TECTONIC DEVELOPMENT OF THE CONTINENTAL MARGINS ON BOTH SIDES OF THE PALAEO-QINLING MARINE REALM
Wang Hongzhen, Xu Chengyan Zhou Zhengguo (Wuhan College of Geology)
This paper endeavours to review the tectonic history of the Qinling fold Region with a view of evolution of continental margins, especially of the development and final extinction of the marine realm in the region. The Qinling region is composed of two opposite continental marginal tracts belonging respectively to the North China and the Yangzi platforms, which were brought to mutual collision after the Indosinian orogenic movement. The boundary between the two tracts falls in with the Fengxian-Shanyang fault in Shaanxi which extends to the Qinghai Lake in the west and to the Nanyang Basin in the east, and may be called the Fengxian-Shanyang converging crustal consumption zone.The northern continental marginal tract may be divided into 3 zones and comprises, from north southwards, the Middle and Upper Proterozoic Zone, mainly composed of the Kuanping and Taowan Groups; the Caledonian Zone, of the Qinling Group with its overlying formations; and the Hercynian Zone, of Devonian and Carboniferous flyshoid sequence. The Caledonian Zone is limited in the south by the Shangnan-Danfeng Fault, which is a subouction zone of Early Palaeozoic age developed within the northern tract, and may be called the Shangnan-Danfeng accretional crustal consumption zone.The continental marginal tract to the north of the Yangzi platform includes two zones, the southern Caledonian Zone composed mainly of Lower Palaeozoic of marginal sea sedimentation type, and a northern Hercynian-Indosinian Zone, of miogeosynclinal Upper Palaeozoic sedimentaries. The boundary in between is marked by several microcontinental massifs formed of Upper Proterozoic epimetamorphic volcano-sedimentaries (e.g. Yunxi Gr.), along the northern side of which there occur also local subduction zones. On both sides of the median converging zone referred to above, there are developed batholithic intrusives of Indosinian and Yanshanian age, evidently resulted from the collision of the two opposite continental blocks.Attention is called to the complicated history and the asymmetrical development and preservation of the continental marginal tracts. It is also remarked that there is no definite relation between the direction of overturned folds and thrusts as seen in surface structures, and the sense of movement of the continental blocks are as a whole in the geological history.