Journal of Asian Earth Sciences 113 (2015) 544–559 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Tectonic evolution of a complex orogenic system: Evidence from the northern Qinling belt, Central China ⇑ Li Tang a, M. Santosh a,b,c, , Yunpeng Dong b a School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China b State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China c Centre for Tectonics Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia article info abstract Article history: The Qinling orogenic belt preserves the records of a long evolution history of convergence between the Received 29 December 2014 North China Craton and the South China Craton. In this study, we present results from new geological, Received in revised form 12 March 2015 geochemical, zircon U–Pb geochronological and Lu–Hf isotopic investigations on a suite of orthogneisses Accepted 13 March 2015 from the Taihua Group (THG) and Tietonggou Group (TGG). We also present geochronological data on Available online 27 March 2015 schist and migmatite from the North Qinling belt (NQB) and metasedimentary rocks from the Wuguan unit (WGU) which is exposed along the southern side of the Shangdan suture zone. Two orthogneisses Keywords: from the THG define several stages of arc magmatism at 2.51 Ga, 2.34 Ga, 2.28 Ga and 2.16 Ga, Geochemistry followed by metamorphism at 1930 ± 31 Ma. Zircons from the TGG trace a tectonothermal event at Zircon U–Pb geochronology Lu–Hf isotopes 1897 ± 15 Ma. Geochemical data on biotite gneiss from the THG and the TTG (tonalite–trondhjemite– Tectonic evolution granodiorite) gneiss from the TGG classify these rocks as dacite and display volcanic arc affinity. Northern Qinling orogenic belt Zircon Lu–Hf isotopic results suggest that the parental magma for the protolith of felsic gneisses were C derived from Mesoarchean crustal components (TDM = 2766–3067 Ma). The amphibole gneiss from the THG classifies as metabasalt and the zircons from this rock show dominantly negative eHf(t) values vary- C ing from À10.3 to À4.6 and TDM range of 3088–3437 Ma, suggesting magma derivation by melting of Paleoarchean–Mesoarchean subducted oceanic crust. Zircons in the schist from the NQB show a wide age population in the range of 937–1131 Ma (peak at 1035 Ma). Zircons from the melanosomes of the migmatite in the NQB define ages between 405 and 379 Ma, correlating with the melting event in the NQB during 450–380 Ma. The WGU shows age populations of 854–803 Ma (with a peak at 829–824 Ma), 2460 Ma, 1802 Ma and 1180–1000 Ma, which are markedly different from that of the NQB and SQB. The ages obtained in our study correlate with the widely reported Grenvillian-aged magmatism in the NQB, and suggest that the NQB might have been a discrete micro-continent during Paleo- and Mesoproterozoic which has been overprinted by Paleozoic tectonic event. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction North China Craton (NCC) and South China Craton (SCC) (Mattauer et al., 1985; Zhang et al., 1995a; Meng and Zhang, 1999, 2000; Tseng Many of the major collisional orogenic belts in the world were et al., 2009; Dong et al., 2011a, 2012, 2013; Wu and Zheng, 2013; constructed through prolonged processes of arc–arc, arc–continent Tang et al., 2014). The QOB has been divided into the Southern mar- and continent–continent collisional events with multiple subduc- gin of the NCC (S-NCC), the North Qinling belt (NQB) and the South tion and accretion regimes (Yin and Harrison, 2000; Brown, 2007, Qinling belt (SQB) (Fig. 1b), and these three terranes are separated 2009; Xiao et al., 2010; Santosh, 2013; Xiao and Santosh, 2014; by the Paleozoic Shangdan suture zone (SSZ) in the north and the Santosh et al., 2010, 2015a, 2015b). The Qinling orogenic belt Mianlue suture zone in the south (Zhang et al., 1995a). The (QOB) in Central China, one of the major collisional orogens in east- Qinling orogenic system is characterized by (1) Archean– ern Asia, resulted from multiple stages of convergence between the Paleoproterozoic basement rocks, (2) Neoproterozoic metasedi- mentary rocks with Grenvillian-aged (Neoproterozoic) magmatic records, (3) Mesoproterozoic–Paleozoic ophiolitic suits, (4) ⇑ Corresponding author at: School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China. Paleozoic metasedimentary rocks, migmatites and HP-UHP E-mail address: [email protected] (M. Santosh). metamorphic rocks and (5) Paleozoic–Mesozoic granitoid plutons http://dx.doi.org/10.1016/j.jseaes.2015.03.033 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. L. Tang et al. / Journal of Asian Earth Sciences 113 (2015) 544–559 545 Fig. 1. Geological sketch map of the North Qinling orogenic belt (modified after Dong et al., 2011a), showing the location of QOB, tectonic units and sample locations. (Zhang et al., 1995a; Yang et al., 2001; Wu et al., 2007; Liu et al., 2. Geological setting 2009a; Dong et al., 2011a, 2014). A number of studies in the past decade have addressed the geo- The nearly east–west trending QOB connects the Dabie–Sulu chemical and geochronological features of the northern part of the orogenic belt to the east and the Qilian–Kunlun orogenic belt to QOB (comprising the S-NCC, NQB and SSZ) (e.g. Dong et al., 2011c, the west (Fig. 1). To the north, the QOB is separated with the 2014; Huang et al., 2013; Shi et al., 2013; Diwu et al., 2014). The NCC by the Lingbao–Lushan–Wuyang intra-continental fault, basement rocks discontinuously exposed in the S-NCC witnessed whereas toward south, the belt is bound by the Mianlue– Neoarchean–Paleoproterozoic magmatism followed by 1.96– Bashan–Xiangguang thrust fault with the SCC (Zhang et al., 1.82 Ga metamorphism (e.g. Huang et al., 2012; Diwu et al., 1995a). Within the Lingbao–Lushan–Wuyang fault, with the 2014; Lu et al., 2014), similar to the records from elsewhere in Luonan–Luanchuan fault, SSZ and Mianlue–Bashan–Xiangguang the NCC (Wan et al., 2014; Yang and Santosh, 2014; Zhai, 2014 thrust fault to the south (Fig. 1), the QOB has been divided into and references therein). Late Paleoproterozoic metamorphism three domains from north to south as S-NCC, NQB and SQB, respec- (1.86–1.80 Ga) has also been recorded from the Trans-North tively (Zhang et al., 1995a). China Orogen (TNCO) associated with the collision between the Western and Eastern Blocks of the NCC (e.g. Guo et al., 2005; 2.1. Southern margin of the North China Craton Zhao et al., 2009; Trap et al., 2009; Zhai and Santosh, 2011; Zhao and Zhai, 2013). Debates surround question whether the NQB The S-NCC is the northernmost zone of the QOB (Fig. 1). The belongs to part of the S-NCC (e.g. Zhang et al., 1995b, 2001), SCC region is mainly composed of amphibolite facies Archean– (e.g. Xue et al., 1996; Shi et al., 2009) or is a discrete micro-conti- Paleoproterozoic basement complexes (e.g. THG, TGG and nent block (e.g. Dong et al., 2003; Yang et al., 2010). The Wuguan Dengfeng Group), weakly metamorphosed Mesoproterozoic vol- unit (WGU) and the migmatites exposed in the Qinling Group pre- canics (Xiong’er Group) and Mesoproterozoic to Mesozoic sedi- serve one of the keys to address this debate, although detailed mentary cover sequences such as Gaoshanhe and Luonan Groups studies have not been carried out as yet from this region. In this (Zhang et al., 1995a, 2001). The THG is mainly scattered along study, we present integrated whole rock geochemistry, in situ zir- the S-NCC in five regions: the Lantian–Xiaoqinling, Xiaoshan, con U–Pb ages and Hf isotopic data for the basement rocks from Xiong’ershan, Lushan, and Wuyang (Fig. 1b) (Xu et al., 2009). The the S-NCC (THG and TGG), schist and migmatite from the NQB THG is traditionally subdivided into the lower and the upper units, and metasedimentary rocks from the WGU. In combination with where the lower unit is mainly composed of amphibolite to gran- previous studies, our data provide important insights to under- ulite facies metamorphosed TTG gneiss and amphibolite, and the stand the complex Qinling orogenic system. upper one includes graphite-bearing gneiss, banded iron formation 546 L. Tang et al. / Journal of Asian Earth Sciences 113 (2015) 544–559 and amphibolite (Liu et al., 2009a). In the Lantian–Xiaoqinling area, (quartzite, mica schist and marble). The youngest detrital zircons the THG is mainly composed of biotite gneiss and amphibole from mica schist show late Neoproterozoic ages (Diwu et al., gneiss, which are unconformably overlain by the TGG unit, which 2010; Zhu et al., 2011; Shi et al., 2013). is dominated by TTG gneisses, metasedimentary rocks and minor The Erlangping Group comprises ophiolitic suite (comprising amphibolites. massive or pillow basalt, sparse ultramafic rock, sheeted dike, gab- bro and some radiolarian chert), clastic sedimentary succession 2.2. North Qinling belt and carbonate. The ophiolitic units show both MORB affinity and subduction-related magmatic character (Sun et al., 1996; Dong The NQB is bound by the Luonan–Luanchuan fault to the north et al., 2011c). Together with the radiolarians within cherts, a and the SSZ to the south (Fig. 1C). From north to south, the NQB has back-arc basin is suggested during Cambrian and Ordovician been divided into three units: the Kuanping Group (KPG), (Wang et al., 1995; Sun et al., 1996), in which the sedimentary Erlangping Group and Qinling Group (QLG) separated by several assemblages were deposited (Lu et al., 2003).