Triassic basalts of the siberian platform in space and time. Petrology 12 (4), 297–311. Bader, T., Franz, L., Ratschbacher, L., de Capitani, C., Webb, A.A.G., Yang, Z., Pfänder, J.A., Hofmann, M., Linnemann, U., 2013. The heart of China revisited: II. Early Paleozoic (ultra) high-pressure and (ultra)high-temperature metamorphic Qinling orogenic collage. Tectonics 32, 922–947. Bao, Z.W., Wang, Q., Zi, F., Tang, G.J., Du, F.J., Bai, G.D., 2009. Geochemistry of the paleoproterozoicLong Wang Zhuang A-type granites on the southern margin of North China craton: petrogenesis and tectonic implications. Geochimica 38, 509–522. Carswell, D.A., 1990. Eclogites and the eclogite facies: definitions and classifications. In: I.D.A.C. (Ed.), Eclogite Facies Rocks. Chapman and Hall, New York, pp. 1–13. Chemenda, A.I., Mattauer, M., Malavieille, J., Bokun, A.N., 1995. A mechanism for syn-collisional rock exhumation and associated normal faulting: results from physical modelling. Earth Planet. Sci. Lett. 132 (1), 225–232. Chen, D.L., Liu, L., 2011. New data on the chronology of eclogite and associated rock from Guanpo Area, North Qinling orogeny and its constraint on nature of North Qinling HP-UHP eclogite terrane. Earth Sci. Front. 18, 158–169. Chen, D.L., Liu, L., Sun, Y., Zhang, A.D., Liu, X.M., Luo, J.H., 2004a. Determination of the Neoproterozoic Shicaotou syn-collisional granite in the Eastern Qinling mountains and its geological implication. Acta Geol. Sin. (Engl. Ed.) 78, 73–82. Chen, D.L., Liu, L., Sun, Y., Zhang, A.D., Liu, X.M., Luo, J.H., 2004b. LA-ICP-MS zircon U-Pb dating for high-pressure basic granulite from North Qinling and its geological significant. Chin. Sci. Bull. 49 (21), 2296–2304 (in Chinese with English abstract). Chen, D.L., Ren, Y.F., Gong, X.G., Liu, L., Gao, S., 2015. Identification and its geological significance of eclogite in Songshugou, the North Qinling. Acta Petrol. Sin. 31 (7), 1841–1854 (in Chinese with English abstract).

78

L. Liu et al. / Earth-Science Reviews 159 (2016) 58–81

Chen, J.L., Xu, X.Y., Wang, Z.Q., Yan, Q.R., Wang, H.L., Zeng, Z.X., Li, P., 2008. Geological features and SHRIMP U- Pb zircon age of the Yanwan- Yinggezui ophiolitic mélange in the Taibai area, West Qinling, China. Geol. Bull. China 27 (4), 500–509. Cheng, H., Zhang, C., Vervoort, J.D., Li, X.H., Li, Q.L., Wu, Y.B., Zheng, S., 2012. Timing of eclogite facies metamorphism in the North Qinling by U–Pb and Lu–Hf geochronology. Lithos 136–139, 46–59. Cheng, H., Zhang, C., Vervoort, J.D., Li, X.H., Li, Q.L., Zheng, S., Cao, D.D., 2011. Geochronology of the transition of eclogite to amphibolite facies metamorphism in the North Qinling orogen of central China. Lithos 125, 969–983. Chopin, C., 2003. Ultrahigh-pressure metamorphism: tracing continental crust into the mantle. Earth Planet. Sci. Lett. 212, 1–14. Coleman, R.G., 1977. Ophiolites, Ancient Oceanic Lithosphere. Spring-Verlag, Berlin. Crawford, A.J., Falloon, T.J., Green, D.H., 1989. Classification, petrogenesis and tectonic setting of boninites. In: Crawford, A.J. (Ed.), Boninites and Related Rocks. Unwin Hyman, London, pp. 1–49. Cui, M.L., Zhang, B.L., Zhang, L.C., 2011. U–Pb dating of baddeleyite and zircon from the Shizhaigou diorite in the southern margin of North China Craton: constrains on the timing and tectonic setting of the Paleoproterozoic Xiong'er group. Gondwana Res. 20, 184–193. Cui, Z.L., Sun, Y., Wang, X.R., 1995. Discovery of radiolarias from the Danfeng ophiolite zone, North Qinling, and their geologic significance. Chin. Sci. Bull. 40, 1686–1688 (in Chinese). Davies, J.H., Blanckenburg, F., 1995. Slab breakoff: a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens. Earth Planet. Sci. Lett. 129, 85–102. Dcbari, S.M., 1994. Petrogenesis of the fiambala gabbroic intrusion, northwestern Argentina, a deep crustal syntectonic pluton in a continental magmatic arc. J. Petrol. 35 (3), 679–713. Dilek, Y., Furnes, H., 2009. Structure and geochemistry of Tethyan ophiolites and their petrogenesis in subduction rollback systems. Lithos 113, 1–20. Dilek, Y., Furnes, H., 2011. Ophiolite genesis and global tectonics: geochemical and tectonic fingerprinting of ancient oceanic lithosphere. Geol. Soc. Am. Bull. 123, 387–411. Dilek, Y., Thy, P., 2009. Island arc tholeiite to boninite melt evolution of the Cretaceous Kizildag (Turkey) ophiolite: model for multi-stage early arc–forearc magmatism in Tethyan subduction factories. Lithos 113, 68–87. Ding, S.P., Pei, X.Z., Li, Y., Hu, B., Zhao, X., Guo, J.F., 2004. Analysis of the disintegration and tectonic setting of the “Liziyuan group” in the Tianshui area, western Qinling. Geol. Bull. China 23 (12), 1209–1214 (in Chinese). Diwu, C.R., Sun, Y., Liu, L., Zhang, C.L., Wang, H.L., 2010. The disintegration of Kuanping group in North Qinling orogenic belts and neoproterozoic N-MORB. Acta Petrol. Sin. 26, 2025–2038 (in Chinese with English abstract). Diwu, C.R., Sun, Y., Zhao, Y., Liu, B.X., Lai, S.C., 2014. Geochronological, geochemical, and Nd-Hf isotopic studies of the Qinling Complex, central China: implications for the evolutionary history of the North Qinling Orogenic Belt. Geosci. Front. 5, 499–513. Doglioni, C., Carminati, E., Cuffaro, M., Scrocca, D., 2007. Subduction kinematics and dynamic constraints. Earth Sci. Rev. 83, 125–175. Doglioni, C., Harabaglia, P., Merlini, S., Mongelli, F., Peccerillo, A., Piromallo, C., 1999. Orogens and slabs vs their direction of subduction. Earth-Sci. Rev. 45, 167–208. Dong, Y.P., Santosh, M., 2016. Tectonic architecture and multiple orogeny of the Qinling Orogenic Belt, Central China. Gondwana Res. 29, 1–40. Dong, Y.P., Zhang, X.N., Liu, X.M., Li, W., Chen, Q., Zhang, G.W., Zhang, H.F., Yang, Z., Sun, S.S., Zhang, F.F., 2015. Propagation tectonics and multiple accretionary processes of the Qinling Orogen. J. Asian Earth Sci. 104, 84–98. Dong, Y.P., Yang, Z., Liu, X.M., Zhang, X.N., He, D.F., Li, W., Zhang, F.F., Sun, S.S., Zhang, H.F., Zhang, G.W., 2014. Neoproterozoic amalgamation of the Northern Qinling Terrain to the North China Craton: constraints from geochronology and geochemistry of the Kuanping ophiolite. Precambrian Res. 255, 77–95. Dong, Y.P., Liu, X.M., Neubauer, F., Zhang, G.W., Tao, N., Zhang, Y.G., Zhang, X.N., 2013. Timing of Paleozoic amalgamation between the North China and South China blocks: evidence from detrital zircon U–Pb ages. Tectonophysics 586, 173–191. Dong, Y.P., Zhang, G.W., Neubauer, F., Liu, X.M., Genser, J., Hauzenberger, C., 2011a. Tectonic evolution of the Qinling orogen, China: review and synthesis. J. Asian Earth Sci. 41, 213–237. Dong, Y.P., Zhang, G.W., Hauzenberger, C., Neubauer, F., Yang, Z., Liu, X., 2011b. Palaeozoic tectonics and evolutionary history of the Qinling orogen: evidence from geochemistry and geochronology of ophiolite and related volcanic rocks. Lithos 122, 39–56. Duan, L., 2010. Detrital Zircon Provenance of the Silurian and Devonian in South Qingling, and the Northwestern Margin of Yangtze Terrane and Its Tectonic Implications (Thesis of master's degree) Northwest University. Ernst, W.G., 2006. Preservation/exhumation of ultrahigh–pressure subduction complexes. Lithos 92 (3–4), 321–335. Ernst, W.G., 2001. Subduction, ultrahigh–pressure metamorphism, and regurgitation of buoyant crustal sliceunits–implications for arcs and continental growth. Phys. Earth Planet. Inter. 127, 253–275. Faure, M., Lin, W., Le Breton, N., 2001. Where is the North China–South China block boundary in eastern China. Geology 29, 119–122. Gao, S., Chen, D.L., Gong, X.K., Ren, Y.F., Li, H.P., 2015. Zircon U-Pb dating of clastic rocks and granites of Kuanping Group in Dongcha areas of Tiansui, an its geological implications. Earth Sci. Front. 22 (4), 255–264. Gao, S., Zhang, B.R., Wang, D.P., Ouyang, J.P., Xie, Q.L., 1996. Geochemical evidence for the Proterozoic tectonic evolution of the Qinling Orogenic Belt and its adjacent margins of the North China and Yangtze cratons. Precambrian Res. 80, 23–48. Gao, S., Zhang, B.R., Gu, X.M., Xie, X.L., Gao, C.L., 1995. Silurian–Devonian provenance changes of South Qinling basins: implications for accretion of the Yangtze (South China) to the North China Cratons. Tectonophysics 250, 183–197.

Gao, S., Zhang, B.R., Xie, Q.L., et al., 1991. Proterozoic intracontinental rifting of the Qingling Orogenic Belt: evidence from the geochemistry of sedimentary rocks. Chin. Sci. Bull. 36 (11), 920–923. Gao, S., Zhang, B.R., 1990. The discovery of Archean TTG gneisses in the Northern Yangtze platform and their implications. Earth Sci. 15, 675–679 (in Chinese with English abstract). Garfunkel, Z., Anderson, C.A., Schubert, G., 1986. Mantle circulation and the lateral migration of subducted slabs. J. Geophys. Res. 91, 7205–7223. Gilotti, J.A., McClelland, W.C., Wooden, J.L., 2014. Zircon captures exhumation of an ultrahigh-pressure terrane, North-East Greenland Caledonides. Gondwana Res. 25, 235–256. Gong, X.K., Chen, D.L., Ren, Y.F., Liu, L., Gao, S., Yang, S.J., 2016. Identification of coesitebearing amphibolite in the North Qinling and its geological significance (in Chinese) Chin. Sci. Bull. 61, 1–14. http://dx.doi.org/10.1360/N972015-01277. Guo, C.L., Chen, D.L., Fan, W., Wang, A.G., 2010. Geochemical and zircon U-Pb chronological studies of the Manziying granite in Erlangping area, western Henan Province. Acta Petrol. Mineral. 29, 15–22 (in Chinese with English abstract). He, Y.H., Zhao, G.C., Sun, M., Xia, X.P., 2009. SHRIMP and LA-ICP-MS zircon geochronology of the Xiong'er volcanic rocks: implications for the Paleo-Mesoproterozoic evolution of the southern margin of the North China Craton. Precambrian Res. 168, 213–222. Heuret, A., Lallemand, S., 2005. Plate motions, slab dynamics and back-arc deformation. Phys. Earth Planet. Inter. 149, 31–51. Hu, J., Liu, X.C., Chen, L.Y., Qu, W., Li, H.K., Gen, J.Z., 2013. A ~2.5 Ga magmatic event at the northern margin of the Yangtze craton: evidence from U-Pb dating and Hf isotope analysis of zircons from the Douling Complex in the South Qinling orogen. Chin. Sci. Bull. 58, 3579–3588. Hu, N.G., Xu, B.Q., Zhao, D.L., 1997. Geochemical characteristics of eclogites and the related rocks from the northern Qinling orogenic belt. J. Xi'an Coll. Geol. 19, 7–13 (in Chinese with English abstract). Hu, N.G., Zhao, D.L., Xu, B.Q., Wang, T., 1995. Petrography and metamorphism study on high-ultrahigh pressure eclogite from Guanpo area, North Qinling Mountain. Mineral. Petrol. 15 (4), 1–9 (in Chinese with English abstract). Hu, N.G., Zhao, D.L., Xu, B.Q., Wang, T., 1994. Discovery and significance of coesite eclogite in Northern Qinling Mountain. Chin. Sci. Bull. 24, 2013 (in Chinese with English abstract). Huang, W., Wu, Z.W., 1992. Evolution of the Qinling orogenic belt. Tectonics 11, 371–380. Huang, Y.H., 1993. Mineralogical characteristics of phlogopite-amphibole-pyroxenite mantle xenoliths included in the alkali mafic-ultramafic subvolcanic complex from Langao county, China. Acta Petrol. Sin. 9 (4), 367–378. Kay, R.W., Senechal, R.G., 1976. The rare earth geochemistry of the Troodos ophiolite complex. J. Geophys. Res. 81, 964–970. Kroner, A., Zhang, G.W., Zhuo, D.W., Sun, Y., 1993. Granulites in the Tongbai area, Qinling belt, China: geochemistry, petrology, single zircon geochronology and implications for tectonic evolution of eastern Asia. Tectonics 12, 245–255. Lallemand, S., Heuret, A., Boutelier, D., 2005. On the relationships between slab dip, backarc stress, upper plate absolute motion and crustal nature in subduction zones. Geochem. Geophys. Geosyst. 6, Q09006. http://dx.doi.org/10.1029/2005GC000917. Lapierre, H., Ortiz, L.E., Abouchami, W., 1992. A crustal section of an intra-oceanic island arc: the Late Jurassic–Early Cretaceous Guanajuato magmatic sequence, Central Mexico. Earth Planet. Sci. Lett. 108, 61–77. Lei, M., 2010. Petrogenesis of Granites and their Relation to Tectonic Evolution of Orogen in the East Part of Qinling Orogenic Belt (Dissertation for Doctoral Degree) Chinese Academy of Geological Sciences. Li, H.K., Lu, S.N., Chen, Z.H., Xiang, Z.Q., Zhou, H.Y., Hao, G.J., 2003. Zircon U-Pb geochronology of rift-type volcanic rocks of the Yaolinghe Group in the South Qinling orogen. Geol. Bull. China 22 (10), 775–781 (in Chinese with English abstract). Li, H.M., Chen, Z.H., Xiang, Z.Q., Li, H.K., Lu, S.N., Zhou, H.Y., Song, B., 2006. Difference in UPb isotope ages between baddeleyite and zircon in metagabbro from the Fushui complex in the Shangnan-Xixia area, Qinling orogen. Geol. Bull. China 25, 653–659. Li, S.G., Chen, Y.Z., Zhang, Z.Q., Ye, X.J., Zhang, G.W., Guo, A.L., 1993. Trace elements and Sr, Nd isotopic geochemistry of the Lajimiao norite-gabbro from the north Qinling belt. Acta Geol. Sin. 67, 310–322. Li, W.Y., Li, S.G., Pei, X.Z., Zhang, G.W., 2007. Geochemistry and zircon SHRIMP U-Pb ages of the Guanzizhen Ophiolite complex, the Western Qinling Orogen, China. Acta Petrol. Sin. 23, 2836–2844 (In Chinese with English abstract). Li, X.H., Wang, X.C., Li, W.X., Li, Z.X., 2008. Petrogenesis and tectonic significance of Neoproterozoic basaltic rocks in South China: from orogenesis to intracontinental rifting. Geochimica 37, 382–398 (in Chinese with English abstract). Li, Y., Yang, J.S., Dilek, Y., Zhang, J., Pei, X.Z., Chen, S.Y., Xu, X.Z., Li, J.Y., 2015. Crustal architecture of the Shangdan suture zone in the early Paleozoic Qinling orogenic belt, China: record of subduction initiation and backarc basin development. Gondwana Res. 27, 733–744. Li, Y., Yang, J.S., Pei, X.Z., Zhang, J., Chen, J.L., Chen, S.Y., Xu, X.Z., 2012a. A model for multi-stage of the Early Palaeozoic Danfeng ophiolite in Qinling orogen belt: from arc to inter-arc basin. Acta Petrol. Sin. 28 (6), 1896–1914 (in Chinese with English abstract). Li, Y., Zhou, H.W., Li, Q.L., Xiang, H., Zhong, Z.Q., Brouwer, F.M., 2014. Palaeozoic polymetamorphism in the North Qinling orogenic belt, Central China: insights from petrology and in situ titanite and zircon U–Pb geochronology. J. Asia Earth Sci. 92, 77–91. Li, Y., Zhou, H.W., Zhong, Z.Q., Xiang, H., Zeng, W., Qi, D.M., Zhang, L., 2012b. Two Eopaleozoic metamorphic events in North Qinling: petrology and zircon U-Pb geochronology evidences from basic rocks in the Songshugou area. Earth Sci. J. China Univ. Geosci. 37, 111–124 (in Chinese with English abstract). Li, Y.L., Zhang, G.W., Song, C.Z., 1998. Characteristics of bidirectional subduction of Erlangping backarc basin in the east Qinling. Geol. J. China Univ. 4 (3), 286–293.

L. Liu et al. / Earth-Science Reviews 159 (2016) 58–81 Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., 1999. The breakup of Rodinia: did it start with a mantle plume beneath South China? Earth Planet. Sci. Lett. 173 (3), 171–181. Liao, X.Y., Liu, L., Wang, Y.W., Cao, Y.T., Chen, D.L., 2016a. Multi-stage metamorphic evolution of retrogressed eclogites with a granulite-facies overprint in the North Qinling belt. Gondwana Res. 30, 79–96. Liao, X.Y., Liu, L., Wang, Y.W., 2016b. U-Pb Ages and Lu-Hf Isotopes of Detrital Zircons from Liuling Sediments in the South Qinling Belt and its Tectonic Implications (in preparation). Lin, D.C., Wang, S.Y., Du, J.S., 1990. Kuangping Group and Boundary Characteristics in Henan Province, Qinling-Dabashan Geological Paper (One). Science and Technology Press, Beijing, pp. 40–46. Ling, W.L., Duan, R.C., Liu, X.M., Cheng, J.P., Mao, X.W., Peng, L.H., Liu, Z.X., Yang, H.M., Ren, B.F., 2010. U–Pb dating of detrital zircons from the Wudangshan Group in the South Qinling and its geological significance. Chin. Sci. Bull. 55, 2440–2448. Ling, W.L., Ren, B.F., Duan, R.C., Liu, X.M., Mao, X.W., Peng, L.H., 2007. Zircon U-Pb isotopic geochronology of Wudangshan Group, Yaolinghe Group and basic intrusions and its geological significance. Chin. Sci. Bull. 52 (12), 1445–1456 (in Chinese). Ling, W.L., Ren, B.F., Duan, R.C., Liu, X.M., Mao, X.W., Peng, L.H., Liu, Z.X., Cheng, J.P., Yang, H.M., 2008. Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication. Chin. Sci. Bull. 53, 2192–2199. Ling, W.L., Gao, S., Cheng, J.P., Jiang, L.S., Yuan, H.L., Hu, Z.C., 2006. Neoproterozoic magmatic events within the Yangtze continental interior and along its northern margin and their tectonic implication: constraint from the LA-ICPMS U-Pb geochronology of zircons from the Huangling and Hannan complexes. Acta Petrol. Sin. 22, 387–396. Ling, W.L., Gao, S., Zhang, B.R., Li, H.M., Liu, Y., Cheng, J.P., 2003. Neoproterozoic tectonic evolution of the northwestern Yangtze craton, South China: implications for amalgamation and break-up of the Rodinia Supercontinent. Precambrian Res. 122, 111–140. Ling, W.L., Cheng, J.P., Wang, X.H., Zhou, H.W., 2002. Geochemical features of the Neoproterozoic igneous rocks from the Wudang region and their implications for the reconstruction of the Jinning tectonic evolution along the south Qinling orogenic belt. Acta Petrol. Sin. 18, 25–36. Ling, W.L., Gao, S., Zhang, B.R., Zhou, L., Zhang, H.F., 1997. Early Precambrian continental crust evolution at the northern margin of Yangtze Craton: constrain from the elemental and isotopic geochemical study of Houhe complex. J. Mineral. Petrol. 17, 26–32 (in Chinese with English abstract). Liou, J.G., Ernst, W.G., Zhang, R.Y., Tsujimori, T., Jahn, B.M., 2009. Ultrahigh–pressure minerals and metamorphic terranes — the view from China. J. Asian Earth Sci. 35 (3–4), 199–231. Liu, G.H., Zhang, S.G., You, Z.D., 1993. Metamorphic Rocks in Qinling Orogen Belt and its Metamorphic Evolution. Geology Press, pp. 68–89 (in Chinese). Liu, H.B., Pei, X.Z., Ding, S.P., Li, Z.C., Sun, R.Q., 2006. LA- ICP- MS zircon U–Pb dating of the Neoproterozoic granitic gneisses in the Yuanlong area, Tianshui city, West Qinling, China, and their geological significance. Geol. Bull. China 25, 1315–1320. Liu, J.F., Sun, Y., Li, H.Y., Yang, L., 2012. LA-ICP-MS zircon dating of Sifangtai mafic-ultramafic complex in the North Qinling orogenic belt. Acta Petrol. Mineral. 31 (4), 524–530 (in Chinese with English abstract). Liu, J.F., Sun, Y., Sun, W.D., 2009. LA-ICP-MS zircon dating from the Lajimiao mafic complex in the Qinling orogenic belt. Acta Petrol. Sin. 25 (2), 320–330 (in Chinese with English abstract). Liu, J.F., Sun, Y., Feng, T., Hu, Y.H., Sun, W.D., 2008. Geochemistry and petrogenesis of Sifangtai mafic–ultramafic complex from North Qinling. Geochimica 37, 174–186. Liu, L., Liao, X.Y., Zhang, C.L., Chen, D.L., Gong, X.K., Kang, L., 2013. Multi-metamorphic timings of HP-UHP rocks in the North Qinling and their geological implications. Acta Petrol. Sin. 29, 1634–1656 (in Chinese with English abstract). Liu, L., Yang, J.X., Chen, D.L., Wang, C., Zhang, C.L., Yang, W.Q., Cao, Y.T., 2010. Progress and controversy in the study of HP–UHP metamorphic terranes in the West and Middle Central China orogen. J. Earth Sci. 5, 581–597. Liu, L., Chen, D.L., Sun, Y., Zhang, A.D., Luo, J.H., 2003. Discovery of relic majoritic garnet in felsic metamorphic rocks of Qinling Omplex, north Qinling Orogenic Belt, China. Alice Wain Memorial Western Norway Eclogite Field Symposium. Selje, Western Noway, p. 82. Liu, L., Zhou, D.W., Wang, Y., Chen, D.L., Liu, Y., 1996. Study and implication of the highpressure felsic granulite in the Qinling complex of East Qinling. Sci. China Ser. D 39, 60–68. Liu, L., Zhou, D.W., 1994. The discovery and preliminary study of UHP granulites from Songshugou Area, Eastern Qinling Mountain. Chin. Sci. Bull. 17, 1599–1601 (in Chinese with English abstract). Liu, S., Jahn, B.M., Wan, Y.S., Xie, H.Q., Wang, S.J., Xie, S.W., Dong, C.Y., Ma, M.Z., Liu, D.Y., 2015. Neoarchean to Paleoproterozoic high-pressure mafic granulite from the Jiaodong terrain, North China Craton: petrology, zircon age determination and geological implications. Gondwana Res. 28, 493–508. Liu, W.R., Wang, R.S., Che, Z.C., 1989. The Erlangping group in Eastern Qinling. J. Northwest Univ. (Nat. Sci. Ed.) 19 (SI), 2–47 (in Chinese). Liu, Y.Q., Gao, Z.L., Liu, Y.X., Song, B., Wang, Z.X., 2005. Zircon U-Pb dating for the earliest Neoproterozoic mafic magmatism in the southern margin of the North China block. Chin. Sci. Bull. 50 (22), 2514–2521. Lu, S.N., Li, H.K., Chen, Z.H., Hao, G.J., Zhou, H.Y., Guo, J.J., Niu, G.H., Xiang, Z.Q., 2003. MesoNeoproterozoic Geological Evolution of the Qinling and Its Respondence to Rodinia Event. Geological Publishing House, Beijing, pp. 1–194 (in Chinese). Lu, S.N., Yu, H.F., Li, H.K., Chen, Z.H., Wang, H.C., Zhang, C.L., Xiang, Z.Q., 2006. Early Paleozoic suture zones and tectonic divisions in the “Central China orogen”. Geol. Bull. China 25 (12), 1368–1380 (in Chinese with English abstract).

79

Lu, S.N., Yu, H.F., Li, H.K., Chen, Z.H., Wang, H.C., Zhang, C.L., 2009. Precambrian Geology of the West and Middle Central China Orogen. Geological Publishing House, pp. 76–98 (in Chinese). Lucente, F.P., Margheriti, L., 2008. Subduction rollback, slab breakoff, and induced strain in the uppermost mantle beneath Italy. Geology 36, 375–378. Maruyama, S., Liou, J.G., Terabayashi, M., 1996. Blueschists and eclogites of the world and their exhumation. Int. Geol. Rev. 38 (6), 485–594. Mattauer, M., Matte, P., Malavieille, J., Tapponnier, P., Maluski, H., Xu, Z.Q., Lu, Y.L., Tang, Y.Q., 1985. Tectonics of the Qinling Belt: build-up and evolution of eastern Asia. Nature 317 (10), 496–500. Mei, Z.C., Meng, Q.R., Cui, Z.L., Qu, H.J., 1999. Devonian depositional system and palaeographic evolution of Qinling orogenic belt. J. Palaeogeogr. 1, 32–40. Meng, Q.R., Zhang, G.W., 2000. Geological framework and tectonic evolution of the Qinling orogen, Central China. Tectonophysics 323, 183–196. Meng, Q.R., Zhang, G.W., 1999. Timing of collision of the North and South China blocks: controversy and reconciliation. Geology 27, 123–126. Meng, Q.R., Yu, Z.P., Mei, Z.C., 1997. Sedimentation and development of the forearc basin at southern margin of North Qinling. Sci. Geol. Sin. 32, 136–145. Meng, Q.R., Mei, Z.C., Yu, Z.P., Cui, Z.L., 1995. A disappeared Devonian highland in the northern margin of the Qinling plate. Chin. Sci. Bull. 40, 254–256. Meng, Q.R., Xue, F., Zhang, G.W., 1994. Conglomerate sedimentation and its tectonic implication, Heihe area within Shangdan zone of the Qinling. Acta Sedimentol. Sin. 12, 37–46. Meng, Q.R., 1994. Late Paleozoic Sedimentation, Basin Development and Tectonics of the Qinling Orogenic Belt. Northwest University, Xi'an, pp. 1–172. Niu, B.G., He, Z.J., Ren, J.S., Wang, J., Deng, P., 2006. SHRMP U–Pb ages of zircons from the intrusions in the western Douling–Xiaomaoling uplift and their geological significances. Geogr. Rev. 52, 826–835 (in Chinese with English abstract). O'Brien, P.J., 2001. Subduction followed by collision: Alpine and Himalayan examples. Phys. Earth Planet. Inter. 127, 277–291. Pallister, J.S., Knight, R.J., 1981. Rare-earth element geochemistry of the Samail ophiolite near Ibra, Oman. J. Geophys. Res. 86 (B4), 2673–2697. Pearce, J.A., Robinson, P.T., 2010. The Troodos ophiolitic complex probably formed in a subduction initiation, slab edge setting. Gondwana Res. 18, 60–81. Pearce, J.A., 1982. Trace element characteristics of lavas from destructive plate boundaries. In: Thorpe, R.S. (Ed.), Andesites. Wiley, Chichester, pp. 525–548. Pei, F., Zhang, Y.G., Liu, C.L., 1995. Discovery and geological significance of the late Paleozoic spore fossils in North Qinling, Hennan Province. Reg. Geol. China 2, 112–117. Pei, X.Z., Ding, S.P., Zhang, G.W., Liu, H.B., Li, Z.C., Li, W.Y., Liu, Z.Q., Meng, Y., 2007. Zircons LA-ICP-MS U–Pb dating of Neoproterozoic granitoid gneisses in the north margin of West Qinling and geological implication. Acta Geol. Sin. 81, 772–786. Pei, X.Z., Liu, H.B., Ding, S.R., Li, Z.C., Hu, B., Sun, R.Q., Hou, Y.H., 2006. Geochemical charecteristics and tectonic significance of the meta-volcanic rocks in the Liziyuan Group from Tianshui area, western Qinling orogeny. Geotecton. Metallog. 30 (2), 193–205. Pei, X.Z., Li, Z.C., Ding, S.P., Li, Y., Hu, B., Liu, H.B., 2005. Geochemical characteristics and zircon U-Pb ages of island-arc basic igneous complexes in the Tianshui area, West Qinling. Geol. China 32 (4), 529–540. Pei, X.Z., Ding, S.P., Hu, B., Li, Y., Zhang, G.W., Guo, J.F., 2004. Definition of the Guanzizhen ophiolite in Tianshui area, western Qinling, and its geological significance. Geol. Bull. China 23 (12), 1202–1208. Peng, P., Wouter, B., Richard, E.E., Ulf, S., Vicki, M., 2011. U-Pb baddeleyite ages, distribution and geochemistry of 925 Ma mafic dykes and 900 Ma sills in the North China craton: evidence for a Nerproterozoic mantle plume. Lithos 127, 210–221. Qian, J.H., Yang, X.Q., Liu, L., Cao, Y.T., Chen, D.L., Yang, W.Q., 2013. Zircon U-Pb dating, mineral inclusion, Lu-Hf isotopic data and their geological significance of garnet amphibolite from Songshugou, North Qinling. Acta Petrol. Sin. 29 (9), 308–3098 (in Chinese with English abstract). Ratschbacher, L., Franz, L., Enkelmann, E., Jonckheere, R., Pörschke, A., Hacker, B.R., Dong, S.W., Zhang, Y.Q., 2006. The Sino-Korean-Yangtze suture, the Huwan detachment, and the Paleozoi-Tertiary exhumation of (ultra) high-pressure rocks along the Tongbai-Xinxian-Dabie Mountains. Geol. Soc. Am. Spec. Pap. 403, 45–75. Ratschbacher, L., Hacker, B.R., Calvert, A., Webb, L.E., Grimmer, J.C., McWilliams, M.O., Ireland, T.R., Dong, S.W., Hu, J.M., 2003. Tectonics of the Qinling (Central China): tectonostratigraphy, geochronology, and deformation history. Tectonophysics 366, 1–53. Ren, F.G., Li, H.M., Yin, Y.J., Li, S.B., Ding, S.Y., Chen, Z.H., 2000. The upper chronological limit of Xionger group's volcanic rock series, and its geological significance. Prog. Precambrian Res. 23, 140–146 (in Chinese with English abstract). Ren, J.S., 1991. The basic characteristics of the tectonic evolution of the continental lithosphere in China. Reg. Geol. China 4, 289–293 (in Chinese with English abstract). Rosenbaum, G., Lister, G., 2005. The Western Alps from the Jurassic to Oligocene: spatio-temporal constraints and evolutionary reconstructions. Earth-Sci. Rev. 69, 281–306. Rubatto, D., Gebauer, D., Fanning, M., 1998. Jurassic formation and Eocene subduction of the Zermatt–Saas–Fee ophiolites: implications for the geodynamic evolution of the Central and Western Alps. Contrib. Mineral. Petrol. 132 (3), 269–287. Rubatto, D., Hermann, J., 2001. Exhumation as fast as subduction? Geology 29, 3–6. Rubatto, D., 2002. Zircon trace element geochemistry: partitioning with garnet and the link between U–Pb ages and metamorphism. Chem. Geol. 184, 123–138. Rubatto, D., Hermann, J., 2003. Zircon formation during fluid circulation in eclogites (Monviso, Western Alps): implications for Zr and Hf budget in subduction zones. Geochim. Cosmochim. Acta 67, 2173–2187. SBGMR, 1989. Regional Geology of Shaanxi Province. Geological Publishing House, Beijing, pp. 1–698.

80

L. Liu et al. / Earth-Science Reviews 159 (2016) 58–81

Shi, Y., Yu, J.H., Santosh, M., 2013. Tectonic evolution of the Qinling orogenic belt, Central China: new evidence from geochemical, zircon U–Pb geochronology and Hf isotopes. Precambrian Res. 231, 19–60. Shi, Y., Yu, J.H., Xu, X.S., Q, J.S., Chen, L.H., 2009. Geochronology and geochemistry of the Qinling Group in the eastern Qinling Orogen. Acta Petrol. Sin. 25 (10), 2651–2670 (in Chinese with English abstract). Song, S.G., Zhang, L.F., Niu, Y., Su, L., Song, B., Liu, D.Y., 2006. Evolution from oceanic subduction to continental collision: a case study of the Northern Tibetan Plateau inferred from geochemical and geochronological data. J. Petrol. 47, 435–455. Song, S.G., Niu, Y.L., Su, L., Zhang, C., Zhang, L.F., 2014. Continental orogenesis from ocean subduction, continental collision/subduction, to orogen collapse, and orogen recycling: the example of the North Qaidam UHPM belt, NW China. Earth Sci. Rev. 129, 59–84. Su, L., Song, S.G., Song, B., Zhou, D.W., Hao, J.R., 2004. The SHRIMP zircon U-Pb ages of the garnet pyroxenite and Fushui complex from Songshugou Area and its constrain on the tectonic evolution of Qinling Orogenic belt. Chin. Sci. Bull. 49 (12), 1209–1211 (in Chinese with English abstract). Sun, S.S., McDonough, W.F., 1989. Chemical and isotope systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in Ocean Basins Vol. 42. Geological Society Publication, pp. 313–345. Sun, W.D., Li, S.G., Sun, Y., Zhang, G.W., Zhang, Z.Q., 1996a. Chronology and geochemistry of a lava pillow in the Erlangping Group at Xixia in the northern Qinling Mountains. Geogr. Rev. 42, 144–153. Sun, Y., Lu, X., Han, S., Zhang, G.W., 1996b. Composition and formation of Paleozoic Erlangping ophiolitic slab, North Qinling: evidence from geology and geochemistry. Sci. China Ser. D 39, 50–59. Von Raumer, J.F., Bussy, F., Schaltegger, U., Schulz, B., Stampfli, G.M., 2013. Pre-Mesozoic Alpine basements—their place in the European Paleozoic framework. GSA Bull. 125, 89–108. Wan, Y.S., Liu, D.Y., Dong, C.Y., Yin, X.Y., 2011. SHRIMP zircon dating of meta-sedimentary rock from the Qinling Group in the north of Xixia, North Qinling Orogenic Belt: constraints on complex histories of source region and timing of deposition and metamorphism. Acta Petrol. Sin. 27 (4), 1172–1178 (in Chinese with English abstract). Wang, H., Wu, Y.B., Gao, S., Liu, X.C., Gong, H.J., Li, Q.L., Li, X.H., Yuan, H.L., 2011. Eclogite origin and timings in the North Qinling terrane, and their bearing on the amalgamation of the South and North China blocks. J. Metamorph. Geol. 29, 1019–1031. Wang, H., Wu, Y.B., Gao, S., Liu, X.C., Liu, Q., Qin, Z.W., Xie, S.W., Zhou, L., Yang, S.H., 2013. Continental origin of eclogites in the North Qinling terrane and its tectonic implications. Precambrian Res. 230, 13–30. Wang, H., Wu, Y.B., Gao, S., Zheng, J.P., Liu, Q., Liu, X.C., Qin, Z.W., Yang, S.H., Gong, H.J., 2014. Deep subduction of continental crust in accretionary orogen: evidence from U-Pb dating on diamond-bearing zircons from the Qinling orogen, central China. Lithos 190-191, 420–429. Wang, J., 2000. Neoproterozoic Rifting History of South China: Significance to Rodinia Breakup. Geological Publishing House, Beijing (in Chinese). Wang, J., Diwu, C.R., Sun, Y., Liu, Y., Wang, W., 2012. LA-ICP-MS zircon U-Pb dating and Hf isotope analysis of the Qinggangping granodiorite in Xixia area of western Henan Province and their geological significance. Geol. Bull. China 31 (6), 884–895 (in Chinese with English abstract). Wang, J., Li, X.H., Duan, T.Z., Liu, D.Y., Song, B., Li, Z.X., Gao, Y.H., 2003. Zircon SHRIMP U-Pb age of Cangshuipu volcanic rocks and new evidence of bottom boundary of Nanhua system. Chin. Sci. Bull. 48, 1726–1731 (in Chinese with English abstract). Wang, J., Liu, B.J., Pan, G.T., 2001. Neoproterozoic rifting history of south China: significance to Rodinia breakup. Mineral. Petrol. 21, 135–145 (in Chinese with English abstract). Wang, T., Wang, X.X., Tian, W., Zhang, C.L., Li, W.P., Li, S., 2009. North Qinling Paleozoic granite associations and their variation in space and time: implications for orogenic processes in the orogens of central China. Sci. China Ser. D Earth Sci. 52, 1359–1384. Wang, T., Zhang, Z.Q., Wang, X.X., Wang, Y.B., Zhang, C.L., 2005. Neoproterozoic collisional deformation in the core of the Qinling orogen and its age: constrained by zircon SHRIMP dating of strongly deformed syn-collisional granites and weakly deformed granitic veins. Acta Geol. Sin. 79, 220–231 (in Chinese with English abstract). Wang, T., Li, W.P., Wang, X.X., 1998. Zircon U-Pb age of the Niujiaoshan granitoid gneisses in the Qinling complex of the Qinling orogenic belt-with a discussion of its geological significance. Reg. Geol. China 17, 39–42 (in Chinese with English abstract). Wang, X.C., Li, X.H., Li, W.X., Li, Z.X., Liu, Y., Yang, Y.H., Liang, X.R., Tu, X.L., 2008. The Bikou basalts in the northwestern Yangtze block, South China: remnants of 820–810 Ma continental flood basalts? Geol. Soc. Am. Bull. 120, 1478–1492. Wang, X.L., Jiang, S.Y., Dai, B.Z., Griffin, W.L., Dai, M.N., Yang, Y.H., 2011. Age, geochemistry and tectonic setting of the Neoproterozoic (ca 830 Ma) gabbros on the southern margin of the North China craton. Precambrian Res. 190, 35–47. Wang, X.R., Hua, H., Sun, Y., 1995. A study on microfossils of the Erlangping Group in Wantan area, Xixia county, Henan province. J. Northwest Univ. (Nat. Sci. Ed.) 25, 353–358. Wang, X.X., Wang, T., Zhang, C.L., 2013b. Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: constraints on orogenic process. J. Asian Earth Sci. 72, 129–151. Wang, Y.W., 2015. Multi-Metamorphism of Amphibolites in Qinling Complex and Its Tectonic Implications (Dissertation for Master Degree) Northwest University. Wang, Y.W., Liu, L., Liao, X.Y., Gai, Y.S., Yang, W.Q., Kang, L., 2016. Multi-matemorphism of amphibolite in the Qinling complex, Qingyouhei area: revelation from trace elements and mineral inclusions in zircons. Acta Petrol. Sin. 32 (5), 1467–1492 (in Chinese with English abstract).

Wang, Z.Q., Yan, Z., Wang, T., Gao, L.D., Yan, Q.R., Chen, J.L., Li, Q.G., Jiang, C.F., Liu, P., Zhang, Y.L., Xie, C.L., Xiang, Z.J., 2009. New advances in the study on ages of metamorphic strata in the Qinling orogenic belt. Acta Geosci. Sin. 30, 561–570 (in Chinese with English abstract). Waschbusch, P., Beaumont, C., 1996. Effect of slab retreat on crustal deformation in simple regions of plate convergence. J. Geophys. Res. 101 (B12), 28,133–28,148. Wood, D.A., 1980. The application of a Th–Hf–Ta diagram to problems of tectono-magmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary Volcanic Province. Earth Planet. Sci. Lett. 50, 11–30. Wu, Y.B., Zheng, Y.F., 2013. Tectonic evolution of a composite collision orogen: an overview on the Qinling-Tongbai-Hong'an-Dabie-Sulu orogenic belt in central China. Gondwana Res. 23, 1402–1428. Xia, L.Q., Xia, Z.C., Li, X.M., Ma, Z.P., Xu, X.Y., 2008. Petrogenesis of the Yaolinghe group, Yunxi group, Wudangshan group volcanic rocks and basic dyke swarms from eastern part of the south Qinling mountains. Northwest. Geol. 41, 1–29 (in Chinese). Xiao, S.Y., Zhang, W.J., Song, Z.J., 1988. Metamorphic Strata in North Qining. Jiaotong Publishing House, Xi'an, pp. 1–32 (in Chinese). Xu, X.Y., He, S.P., Wang, H.L., Zhang, E.P., Chen, J.L., Sun, J.M., 2008. Tectonic framework of North Qinling Mountain and North Qilian Mountain conjunction area in Early Paleozoic: a study of the evidences from strata and tectonic-magmatic events. Northwest. Geol. 41, 1–21 (in Chinese). Xu, X.Z., Yang, J.S., Robinson, P.T., Xiong, F.H., Ba, D.Z., Guo, G.L., 2015. Origin of ultrahigh pressure and highly reduced minerals in podiform chromitites and associated mantle peridotites of the Luobusa ophiolite, Tibet. Gondwana Res. 27, 686–700. Xu, Z.Q., Lu, Y.L., Tang, Y.Q., Mattauer, M., Matte, P.H., Malavieille, J.P., Tapponnier, 1986. Deformation characterisitics and tectonic evolution of the Eastern Qinling orogenic belt. Acta Geograph. Sin. 3, 238–247 (in Chinese with English abstract). Xue, F., Lerch, M.F., Kroner, A., Reischmann, T., 1996. Tectonic evolution of the East inling Mountains, China, in the Palaeozoic: a review and new tectonic model. Tectonophysics 253, 271–284. Yan, Q.R., Chen, J.L., Wang, Z.Q., Yan, Z., Wang, T., Li, Q.G., Zhang, Z.Q., Jiang, C.F., 2008. Zircon U–Pb and geochemical analyses for leucocratic intrusive rocks in pillow lavas in the Danfeng group, north Qinling Mountains, China. Sci. China Ser. D Earth Sci. 51, 249–262. Yan, Q.R., Wang, Z.Q., Chen, J.L., Yan, Z., Wang, T., Li, Q.G., Jiang, C.F., Zhang, Z.Q., 2007. Tectonic setting and SHRIMP age of volcanic rocks in the Xieyuguan and Caotangou groups: implications for the North Qinling Orogenic Belt. Acta Geol. Sin. 81, 488–500 (in Chinese with English abstract). Yan, Q.R., Wang, Z.Q., Yan, Z., Andrew, D.H., Peter, A.D., Liu, D.Y., Song, B., Jian, P., Wang, T., 2003. Geochronology of the Bikou group volcanic rocks: newest results from SHRIMP zircon U-Pb dating. Geol. Bull. China 22, 456–458 (in Chinese with English abstract). Yan, Z., Wang, Z.Q., Wang, T., Yan, Q.R., Xiao, W.J., Li, J.L., Han, F.L., Chen, J.L., 2007. Tectonic setting of Devonian sediments in the Qinling orogen: constraints from detrital modes and geochemistry of clastic rocks. Acta Petrol. Sin. 23 (5), 1023–1042. Yang, J.S., Liu, F.L., Wu, C.L., Xu, Z.Q., Shi, R.D., Chen, S.Y., Deloule, E., Wooden, J.L., 2005. Two ultrahigh-pressure metamorphic events recognized in the Central Orogenic Belt of China: evidence from the U–Pb dating of coesite-bearing zircons. Int. Geol. Rev. 47, 327–343. Yang, J.S., Liu, F.L., Wu, C.L., Wan, Y.S., Zhang, J.X., Shi, R.D., Chen, S.Y., 2003. Two ultrahigh pressure metamorphic events recognized in the Central orogenic belt of China: evidence from the U–Pb dating of coesite-bearing zircons. Acta Geol. Sin. 77, 463–477 (in Chinese with English abstract). Yang, J.S., Xu, Z.Q., Pei, X.Z., Shi, R.D., Wu, C.L., Zhang, J.X., Li, H.B., Meng, F.C., Rong, H., 2002. Discovery of diamond in North Qinling: evidence for a Giant UHPM Belt across Central China and Recgnition of Paleozoic and Mesozoic dual deep subduction between North China and Yangtze plates. Acta Geol. Sin. 76 (4), 484–495 (in Chinese with English abstract). Yang, L., Chen, F.K., Yang, Y.Z., Li, S.Q., Zhu, X.Y., 2010. Zircon U-Pb ages of the Qinling group in Danfeng area: recording Mesoproterozoic and Neoproterozoic magmatism and Early Paleozoic metamorphism in the North Qinling terrain. Acta Petrol. Sin. 26 (5), 1589–1603 (in Chinese with English abstract). Yang, M., Liu, L., Wang, Y.W., Liao, X.Y., Kang, L., Gai, Y.S., 2016. Geochorology of detrital zircon of sediments in Erlangping Complex of North Qinling belt: constraint to formation age and tectonic setting. Acta Petrol. Sin. 32 (5), 1452–1466. Yang, Z., Dong, Y.P., Liu, X.M., Zhang, J.H., 2006. LA-ICP-MS zircon U-Pb dating of gabbro in the Guanzizhen ophiolite, Tianshui, West Qinling, China. Geol. Bull. China 25 (11), 1321–1325. Ye, K., Cong, B.L., Ye, D.N., 2000. The possible subduction of continental material to depths greater than 200 km. Nature 407, 734–736. You, Z.D., Suo, S.T., Han, Y.J., Zhong, Z.Q., Chen, N.S., 1991. The Metamorphic Progresses and Tectonic Analyses in the Core Complex of an Orogenic Belt: An Example from Eastern Qinling Mountains. China University of Geosciences Press, Wuhan (in Chinese). You, Z.D., Han, Y.J., Suo, S.T., Chen, N.S., Zhong, Z.Q., 1993. Metamorphic history and tectonic evolution of the Qinling Complex, eastern Qinling Mountains, China. J. Metamorph. Geol. 11, 549–560. Yu, H., Zhang, H.F., Li, X.H., Zhang, J., Santosh, M., Yang, Y.H., Zhou, D.W., 2016. Tectonic evolution of the North Qinling Orogen from subduction to collision and exhumation: evidence from zircons in metamorphic rocks of the Qinling group. Gondwana Res. 30, 65–78. Yu, Z.P., Meng, Q.R., 1995. Late Paleozoic sedimentary and tectonic evolution of the Shangdan suture, eastern Qinling, China. J. SE Asian Earth Sci. 11, 237–242. Zhai, M.G., Hu, B., Peng, P., Zhao, T.P., 2014. Meso-Neoproterozoic magmatic events and multi-stage rifting in the NCC. Earth Sci. Front. 21, 100–119. Zhai, X.M., Day, H.W., Hacker, B.R., You, Z.D., 1998. Paleozoic metamorphism in the Qinling orogen, Tongbai Mountains, central China. Geology 26, 371–374.

L. Liu et al. / Earth-Science Reviews 159 (2016) 58–81 Zhang, A.D., Liu, L., Wang, Y., Chen, D.L., Luo, J.H., 2003. Geochemistry and tectonic setting of the protolith of eclogites in north Qinling. J. Northwest Univ. 33, 191–195 (in Chinese with English abstract). Zhang, B.R., Gao, S., Zhang, H.F., Han, Y.W., 2002. Geochemistry of the Qinling Orogenic Belt. Science Press, Beijing, pp. 1–187 (in Chinese). Zhang, B.R., Zhang, H.H., Zhao, Z.D., 1996. Geochemical zonation, evolution and tectonic significance and crust and mantle for East Qinling and adjacent areas. Sci. China Ser. D 26 (3), 201–208 (in Chinese). Zhang, C.L., Liu, L., Wang, T., Wang, X.X., Li, L., Gong, Q.F., Li, X.F., 2013. Granitic magmatism related to early Paleozoic continental collision in North Qinling. Chin. Sci. Bull. 35, 4405–4410. Zhang, C.L., Gao, S., Yuan, H.L., Zhang, G.W., Yan, Y.X., Luo, J.L., Luo, J.H., 2007. Sr–Nd–Pb isotopes of the Early Paleozoic mafic–ultramafic dykes and basalts from South Qinling belt and their implications for mantle composition. Sci. China Ser. D Earth Sci. 50, 1293–1301 (in Chinese). Zhang, C.L., Liu, L., Zhang, G.W., Wang, T., Chen, D.L., Yuan, H.L., Liu, X.M., Yan, Y.X., 2004. Determination of Neoproterozoic post-collisional granites in the north Qinling Mountains and its tectonic significance. Earth Sci. Front. 11, 33–42 (in Chinese with English abstract). Zhang, G.W., Zhang, B.R., Yuan, X.C., Xiao, Q.H., 2001. Qinling Orogenic Belt and Continental Dynamics. Science Press, Beijing, pp. 1–855 (in Chinese). Zhang, G.W., Zhang, Z.Q., Dong, Y.P., 1995. Nature of main tectonic-lithostratigraphic units of Qinling orogen: implications for the tectonic evolution. Acta Petrol. Sin. 11 (2), 101–114 (in Chinese with English abstract). Zhang, G.W., 1988. Formation and Evolution of the Qinling Orogen. Northwest University Press, Xi'an, pp. 1–192 (in Chinese). Zhang, H.F., Lu, H., Zhou, D.W., Zhang, J., Dong, Y.P., Zhang, G.W., 2015. The meta-gabbroic complex of Fushui in north Qinling orogen: a case of syn-subduction mafic magmatism. Gondwana Res. 35, 4405–4410. Zhang, H.Y., 2006. Structures, Evolution and Tectonic Implications of the Erlangping Group in North Qinling (Dissertation for Doctoral Degree) Chinese Academy of Geological Sciences (in Chinese with English abstract). Zhang, J.X., Yu, S.R., Meng, F.C., Li, J.P., 2009. Paired high-pressure granulite and eclogite in collision orogens and their geodynamic implications. Acta Petrol. Sin. 25 (9), 2050–2066 (in Chinese with English abstract). Zhang, J.X., Yu, S.Y., Meng, F.C., 2011. Polyphase Early Paleozoic metamorphism in the northern Qinling orogenic belt. Acta Petrol. Sin. 27 (4), 1179–1190. Zhang, Q., 1990. A preliminary study on the geochenistry and origin of boninites and boni-basalts. Geochenica 3, 207–215. Zhang, Q., Zhou, G.Q., 2001. Ophiolites of China. Science Press, Beijing, pp. 1–189 (in Chinese). Zhang, S.G., Wan, Y.S., Liu, G.H., 1991. Metamorphic Geology in Kuangping Group, North Qinling. Science and Technology Press, Beijing, pp. 1–119 (in Chinese). Zhang, W.S., An, S.Y., 1990. Characteristics and origin of the Qinwangshan mafic body. Acta Petrol. Sin. 4, 59–66 (in Chinese with English abstract).

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Zhang, Z.J., 1999. Metamorphic Evolution of Garnet-Clinopyroxene-Amphibole Rocks from the Proterozoic Songshugou Mafic-Ultramafic Complex, Qinling Mountains, Central China. The Island Arc Vol. 8 pp. 259–280. Zhang, Z.Q., Liu, D.Y., Fu, G.M., 1994. Study of Isotope Geochronology of Metamorphic Stratigraphy of North Qinling. Geological Publishing House, Beijing, pp. 1–191 (in Chinese). Zhao, G.C., He, Y.H., Sun, M., 2009. The Xiong'er volcanic belt at the southern margin of the North China craton: petrographic and geochemical evidence for its outboard position in the Paleo-Mesoproterozoic Columbia supercontinent. Gondwana Res. 16, 170–181. Zhao, J., Chen, D.L., Tan, H.Q., Chen, M., Zhu, X.H., Guo, C.L., Liu, L., 2012. Zircon LA-ICP-MS U-Pb dating of basic volcanics from Erlangping group of the North Qinling, eastern Qinling Mountains and its geological implications. Earth Sci. Front. 19 (4), 118–125 (in Chinese with English abstract). Zhao, J.H., Zhou, M.F., 2008. Neoproterozoic adakitic plutons in the northern margin of the Yangtze block, China: partial melting of a thickened lower crust andimplications for secular crustal evolution. Lithos 104, 231–248. Zhao, J.H., Zhou, M.F., 2009. Secular evolution of the Neoproterozoic lithospheric mantle underneath the northern margin of the Yangtze block, South China. Lithos 107, 152–168. Zhao, J.H., Zhou, M.F., Zheng, J.P., Fang, S.M., 2010. Neoproterozoic crustal growth and reworking of the Northwestern Yangtze block: constraints from the Xixiang dioritic intrusion, South China. Lithos 120, 439–452. Zhao, T.P., Zhai, M.G., Xia, B., Li, H.M., Zhang, Y.X., Wan, Y.S., 2004a. SHRIMP geochronology of Xiong'er vocanic rocks: constraints for initial time of the cover, North China craton. Chin. Sci. Bull. 49, 2342–2349. Zhao, T.P., Chen, F.K., Zhai, M.G., Xia, B., 2004b. Single zircon U-Pb ages and their geological significance of the Damiao anorthosite complex, Hebei Province, China. Acta Petrol. Sin. 20 (3), 685–690 (in Chinese with English abstract). Zhao, T.P., Zhou, M.F., Jin, C.W., Guan, H., Li, H.M., 2001. Discussion on age of the Xiong'er group in southern margin of North China craton. Chin. J. Geochem. 36, 326–334. Zheng, Y.F., Ye, K., Zhang, L.F., 2009. Developing the plate tectonics from oceanic subduction to continental collision. Chin. Sci. Bull. 54, 2549–2555. Zheng, Y.F., Chen, Y.X., Dai, L.Q., Zhao, Z.F., 2015. Developing plate tectonics theory from oceanic subdaction zones to collisional orogens. Sci. China Earth Sci. 58, 1045–1069. Zhou, D.W., Liu, L., Zhang, C.L., Wang, J.L., Ren, J.F., 2002. The comparative research on convergence and extention events of ancient North China block and Yangtze block in the Middle-Neo Proterozoic. J. Northwest Univ. 32 (2), 109–113 (in Chinese with English abstract). Zhu, B.Q., Chang, X.Y., Qiu, H.N., Sun, D.Z., 1998. Characteristics of Proterozoic basements on the geochemical steep zones in the continent of China and their implications for setting of superlarge deposits. Sci. China Ser. D 41 (Supplement), 54–64 (in Chinese with English abstract). Zhu, X.Y., Chen, F.K., Li, S.Q., Yang, Y.Z., Nie, H., Siebel, W., Zhai, M.G., 2011. Crustal evolution of the North Qinling terrain of the Qinling Orogen, China: evidence from detrital zircon U-Pb ages and Hf isotopic composition. Gondwana Res. 20 (1), 194–204.