http://www.paper.edu.cn Gondwana Research 12 (2007) 121–143 Collision leading to multiple-stage large-scale extrusion in the Qinling orogen: Insights from the Mianlue suture ⁎ Sanzhong Li a, , Timothy M. Kusky b, Lu Wang c, Guowei Zhang d, Shaocong Lai d, Xiaochun Liu e, Shuwen Dong e, Guochun Zhao f a Department of Marine Geology, College of Marine Geoscience, Ocean University of China, No. 238, Songling Road, 266100, Qingdao, China b Department of Earth and Atmospheric Sciences, St. Louis University, 3507 Laclede Avenue, St. Louis, MO 63103, USA c College of Marine Geoscience, Ocean University of China, Qingdao, China d Department of Geology, Northwest University, Xi'an, China e Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, China f Department of Earth Science, The University of Hong Kong, Hong Kong, China Received 1 March 2006; received in revised form 13 November 2006; accepted 13 November 2006 Available online 16 December 2006 Abstract The geologic framework of the Phanerozoic Qinling–Dabie orogen was built up through two major suturing events of three blocks. From north to south these include the North China craton (including the north Qinling block), the Qinling–Dabie microblock, and the South China craton (including the Bikou block), separated by the Shangdan and Mianlue sutures. The Mianlue suture zone contains evidence for Mesozoic extrusion tectonics in the form of major strike–slip border faults surrounding basement blocks, a Late Paleozoic ophiolite and a ca. 240–200 Ma thrust belt that reformed by 200–150 Ma thrusts during A-type (intracontinental) subduction. The regional map pattern shows that the blocks are surrounded by complexly deformed Devonian to Early Triassic metasandstones and metapelites, forming a regional-scale block-in-matrix mélange fabric. Five distinct tectonic units have been recognized in the belt: (1) basement blocks including two types of Precambrian basement, crystalline and transitional; (2) continental margin slices includingEarly Paleozoic strata, and Late Paleozoic fluviodeltaic sedimentary rocks, proximal and distal fan clastics, reflecting the development of a north-facing rift margin on the edge of the South China plate; (3) out of sequence oceanic crustal slices including strongly deformed postrift, deep-water sedimentary rocks, sheeted dikes, basalts, and mafic–ultramafic cumulates of a Late Paleozoic ophiolite suite, developing independent of the rift margin in a separate basin; (4) out-of-sequence island-arc slices; (5) accretionary wedge slices. All the tectonic units were deformed during three geometrically distinct deformation episodes (D1,D2 and D3 during 240–200 Ma). Units 2–4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the D1 episode. Thrust slices 20 km south of the Mianlue suture are related to this vertical extrusion due to the same rock assemblages, ages and kinematics. The D2 and D3 episodes folded all the units in a thick-skinned style about east– west (D2) and west–northwest (D3) axes in the Mianlue suture zone. An early foreland propagating sequence of accretion of Late Paleozoic rocks deposited above the Yangtze craton is not involved in D1 deformation but is temporally equivalent to the D2 and D3 deformation in the Mianlue suture. Two stages of strike–slip faulting mainly occurred at the end of D2 and D3, respectively. During D2 deformation, the Bikou block was obliquely indented to the ESE into the Mianlue suture, rather than being thrust over the Mianlue suture from the north as a part of the Qinling–Dabie microblock. During D3 deformation, however, the Bikou block was bounded by the south boundary fault of the Mianlue suture, and the Yangpingguan fault on the south. These faults are coeval strike–slip faults, but of opposite senses, and accommodated minor southwestward extrusion of the Bikou block into Songpan–Ganze orogen. The other basement blocks north of the Mianlue suture were extruded eastward by about 20 km of lateral displacement, based on the offset of the Wudang dome, during the D3 episode due to the northeastward indentation of the Hannan complex of the South China craton. Post-D3 emplacement of granite, cutting across the strike–slip faults such as the Mianlue suture, provides a minimum age of 200 Ma for D3 deformation. Therefore, based on insights from the evolution of the Mianlue suture, the D2 and D3 episodes in the Mianlue suture and its neighbors are not responsible for and associated with the two-stage extrusion of the Dabie UHP-HP terranes from the Foping dome to the present erosional surface (more than 350 km). © 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Mianlue suture; Tectonic evolution; Extrusion tectonics; Indentation tectonics; Qinling; Deformation ⁎ Corresponding author. Tel.: +86 532 66781971 (office). E-mail address: [email protected] (S. Li). 1342-937X/$ - see front matter © 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2006.11.011 转载 中国科技论文在线 http://www.paper.edu.cn 122 S. Li et al. / Gondwana Research 12 (2007) 121–143 1. Introduction that orogen-parallel eastward extrusion occurred diachronously from 240 Ma in the east to 225–210 Ma in the west. The Qinling–Dabie Orogen marks the irregular suture Ratschbacher et al. (2000) described the Cretaceous and between the North and South China cratons (Fig. 1), and Cenozoic unroofing with eastward tectonic escape and Pacific contains the largest belt of ultrahigh pressure (UHP) backarc extension in the Early Cretaceous, and Pacific metamorphic rocks in the world. It is a major part of the E– subduction in the mid-Cretaceous. Wang et al. (2003) proposed W-trending Central China Orogen of central China (Jiang et that the Dabie HP-UHP metamorphic rocks were originally al., 2000), extending 1500 km westward from the Qinling located beneath the Foping dome, a dome in the narrowest part range, through the Kunlun range, and 600 km eastward of the Qinling orogen (Fig. 1), where it underwent ultrahigh- through the Tongbai–Dabie range, then continues northeast- pressure metamorphism in the Early Triassic. Then it was ward through the Sulu area of the Shandong peninsula into the extruded eastward to its present-day location. Imjingang or Hongseong–Odesan fold belt of Korea (Fig. 1) Since so many different models for extrusion mechanisms (Ratschbacher et al., 2003; Oh and Kusky, in press). Large and timing have been proposed, we further focus on the amounts of continent–continent convergence have been Mianxian–Lueyang (abbreviated to the Mianlue) suture south accommodated along the geometrically irregular suture, but of the Foping dome of the Qinling Orogen to provide structural the convergence was diachronous in time and inhomogeneous constraints on whether or not, and how the extrusion of the in space so that the related indentation, extrusion and rotation Dabie UHP terranes from the Foping dome to the present-day has a complex spatial and temporal pattern (Tapponnier et al., location is associated with the Mianlue suture (Wang et al., 1982; Ratschbacher et al., 1991; Davison et al., 1995; Zhang 2003). Furthermore, we discuss an alternative tectonic model in et al., 1995; Jones et al., 1997; Thompson et al., 1997a,b; the Qinling–Dabie Orogen using our detailed field data from the Kusunoki and Kimura, 1998; Hacker et al., 2000; Ratschba- Mianlue suture of the Qinling orogen. cher et al., 2000; Johnston et al., 2000; Beaumont et al., 2001; Xypolias and Koukouvelas, 2001; Hatcher, 2002; Ratschba- 2. Geological background cher et al., 2003; Xypolias et al., 2003; Wang et al., 2005). Especially extrusion and indentation tectonics in Asia are The geologic framework of the Qinling–Dabie orogen was evident tectonic phenomena. Consequences of Cenozoic and built up through two major suturing events of three blocks. Mesozoic indentation tectonics throughout Eurasia are mainly From north to south these include the North China craton driven by active indentors such as the Indian plate into the (including the north Qinling block), the Qinling–Dabie micro- Eurasian plate (Tapponnier et al., 1982) and the South China block (including, from west to east, the Qaidam, the West craton into the North China craton (Yin and Nie, 1993), Qinling, South Qinling and Dabie–Sulu blocks), and the South respectively. Some basement blocks or microblocks between China craton, separated by the Shangxian–Danfeng (abbrevi- or in these orogens may have undergone lateral and/or vertical ated to the Shangdan) and the Mianlue sutures. The Shangdan (upward) extrusion tectonics. For example, Mesozoic and suture resulted from Middle Paleozoic closure of the Shangdan Cenozoic convergent tectonics in southeast Asia (Tapponnier Ocean and collision of the North China craton and the Qinling– et al., 1982; Morley, 2002) included lateral extrusion of south Dabie microblock. The Mianlue suture, however, resulted from China (Zhang et al., 1995) and large-scale eastward or upward Late Triassic closure of the Mianlue ocean and collision of the extrusion of the Qinling–Tongbai–Dabie belt (Maruyama et Qinling–Dabie microblock and the South China craton (Liu al., 1994; Hacker et al., 2000; Ratschbacher et al., 2000; et al., 2004; Meng et al., 2005; Zhang et al., 2005). Hacker et al., 2000; Li et al., 2002; Wang et al., 2003). Other Rocks in the Qinling orogen record