Abstract:

The South China Sea is tectonogeographically composed of the central ocean crust, continental slopes, and continental shelves. The tectonic evolution of the marginal oceanic basin in the South China Sea includes two cycles: Paleo and New South China Sea tectonic periods, both of which had undergone formation and shrink stages. Prior to the PaleoSouth China Sea, there used to be a united basement in the present basin area before the Cenozoic. The PaleoSouth China Sea had undergone rifting, drifting and subduction stages. The two former stages are characterized by extension in the periods from the Late Cretaceous to the Eocene. The subsequent shrinking period was from the Oligocene to the Quaternary, and the related oceanic crust had been subducted and disappeared. The new South China Sea had undergone two construction stages including intracontinental rifting during the Paleocene to the Eocene and marginal continental drifting during the late Oligocene to the middle Miocene, which were followed by the shrinking episode since the middle Miocene. The shrinking stage was characterized by ceasing of the northsouth expansion in the area probably owing to the Philippine island arc westward obduction from the middle Miocene to the present. The two tectonic cycles of marginal oceanic basin controlled the regional tectonic patterns, natures of the component blocks, and attributes of the basin margins. As the results of the two tectonic cycles, the northern margin is a passive continental margin; its southern Nansha block is a drifted block from south; the southern edge is a kind of polyphase active continental margin; its western margin is bounded by strikeslip fault system; and the eastern part is enclosed by the Philippine Island Arc showing compressional features.

Key words: tectonic cycle of marginal oceanic basin, sea floor spreading, subduction of previouslyexisted marginal ocean, South China Sea