Neoproterozoic post-collisional extension of the central Jiangnan Orogen: Geochemical, geochronological, and Lu-Hf isotopic constraints from the ca. 820-800 Ma magmatic rocks

Neoproterozoic magmatic rocks in South China contain important information on evaluating crustal reworking during the Yangtze-Cathaysia collision and post-collisional extension. We present here geochemical, geochronological, and Lu-Hf isotopic data of a suite of granitoids and diorites from the Jiuling and Meixian plutons of the central Jiangnan Orogen. The granitoids display intermediate geochemical features between S-type and I-type granites. They exhibit arc-like patterns of REE and trace element partition, reflecting inheritance of juvenile arc-derived crust. Igneous zircons from the Jiuling and Meixian granitoids yield U-Pb ages of 822-819 Ma and 816-815 Ma, respectively. Inherited zircons from the granitoids commonly yield a major age population of 980-860 Ma, consistent with the time of the Shuangxiwu volcanic arc. The igneous and inherited zircons have highly variable epsilon(Hf)(t) values ranging from -9 to +12.2. We interpret the granitoids to have been generated by remelting and binary mixing of (1) juvenile arc-derived crustal material and (2) supracrustal material of the Shuangqiaoshan meta sedimentary rocks. The previous crustal thickening achieved by the Yangtze-Cathaysia collision is a prerequisite for their generation. The two granitoids, together with regional 825-815 Ma S-type granites, indicate incipient post-collisional collapse of thickened crust, heralding tectonic switch from compression to extension. The Meixian diorites display arc-like geochemical characteristics, and yield zircon U-Pb ages of 805-804 Ma and neutral to positive zircon epsilon(Hf)(t) values (-0.1-+7.5). The diorites were generated by decompression melting of arc-derived lower crust, associated with asthenospheric mantle upwelling during continental rifting. Such rifting may be part of global Neoproterozoic rifting events that finally led to breakup of the Rodinia supercontinent. (C) 2017 Elsevier B.V. All rights reserved.Natural Science Foundation of China (NSFC) Project [41190075, 41502197]; research project of NSFC Major Program [41190070]; Hong Kong RGC GRF [HKU7063/13P, 17301915]; Basic Science Foundation of Institute of Geomechanics [DZLXJK201601]; Chinese Geological Survey Project [12120115069501]; Hong Kong Scholars ProgramSCI(E)ARTICLE91-11029