BASIC STRCUTURAL PATTERN AND TECTONIC MODELS OF THE SOUTH CHINA SEA: PROBLEMS,ADVANCES AND CONTROVERSIES

The South China Sea is located at a juncture among the Eurasian,the Indian-Australian and the Pacific plates,being the largest continental marginal sea along the East Asian continental margin.It has experienced a complex transition of continental marginal types.The northern margin was an Andean-type continental margin before 80 Ma,then gradually transferred into a rifted continental margin in the Eocene and a typical passive continental margin since the middle Miocene.The eastern margin was an open water before 17 Ma and gradually became a subduction zone of the trench-arc-basin system by one-way subduction to double-way subduction,when the South China Sea became semi-closed basin since 6 Ma.The western boundary gradually transformed into a continental margin with strike-slipping faulting or transform faulting since 34 Ma.The southern margin was an asymmetric rift-type continental margin corresponding to the northern margin before 34 Ma,and became a passive continental margin during 34~16 Ma and gradually a thrusting-type continental margin after 16 Ma.Complex dynamic settings of the South China Sea have caused many controversies on their origin.The plate dynamic factors include either the Pacific Plate subduction and the indentation of the Philippine Sea Plate along the Taiwan Orogen to the east side the South China Sea,or the Indian Plate oblique subduction and mid-ocean ridge subduction to the west side.They may also be responsible for the uplifting of the Tibetan Plateau and the related extrusions of continental blocks to the north side.At the same time,the mantle dynamics of deep-seated magma underplating,delamination,mantle plume and mantle-hydrated process should not be ignored.