Palaeozoic tectonics and evolutionary history of the Qinling orogen: Evidence from geochemistry and geochronology of ophiolite and related volcanic rocks Yunpeng Dong a, ⁎, Guowei Zhang a , Christoph Hauzenberger b , Franz Neubauer c , Zhao Yang a,d , Xiaoming Liu a a State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Northern Taibai Str.229, Xi'an 710069, China b Institute for Earth Sciences, University of Graz, Heinrich Str. 26, A-8010 Graz, Austria c Department Geography and Geology, University of Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria d Institute for Geology, Technical University of Bergakademie Freiberg, Bernhard von Cotta Str. 2, D-09599 Freiberg/Sachsen, Germany abstract article info Article history: Received 30 January 2010 Accepted 25 November 2010 Available online 1 December 2010 Keywords: Early Palaeozoic MORB Ophiolite Subduction Back-arc basin Qinling orogenic belt The tectonic framework and the evolutionary history of the Qinling orogenic belt are keys for understanding the convergent processes between the North China and South China blocks. The widely exposed ophiolitic and subduction-related volcanic melange along the Shangdan and Erlangping belts provides important constraints on the tectonic evolutionary processes of the Qinling orogen. The melange in the Shangdan zone is predominantly composed of ultramafic and mafic rocks that can be divided into three geochemical groups: (1) N- MORB type; (2) E-MORB type; and (3) island-arc/active continental margin-related basalts. The samples with N- and E-MORB affinity are characterized by depletion or slight enrichment of LREE without fractionation of HFSE and no negative Nb–Ta anomaly. The island-arc/active continental margin-related basalts are typically depleted in Nb–Ta and Ti. It is inferred that the melange within the Shangdan suture represents remnants of an oceanic crust and associated volcanics. An age for the melange can be constrained by a U–Pb zircon age of 517.8 ± 2.8 Ma, obtained from the gabbro within the E-MORB-type ophiolite in the Yanwan area. To the north of the suture zone, the Erlangping melange consists similarly of ultramafic and mafic rocks, andesites and rhyolites. The mafic and andesitic rocks exhibit strong depletion of Nb–Ta and Ti indicating a subduction-related affinity. However, their depletion in Nb–Ta is weaker than that of the island-arc/active continental margin-related volcanic rocks. Taken together, the two ophiolitic melange zones indicate the existence of an early Palaeozoic Shangdan Ocean that was associated with a back-arc basin on the northern North Qinling Island arc terrane, separating the South China from the North China blocks. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The Qinling orogenic belt was constructed by northward subduc- tion and eventual collision of the South China Block (SCB) with the North China Block (NCB) (Fig. 1) (e.g. Enkin et al., 1992; Kröner et al., 1993; Li et al., 1993a; Okay and Sengör, 1993; Ames et al., 1996; Hacker et al., 1998; Zhai et al., 1998; Meng and Zhang, 1999; Zhang et al., 2001). Most authors believe that the subduction and collision events mainly occurred along the Shangdan suture zone, however, the timing of these events is widely disputed. Suggestions for the timing of final continent–continent collision vary between early Palaeozoic, Devonian and Triassic (e.g., Enkin et al., 1992; Kröner et al., 1993; Li et al., 1993a; Okay and Sengör, 1993; Yin and Nie, 1993; Li, 1994; Gao et al., 1995; Ames et al., 1996; Zhang et al., 1997a; Hacker et al., 1998; Zhai et al., 1998; Zhang et al., 2001). Along with disputes about the timing of the final collision are opposing views about the precise nature of the Shangdan suture zone and the tectonic models for the direction of subduction. For example, one model suggests that the major suture zone is marked by the Erlangping ophiolitic melange, and was accompanied by the Shangdan back-arc basin, which was caused by the southward subduction of the Erlangping Ocean (Xue et al., 1996a). Others proposed a northward subduction along the Erlangping zone, and the Danfeng ophiolitic melange is just a nappe overthrusted from the Erlangping melange belt (Faure et al., 2001; Ratschbacher et al., 2003, 2006). Two ophiolites and related magmatic melanges are exposed along both sides of the Qinling terrane, and are traditionally designated the Shangdan suture zone in the south and Erlangping zone in the north (Fig. 2). It is argued that both melange zones were formed in an island-arc setting (e.g. Zhang et al., 1994a; Xue et al., 1996a,b; Sun Lithos 122 (2011) 39–56 ⁎ Corresponding author. Tel.: + 86 29 88303028. E-mail address: dongyp@nwu.edu.cn (Y. Dong). 0024-4937/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2010.11.011 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos