Tectonic evolution of the Qinling orogen, China: Review and synthesis

Journal of Asian Earth Sciences 41 (2011) 213–237

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Journal of Asian Earth Sciences

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Review

Tectonic evolution of the Qinling orogen, China: Review and synthesis

Yunpeng Dong a,⇑, Guowei Zhang a, Franz Neubauer b, Xiaoming Liu a, Johann Genser b,Christoph Hauzenberger c

a State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Northern Taibai Str. 229, Xi’an 710069, Chinab Department of Geography and Geology, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austriac Institute for Earth Sciences, University of Graz, Heinrich Str. 26, A-8010 Graz, Austria

a r t i c l e i n f o

Article history:Received 21 October 2010Received in revised form 10 February 2011Accepted 2 March 2011Available online 21 March 2011

Keywords:GeochemistryGeochronologySubduction and collisionTectonic evolutionQinling orogenic belt

1367-9120/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.jseaes.2011.03.002

⇑ Corresponding author. Tel.: +86 29 88303028.E-mail address: [email protected] (Y. Dong).

a b s t r a c t

This contribution reviews the tectonic structure and evolution of the Qinling orogenic belt, which extendseast–west nearly 2500 km across Central China and is a giant orogenic belt formed by the convergenceand collision between North China and South China Blocks. The principal tectonic elements includingmetamorphic basement and its Neoproterozoic to Triassic cover, ophiolitic sutures, nature and ages ofgranitoid belts, provenance studies and tectonometamorphic studies of metamorphic belts allow tracingthe polarity of two stages of plate convergence and collision and the further tectonic history. In thisreview, we present new distribution maps of the Early Paleozoic ophiolites and associated volcanics inthe Shangdan suture zone and the Middle Devonian–Middle Triassic ophiolitic melange in the Mianluesuture zone, as well as the maps of granitoid and metamorphic belts displaying various ages (Silurian–Devonian, Triassic, Late Jurassic–Early Cretaceous). These maps allow better constrain the polarity of sub-duction and collision. We also discuss the significance of the Early Cretaceous Yanshanian events, whichrepresent a linkage between tectonic events in the Tethyan and East China/Pacific realms.

Two ophiolitic sutures, the Shangdan suture zone in the north and the Mianlue suture in the south,have been intensively studied during the past two decades. The Qinling Orogen is divided into the NorthQinling and the South Qinling Belts by the Shangdan suture zone, and this suture zone is thought to rep-resent the major suture separating the North China and South China Blocks. However, the timing and pro-cesses of convergence between these two blocks have been disputed for many years, and Silurian–Devonian or Late Triassic collision has been proposed as well. Based on the recent results, a detailed con-vergent evolutionary history between the North China and South China Blocks along the Shangdan sutureis here proposed. The Mianlue suture zone is well documented and represents the Mianlue ocean whichseparates the South Qinling from the South China Block in Devonian to Mid Triassic times. After the clo-sure of the Mianlue ocean, the South Qinling Belt was emplaced onto the Yangtze Block along the MiddleTriassic Mianlue suture zone in Late Triassic–Jurassic times. This suture was overprinted by the south-directed overthrust of the Mianlue–Bashan–Xiangguang thrust fault operative in Late Jurassic-Cretaceoustimes.

Furthermore, we note that the Yanshanian tectonic events play a major role for rapid Early Cretaceousexhumation of significant portions of the Qinling orogenic belt. In contrast, although high topographicgradients, the Cenozoic tectonism related to lateral extrusion of the Tibet plateau resulted in minorand continuous exhumation and erosion along major transtensional and strike-slip faults were activated.

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Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2142. Geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2153. Tectonics in the Shangdan suture and North Qinling Belt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

3.1. Ophiolite and volcanic rocks in the Shangdan suture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2183.2. Island-arc intrusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2193.3. Back-arc basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

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214 Y. Dong et al. / Journal of Asian Earth Sciences 41 (2011) 213–237

3.4. Fore-arc prism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2263.5. Closure of the Shangdan ocean. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

4. Tectonics along the Mianlue suture zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
4.1. Ophiolites and volcanic rocks in the Mianlue suture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2284.2. Timing of the Mianlue ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2294.3. Triassic syn- and post-collisional granitoids in the western SQB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
5. Diversity of exhumation paths of the NQB and SQB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
5.1. Evidence from lithostratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305.2. Metamorphic P–T constraints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2315.3. Chronological evidence for age of metamorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
6. Tectonic model and evolutionary history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
6.1. Discussion on the Precambrian evolution in the NQB and adjacent region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2316.2. Early Paleozoic subduction orogen in the NQB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2316.3. Late Paleozoic to Triassic subduction-collision along Mianlue zone between the SQB and SCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2336.4. Jurassic to Cretaceous intracontinental tectonism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2336.5. A note to Cenozoic tectonism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
1. Introduction

The Qinling Mountains are located in a key tectonic positionlinking the Dabie Mountains in the east with the Qilian and theKunlun Mountains in the west (Fig. 1). Previous interpretationsproposed that the Qinling orogenic belt was built through north-ward subduction of the Shangdan oceanic crust and subsequentcollision between the North China Block (NCB) and South ChinaBlock (SCB) along the Shangdan suture zone (e.g. Mattauer et al.,1985; Sengör, 1985; Hsü et al., 1987; Zhao and Coe, 1987; Enkinet al., 1992; Kröner et al., 1993; Li et al., 1993; Okay and Sengör,1993; Li, 1994; Zhang et al., 1995a, 2001; Ames et al., 1996; Hackeret al., 1998; Zhai et al., 1998). However, based on geological, geo-chemical and geochronological work, the existence of the Mianluesuture zone between the SCB and the South Qinling micro-platehas been recognized and a ‘‘three-plate with two-suture zone’’

Fig. 1. Simplified tectonic map of the Qinling orogenic belt. Insert map in up

model has been proposed and documented (Zhang et al., 1995a,2001; Meng and Zhang, 1999; Li et al., 1996; Dong et al., 2004).Although most authors believe that subduction and collisionevents mainly occurred along the Shangdan suture zone, there isstill much dispute about the timing of the closure of the Shangdanocean: (1) Some authors proposed an Early Paleozoic age of colli-sion between the NCB and SCB (Mattauer et al., 1985; Kröneret al., 1993), as well as a Devonian age of collision based on thePb isotopic composition of granitoids (Zhang et al., 1997b) andgeochemistry of Devonian fine-grained sediments exposed to thesouth of the Shangdan zone (Gao et al., 1995). (2) Based on theage of ultrahigh-pressure metamorphism at �230 Ma in the east-ernmost part of the Qinling-Dabie belt (e.g., Li et al., 1993; Okayand Sengör, 1993; Ames et al., 1996; Hacker et al., 1998) and paleo-magnetic data (Zhao and Coe, 1987; Enkin et al., 1992), variousmodels of a Late Triassic age of continent–continent collision have

per-right corner shows the location of the Qinling orogen within China.

Fig. 2. Cross-section showing main tectonic units across the eastern Qinling orogenic belt.

Y. Dong et al. / Journal of Asian Earth Sciences 41 (2011) 213–237 215

been proposed (Sengör, 1985; Hsü et al., 1987; Li, 1994). (3) Yinand Nie (1993) argued that collision between the NCB and SCB be-gan by the interdigitation of the northeastern SCB and the south-eastern NCB in Late Permian times and this process continueduntil Late Triassic. Additionally, some authors (e.g. Xue et al.,1996b; Faure et al., 2001; Ratschbacher et al., 2003, 2006) favoredthat the suture between the NCB and SCB is represented by theErlangping zone, and located to the north of the North Qinling ter-rane (NQT). However, two different tectonic models have beenpostulated to account for the subduction between the NCB andSCB. Xue et al. (1996b) suggested that the major ocean betweenthe NCB and SCB was occurring southward subduction along thenorthern edge of the NQT, and resulted in spreading of the Shang-dan back-arc basin to the south of the NQT (island-arc). In compar-ison, although the other model favoured the suture is located to thenorthern edge of the NQT, the direction of subduction was pro-posed towards north, where as the Danfeng ophiolitic melangewas a nappe overthrusted from the Erlangping melange (Faureet al., 2001; Ratschbacher et al., 2003, 2006).

More detailed geological, geochemical and geochronologicaldata have been accumulated since 1990s, which allow us to recon-struct the tectonic framework and detailed evolutionary history ofthe Qinling Mountains. The principal goal of this contribution is toreview the recent new dataset of the ophiolites, granitoids, volca-nic and sedimentary units, and related tectonothermal eventsalong the Shangdan and Mianlue sutures in terms of their geo-chemical characteristics and ages. Based on these data we attemptto synthesize and outline the tectonic framework and evolutionaryhistory of the Qinling orogenic belt. However, most records of thePrecambrian tectonic movement in the Qinling belt have beenoverprinted by the intense Paleozoic–Mesozoic tectonic events.To draw a detailed tectonic map and reconstruct the evolutionaryprocess, it needs further detailed investigations. So, the time limitin the review is mainly drawn within Paleozoic and Mesozoic.

2. Geological setting

The Qinling Mountains are bounded by the Lingbao–Lushan–Wuyang fault (LLWF) in the north and the Mianlue–Bashan–Xiangguang fault (MBXF) in the south. Along both faults the orogen

was outwardly thrust onto the southern margin of the NCB andnorth margin of the SCB (Figs. 1 and 2), respectively. The LLWF isan intra-continental northward-thrust formed in Cretaceous time.The MBXF is a south-directed overthrust in Late-Jurassic and Creta-ceous time, which overprinted the Middle Triassic Mianlue suture.Two sutures with ophiolitic melanges, the Shangdan suture in thenorth (Zhang et al., 1994a; Zhang et al., 1995a, 1995b, 2001; Donget al., 1997, 2011a; Sun et al., 2002b) and the Mianlue suture in thesouth (Zhang et al., 1995a, 2004b; Li et al., 1996, 2004a; Dong et al.,1999, 2004; Xu et al., 2002; Li et al., 2007c) are well documented.With these two sutures and several major faults, the Qinling oro-gen can be divided into four zones (Figs. 1 and 2): the SouthernNorth China Block (S-NCB), North Qinling Belt (NQB), South QinlingBelt (SQB) and Northern South China Block (N-SCB, Fore-land Belt)from north to south.

The S-NCB, bounded to the south by the Luonan–Luanchuanfault (Fig. 1), is characterized by the highly deformed and meta-morphosed Neoarchean to Neoproterozoic plutonometamorphicbasement rocks (Zhang et al., 2000a), which are overlain by Meso-proterozoic rift-related volcanic rocks, marine facies clastic andcarbonate sequence, Uppermost Proterozoic tillite (Zhang et al.,2001) and succeeding Cambrian to Ordovician passive continentalmargin sequences (Xue et al., 1996b). The S-NCB was originally thesouthern part of the North China Block, which was involved intothe Mesozoic–Cenozoic intra-continental orogenic deformation(Zhang et al., 1995a, 2001), and intruded by numerous Cretaceousgranitoid plutons (e.g. Lantian, Laoniushan and Huashan grani-toids) (Mao et al., 2005; Li et al., 2006a; Ye et al., 2006; Zhuet al., 2008a; Zhang et al., 2010).

To the south, the NQB mainly comprises Precambrian basementunits, Neoproterozoic and Early Paleozoic ophiolites, volcanic-sed-imentary assemblages, which are unconformably covered by lo-cally occurring Carboniferous and/or Permian clastic sediments.From north to south, the main lithological units in the NQB arethe Kuanping, Erlangping and Qinling Groups, and the SongshugouProterozoic ophiolite, which are separated from each other bythrust faults or ductile shear zones (Figs. 1 and 3).

The Kuanping Group comprises chiefly greenschists, amphibo-lites, quartz-rich micaschists and marbles. Although the previousstudies suggested that the Kuanping Group represented a Meso-proterozoic ophiolitic melange in a back-arc basin setting (Zhang

Fig. 3. Simplified map with the principal tectonostratigraphic units within the North Qinling belt. (a) Showing the distributions of the Shangdan suture zone, Erlangpingback-arc basin and representative island-arc gabbroic and granitoids intrusions in the North Qinling Belt. The age of the ophiolites along the Shangdan suture zone is showedin purple box, and the Erlangping ophiolite in green box. (b) Showing the main tectonic divisions of the Qinling orogenic belt and the location of the Figs. 3a and 7.


et al., 1994b, 1995a, 2001; Zhang and Zhang, 1995) or a marginalbasin sequence (e.g. Xue et al., 1996a,b; Zhai et al., 1998; Ratschb-acher et al., 2003, 2006; Hacker et al., 2004), the recent investiga-tion indicated that the so-called Kuanping Group actually includestwo tectonic units characterized by different lithology, petrogene-sis and age. They are a meta-basaltic unit and a meta-clastic unit.The meta-clastic unit is composed of metamorphosed terrestrialclastic sediments deposited in Early Paleozoic times. The protolithsof the meta-basaltic unit (mainly comprising greenschists andamphibolites) are N-MORB type and T-MORB type tholeiitic basalts(Zhang and Zhang, 1995; Diwu et al., 2010), which represent crustremnants of a back-arc basin. The LA-ICPMS zircon age of 943 Maconstrains the formation time of the ocean (Diwu et al., 2010),which is accordance with Sm–Nd whole-rock isochron ages rang-ing from 1.2 to 0.94 Ga (Zhang et al., 1994b). These ages may con-strain the age of back-basin rifting related to the northwardsubduction of the Mesoproterozoic oceanic crust being representedby the Songshugou ophiolite. The Proterozoic Songshugou ophio-lite consists mainly of amphibolite facies metamorphosed maficand ultramafic rocks, and crops out as a rootless nappe in thesouthern Qinling Group. Trace element geochemistry and isotopiccomposition show that the meta-basalts are mainly E-MORB andT-MORB rocks, most likely originating from the spreading centerof an initial stage of an ocean (Dong et al., 2008a). Regional geologyand abundant isotopic age data reveal that the ocean evolved theGrenvillian orogenic event from ca. 1.4 to 1.0 Ga (Zhang et al.,1994b; Chen et al., 2002; Dong et al., 2008a).

The Erlangping Group is composed of an ophiolitic unit, clasticsedimentary successions and carbonates. The ophiolitic unit con-tains sparse ultramafic rock, massive basalt, pillow basalt, and rareintercalations of radiolarian chert which will be fully discussed inthe following sections. However, it is noticeable, that the meta-sedimentary assemblage of Erlangping Group, as well as themeta-clastic unit of the Kuanping Group with Early Paleozoicdepositional ages (author’s unpublished data) are mostly attrib-uted to a tectono-stratigraphic assemblage in an island-arc andback-arc basin settings related to the Early-Paleozoic subductionevent along the Shangdan suture zone.

The Qinling Group predominantly comprises gneisses, amphib-olites and marbles, whose protoliths are clastic rocks, limestones(You et al., 1991) and interlayer of continental tholeiitic lavas(Zhang et al., 1994b), respectively. U–Pb zircon ages of gneissesrange from 2172 to 2267 Ma, whereas the Sm–Nd whole-rock iso-chron age of the amphibolite (meta-tholeiite) is 1987 ± 49 Ma(Zhang et al., 1994b). Further age data indicates that the QinlingGroup is a Paleoproterozoic complex, which underwent amphibo-lite facies metamorphism at 990 ± 0.4 Ma and a greenschist faciesmetamorphic overprint at ca. 425 ± 48 Ma (Chen et al., 1991).

The Shangdan suture zone is characterized by broadly out-spreading ophiolite, subduction-related volcanic and sedimentaryrocks, which was traditionally named as Danfeng ophiolite orDanfeng Group. These rocks mark the main tectonic boundary be-tween the NQB and SQB, and will be discussed later in detail.

To the south of the Shangdan suture, the SQB is situated be-tween the Shangdan suture and the Mianlue suture zones. It is welldocumented that the SQB had been separated from the northerncontinental margin of the SCB by the Mianlue ocean during Mid-Devonian to Mid-Triassic times (Zhang et al., 1995a, 2001; Liet al., 1996; Dong et al., 1999, 2004; Xu et al., 2000a, 2000b,2002; Li et al., 2004a, 2007c), which will be discussed in the follow-ing section.

The SQB, bounded to the south by the Mianlue–Bashan–Xiangguang Fault (MBXF) zone, is characterized by thin-skinnedstructures which include south-vergent imbricated thrust-fold sys-tem (Zhang et al., 2001; Dong et al., 2008b). It consists of a pre-Sin-ian basement overlain by a thick pile of Sinian (Neoproterozoic) toTriassic sediments. The basement is identified as two types, whichare Archean-Paleoproterozoic plutonometamorphic basement inthe Tongbai–Dabie area (Zhang et al., 2000a) and Meso- to Neopro-terozoic transitional basement in the East Qinling area (Zhanget al., 2001). The transitional basement in the East Qinling consistsmainly of rift-type volcanic-sedimentary assemblages (Ling et al.,2008) metamorphosed under greenschist facies conditions (Zhanget al., 2000a). All these basements are unconformably overlain byuppermost Proterozoic clastic and carbonate rocks, Cambrian–Or-dovician limestones, Silurian shales, Devonian to Carboniferous

Fig. 4. Chondrite-normalized REE patterns and primitive mantle-normalized trace element spider diagrams for the ophiolite and associated volcanic rocks along theShangdan suture zone, Qinling orogen. All the geochemical data are from Dong et al. (2011a). The values of OIB, E-MORB, N-MORB and Primitive Mantle are from Sun andMcDonough (1989).


clastic rocks with interlayered limestones. A few Permian-LowerTriassic sandstones are present in the northern part of the SQB(Zhang et al., 2001).

The middle and southern SQB are mainly characterized by aPrecambrian transitional basement overlain by a thick pile of

uppermost Proterozoic to Silurian shallow-marine deposits, whichwere intruded by abundant alkaline diabase dyke swarms in Silu-rian times (Zhang et al., 2007a). The northern part of the SQB ischaracterized by extensively present Devonian strata (Fig. 1) be-side a few Carboniferous, Permian and/or Triassic clastic deposits


in some areas. The Devonian strata mainly consist of limestones inthe lower part, pelagic turbidites and shales in middle and upperparts. Lower Devonian strata were documented to representdeposits of a shallow-marine passive continental (Meng, 1994).However, the tectonic setting and implications of the Middle toUpper Devonian turbidites and shales are disputed for decades,and passive-continental shelf (Meng, 1994; Zhang et al., 2001)and foreland basin (Li et al., 1994) were proposed. Its tectonic set-ting and significance are therefore still unclear. Additionally, in thenorthmost SQB, a ca. 1–3 km wide strip of conglomerates with vol-canic-sedimentary associations is present. The age and tectonicimplications of this unit are still unclear. All these controversieswill be discussed in the following sections to constrain the evolu-tionary history along the Shangdan suture zone.

To the south of the SQB, the foreland fold-thrust belt is sepa-rated from the SQB by the MBXF (Figs. 1 and 2), and it progres-sively grade into the undeformed Jurassic to Cretaceoussequences within Sichuan and Jianghan basins in the south. Thestrata of this belt are mainly composed of uppermost Proterozoicsandstones and limestones, Cambrian to Ordovician limestones,Silurian shales and Permian to Mid-Triassic limestones, whichare unconformably covered by Upper Triassic to Cretaceous terres-trial conglomerates and sandstones.

3. Tectonics in the Shangdan suture and North Qinling Belt

3.1. Ophiolite and volcanic rocks in the Shangdan suture

The Shangdan suture zone is marked by a discontinuously ex-posed tectonic melange, which mainly comprises ophiolitic assem-blages, and arc-related volcanic rocks (Fig. 3). The melange wasoverprinted by intense deformation and greenschist to loweramphibolite facies metamorphism in various regions. Most authorsbelieve that these volcanic assemblages, the Danfeng Group, repre-sent an ophiolitic melange, which is further confirmed by Zhanget al. (1994a, 1995b, 2001) and Zhou et al. (1995). However, Rats-chbacher et al. (2003, 2006) argued for an island-arc setting for theDanfeng Group. Moreover, a detailed and synthetic investigation ofthe geology and geochemistry of the ultramafic and mafic rocksalong this belt has been done recently by Dong et al. (2011a).The investigations reveal that the ophiolite sequence and subduc-tion-related volcanic rocks consist mainly of metamorphosed ma-fic and ultramafic rocks outcropping, from west to east, atYuanyangzhen-Wushan, Guanzizhen, Tangzang, Yanwan, Heiheand Danfeng regions (Fig. 3a) (Dong et al., 2011a).

The ophiolite suite in Yuanyangzhen-Wushan area consistsmainly of meta-peridotite, gabbro and basalt. The basaltic rockshave slight enrichment of LREE in chondrite-normalized REE dia-grams (Fig. 4a), and flat distribution patterns of HFSE withoutany Nb, Ta and Ti anomalies in the primitive mantle-normalizedtrace element spiderdiagrams (Fig. 4b), which is consistent withthe distribution pattern of a typical E-MORB. The geochemicalcharacteristics suggest derivation of these rocks from a mid-oce-anic ridge or at transitional ridge segments of a mid-ocean ridge,and were interpreted having formed at the spreading center ofthe Shangdan ocean (Dong et al., 2007). Zircons from a gabbro gavea LA-ICPMS U–Pb age of 457 ± 3 Ma (Li, 2008), which is interpretedas the upper age limit of the ophiolite.

Fifty kilometers to the east, the ophiolite in the Guanzizhen areais exposed in several thrusted fragments of metaperidotite, gabbro,basalt and oceanic plagiogranite (Dong et al., 2011a). The basaltsshow significant depletion of LREE, and their chondrite-normalizedREE element patterns coincide with that of N-MORB (Fig. 4c). Nei-ther HFSE fractionation nor depletion of Nb–Ta and Ti exist in theprimitive mantle-normalized trace element spidergrams (Fig. 4d).

These geochemical features indicate that the ophiolite in Guanziz-hen was formed in a depleted mantle at the mid-ocean ridge of theShangdan ocean (Dong et al., 2011a). LA-ICPMS in situ U–Pb agedating of the zircons of a middle-ocean ridge gabbro (MORG) gavean age of 471 ± 1.4 Ma (Yang et al., 2006) and was interpreted asthe formation age of the ophiolite. Li (2008) reported SHRIMP U–Pb zircon ages of 534 ± 9 Ma and 517 ± 8 Ma for the Liushuigougabbro and oceanic Guanzigou plagiogranite, respectively. Addi-tionally, some basaltic rocks with island-arc basaltic chemicalaffinity, which related to the subduction of the Shangdan oceaniclithosphere, were reported within the melange, and the formationage was constrained by the U–Pb zircon ages of 499.7 ± 1.8 Ma (LA-ICPMS; Pei et al., 2007a) and 507.5 ± 3.0 Ma (TIMS; Pei et al., 2005).All above data constrain the formation age of the ophiolite inGuanzizhen area to be at ca. 534–471 Ma.

Along the suture zone, 150 km to the east at Tangzang and Yan-wan areas (Fig. 3a), mainly metamorphosed basalt, gabbro and dia-base are exposed. The basalts have a slight enrichment of LREE(Fig. 4e) and flat distribution pattern of HFSE without any Nb, Taand Ti anomalies (Dong et al., 2011a), which is consistent with atypical E-MORB pattern (Fig. 4f). These geochemical characteristicssuggest the basalts derivated from an initial stage of extension atmid-oceanic ridge or at transitional ridge segments of a mid-oceanridge such as the Mid-Atlantic Ridge and the East Pacific Rise (Donget al., 2007). LA-ICPMS age dating of the zircons from the gabbro inYanwan ophiolite yields a U–Pb age of 518 ± 2.9 Ma (Dong et al.,2011a). Zircons from the basalt give a U–Pb ages of 483 ± 13 Ma(SHRIMP; Chen et al., 2008b) and 523 ± 26 Ma (TIMS; Lu et al.,2003) constraining the formation time of the ophiolites.

Further to the east, a large part of thrusted ophiolite and sub-duction-related volcanic rocks, mainly pillow lavas and massivebasalts, are exposed at the Heihe and Xiaowangjian area. The pil-low lavas and most of basalts have an island-arc chemical signa-ture (Sun et al., 1995; Yan et al., 2008; Dong et al., 2011a). Forinstance, both the basalts from Heihe and Xiaowangjian displayenrichment of LREE in the chondrite-normalized REE pattern(Fig. 4g), and strong depletion of Nb–Ta, Zr and Ti, as well asenrichment of LILE and Sr in the primitive mantle-normalized traceelement spider diagrams (Fig. 4h). These arc-signatures suggestthat the basalts were formed in an island-arc setting, and the mag-ma was derived from a mantle wedge above a subducted slab(Dong et al., 2011a). Additionally, a few massive basalts in theXiaowangjian section with N-MORB affinity are identified withdepletion of LREE (Fig. 4i) and non HFSE fractionations (Fig. 4j). ASHRIMP U–Pb zircon age of 442 ± 7 Ma has been reported fromthe subduction related diorite at Xiaowangjian (Yan et al., 2008),which intruded in the above basalt and constrains the formationage of the basalts as well as time of subduction.

Around 250 km to the east, the Danfeng area is the traditionallystudied area of the ophiolite in Shangdan suture zone. The basaltsfrom Ziyu exhibit a typical N-MORB chemical composition, whichare significantly depleted in LREE (Fig. 4i) and LILE, as well as flatHFSE pattern without any Nb–Ta and Ti anomalies in the primitivemantle-normalized trace element distribution patterns (Fig. 4j).Thus these rocks are explained to derive from a depleted middle-ocean ridge mantle (Dong et al., 2011a). The basalts from Shangz-hou and Guojiagou have island-arc signatures of strong depletingof Nb–Ta and Ti, and were interpreted as having formed in an oce-anic island-arc setting (Zhang et al., 1994a, 1995b). This conclusionis also supported by isotopic compositions of eNd(t) = +4.9 to +7.3and eSr(t) = �3 to +32, which reflect the mixing between depletedmantle member and enriched mantle II material (Zhang et al.,1995b). Some Cambrian–Ordovician fossils were reported fromthe interlayered cherts in the basalts at Guojiagou valley (Cuiet al., 1995). Accordingly, the subduction of the Shangdan oceanmight have occurred in Cambrian–Ordovician times.

Table 1Geochronological data of the ophiolite and subduction-related gabbros in the North Qinling.

Region Position Rock Method Age and error (Ma) Interpretation Author(s)

Ophiolites in the Shangdan sutureWushan Hualingou Subduction gabbro U–Pb zircon SHRIMP 440 ± 5 Formation Li (2008)

Yuanyangzhen Ophiolitic gabbro U–Pb zircon SHRIMP 457 ± 3 Formation Li (2008)Tianshui Guanzizhen Ophiolitic gabbro U–Pb zircon LA-ICPMS 471 ± 1.4 Formation Yang et al. (2006)

Guanzizhen Ophiolitic gabbro U–Pb zircon SHRIMP 534 ± 9 Formation Li (2008)Guanzizhen Ophiolitic gabbro U–Pb zircon SHRIMP 489 ± 10 Formation Li (2008)Guanzizhen Plagiogranite U–Pb zircon SHRIMP 517 ± 8 Formation Li (2008)Guanzizhen Plagio granite 40Ar/39Ar Amp.plateau 395 ± 5.2 Metamorphism Li (2008)

Fengxian Luohansi Meta-rhyolite U–Pb zircon SHRIMP 524 ± 1.5 Formation Lu et al. (2003)Luohansi Gabbro U–Pb zircon LA-ICPMS 475 ± 4 Intrusion Liu et al. (2007)

Meixian Yanwan Ophiolitic gabbro U–Pb zircon LA-ICPMS 518 ± 2.9 Formation Dong et al. (2011a)Yanwan Basalt U–Pb zircon SHRIMP 483 ± 13 Formation Chen et al. (2008b)Yanwan Basalt U–Pb zircon TIMS 523 ± 26 Formation Lu et al. (2003)

Zhouzhi Xiaowangjian Pillow-lava 40Ar/39Ar Amp.plateau 426 ± 2 Metamorphism Sun et al. (2002b)Shangluo Puyu Pillow-lava Rb–Sr isochron 411 ± 5 Metamorphism Sun et al. (2002b)Danfeng Guojiagou Chert microfossil Cam.-Ordo. Formation Cui et al. (1995)

Subduction related gabbroic-dioritic intrusionsTianshui Guanzizhen Island-arc gabbro U–Pb zircon LA-ICPMS 499 ± 1.8 Intrusion Pei et al. (2005)

Guanzizhen Island-arc gabbro U–Pb zircon TIMS 507 ± 3 Intrusion Pei et al. (2005)Baihua Island-arc diorite U–Pb zircon LA-ICPMS 434 ± 1.5 Intrusion Pei et al. (2007b)

Heihe Houzhenzi Island-arc gabbro U–Pb zircon LA-ICPMS 475 ± 4 Intrusion Liu et al. (2007)Zhouzhi Xiaowangjian Diorite dyke U–Pb zircon SHRIMP 442 ± 7 Intrusion Yan et al. (2008)Shangluo Lajimiao Island-arc gabbro U–Pb zircon LA-ICPMS 422 ± 7 Intrusion Liu et al. (2009)

Lajimiao Gabbro Sm–Nd mineral 402 ± 17 Metamorphism Lu et al. (2003)Shangnan Fushui Island-arc gabbro U–Pb zircon TIMS 514 ± 1.3 Intrusion Chen et al. (2004b)

Fushui Island-arc gabbro U–Pb zircon SHRIMP 501 ± 1.2 Intrusion Li et al. (2006a)Fushui Island-arc gabbro U–Pb zircon SHRIMP 490 ± 10 Intrusion Su et al. (2004)

Tongbai Poshan Kersantite U–Pb zircon SHRIMP 462 ± 9.7 Intrusion Jiang et al. (2009)Yintongpo Gabbro U–Pb zircon SHRIMP 432 ± 8.3 Intrusion Jiang et al. (2009)Yintongpo U–Pb zircon SHRIMP 432 ± 7.5 Intrusion Jiang et al. (2009)Yintongpo U–Pb zircon SHRIMP 470 ± 8.3 Intrusion Jiang et al. (2009)

Ophiolite in the Erlangping back-arc basinQingshui Xincheng Dacite U–Pb zircon SHRIMP 447 ± 8 Formation Li (2008)

Xincheng Dacite U–Pb zircon SHRIMP 448 ± 8 Formation Li (2008)Hongtubao Pillow lava U–Pb zircon LA-ICPMS 443 ± 1.7 Formation He et al. (2007)

Meixian Xieyuguan Basalt U–Pb zircon SHRIMP 472 ± 11 Formation Yan et al. (2007a)Xixia Wantan Pillow lava U–Pb zircon SHRIMP 467 ± 7 Formation Lu et al. (2003)

Wantan Pillow lava Rb–Sr WR isochron 402 ± 22 Metamorphism Sun et al. (2002b)Wantan Chert Radiolarian Cam.-Ordo. Formation Wang et al. (1995)Wantan Chert Radiolarian Cam.-Ordo. Formation Pei et al. (1995)


Further to the east on the northern side of the Tongbai–DabieShan, the Shangdan suture zone is marked by an ophiolitic mel-ange zone (Zhang, 1985; Yan et al., 1989; Xie et al., 1999) with is-land-arc basalts which was formed at 472 ± 17 Ma (Liu et al., inpreparation). They were overprinted by metamorphic events at401 Ma (Liu et al., 1993) and 320 ± 12 Ma (Liu et al., in prepara-tion). The melange zone was overstepped by the Hefei basin sedi-ments (Zhang et al., 2001; Jiang et al., 2005).

The presented geochronological evidence (Table 1) suggeststhat the spreading and formation of the Shangdan oceanic crustshould be from ca. 534 Ma at least to ca. 457 Ma.

3.2. Island-arc intrusions

The NQT is located between the Shangdan suture zone and themelange zone of the Erlangping back-arc basin, also bounded byZhuxia fault in the north. Increasing evidence suggests that theNQT with abundant intrusive complexes represents an island-arcterrane above a subduction zone during Early Paleozoic times(Dong et al., 2007). The island-arc terrane is mainly composed ofPaleoproterozoic plutonometamorphic basement of the QinlingGroup and Early Paleozoic gabbro-granitoid intrusions. The QinlingGroup is exposed in several lenticular blocks along the northernside of the Shangdan suture zone, and was intruded by Early Paleo-zoic and Neoproterozoic intrusions (Zhang et al., 2004a; Lu et al.,2003; Wang et al., 2005). The Neoproterozoic intrusions mainly in-clude the Tianshui granitoid in West Qinling with a LA-ICPMS U–Pb

zircon age of 923 ± 3 Ma (Liu et al., 2006) and 915–978 Ma (Peiet al., 2007c), Dehe granite at 964 ± 5.2 Ma (TIMS) and943 ± 18 Ma (SHRIMP) (Chen et al., 2004b), Niujiaoshan granitewith TIMS U–Pb zircon age of 959 ± 3.6 Ma (Wang et al., 1998)and SHRIMP age of 955–929 Ma (Wang et al., 2005), and Caiwagranite of LA-ICPMS U–Pb zircon age of 889 ± 10 Ma (Zhanget al., 2004a) in East Qinling. Additionally, the Qinling Groupunderwent amphibolite facies metamorphism at ca. 990 ± 0.4 Ma(Chen et al., 1991) and ca. 517 Ma (Dong et al., 2011b), greenschistfacies metamorphism at ca. 425 ± 48 Ma (Chen et al., 1991). TheseNeoproterzoic magmatic and metamorphic records reflect the Neo-proterozoic aggregation of the NQT to the NCB (Dong et al., 2008a).

The North Qinling island-arc terrane is characterized by largeamount of Lower Paleozoic gabbroic and granitic intrusions,which related to the subduction along the Shangdan suture zone.Several gabbroic intrusions with typical island-arc geochemicalsignatures are distributed along the island-arc terrane, from westto east, at Guanzizhen (Pei et al., 2005), Baihua (Pei et al., 2007b),Sifangtai (Liu et al., 2008a), Qinwangshan (Zhang and An, 1990),Lajimiao (Li et al., 1993), and Fushui (Dong et al., 1997) (Fig. 3).For instance, the Fushui gabbros show enrichment of LREE, LILEand depletion of Nb–Ta, as well as low initial 143Nd/144Nd ratios(0.51143–0.51162) and eNd values (�3.5 to +2.0), and high eSr

values ranging from +81 to +135, suggesting the magma was de-rived from a mantle wedge where was influenced by subductionmaterials (Dong et al., 1997). The Lajimiao mafic intrusions arecharacterized by high Ba, Pb and Sr contents, low Nb, Zr and Ni

Fig. 5. Sketch map showing the ages and distributions of the granitoid, diorite and gabbroic plutons in the Qinling orogen.


contents, and constant eNd values of +2.0 while eSr values rangingfrom �6.4 to +31.2, suggesting large amount of sediments hadbeen carried into the mantle by the subduction of the Shangdanoceanic crust (Li et al., 1993). This conclusion is also supportedby the geochemical characteristics of significant depletion ofNb–Ta and Ti, and enrichment of Th, Pb and Sr in the mafic rocksfrom Guanzizhen, Baihua and Sifangtai intrusions (Pei et al.,2005, 2007b; Liu et al., 2008a). Detailed geochemical studies re-vealed that these mafic intrusions were derived from a mantlewedge source above the subducted slab. U–Pb zircon ages of507 ± 3.0 Ma and 499 ± 1.8 Ma are from Guanzizhen (TIMS; Peiet al., 2005), 434 ± 1.5 Ma from Baihua (LA-ICPMS; Pei et al.,2007b), 475 ± 4 Ma from Houzhenzi (LA-ICPMS; Liu et al.,2007), 422 ± 7 Ma from Lajimiao (LA-ICPMS; Liu et al., 2009),and 514 ± 1.3 Ma (TIMS; Lu et al., 2003), 501 ± 1.2 Ma (SHRIMP;Li et al., 2006a) and 490 ± 10 Ma (SHRIMP; Su et al., 2004) fromFushui. Further to the east, this subduction-related mafic mag-matic zone can be connected with the gabbros to the north ofthe Tongbai Mountains, which yields SHRIMP U–Pb zircon agesranging of 470–432 Ma (Jiang et al., 2009). All these ages (Table 1)suggest that the subduction along the Shangdan zone occurredfrom ca. 514 to ca. 422 Ma.

A large number of subduction and/or collisional granitoids in-truded into the NQT on the northern side of the Shangdan suture(Zhang et al., 2001; Wang et al., 2009b), which are, from west toeast, the Tangzang diorite, Taibai and Heihe granitoids, Laoyuand Zhongnanshan granitoids, Zaoyuan, Huangbaicha and Tieyupugranitoids in Danfeng area, Huichizi granitioid in Shangnan, Piao-chi and Anjiping granitoids in west Henan area, etc. (Fig. 5). InWest Qinling, the Early Paleozoic granitoids are mostly character-ized by I-type geochemical compositions (Wang et al., 2009b)and U–Pb formation ages of 455–414 Ma (Table 2), which are rep-resented by Caochuanpu granite (434 ± 10 Ma), Yanjiadian diorite(441 ± 10 Ma) (Zhang et al., 2006), Wangjiacha diorite (455 ±1.7 Ma), Tangzang granitoid (455 ± 1.9 Ma) (Chen et al., 2008a),and Honghuapu diorite (414 ± 1.5 Ma) (Xu et al., 2007). Lu (2000)also reported a whole-rock Rb–Sr age of 455 Ma for the Taibaigranite. It is noticeable that all these Early Paleozoic plutons onlydistributed on the northern side of the Shangdan suture zone,especially within the North Qinling island-arc terrane, while the

Triassic granitoids are almost only exposed in the western SouthQinling belt (Fig. 5).

In middle part of the NQT, the granitic plutons still show I-typeaffinity (Wang et al., 2009b) and U–Pb formation ages of 442–401 Ma (Table 2) for the granitoids exposing from Heihe to Zhon-gnanshan areas. Except a U–Pb age of 434 ± 5.5 Ma (Lu et al.,2003) from Laoyu valley, the other seven U–Pb ages ranging from442 to 401 Ma were from Heihe area (Fig. 5 and Table 2). The eastNQT is characterized by S-type granitoids, such as the Piaochi gran-ite with U–Pb zircon ages of 495 ± 6 Ma and 492 ± 14 Ma (Wanget al., 2009b), as well as a Rb–Sr age of 486 Ma (Lu, 2000). Mean-while, the Anjiping S-type granite also yields an Rb–Sr age of452 ± 2 Ma (Chen et al., 1991). Except a few S-type granitoids ex-posed in Piaochi, Danfeng and Erlangping areas, most of the gra-nitic plutons in the Danfeng–Shangnan region belong to I-typeseries (Wang et al., 2009b). Isotopic geochemistry indicates thatthese plutons can be attributed to the northward subduction ofthe Shangdan ocean crust (Chen et al., 1995). U–Pb zircon ages of488–403 Ma (487 ± 1.1 Ma, 488 ± 1.4 Ma, Xue et al., 1996a;446 ± 19 Ma, Zhang et al., 2006; 440 ± 10 Ma, 428 ± 7 Ma and409 ± 4 Ma, Lu et al., 2003; 452 Ma and 403 Ma, Lu, 2000) andwhole rock Rb–Sr ages of 457–411 Ma (Lu, 2000) (Fig. 5 andTable 2) of the granitoids suggest the subduction and subsequentcollision occurred within 488–403 Ma.

Debates still are existed whether the Huichizi granitoid belongto S-type granite (Zhang et al., 1996; Li et al., 2001) or I-type gran-ite series (Wang et al., 2009b). Based on petrogenesis and geo-chemical investigations, however, all authors suggested that theformation of the Huichizi granite was related to the convergencealong the Shangdan suture. U–Pb zircon ages of 445 ± 4.6 Ma (Donget al., 2011b), 437 ± 58 Ma (Li et al., 2000a,b) and 434 ± 7 Ma(Wang et al., 2009b), as well as a Rb–Sr isochron age of486 ± 15 Ma (Zhang et al., 1996) give limitations to the formationtiming of the Huichizi granitoids as well as for subduction.

Additionally, elaborated mapping reveals several plutons, suchas the Xizhuanghe and Wuduoshan granitoids, which intruded intothe Erlangping melange in west Henan areas (Figs. 3 and 5). De-tailed geochemical studies (Guo, 2010) suggest that the Xizhuan-ghe granitoid was formed by mixing of the re-melted subductedoceanic slab and partial melts from the overlying mantle wedge.

Table 2Geochronological data of the plutons from the Qinling orogen.

Position Pluton Rock Method Age and error (Ma) Interpretation Author(s)

Southern margin of the North China BlockXi’an Lantian Granite U–Pb zircon SHRIMP 138 ± 2.5 Intrusion Mao et al. (2005)

Huanshan Granite U–Pb zircon SHRIMP 146 ± 15 Intrusion Mao et al. (2005)Huashan Granite 40Ar/39Ar Bio. 106 ± 1.4 Cooling Zhu (1995)Niangniangshan Granite U–Pb zircon SHRIMP 141 ± 2.5 Intrusion Mao et al. (2005)Cuihuashan Granite 40Ar/39Ar Mus. 100 ± 2.3 Cooling Zhu (1995)Mangling Granite 40Ar/39Ar Bio. 136 ± 2.6 Cooling Zhu (1995)

Xiao Qinling Donggou Granite-porphyry U–Pb zircon SHRIMP 112 ± 1 Intrusion Ye et al. (2006)Donggou Molybdenite Re–Os ICP-MS 116 ± 1.7 Metallogenic age Ye et al. (2006)Nannihu Molybdenite Re–Os ICP-MS 141 ± 2.1 Metallogenic age Li et al. (2003)Nannihu Granite-porphyry U–Pb zircon SHRIMP 158 ± 3 Intrusion Mao et al. (2005)Nannihu Molybdenite Re–Os ICP-MS 148 ± 10 Metallogenic age Huang et al. (1994)Shangfanggou Granite-porphyry U–Pb zircon SHRIMP 157 ± 2.7 Intrusion Mao et al. (2005)Shangfanggou Molybdenite Re–Os ICP-MS 144 ± 2.1 Metallogenic age Li et al. (2003)Sandaozhuang Molybdenite Re–Os ICP-MS 145 ± 2.2 Metallogenic age Li et al. (2003)Majiawa Molybdenite Re–Os ICP-MS 232 ± 11 Metallogenic age Wang et al. (2010)Huanglongpu Molybdenite Re–Os ICP-MS 221 ± 0.3 Metallogenic age Stein et al. (1997)Huanglongpu Molybdenite Re–Os ICP-MS 216 ± 2 Metallogenic age Du et al. (1994)Huanglongpu Molybdenite Re–Os ICP-MS 222 ± 2 Metallogenic age Huang et al. (1994)Jinduncheng Molybdenite Re–Os ICP-MS 138 ± 0.5 Metallogenic age Stein et al. (1997)Jinduncheng Molybdenite Re–Os ICP-MS 141 ± 4 Metallogenic age Du et al. (1994)Jinduncheng Molybdenite Re–Os ICP-MS 127 ± 0.5 Metallogenic age Huang et al. (1994)Jinduncheng Molybdenite Re–Os ICP-MS 129 ± 4 Metallogenic age Huang et al. (1994)Jinduncheng Molybdenite Re–Os ICP-MS 139 ± 23 Metallogenic age Du et al. (1994)Jinduncheng Molybdenite Re–Os ICP-MS 135 ± 6 Metallogenic age Du et al. (1994)Jinduncheng Granite-porphyry U–Pb zircon LA-ICPMS 141 ± 0.45 Intrusion Zhu et al. (2008a)Laoniushan Monzonite U–Pb zircon LA-ICPMS 146 ± 0.55 Intrusion Zhu et al. (2008a)Lianhuagou Diorite U–Pb zircon LA-ICPMS 147 ± 2.0 Intrusion Zhang et al. (2010)

Monzoporphyry U–Pb zircon LA-ICPMS 144 ± 8.9 Intrusion Zhang et al. (2010)Qiushuwan Copper platinum Re–Os ICP-MS 146 ± 1.8 Metallogenic age Guo et al. (2006)Qiushuwan Molybdenite Re–Os ICP-MS 147 ± 4 Metallogenic age Guo et al. (2006)Leimengou Granite-porphyry U–Pb zircon SHRIMP 136 ± 1.5 Intrusion Li et al. (2006b)Leimengou Molybdenite Re–Os ICP-MS 132 ± 2 Metallogenic age Li et al. (2006b)Dahu Molybdenite Re–Os ICP-MS 234 ± 18 Metallogenic age Li et al. (2008)

Lingbao Dahu Molybdenite Re–Os ICP-MS 223 ± 2.8 Metallogenic age Li et al. (2007b)Quanjiayu Molybdenite Re–Os ICP-MS 130 ± 1.5 Metallogenic age Li et al. (2007b)

Luoshan Baishipo Granite-porphyry U–Pb zircon SRIMP 142 ± 4.3 Intrusion Li et al. (2007a)Baofeng Dayiing Trachyandesite U–Pb zircon SHRIMP 117 ± 2 Formation Xie et al. (2007)

TongbaiTongbai Laowan Monzonite U–Pb zircon SHRIMP 132 ± 2.4 Intrusion Liu et al. (2008b)Weishancheng Liangwan Granodiorite U–Pb zircon SHRIMP 133 ± 2.3 Intrusion Jiang et al. (2009)

Liangwan Monzonite U–Pb zircon SHRIMP 137 ± 3.4 Intrusion Jiang et al. (2009)Liangwan Plagioclase granite Rb–Sr whole rock 128 ± 9.5 Intrusion Zhang et al. (2000b)Liangwan Granodiorite U–Pb zircon SHRIMP 133 ± 2.3 Intrusion Jiang et al. (2009)

Granitoids in the North Qinling BeltTianshui Guanzizhen Plagiogranite 40Ar/39Ar Amp. 395 ± 5.2 Cooling Li (2008)

Baihua Granite Rb–Sr 430 Cooling Li et al. (2005)Dangchuan Granite Rb–Sr 391 ± 21 Cooling Wen et al. (2008)Huoyanshan Granite Rb–Sr 399 ± 7 Cooling Wen et al. (2008)

Granitoids in the North Qinling BeltZhangjiachuan Yanjiadian Diorite U–Pb zircon 441 ± 10 Intrusion Li (2008)Gangu Guanzizhen Granodiorite U–Pb zircon TIMS 507 ± 3 Intrusion Lu et al. (2003)Tianshui Baihua Gabbro U–Pb zircon LA-ICPMS 449 ± 3.1 Intrusion Pei et al. (2007d)Tianshui Caochuanpu Granite U–Pb zircon 434 ± 10 Intrusion Zhang et al. (2006)

Dangchuan Monzogranite U–Pb zircon LA-ICPMS 438 ± 3 Intrusion Wang et al. (2008)Longxian Wangjiacha Quartz-diorite U–Pb zircon LA-ICPMS 455 ± 1.7 Intrusion Chen et al. (2007)Longshan Longshan Basic dyke group U–Pb zircon 440 Ma Intrusion Chen et al. (2006)Fengxian Tangzang Quartz-diorite U–Pb zircon LA-ICPMS 455 ± 1.9 Intrusion Chen et al. (2008a)Fengxian Honghuapu Tonalite U–Pb zircon LA-ICPMS 450 ± 1.8 Intrusion Wang et al. (2006)

Honghuapu Tonalite U–Pb zircon LA-ICPMS 414 ± 1.5 Intrusion Xu et al. (2008)Shangdan fault Yanwan Monzogranite U–Pb zircon 414 ± 1.9 Intrusion Wang et al. (2009a)Zhouzhi Heihe Granite U–Pb zircon 401 ± 14 Intrusion Lerch et al. (1995)

Heihe Granodiorite Pb-Pb zircon 402 ± 0.8 Intrusion Xue et al. (1996a)Heihe Diorite U–Pb zircon 406 ± 4 Intrusion Lerch et al. (1995)Heihe Granite U–Pb zircon 410 ± 11 Intrusion Lerch et al. (1995)Heihe Granite U–Pb zircon 414 ± 4 Intrusion Lerch et al. (1995)Heihe Granite U–Pb zircon 422 ± 4 Intrusion Lerch et al. (1995)Heihe Granodiorite U–Pb zircon 470 ± 9 Intrusion Xue et al. (1996a)

Zhouzhi Xiaowangjian Diorite dyke U–Pb zircon SHRIMP 442 ± 7 Intrusion Yan et al. (2007a)Huxian Laoyu Granodiorite U–Pb zircon TIMS 434 ± 5.5 Intrusion Lu et al. (2003)Danfeng Danfeng Granite U–Pb zircon SHRIMP 409 ± 3.6 Intrusion Lu et al. (2003)

Taohuapu Diorite U–Pb zircon 487 ± 1.1 Intrusion Xue et al. (1996a)Nangou Trondjemite Pb-Pb zircon 487 ± 6 Intrusion Sun (1991)

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Table 2 (continued)

Position Pluton Rock Method Age and error (Ma) Interpretation Author(s)

Taohuapu Trondjemite U–Pb zircon 488 ± 1.4 Intrusion Xue et al. (1996a)Ziyu Monzonite U–Pb zircon 446 ± 19 Intrusion Zhang et al. (2006)Wuguan Monzonite U–Pb zircon TIMS 439 ± 9.5 Intrusion Lu et al. (2003)

Shangnan Shangnan Granite vein U–Pb zircon SHRIMP 499 ± 4.3 Intrusion Lu et al. (2003)Zaojiao Diorite U–Pb zircon SHRIMP 428 ± 6.7 Intrusion Lu et al. (2003)

Shangnan Huichizi Granite U–Pb zircon LA-ICPMS 421 ± 27 Ma Intrusion Wang et al. (2009b)Huichizi Granodiorite U–Pb zircon LA-ICPMS 434 ± 7 Intrusion Wang et al. (2009b)Huichizi Granite vein U–Pb zircon SHRIMP 492 ± 14 Intrusion Wang et al. (2005)Huichizi Granite U–Pb zircon SIMS 434 ± 7 Ma Intrusion Wang et al. (2009b)

Shiziping Huichizi Granodiorite U–Pb zircon 437 ± 58 Intrusion Li et al. (2000b)Luanchuan Zhangjiadazhuang Granodiorite U–Pb zircon 399 ± 14 Intrusion Tian (2003)Erlangping Manziying Granite U–Pb zircon LA-ICPMS 459 ± 0.9 Intrusion Guo et al. (2010)

Xizhuanghe Quartz-diorite U–Pb zircon 480 ± 7 Intrusion Xue et al. (1996a)Xizhuanghe Granite U–Pb zircon LA-ICPMS 460 ± 0.9 Intrusion Guo (2010)Xizhuanghe Mafic enclusive U–Pb zircon LA-ICPMS 461 ± 1.4 Intrusion Guo (2010)

Nanzhao Banshanping Tonalite U–Pb zircon 430 ± 16 Intrusion Tian (2003)Xixia, Henan Erlangping Granite U–Pb zircon TIMS 441 ± 0.7 Intrusion Lu et al. (2003)Wulichuan Piaochi Monzonite U–Pb zircon LA-ICPMS 495 ± 6 Intrusion Wang et al. (2009b)Tongbai Poshan, Weishancheng Kersantite U–Pb zircon SHRIMP 462 ± 9.7 Intrusion Jiang et al. (2009)

Yintongpo Gabbro U–Pb zircon SHRIMP 432 ± 8.3 Intrusion Jiang et al. (2009)Yintongpo Gabbro U–Pb zircon SHRIMP 432 ± 7.5 Intrusion Jiang et al. (2009)Yintongpo Gabbro U–Pb zircon SHRIMP 470 ± 8.3 Intrusion Jiang et al. (2009)Taoyuan Quartz-diorite U–Pb zircon SHRIMP 431 ± 8.2 Intrusion Jiang et al. (2009)Taoyuan Granodiorite U–Pb zircon SHRIMP 433 ± 11 Intrusion Jiang et al. (2009)Taoyuan Biotite-granite U–Pb zircon SHRIMP 427 ± 9.1 Intrusion Jiang et al. (2009)

Shangnan, Shaanxi Shangnan Granite Rb–Sr 375 ± 23 Ma Cooling Wen et al. (2008)Granite Rb–Sr 375 ± 6 Ma Cooling Wen et al. (2008)

Granitoids in the Southern Qinling BeltWest Qinling Yeliguan Granite U–Pb zircon SRIMP 245 ± 6 Intrusion Jin et al. (2005)

Xiahe Granite U–Pb zircon SRIMP 238 ± 4 Intrusion Jin et al. (2005)Tianshui Yindaosi Rhyolite U–Pb zircon LA-ICPMS 211 ± 2.6 Intrusion Xu et al. (2007)East Tianshui Wuzhai Granite U–Pb zircon TIMS 174 ± 35 Intrusion Li et al. (2005)

Shimen Monzogranite U–Pb zircon LA-ICPMS 220 ± 2 Intrusion Wang et al. (2008)Chengxian Mishuling Mafic enclaves U–Pb zircon LA-ICPMS 212 ± 5 Intrusion Qin et al. (2009b)

Mishuling Monzogranite U–Pb zircon LA-ICPMS 213 ± 3 Intrusion Qin et al. (2009b)Chengxian Miba Monzogranite U–Pb zircon 220 ± 1 Intrusion Sun et al. (2000)

Miba Monzogranite U–Pb zircon 211 ± 2 Intrusion Sun et al. (2000)Lueyang Xinyuan Diorite granite U–Pb zircon 214 ± 2 Intrusion Sun et al. (2000)

Jiangjiaping Monzogranite U–Pb zircon 206 ± 2 Intrusion Sun et al. (2000)Lueyang Zhangjiaba Granite U–Pb zircon 219 ± 2 Intrusion Sun et al. (2000)Mianxian Guangtoushan Monzogranite U–Pb zircon LA-ICPMS 199 ± 4 Intrusion Wu et al. (2009)

Guangtoushan Tonalite U–Pb zircon LA-ICPMS 221 ± 6 Intrusion Wu et al. (2009)Mianxian Guangtoushan Bio-plagiogranite U–Pb zircon 216 ± 2 Intrusion Sun et al. (2000)

Guangtoushan Monzogranite U–Pb zircon 209 ± 3 Intrusion Chen et al. (2009)Guangtoushan Monzogranite U–Pb zircon 196 ± 3 Intrusion Chen et al. (2009)

Foping Xichahe Granites U–Pb zircon LA-ICPMS 212 ± 2 Intrusion Qin et al. (2008a)Foping Xichahe Adakitic tonalite U–Pb zircon LA-ICPMS 213 ± 2.2 Intrusion Qin et al. (2007a)Foping Wulong Granite U–Pb zircon LA-ICPMS 208 ± 2 Intrusion Qin et al. (2008a)Foping Laocheng Granite U–Pb zircon SRIMP 217 ± 3.4 Intrusion Jiang et al. (2010)Ningshan Yanzhiba Granite U–Pb zircon SRIMP 210 ± 5.0 Intrusion Jiang et al. (2010)Ningshan Dongjiangkou Monzogranite U–Pb zircon 210 ± 3 Intrusion Sun et al. (2000)

Dongjiangkou Monogranite U–Pb zircon SRIMP 218 ± 2.4 Intrusion Jiang et al. (2010)Dongjiangkou Monzogranite U–Pb zircon concorde 219 ± 2 Intrusion Yang et al. (2009)

Qinling Cuihuashan Granite U–Pb zircon SRIMP 227 ± 3.6 Intrusion Jiang et al. (2010)Zhashui Zhashui Granite U–Pb zircon LA-ICPMS 224 ± 1.1 Intrusion Gong et al. (2009)

Zhashui Rapakivi granite U–Pb zircon 213 ± 1.8 Intrusion Hu et al. (2004)Zhashui Monzogranite U–Pb zircon concorde 209 ± 2 Intrusion Yang et al. (2009)

Zhaoshui Caoping Granite U–Pb zircon LA-ICPMS 224 ± 1.1 Intrusion Gong et al. (2009)Shangzhou Shahewan Rapakivi 40Ar–39Ar Bio. 213 ± 2 Intrusion Zhang et al. (1999)

Shahewan Rapakivi Rb–Sr mineral 213 ± 0.5 Intrusion Zhang et al. (1999)Shahewan Rapakivi U–Pb zircon 212 ± 1.8 Intrusion Zhang et al. (1999)Shahewan Rapakivi U–Pb zircon LA-ICPMS 212 ± 0.93 Intrusion Gong et al. (2009)Shahewan Rapakivi U–Pb zircon 209 ± 1.4 Intrusion Zhang et al. (2009a)

Mafic enclaves U–Pb zircon 197 ± 3.4 Intrusion Zhang et al. (2009a)Baoji Qinlingliang Rapakivi U–Pb zircon 217 ± 3.2 Intrusion Lu et al. (1999)Baoji Laojunshan Rapakivi U–Pb zircon 214 ± 3 Intrusion Lu et al. (1999)Taibai Xiba Monzogranite U–Pb zircon LA-ICPMS 219 ± 1 Intrusion Zhang et al. (2009b)

Xiba Granodiorite U–Pb zircon LA-ICPMS 218 ± 1 Intrusion Zhang et al. (2009b)Foping Foping Granulite U–Pb zircon 221 ± 3.6 Metamorphism Yang et al. (1999)

Northwest margin of the South China BlockBikou Yangba Host monzogranite U–Pb zircon LA-ICPMS 207 ± 2 Intrusion Qin et al. (2009a)Bikou Yangba Mafic enclaves U–Pb zircon LA-ICPMS 208 ± 2 Intrusion Qin et al. (2009a)Bikou Yangba Granites U–Pb zircon LA-ICPMS 209 ± 2 Intrusion Qin et al. (2008a)Bikou Yangba Granodiorite U–Pb zircon LA-ICPMS 215 ± 8.3 Formation Qin et al. (2005)


Fig. 6. Chondrite-normalized REE patterns and primitive mantle-normalized trace element spider diagrams for the ophiolite and associated volcanic rocks along theErlangping back-arc basin, Northern Qinling. The geochemical data are from Dong et al. (2011a) except for the data of Tuanhe basalts are from Sun et al. (1996a,b). The valuesof OIB, E-MORB, N-MORB and Primitive Mantle are from Sun and McDonough (1989).


Therefore, LA-ICPMS U–Pb zircon ages of 460 ± 0.9 Ma for graniteand 461 ± 1.4 Ma for mafic enclaves, as well as the U–Pb age of459 ± 0.9 Ma for the Manziying granitoid (Guo et al., 2010) canbe interpreted as the time of subduction. The timing of subduction

is also supported by the U–Pb zircon ages of 458–442 Ma for theWuduoshan granitoid (Zhang et al., 2001).

Taking in account all the ages of gabbros and granites in theNQT (Table 2), we propose that the northward subduction of the

Table 3Geochronological data of the metamorphism in the North Qinling.

Position Unit Rock Method Age and error (Ma) Interpretation Author(s)

High–ultrahigh pressure metamorphismLushi, Henan Shiziping Elogite U–Pb zircon SHRIMP 507 ± 38 Metamorphism Yang et al. (2003)Lushi, Henan Shiziping Gneiss U–Pb zircon LA-ICPMS 509 ± 12 Metamorphism Liu et al. (2003)Shangnan, Shaanxi Xigou Basic granulite U–Pb zircon LA-ICPMS 485 ± 3.3 Metamorphism Chen et al. (2004a)Shangnan, Shaanxi Xigou Leptite U–Pb zircon LA-ICPMS 518 ± 12 Metamorphism Liu et al. (2003)Shangnan, Shaanxi Songshugou Garnet-amphibolite U–Pb zircon LA-ICPMS 514 ± 9 Metamorphism Liu et al. (2003)Shangnan, Shaanxi Songshugou Garnet pyroxenite U–Pb zircon SHRIMP 501 ± 10 Metamorphism Su et al. (2004)

Amphibolite-facies metamorphism and coolingLushi, Henan Shiziping Eclogite Sm–Nd mineral 400 ± 16 Exhumation Hu et al. (1996)Xinyang, Henan Shisanliqiao Amphibolite 40Ar/39Ar Amp. 401 ± 3.8 Cooling Liu et al. (1993)Xixia, Henan Erlangping Meta-basalt Rb–Sr Whole rock 401 ± 6.3 Metamorphism Sun et al. (1996a)Shangluo, Shaanxi Lajimiao Norite gabbro Sm–Nd mineral 402 ± 17 Metamorphism Li et al. (1993)Erlangping, Henan Wantan Pillow lava Rb–Sr whole rock 402 ± 22 Metamorphism Sun et al. (2002b)Shangxian, Shaanxi Puyu Pillow-lava Rb–Sr whole rock 411 ± 5 Metamorphism Sun et al. (2002b)Tianshui Dongcha Kuanping Amphibolite U–Pb zircon 415 ± 2 Metamorphism He et al. (2007)Zhouzhi, Shaanxi Xiaowangjian Pillow-lava 40Ar/39Ar Amp. 426 ± 2 Cooling Sun et al. (2002b)

Deformation and cooling ageTianshui Yuanlong Granite-mylonite 40Ar/39Ar Bio. 351 ± 1.7 Deformation Ding et al. (2009)Xinyang, Henan Xinyang Granite-mylonite 40Ar/39Ar Bio. 347 ± 2.2 Deformation Ding et al. (2009)Xixia, Henan Qinling Group Hornblende 40Ar/40Ar Amp. 353 ± 0.2 Cooling You et al. (1991)Xixia, Henan Qinling Group Migmatite 40Ar/39Ar Bio. 358 ± 1.4 Cooling Zhu (1995)Luanchuan Machaoying Mica schist 40Ar/39Ar Mus. 372 Ma Deformation Song et al. (2009)


Shangdan oceanic lithosphere along the southern edge of NQT wasduring ca. 514 Ma to ca. 402 Ma.

3.3. Back-arc basin

The existence of a back-arc basin is indicated by the exposure oflarge amounts of ophiolitic ultramafic–mafic suite and associatedvolcanic rocks distributed along the northern side of the North Qin-ling (island-arc) terrane at the Qingshui, Boyang, Caoliangyi andYinggezui in Western Qinling, and Wantan in Eastern Qinling(Fig. 3).

In the Western Qinling belt, the Qingshui volcanic unit com-prises predominantly pillow basalt in the south, and minor andes-ite and rhyolite in the north. These lithologies are separated fromeach other by either brittle faults or ductile shear zones. Ten kilo-meters to the southeast, dark-green massive metabasalts are ex-posed at Boyang (Fig. 3a). The geochemical composition indicatesthat the basaltic magmas of Qingshui and Boyang are characterizedby slight enrichment of LREE in the chondrite-normalized REE pat-terns (Fig. 6a), and approximate flat HFSE distribution patternswith slight negative Nb–Ta Ti anomalies in the primitive mantle-normalized trace element spider diagrams (Fig. 6b). Therefore, theyare inferred that was derived from a primitive or slightly enrichedmantle with an affinity to E- or T-MORB in a spreading center butimposed by subducted material (Dong et al., 2011a). Taking on theregional geology, the bimodal rock association (Li, 2008), and com-parison with samples from the other localities of the study area, itcan be inferred that the Boyang succession most likely formed in aback-arc basin. The basalts yield a LA-ICPMS U–Pb zircon age of443 ± 1.7 Ma, which were intruded by a diabase dyke with a U–Pb zircon age of 386 ± 7.9 Ma (He et al., 2007). Additionally, Li(2008) also reported SHRIMP U–Pb zircon ages of 447 ± 8 Ma and448 ± 8 Ma from dacites exposed within the melange. Therefore,we prefer the ages of 450–440 Ma to constrain the time of spread-ing of the back-arc basin (Table 1).

Further east, the Caoliangyi volcanic unit is a part of the Caotan-gou Group (same as Erlangping Group in East Qinling), which com-prises mostly metamorphosed basalt, andesite, rhyolite and clasticsediments with Ordovician fossils (Zhang et al., 2001). The metaba-salts are mostly showing flat REE and HFSE distribution patterns(Figs. 6c and d), however, the strong negative Nb–Ta anomalies

and positive Sr anomalies suggest that the magma source wasmodified by subducted materials (Dong et al., 2011a). This is alsosupported by the isotopic geochemistry of high eNd values (+5.4to +12.8) and initial 87Sr/86Sr ratios of 0.703438–0.708329 (Yanet al., 2007a). Around twenty kilometers east, the Yinggezui ophi-olite and associated volcanic units are exposed within a fault-bounded tectonic nappe emplaced along the NE trending Taibai–Fengxian thrust, which was reactivated by Mesozoic sinistralstrike-slip motion. Along the Yinggezui section, highly deformedimbricates of ultramafic rocks, gabbro, basalt and andesite blocksare well preserved in fault or shear zone contact with each other.Detailed geochemical studies reveal that the basalts show MORBaffinity while the gabbros display MORG geochemical signaturewith strong depletion of LREE and positive Eu anomalies in thechondrite-normalized REE patterns (Fig. 6 e). However, the ande-sites are characterized by strongly depleted in Nb–Ta, P and Ti,and enriched in LILE and Sr (Fig. 6f) showing subduction-relatedfeatures (Chen et al., 2008b; Dong et al., 2011a). Therefore, it is pro-posed that the ultramafic rocks, gabbros, basalts and andesiteswere formed in a back-arc basin. However the mantle sourcemay be either inhomogeneous or different for the observed rocksuite. The basalt from Xieyuguan has a SHRIMP U–Pb zircon ageof 472 ± 11 Ma (Yan et al., 2007a), which is consistent with theage of fossils, and suggests the formation of the back-arc basinwas during Ordovician.

In the eastern part of the Qinling Mountains, the Wantan area(Fig. 3) exposes the classical outcrops of the Erlangping ophiolite,which is one of the three units of the Erlangping Group. Alongthe Wantan section, pillow lavas and massive basalts are interlay-ered with radiolarian cherts. The basaltic rocks are characterizedby enrichment of LREE (Fig. 6g), strong depletion of Nb, Ta and Ti(Fig. 6h), which are regarded as fingerprints of subduction (Sunet al., 1996a; Xue et al., 1996b; Lu et al., 2003; Dong et al.,2011a), However, such signatures can also be produced in the ini-tial stage of extension of a back-arc basin (Dong et al., 2011a). Sev-eral kilometers to the east, the Erlangping basalts are characterizedby slight enrichment of LREE (Fig. 6i) and flat HFSE distributionpatterns (Fig. 6j) showing E-MORB ophiolite chemical composition(Sun et al., 1996b). Taking into account regional geology and theErlangping association in the other regions, we propose that thebasaltic rocks in the Wantan section were formed in a back-arc ba-


sin, where an initial spreading center was superimposed by someNb–Ta depleted material.

Although the Erlangping and Danfeng volcanic units were pro-posed as nappes that represent a same unit (Faure et al., 2001), de-tailed mapping as well as geological and geochemicalinvestigations revealed that the Danfeng unit is different fromthe Erlangping rocks in composition, deformation and metamor-phism. Additionally, Xue et al. (1996a,b) proposed that the Erlang-ping zone is the major suture between NCB and SCB whileShangdan zone represents a back-arc basin related to the south-ward subduction of Erlangping oceanic crust. This hypothesis is ru-led out by the following evidences. (1) The Erlangping melangecomprises basaltic rocks, andesites and rhyolites, with a few ofultramafic rocks in Western Qinling, bearing clastic rocks and min-or marbles. In comparison, the Danfeng melange consists mainly ofgabbros, basalts, andesites and amount of ultramafic rocks withoutany rhyolites. These petrological compositions indicate that Shang-dan (Danfeng) ocean was more evolved and larger than Erlangpingocean. The occurrence of rhyolites in Erlangping melange may im-plies that Erlangping ocean was evolved from a continental rift. (2)Although Some workers argued that the Erlangping Group formedin intra-oceanic arc (e.g. Okay and Sengör, 1993; Xue et al.,1996a,b; Zhai et al., 1998; Ratschbacher et al., 2003, 2006; Hackeret al., 2004), both Danfeng melange and Erlangping melange havearc-type rocks. However, the Danfeng melange is characterized bycomposing of N-MORB and E-MORB as well as arc-related volcanicrocks, whereas the Erlangping melange is mainly of arc-related vol-canic rocks with E-MORB rocks. Additionally, the main boundariesof exhumation, deformation and metamorphism between NCB andSCB are located along the Shangdan zone. Therefore, we prefer thatthe Shangdan suture represents the boundary between NCB andSCB, whereas the Erlangping zone was formed by closure of aback-arc basin.

Lu et al. (2003) reported a SHRIMP U–Pb zircon age of467 ± 7 Ma from the pillow lava, which can be regarded as the for-mation age of the back-arc basin. This result is also supported byother indirect age dating, such as the basalts were intruded bythe Xizhuanghe granite at 460 ± 0.9 Ma (Guo, 2010), and over-printed by greenschist facies metamorphism with a whole rockRb–Sr isotopic isochron age of 402 ± 22 Ma for the pillow-lava

Fig. 7. Sketch map showing the ages and distributions of the ophio

(Sun et al., 1996a). Early to Middle Ordovician radiolarians andCambrian microfossils within cherts of the Erlangping ophiolitein Wantan were also reported (Wang et al., 1995).

Additional geochronological age dating suggests that the back-arc basin has been in existence since Early Paleozoic times. De-tailed work indicates that some meta-clastic rocks related to theclosure of the Erlangping back-arc basin can be distinguished fromthe Kuanping Group. A geochronological study of meta-clasticrocks reveals that the detrital zircon ages yield two main clustersof about 3319 Ma and ca. 2153–1806 Ma, which were attributedto S-NCB and NQT respectively, suggesting the clastic materials de-rived from both the S-NCB and NQT (Zhang et al., 1994b). Theyoungest detrital zircon age cluster from micaschist samplesranges from ca. 610 to ca. 500 Ma (Zhang et al., 1994b, 2004a;Yan et al., 2008), and the micaschists can be interpreted as overly-ing accretionary wedge material related to the closure of theErlangping back-arc basin.

On basis of high/ultra-high pressure metamorphism on thenorthern edge of the NQT, which is supported by the existence ofeclogites (Hu et al., 1995, 1996) and diamond (Yang et al., 2003),the closure age of the back-arc basin can be constrained. WithN-MORB and OIB geochemical compositions, the protolith of eclog-ite was suggested to derive from oceanic crust (Zhang et al., 2003).Both the eclogites and associated gneisses bearing diamonds (Yanget al., 2003) indicate that both the oceanic crust and the adjacentcontinental crust have undergone deep burial during subduction.Zircons within the gneiss give U–Pb ages of 507 ± 38 Ma (SHRIMP;Yang et al., 2003) and 509 ± 12 Ma (LA-ICP-MS; Liu et al., 2003) forpeak metamorphic conditions. In view of the HP–UHP rocks em-placed at the northern edge of NQT, therefore, the subduction ofthe Erlangping back-arc basin is likely to be towards south, andpeak-metamorphic ages are likely to represent ages of subductionof the Erlangping back-arc basin. This tectonic event is also sup-ported by the occurring of the basic granulite with peak-metamor-phic age of 485 ± 3.3 Ma (LA-ICP-MS; Chen et al., 2004a) and theleptite with age of 518 ± 12 Ma (LA-ICP-MS; Liu et al., 2003) withinthe NQT.

Taking into account all the isotopic ages and fossils from Qing-shui, Caoliangyi and Wantan areas (Table 1 and Fig. 3), we proposethat the existence period of the back-arc basin was from ca. 508 to

lite and associated volcanic rocks of the Mianlue suture zone.

Fig. 8. Chondrite-normalized REE patterns for the ophiolite and associated volcanic rocks along the Mianlue suture zone, Qinling orogen. The geochemical data for each unitare from the following literatures: Eastern Kunlun (a) data are from Chen et al. (2000); Nanping-Kangxian (b) data are from Lai et al. (1998, 2002, 2004a,b); Sanchazi andPianqiaogou (c) data are from Lai et al. (1998) and Li et al. (2004a,b); Zhuangke and Wenjiagou (d) data are from Xu et al. (1998), Lai et al. (1998) and Li et al. (2004a,b);Heigouxia and Qiaozigou (e) data are from Li et al. (1996) and Lai et al. (1998); Lianghe-Wuliba and Anzishan (f) data are from Xu et al. (2000a,b) and Lai et al. (1998, 2000,2002); Huanshan (g and h) data are from Dong et al. (1999, 2004). The values of OIB, E-MORB, N-MORB and Primitive Mantle are from Sun and McDonough (1989).


440 Ma, and closure was before ca. 434 Ma in view of the mag-matic and metamorphic ages (Table 3). These results fit well withtiming (Table 2) of the North Qinling island-arc development.

The western part of suture of the back-arc basin is characterizedby having more rhyolites (Zhang et al., 2001), as well as by forma-tion ages of volcanic rocks at 450–440 Ma that is younger thanthose of east at 510–467 Ma. These facts indicate that the openingof the eastern part of the back-arc basin was earlier than that of thewestern sectors.

3.4. Fore-arc prism

The fore-arc prism (FAP), extending around 3 km wide and up to50 km long from west to east, is located to the southern side of theShangdan ophiolitic melange zone and bounded by the Shangdan

fault (Fig. 1). On the southern side, the FAP zone is separated fromthe Devonian Liuling Group of the South Qinling belt by the Mian-yuzui-Maanqiao ductile shear zone (Yu and Meng, 1995). The FAPzone is exposed as intensely deformed thrust slices composed ofdifferent litho-tectonic units from east to west due to the multipletectonic movements along the Shangdan suture. Detailed mappingreveals that the FAP consists mainly of low-grade metamorphosedsandstones with some isolated lenticular conglomerates (exposed,i.e., in the Shaliangzi and Hubaohe areas of Heihe valley), volcani-clastic rocks and limestones. This unit, especially the conglomer-ates, was previously considered as typical Upper Devonian post-orogenic molasse (Mattauer et al., 1985), or as representing an Or-dovician-Carboniferous fore-arc sedimentary wedge (Meng, 1994;Yu and Meng, 1995; Zhang et al., 2001). Based on geochemicalstudies of the graywackes of the Tianshui section in West Qinling

Fig. 9. Primitive mantle-normalized trace element spider diagrams for the ophiolite and associated volcanic rocks along the Mianlue suture zone, Qinling orogen. Thegeochemical data for each unit are from the following literatures: Eastern Kunlun (a) data are from Chen et al. (2000); Nanping-Kangxian (b) data are from Lai et al. (1998,2002, 2004a,b); Sanchazi and Pianqiaogou (c) data are from Lai et al. (1998) and Li et al. (2004a,b); Zhuangke and Wenjiagou (d) data are from Xu et al. (1998), Lai et al. (1998)and Li et al. (2004a,b); Heigouxia and Qiaozigou (e) data are from Li et al. (1996) and Lai et al. (1998); Lianghe-Wuliba and Anzishan (f) data are from Xu et al. (2000a,b) andLai et al. (1998, 2000, 2002); Huanshan (g and h) data are from Dong et al. (1999, 2004). The values of OIB, E-MORB, N-MORB and Primitive Mantle are from Sun andMcDonough (1989).


(Xu, 2005) and the Shangxian section in East Qinling (Song et al.,1995; Zhang et al., 2001), the clastic rocks were documented thatdeposited in a fore-arc setting. The conglomerates are exposed astwo intercalated beds within the sandstones and volcanic rocksin Heihe area (Meng, 1994). The geochemistry of the igneous grav-els was documented that they were derived from erosion of theNorth Qinling island-arc (Zhang et al., 1997a). Our new investiga-tions (Dong et al., unpublished data) indicate that the clastic rockscomprise the youngest detrital zircon age group of ca. 450 Ma,which limits the maximum age of FAP. Meanwhile, the FAP was in-truded by a diabase dyke with a U–Pb zircon age of ca. 430 Ma.Therefore, it is reasonably inferred that the FAP deposited in theperiod between ca. 450 Ma and ca. 430 Ma. In addition, the detritalzircon age clusters reveal that the material of the FAP only derived

from the North Qinling (island-arc) terrane, without any contribu-tion typical for the SQB (Dong et al., unpublished data). This factsuggests the existence of the Shangdan ocean between the NCBand SCB during FAP deposition. Furthermore, it is also can be con-cluded that the deposition of the FAP was related to subduction in-stead of collision.

3.5. Closure of the Shangdan ocean

The northern South Qinling belt is characterized by the Middle-Upper Devonian turbidite succession named Liuling Group (Zhanget al., 2001). The turbidite succession was proposed to have depos-ited in a passive-continental marginal basin (Meng, 1994; Meiet al., 1999), which would mean that the Shangdan ocean still ex-


isted in Middle Devonian times. Zhang et al. (2001) proposed thatthe turbidites of Liuling Group were formed in a remnant basin,while others argued a foreland basin (Li et al., 1994) or a fore-arcaccretion zone along an active-continental margin (Yan et al.,2007b).

As discussed previously, the detrital zircon age dating of theclastic rocks indicates an origin of the FAP detritus from North Qin-ling (island-arc) terrane without any contribution from the SouthQinling belt. This suggests that the Shangdan ocean had not yetclosed until 450–430 Ma in Late Ordovician to Early Silurian times.The following evidence implys this ocean had already closed atMid-Late Devonian. Geochemical composition of the sandstonesfrom the Mid-Upper Devonian Liuling Group indicated that theclastic materials came both from North Qinling and South Qinlingbelts (Gao et al., 1995). This result was confirmed by the age clus-ters of the detrital zircons from Liuling Group and the Devonianstrata in southwest Qinling (Yan et al., 2007b). The detailed map-ping revealed that the Liuling Group unconformably covers Cam-brian–Ordovician dolomite sequences (Meng, 1994; Zhang et al.,2001) in the north and Lower Silurian phylites and slates in thesouth (Mei et al., 1999).

The North Qinling terrane was overprinted by two phases of themetamorphism in Paleozoic (Table 3). The first one is a high–ultra-high pressure (HP–UHP) metamorphism during ca. 518–485 Ma,which related to the subduction of the Shangdan ocean and Erlang-ping back-arc basin. The second is an amphibolite-greenschist fa-cies metamorphism occurred at ca. 415–400 Ma related to theclosure of the Shangdan ocean.

In view of all above geological and geochronological data, to-gether with the age dating results on the ophiolite (Table 1) andintrusions (Table 2) in the North Qinling (island-arc) terrane, wepropose that the closure of the Shangdan ocean between the NCBand SCB was in Early Devonian times.

4. Tectonics along the Mianlue suture zone

4.1. Ophiolites and volcanic rocks in the Mianlue suture

The Mianlue suture zone being defined as a series of fault zonesconsisting mainly of south-verging thrusts and nappes, representsthe south boundary of the South Qinling Belt (Zhang et al., 2001,2004b; Dong et al., 2008b). It is a composite tectonic zone formedon the basis of the Qinling-Dabie subduction-collision suture andsuperimposed by the Mesozoic and Cenozoic intracontinentalstructures (Zhang et al., 2001). There are ophiolites, oceanic islandand island-arc volcanic rocks exposed along the Mianlue tectoniczone (Figs. 1 and 7), From west to east, they are distributed inthe Derni (Chen et al., 2000), Nanping-Pipasi-Kangxian (Lai et al.,2004a), Sanchazi (Xu et al., 2000a), Heigouxia (Li et al., 1996),Wenjiagou-Zhuangke (Lai and Yang, 1997), Anzishan (Xu et al.,2000b), Lianghe-Wuliba areas (Lai et al., 2000). Further to the east,it connects with the ophiolite and associated volcanic rocks in theDahongshan (Dong et al., 1999, 2004) and Qingshui area (Lai et al.,2004b) on the south of Tongbai–Dabie Mountains (Fig. 1).

In the west, at Derni, the Mianlue suture joins with the Anima-qin suture of the East Kunlun orogen, where an ophiolite is ex-posed including meta-peridotite, pyroxenite, gabbro, meta-basalt,radiolaria-bearing cherts and argillite. The basalts are character-ized by strongly depleted in LREE (Fig. 8a), LILE and flat HFSE dis-tribution patterns in the primitive mantle-normalized traceelement spider diagrams (Fig. 9a), and define a typical N-MORBchemical affinity (Chen et al., 2000). The Derni ophiolite is consid-ered to derive from a depleted asthenospheric mantle source of amid-ocean ridge, and the 40Ar/39Ar plateau age of 345 ± 7.9 Ma ofbasalt represents the formation age of the oceanic crust (Chenet al., 2001).

Ca. 300 km east from Derni, the suture zone displays as anophiolitic melange consisting mainly of some fragments of oceaniccrust, oceanic island basalt from Nanping, Pipasi to Kangxian. Espe-cially, the N-MORB type ophiolite outcropping in Pipasi sectionshows depletion of LREE in chondrite-normalized REE patterns(Fig. 8b) and flat distribution trends of HFSE in the trace elementdistribution diagrams (Fig. 9b), suggesting a typical geochemicalcomposition of a depleted asthenospheric mantle of a typicalmid-oceanic ridge (Lai et al., 2002). Based on geological and geo-chemical investigations, some fragments of the oceanic island bas-alts, which are characterized by enrichment of LREE (Fig. 8b) aswell as highly fractionated in HFSE in the primitive mantle-nomal-ized trace element spider diagrams (Fig. 9b), were identified fromthe slices of thrusted ophiolitic melange (Lai et al., 2004b).

Further east, in the Mianxian-Lueyang area, where is the tradi-tional study region for the Mianlue ophiolite, a large amount offragments of ophiolite and associated island-arc volcanics andsome bimodal volcanics (Figs. 8 and 9) were identified and welldocumented (Zhang et al., 1995a, 2001, 2004b; Li et al., 1996; Xuet al., 2000a,b). Therefore, a full evolutionary history of the Mianlueocean can be constituted from rifting, through subduction and finalclosure of the oceanic basin.

The initial spreading of the Mianlue ocean is indicated by bimo-dal volcanic rocks in Heigouxia area, which consist of meta-basaltsand a small amount of dacites and rhyolites. The meta-basalts dis-play enrichment of LREE, Th, U, Sr and Zr with minor negative Tianomalies (Figs. 8e and 9e). These petrological and geochemicalfeatures indicate they were formed either in a rift setting (Liet al., 1996) or in a transitional setting where an initial continentrift was expanding into a mature oceanic basin (Zhang et al.,2004b).

The typical oceanic ophiolite suite occurs in the Wenjiagou-Zhuangke and Anzishan areas. Basalts from Wenjiagou-Zhuangkedisplay typical N-MORB chemical compositions, which are charac-terized by strong depletion of LREE in the chondrite-normalizedREE patterns (Fig. 8d), low concentrations of HFSE (e.g. Nb, Ta, La,Ce, Pr, P, Nd, Zr, Sm, Eu and Ti) and flat HFSE distribution patternsin the primitive mantle-normalized trace element distribution dia-grams (Fig. 9d). Therefore, the basalts from Wenjiagou andZhuangke are indicated as derivation of depleted asthenosphericmantle source (Lai and Yang, 1997). In addition to, the basalts fromAnzishan area (Figs. 8f and 9f) show the same geochemical charac-teristics as that of the Wenjiagou-Zhuangke basalts. Take into ac-count the geochemical features of the basalts, and theserpentinized peridotites which exhibit typical asthenosphericperidotitic compositions, the ophiolite from Anzishan section wassuggested as derivated from a depleted oceanic mantle source(Xu et al., 2000b). These characters also indicate that the Mianlueocean had been evolved into mature spreading.

Afterwards, spreading was followed by subduction which isindicated by the ophiolitic melange at Sanchazi. The andesitesand gabbros show enrichment of LREE (Fig. 8c), and high-degreefractionation of HFSE with depletion of Nb–Ta and Ti (Fig. 9c). To-gether with co-occurring high-Mg and adakitic andesites suggest-ing subduction of an oceanic slab (Xu et al., 2000a), this melangeis indicated that formed in a subduction setting. Additionally, bas-alts with island-arc geochemical features were also identified fromPianqiaogou and Hengxianhe areas near Lueyang city (Lai andYang, 1997). In the Lianghe-Raofeng-Wuliba area, detailed studiesindicate that a typical island-arc magmatic zone exists. Both meta-basalts from Lianghe and Wuliba sections display enrichment ofLREE in the chondrite-normalized REE patterns (Fig. 8f), as wellas enrichment of LILE and high-degree fractionation of HFSE withnegative Nb–Ta, Sr and Ti anomalies in the primitive mantle-nor-malized trace element distribution diagrams (Fig. 9f). In view ofthe co-occurring of the above basalts, continental marginal ande-


sites and bimodal volcanics, the volcanic assemblage in Lianghe-Wuliba was inferred that derived from rift setting within an is-land-arc (Lai et al., 2000).

Further east to the south of the Tongbai Mountains, N-MORBand E-MORB ophiolite (Dong et al., 1999) and subduction-relatedvolcanics (Dong et al., 2004) were reported in Dahongshan area.Most basalts display slight enrichment of LREE while a few of sam-ples show depletion of LREE in the chondrite-normalized REE pat-terns (Fig. 8g), and flat distributions of HFSE in the primitivemantle-normalized trace element spider diagrams (Fig. 9g). Thesefeatures indicate the magmas of the basalts were mainly derivedfrom a slightly enriched MORB mantle source, whereas a few ofthem were from depleted MORB mantle source. On the other hand,basalts and andesites in Xiaofu and Sanligang areas show enrich-ment of LREE or flat REE distributions (Fig. 8h), and differentiationof HFSE, as well as negative Nb–Ta and Ti anomalies in the primi-tive mantle-normalized trace element distribution patterns(Fig. 9h). These arc-signatures imply they were related to a subduc-tion process. All these MORB type and subduction-related volcanicrocks constrain that the Mianlue ocean and its subduction might beexisted to the south of the Tongbai Mountains.

Moreover, to the south of the Dabie Mountains, some fragmentsof ultramafic rocks, gabbros, pyroxenites and andesites have beenidentified from diverse places along the main boundary fault.Based on geochemical studies, Lai et al. (2004b) reported that thegabbro derived from a depleted asthenosphere, while the andesiteformed in an active continental margin setting.

In summary, based on detailed investigations, the above men-tioned ophiolite and associated oceanic island volcanics, island-arc volcanics and bimodal volcanics are discontinuously exposedin more than twenty localities along the Mianlue tectonic zonestretching 1500 km from east to west. This represents evidencefor the existence of a Mianlue juvenile oceanic basin, which latervanished on the southern margin of the Qinling-Dabie orogenicbelt.

4.2. Timing of the Mianlue ocean

Besides the studies of the ophiolite and associated volcanicsmentioned above, the research of the sedimentary evolution inthe Qinling-Dabie orogenic belt (Meng and Zhang, 1999; Liu andZhang, 1999; Liu et al., 2005) also demonstrates that the Mianlue

Table 4Geochronological data of the ophiolites and associated rocks from the Mianlue suture.

Region Position Rock Method

Age of the ophioliteAnimaqin Derni Basalt 40Ar/39Ar whole rockLueyuan Nanping Andesite U–Pb zircon LA-ICPMSMianxian Sanchazi Diabase U–Pb zircon LA-ICPMS

Sanchazi Plagiogranite U–Pb zircon SRIMPAnimaqin Animaqin Chert RadiolariaLueyang Kangxian Chert RadiolariaMianxian Sanchazi Chert RadiolariaHangzhong Xixiang Chert Radiolaria

Age of the metamorphism and deformationMianxian Heigouxia Metabasalt Sm–Nd isochron

Metabasalt 40Ar/39Ar whole rockHeigouxia Metabasalt Rb–Sr Whole rock

Metabasalt 40Ar/39Ar whole rockAnzishan Granulite Sm–Nd mineral

Granulite 40Ar/39Ar Bio.Hengxianhe Shimengou Muscovite quartzite 40Ar–39Ar Mus.Lueyang Wenjiagou Muscovite quartzite 40Ar–39Ar Mus.Wudu Chenjiaba Muscovite quartzite 40Ar–39Ar Mus.Foping Foping Granulite U–Pb zircon SHRIMP

Foping Gneiss U–Pb zircon SHRIMP

oceanic basin opened up in the uplifted rift zone forming a passivecontinental margin of the northern SCB since the Devonian, and anew Qinling plate became prevailing during Late Paleozoic to Tri-assic times (Zhang et al., 2004b). According to the systematic studyof tectonic evolution and characteristics of the basin sedimentaryinfill (Zhang et al., 2001, 2004b), the evolution of the Mianlue oce-anic basin can be constituted as two stages, one for initial riftingand formation of the juvenile oceanic basin from the Devonian tothe Carboniferous, and another for development of mature oceanfrom Permian to Early Triassic times. After the Mid Triassic, theMianlue ocean was closed and the marginal basin on southern sideof the Mianlue zone was entirely transformed to a foreland basin(Zhang et al., 2001). However, the major successions deposited inthe foreland basin have been reworked or buried by late intensethrusting and nappe stacking except for a few outcrops, which re-mained along the Bashan fault (BSF) (Dong et al., 2008b).

Combined with regional geology, the studies of both the isoto-pic geochronology and paleontology gave rise to an age range of345–200 Ma (Table 4) for the formation and existence of the Mian-lue oceanic basin, and formation of a subduction-collision suture isin correspondence to the period of Late Paleozoic to Early Meso-zoic. Feng et al. (1996) reported a Carboniferous radiolarian faunain cherts interlayered within the ophiolite of the Mianlue segment.This is consistent with the Late Devonian to Carboniferous radio-larian fauna from interlayered cherts in the volcanics from bothXixiang area (Wang et al., 1999) and the ophiolite melange of Kan-gma segment (Lai et al., 2004a,b). In addition to, the Carboniferous,Permian and Early-Middle Triassic fossils were discovered from theophiolite-related siliceous rocks in the Animaqin segment (Bianet al., 2001).

Isotopic ages obtained from the ophiolite and the related vol-canics and granites range from ca. 345 to 200 Ma, which is be-tween Carboniferous and Late Triassic. For example, the LA-ICP-MS U–Pb zircon age of 246 ± 3 Ma from the andesite (Qing et al.,2008c) in the Nanping area represents the time of subduction.MORB-type basalts from the Derni ophiolite give a whole-rock40Ar/39Ar plateau age of 345 ± 7.9 Ma (Chen et al., 2001) beingidentical to Early Carboniferous. The plagiogranite associated withthe basic volcanics of the ophiolite in the Mianlue segment yields aU–Pb zircon age of 300 ± 61 Ma (Li et al., 2004a). These ages areconsistent with Late Devonian to Early Carboniferous radiolariasmentioned above. The timing results given by both the fossils

Age and error (Ma) Interpretation Author(s)

345 ± 7.9 Formation Chen et al. (2001)246 ± 3 Subduction Qin et al. (2008c)264 ± 3 Formation Lai and Qin (2010)300 ± 61 Formation Li et al. (2004a)Permo-Triassic Deposition Bian et al. (2001)Upper Devo-Carb. Deposition Lai and Yang (1995)Carboniferous Formation Feng et al. (1996)Upper Devo-Carb. Deposition Wang et al. (1999)

242 ± 21 Metamorphism Li et al. (1996)219 ± 1.4 Metamorphism Li et al. (1999)221 ± 13 Metamorphism Li et al. (1996)227 ± 0.9 Metamorphism Li et al. (1999)206 ± 55 Metamorphism Zhang et al. (2002b)200 ± 1.7 Exhumation Zhang et al. (2002b)219.5 ± 1.4 Deformation Li et al. (1999)226.9 ± 0.9 Deformation Li et al. (1999)194.5 ± 3.0 Deformation Li et al. (1999)221 ± 3.6 Min.metamorphism Yang et al. (1999)271 ± 15 Max.metamorphism Yang et al. (1999)


and isotopic ages of the Mianlue zone determine that opening andexpanding period of the Mianlue oceanic basin is from Mid-LateDevonian to Early Permian.

As discussed previously, an Late Triassic foreland basin devel-oped in front of the Mianlue suture zone, which indicates con-sumption of the Mianlue ocean before Late Triassic and the platecollision no later than Mid Triassic. The Mid Triassic collision mod-el was also supposed by the prevailing syn- and post-collisionalgranites within the western SQB with ages of 245–200 Ma (Ta-ble 4). This idea can be also proven by a series of metamorphic iso-topic ages (Table 4) acquired from the metabasites in the ophiolitemelange of the Mianlue zone, such as Sm–Nd isochron age of242 ± 21 Ma and Rb–Sr isochron age of 221 ± 13 Ma (Li et al.,2004a), as well as 40Ar/39Ar ages of 227 ± 0.9 Ma to 219 ± 1.4 Ma(Li et al., 1999). In particular, the Anzishan quasi-high pressuregranulite in the Mianlue zone yields 199–192 Ma Sm–Nd and40Ar/39Ar ages (Zhang et al., 2002b), which was interpreted as thetiming of exhumation of granulite through post-collisional eventsafter the subducted oceanic crust underwent high-pressure granu-lite facies metamorphism at depth (Zhang et al., 2004b).

4.3. Triassic syn- and post-collisional granitoids in the western SQB

The Phanerozoic plutons in the Qinling orogen are characterizedby three phases of intrusions in different tectonic units (Fig. 5),which comprise Paleozoic gabbros and granites, Triassic granitoidsand Late Jurassic–Early Cretaceous granites. As discussed in theprevious section, the Paleozoic gabbroic-granitic intrusions aremostly exposed in the NQT between the Shangdan fault and theLuonan–Luanchuan fault (Fig. 5), and are related to the conver-gence along the Shangdan suture zone. In comparison, the Triassicgranitoids typically occurred in the western part of the SQB,whereas the Late Jurassic-Early Cretaceous granitoids mostly in-truded into the S-NCB (Fig. 5). It is well documented that these Tri-assic granitoids in western SQB (Sun et al., 2000, 2002a; Hu et al.,2004; Jin et al., 2005; Qin et al., 2007a,b, 2009b; Zhang et al., 2008;Gong et al., 2009; Jiang et al., 2010) are related to the convergenttectonic processes along the Mianlue suture zone. These granitoidintrusions can be divided into syn-collisional and post-collisionalgranite groups with diverse ages (Table 2).

The syn-collisional granitoids include the intrusions in theCaoping (217 Ma, Zhang et al., 2006; 220 Ma, Jiang et al., 2010),Cuihuashan (227 Ma, Jiang et al., 2010), Zhashui (214 Ma, Huet al., 2004), Dongjiangkou (219 Ma, Jiang et al., 2010), Yanzhiba(211 Ma, Jiang et al., 2010), Wulong (208 Ma, Qin et al., 2008b;218 Ma, Jiang et al., 2010), Xichahe (210 Ma, Zhang et al., 2008;214 Ma, Qin et al., 2007a; 212 Ma, Qin et al., 2008a), Mishuling(237 Ma, Li et al., 2004b; 212–213 Ma, Qin et al., 2009b), Xiba(222–201 Ma, Zhang et al., 2006), Baoji (213 Ma, Lu, 2000) Huay-ang, Liuba (221–215 Ma, Zhang et al., 2006), Guangtoushan(216 Ma, Sun et al., 2000), Jiangjiaping (206 Ma), Zhangjiaba(219 Ma), Xinyuan (214 Ma), Miba (220 Ma) (Sun et al., 2002a,2002b), Caoguan (205 Ma Li et al., 2004b), Yeliguan (245 Ma, Jinet al., 2005), Xiahe (238 Ma, Jin et al., 2005), and Luoba, etc. Thesegranites are chiefly characterized by metaluminous to peralumi-nous and moderate- to high-K calc-alkaline compositions, enrich-ment of LILE and LREE, and depletion of HFSE, Nb and Ta (Zhanget al., 2008), which indicate a derivation of island-arc or collisionalsetting (Kelemen et al., 1990; Stolz et al., 1996). However, accord-ing to geochemistry (i.e. high Sr and low Y contents), the Wulonggranodiorite and Xichahe tonalite granitoid are identified as adak-itic granites (Zhang et al., 2002a; Qin et al., 2008b), so as inter-preted to have been derived from the thickened crust of the SQBduring the syn-collisional process between 225 and 208 Ma. Thecrust thickening process of the SQB is also proven by the fact thatmost granitoids in SQB have mafic enclaves (Zhang et al., 2008). For

instance, there is a large amount of microgranular enclaves withinthe Mishuling I-type monzogranite representing the petrogenesisof mixing of mantle and crust magmas (237–212 Ma, Li et al.,2004b; Qin et al., 2009b). Further to the west, in the Xiahe area,the Yeliguan and Xiahe granitoids were documented to derive fromsubducted slab at 245 ± 6 Ma and 238 ± 4 Ma, respectively (Jinet al., 2005). Therefore, we propose that these granitoids can beused to constrain the evolving syn-collision process between 237and 215 Ma in the SQB.

The post-collisional granitoids include the rapakivi-type granitsin the Shahewan (212 ± 1.8 Ma, Zhang et al., 1999; 213 ± Ma, Zhanget al., 2006; 211 ± Ma, Wang et al., 2007; 209–205 Ma(rapakivi),200–199 Ma (enclave), Zhang et al., 2008), Qinlingliang(217 ± 3.2 Ma, Lu et al., 1999), Taibailiang (216 ± Ma, Zhang et al.,2006) and Laojunshan (214 ± 3.0 Ma, Lu et al., 1999). These gran-ites are characterized by their rapakivi-texture and transitionalgeochemical compositions from I- to A-type granite (Zhang et al.,2008). These features indicate that these rapakivi granitoids wereformed in an extensional setting during a post-collision stage.The above granitoids have ages ranging from 217 to 200 Ma (Ta-ble 2 and Fig. 4), which represent the time after plate collision.The geochemical characters of the Yangba granitoid in the Bikouterrane show that they were formed in response to lithosphericextension subsequent to the continental collision between theSCB and NCB and the LA-ICP-MS zircon ages vary between 215 ±8.3 Ma and 207 ± 2 (Qin et al., 2009a). Accordingly, we proposethe SQB evolved in post-collision process during 215–200 Ma.

The data presented above allow summarize the tectonic evolu-tionary history along the Mianlue suture. The geological and geo-chemical synthetic analyses imply that the Mianlue oceanic basinwas a northern branch of the east Paleo-Tethys (Zhang et al.,1995a, 2001; Xu et al., 2002), and experienced Devonian to MiddleTriassic formation, development and closure of the oceanic basin,and finally forming a major suture along which the NCB and SCBamalgamated during Indosinian tectonic events. The suture wassubsequently overprinted by southward overthrust along theMianlue- Bashan-Xiangguang fault during Late Jurassic–Early Cre-taceous times (Zhang et al., 2001; Dong et al., 2005, 2008b). Theformation process and evolution history of the Mianlue suturezone was simply outlined in six stages (Zhang et al., 2004b),including Mid Devonian–Early Carboniferous opening of the ocean,Carboniferous development of the limited ocean, Permian-MiddleTriassic subduction, Mid to Late Triassic (Carnian) collision, LateTriassic (Norian) to Early Jurassic SQB extensional collapse andforeland thrusting, Middle Jurassic to Cenozoic post-orogenicintracontinental tectonic evolution.

5. Diversity of exhumation paths of the NQB and SQB

5.1. Evidence from lithostratigraphy

The North Qiling belt is characterized by the occurrence ofamphibolite facies metamorphic Precambrian basement (Zhanget al., 1994b, 2000a; Chen et al., 1998) and penetrative ductiledeformation (Zhang et al., 2001) under high geothermal gradientsreaching migmatization (Dong et al., 2011b). The basement withmetamorphosed Ordovician sequence was unconformably coveredby unmetamorphosed Carboniferous and Permian fluvial faciessandstones. This fact indicates that the exhumation of the NorthQinling belt occurred during Silurian–Devonian. In comparison,the SQB exposes greenschist facies metamorphic Meso-Neoprote-rozoic basement, which was covered by non-metamorphic Neo-proterozoic to Triassic sedimentary sequences. Except for theunconformity occasionally existed beneath the Mid Devonian stra-ta in the SQB, there is no distinct regional angular unconformitywithin the Neoproterozoic to Triassic strata. Although all the strata


in the SQB were involved into south-vergent fold-thrust systemand are unconformably covered by a Jurassic redbed sequence,they were related to the regional compression, which resultedfrom the closure of the Mianlue ocean (Paleo-Tethys). These factsargue a Middle Triassic collisional model for the convergence be-tween the SQB and SCB.

5.2. Metamorphic P–T constraints

As described above, the SQB is characterized by exposure ofgreenschist facies metamotphosed basement rocks and un-meta-morphosed Neoproterozoic to Triassic sedimentary cover se-quences. In comparison, the NQB was highly overprinted byseveral phases metamorphism (Zhang et al., 2001) with variablefeatures in different units. The Qinling Group is characterized bytwo phases metamorphism with clockwise P–T paths in Jinning(ca. 1000 Ma) and Early Paleozoic time (Liu et al., 1993). First onedisplays pressure decreasing with temperature increasing at ca.1000 Ma (Chen et al., 1991; Liu et al., 1993). The second one sug-gests a increasing pressure and temperature during early stage(�ca. 425), and followed by decreasing pressure and temperature(425–353 Ma), then decreasing temperature with constant pres-sure during last stage (after 353 Ma) (Liu et al., 1993). The featuresof the Early Paleozoic metamorphic P–T-(t) conditions reveal thatthe Qinling Group evolved a compressure and crust thickening at�ca. 425 Ma, exhumation during ca. 425–353 Ma. The UHP/HPmetamorphic rocks of 509–507 Ma (Yang et al., ; Liu et al., 2003)outcropping on the northern edge of the NQT, as well as the gran-ulite of 518–485 Ma (Liu et al., 2003; Chen et al., 2004a) in south-ern Qinling Group were related to the closure of the Erlangpingback-arc basin. Therefore, the P–T-(t) path of the Qinling Groupcan be interpreted that resulted in the subduction along the Shang-dan suture and closure of the Erlangping back-arc basin. This con-clusion is also supported by the metamorphic P–T condition of theKuanping Group, which shows increasing pressure and tempera-ture in early stage and decreasing pressure with increasing tem-perature in late stage (Liu et al., 1993).

5.3. Chronological evidence for age of metamorphism

The timing of metamorphism and deformation in relation tosedimentation was proven by the previous and our new geochro-nological datasets. The new results of 40Ar/39Ar mineral datingincluding amphibole, white mica and biotite from both QinlingGroup in the NQT and FAP in the SQB reveal the existence ca.80 Ma difference between the exhumation history of the NQBand SQB.

The LA-ICP-MS U–Pb zircon ages ranging from 517 to 455 Ma ofmigmatitic leuco-granite (Dong et al., 2011b) suggest that there oc-curred migmatization and anatexis in the deep crust of the NorthQinling terrane in Mid Cambrian–Mid Ordovician. According tothe prevailing contemporaneous magmatism in the North Qinlingterrane, this tectonothermal event can be interpreted as the resultof the remelting of the thickened island-arc crust. New 40Ar/39ArHornblende ages suggest that the basement of the North Qinlingterrane started exhumation and cooling at least before 432 Ma,and might be preserved at 20 km (500 �C) depth from 432 to405 Ma (Dong et al., 2011b). This age range was also supportedby 40Ar/39Ar hornblende ages of 404 ± 5 (Zhai et al., 1998) and426 ± 2 Ma (Sun et al., 1996a) on Erlangping amphibolite,404 ± 2 Ma on Qinling granulite (Zhai et al., 1998), 420 ± 30 Maon the amphibolite at Songshugou (Ratschbacher et al., 2003)and 401 ± 3.8 Ma (Liu et al., 1993) at Xinyang area. It was followedby rapid cooling at 350–400 �C at 389 Ma, and evolved into slowcooling at 333 to 329 Ma (Dong et al., 2011b). The 40Ar/39Ar agedata of muscovite and biotite from the Kuanping Group show a

similar cooling history to that of the NQT indicating that the NQTmight have collided with the NCB after closure of the Erlangpingback-arc basin. However, the 40Ar/39Ar age data of the amphibole,muscovite and biotite from the FAP (northern SQB) suggest thatthe cooling of the northern SQB below about 500 �C occurred atabout 322–311 Ma, below 425 �C at 306 Ma, and below 300 �C atca. 249 Ma (Dong et al., unpublished results). These are accordancewith the reported 40Ar/39Ar ages of 316 Ma on hornblende (Zhaiet al., 1998), 301 Ma on muscovite, and 264 Ma on biotite fromthe Liuling unit (Mattauer et al., 1985).

Thermochronological constraints from North Qinling and SouthQinling units indicate different Late Paleozoic cooling historieswith an 80 Ma difference, which means that the North Qinlingand South Qinling have evolved into a different exhumation his-tory. Taking the differences of sedimentation, metamorphism,deformation and thermal geochronology, we propose a northwardcontinental subduction model instead of a collision model to ex-plain the convergence between the NQT and SQB after the Shang-dan oceanic curst vanished.

6. Tectonic model and evolutionary history

6.1. Discussion on the Precambrian evolution in the NQB and adjacentregion

The Proterozoic ophiolite, subduction-collisional granitoids andback-arc basin volcanics indicate the existence of a Grenvillian oro-gen on southern margin of the NCB (Dong et al., 2008a). The Song-shugou ophiolite was documented to represent the remnant ofoceanic crust with ages ranging from 1.4 Ga to 1.0 Ga (Zhanget al., 1994b; Chen et al., 2002; Dong et al., 2008a). This oceanwas subducted and formed a back-arc basin, which was repre-sented by the Kuanping mafic and ultramafic rock assemblageswith ages of 1.2–0.94 Ga (Zhang et al., 1994b, 2001; Zhang andZhang, 1995; Diwu et al., 2010). Furthermore, between the Song-shugou and Kuanping ophiolites, some Neoproterozoic collisionalgranitoids are exposed, such as the Dehe granitoid with LA-ICPMSU–Pb zircon age of 898 ± 8 Ma (Zhang et al., 2004a), Niujiaoshangranitoid with U–Pb zircon age of 958 ± 7 Ma (Wang et al., 2003)and the Shangnan granitoid at 889 ± 10 Ma (Pei et al., 2003).Numerous Rb–Sr, Ar–Ar, and Sm–Nd ages range from 978 to859 Ma (You et al., 1991; Chen et al., 1991; Zhang et al., 1994b;Wang et al., 2003), proving Grenvillian metamorphism. AlthoughDong et al. (2008a) proposed a Grenvillian orogen on the southernmargin of the NCB, which resulted from the subduction-collisionbetween the NCB and a southern block in Proterozoic times, thesouthern block remains unknown. The SQB (SCB) displays differentlithostratigraphy, metamorphism and deformation in the basementand the Lower Paleozoic cover sequences compared with the NCB(Zhang et al., 2000a, 2001). Therefore, it is difficult to concludewhether the southern block, which collided with the NCB andformed the Grenvillian orogen, is the SCB or not. The Precambriantectonic evolution of the Qinling is still an open issue at present.However, the Phanerozoic evolutionary process of the Qinling oro-gen is getting clear which can be simply drawn as follows (Fig. 10).

6.2. Early Paleozoic subduction orogen in the NQB

Represented by the 534 Ma oceanic gabbros of the Tianshuiarea, the Shangdan ocean was already established before ca.534 Ma, and the ocean separated the SCB from NCB (Fig. 10a).According to the field relationships, geochemistry and geochronol-ogy shown in this paper with the regional geological evidences, theformation of the Shangdan ocean, which was a branch of the Proto-Tethyan ocean, could be attributed to the break-up of the Rodinia

Fig. 10. Schematic cartoon showing the tectonic evolutionary history of the Qinling orogen. For explanation see text.


in early of Neoproterozoic time. At the same time, the SQB is stillthe northern part of the SCB (Fig. 10a), and both of them continu-ally deposited shallow-marine carbonates in an intracratonic basinsetting during Cambrian.

Before ca. 514 Ma, the Shangdan ocean kept extension as before,suggested by the formation of the Yanwan E-MORB type ophiolitein ca. 517 Ma. However, on the northern edge of the Shangdan

ocean, a subduction zone towards north possibly existed, whichcaused extension and formation of the Erlangping back-arc basin(Fig. 10b). Between the Shangdan ocean and Erlangping back-arcbasin, the North Qinling island-arc terrane (NQT) existed(Fig. 10b). The predominant subduction along the southern sideof the NQT brought gabbroic intrusions at 514–508 Ma, and re-sulted in the thickening of the NQT crust and migmatization at


517 Ma. Above the subduction zone, an oceanic island-arc formedin front of the NQT, which is indicated by basalts with an oceanicisland-arc geochemical signature exposed within the Shangdanmelange. To the south of the Shangdan ocean, being the northernpart of the SCB, the SQB and the SCB had been a depressionalintracratonic basin setting with carbonates and black shales.

Between 508 and 485 Ma, the Shangdan ocean was still spread-ing and produced oceanic gabbros exposed now in the West Qinlingarea. At ca. 485 Ma, the intense subduction and compression alongthe trench might have caused the continental crust of the NQTbeing scrapped off and subducted forming the HP granulites occur-ring in East Qinling. In the NQT, the ongoing subduction of theShangdan ocean resulted in the intrusion of S-type granites during495–457 Ma. Further to the north, the Erlangping back-arc basinstarted subduction towards south under the NQT before 508 Ma(Fig. 6c), which is indicated by the UHP–HP metamorphic rocks ofan age of ca. 508 Ma occurring on the northern side of the NQT.

From 485 to 457 Ma, there was still formation of oceanic crustalong the ridge of the Shangdan ocean and produced the Guanziz-hen N-MORB ophiolite at 471 Ma. At ca. 457 Ma, as a result of sub-duction, the gabbros and diorites intruded into the Baihua area inthe western NQT, and afterwards some portions of Huichizi com-posite batholiths were also intruded into the NQT. Behind theNQT, the Erlangping back-arc basin developed cherts with radiola-rias and other deep-marine microfossils, while the pre-emplacedrelics of the crust of Erlangping back-arc basin were intruded bythe Xizhuanghe granitoid at ca. 466 Ma. The whole SCB were cov-ered by shallow marine limestones at the same time.

In the period of 457–430 Ma, the arc-continent collision be-tween the NQT and NCB took place after closing of the Erlangpingback-arc basin. Meanwhile, the persistent northward subduction ofthe Shangdan oceanic crust generated a great quantity of granitesintruded into the NQT. In front of the NQT, a fore-arc basin wasformed at 450–430 Ma and accumulated sediments in the fore-arc prism (Fig. 10d), which were eroded from the uplifting NQT.To the south, a rift developed within the northern part of the SCBalong the present Mianlue zone, which was indicated by large-scale of Lower Silurian diabase dyke swarms in Bashan area (Zhanget al., 2007a) and basalts exposed to the south of the TongbaiMountains (Dong et al., 1999). Furthermore, the Silurian in SCB ischaracterized by accumulation of shales and siltstones.

The Shangdan ocean was likely still in existence during EarlySilurian times and was finally closed prior to Middle Devonian.However, there was no full collision between the blocks after theclosure of the Shangdan ocean, which was indicated by the contin-uous deposition from Devonian to Lower Triassic successions in theSQB. We propose a subduction orogen model for evolution of theQinling belt in the Paleozoic time (Fig. 10a–e).

6.3. Late Paleozoic to Triassic subduction-collision along Mianlue zonebetween the SQB and SCB

In the Early Devonian, the consumption of the residual oceanresulted in the closure of the Shangdan ocean and the metamor-phism in NQT at ca. 400 Ma. Closure was accompanied by intru-sions of large-scale I-type granitoid plutons in the NQT.Extension and subsidence began from Mid Devonian onwards,and the Mianlue basin developed within the northern margin ofthe SCB (Fig. 10e). However, to the south of the Shangdan suture,amount of Middle to Upper Devonian turbidites were depositedin a foreland basin on the northern margin of the SQB. In theNQT, uplift and exhumation of the basement were still occurred.This extension in the south and insignificant (without collision)compression could have been related to migration of the exten-sional geodynamics of Paleo-Tethyan tectonic domain from south-west to northeast.

In Carboniferous, the Mianlue basin evolved into a small-scaleoceanic basin separating the SQB from SCB as an independent mi-cro-plate (Fig. 6f). However, SQB had already connected with theNQB (NCB) along the Shangdan suture zone, and the FAP (with agesof 450–430 Ma) was metamorphosed and exhumed from ca.330 Ma to 250 Ma. Continuous Carboniferous sedimentation ofsandstones and limestones indicate the existence of a basin onthe northern margin of the SQB. However, there developed somefault-bounded basins along the Zhuxia fault between the NQTand S-NCB, which relate to uplifting of the NQT and reactivationof the fault.

The Mianlue oceanic crust suffered northward subduction be-neath the SQB from Permian to Early Triassic (Fig. 10g), whichwas indicated by the island-arc volcanics and subduction-relateddeformation. However, on northern margin of the SQB, depositionof sediments continued from Permian to Lower Triassic. In compar-ison, to the north of the Shangdan suture zone, beside the Permianand Triassic sandstones occurring along the boundary faults of NQTand S-NCB, Permian coal measures unconformably cover metamor-phosed Ordovician schists and Proterozoic basement rocks of the S-NCB.

After the extinction of the Mianlue oceanic crust, the collisionbetween the SCB and SQB occurred in Mid-Late Triassic times alongthe Mianlue suture zone (Fig. 10h). Oblique convergence resultedin the Mid Triassic collision in the east and Carnian collision inthe west (Liu et al., 2005). The Carnian collision generated syn-col-lisional granitoids with an age of 228–215 Ma prevailing in thewestern part of the SQB, as well as the granulite facies metamor-phism at ca. 206 Ma in Mianxian (Li et al., 2000a,b; Zhang et al.,2002a,b) and at ca. 218 Ma in Foping (Wei et al., 1998; Yanget al., 1999). Due to the collision, both SQB and NQT were involvedinto intense compressional deformation, and the NQT also devel-oped lateral escape structures along the major strike-slip faults.

Up to Norian times, the NQB and SQB gradually conversed intopost-collisional collapse and generated the rapakivi-texturedgranitoids of an age of 215–200 Ma. The collapse of the thickenedorogen was accompanied by formation of Early Jurassic fault-bounded basins (e.g. the Mianxian, Hongchunba, and Qingfeng ba-sins) developed in the uplifted area inside the Mianlue zone andSQB. (Fig. 10i). At the same time, the Upper Triassic–Lower Jurassicforeland basin formed in front of the foreland fold-thrust belt as aresult of the later orogenic uplift.

6.4. Jurassic to Cretaceous intracontinental tectonism

From Late Jurassic to Cretaceous, the occurrence of the south-ward intracontinental subduction of the NCB (Fig. 10j) along theLingbao–Lushan–Wuyang fault (LLWF) was well explored by geo-physical investigations (Yuan, 1996) and the well logging (Zhanget al., 2001). This intracontinental subduction resulted in amountof granitoids intruded into the S-NCB (Fig. 5) during the period of150–100 Ma (Table 2) (Zhu, 1995; Mao et al., 2005; Ye et al.,2006; Zhu et al., 2008a), which accompanied by massive goldand molybdenite mineralizations (Du et al., 1994; Huang et al.,1994; Stein et al., 1997; Li et al., 2003; Zhu et al., 2008b). Mean-while, within the orogen, the Lower Jurassic strata were overthru-sted, and the foreland fold-thrust belt formed in front of theMianlue–Bashan–Xiangguang fault. Evidence for rapid exhumationof some sectors of the Qinling orogen and adjacent areas is alsofound in thermochronological studies (Zheng et al., 2004; Huet al., 2005; Shen et al., 2007; Chang et al., 2010).

6.5. A note to Cenozoic tectonism

High topographic gradients between the Qinling orogen and theCenozoic Weihe basin in the north as well as seismicity imply


important Cenozoic tectonism likely related to lateral extrusion ofthe Tibet plateau. This resulted in relative minor and continuousexhumation and erosion of the orogen although major transten-sional and strike-slip faults were activated.

Acknowledgments

Yunpeng Dong acknowledges Timothy Horscroft and BorminJahn for their invitation, encouragement and constructive sugges-tions to write this review paper on the evolution of the Qinling oro-gen. The two anonymous journal reviewers are grateful for theirconstructive reviews and comments which substantially improvedthis work. Financial support for this study was jointly provided bythe National Natural Science Foundation of China (Grants:40772140, 40972140), and MOST Special Fund from the StateKey Laboratory of Continental Dynamics, Northwest University.

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Tectonic evolution of the Qinling orogen, China: Review and synthesis