Kinematics of Cenozoic extension on the South China Sea continental margin and its implications for the tectonic evolution of the region

In the northern South China Sea several large sedimentary basins developed during the Cenozoic, characterized by episodic rifting, clockwise rotation of the rifts, an eastward aging breakup unconformity, and intensifying crustal extension to the east. These features may be summarized by a "scissors" model. The maximum rifting occurred north of the maximum thermal subsidence, which was in turn north of the seafloor opening. In contrast, the Nansha microcontinent south of the South China Sea Basin was dominated by compressional deformation during the Cenozoic. Extension was of subordinate significance and manifested mainly by block faulting and tilting in the late Early Oligocene. Maximum tilting occurred in the southern part of the Nansha microcontinent, at distance from the deep-sea basin of the South China Sea. The asymmetric development of extensional structures around the South China Sea Basin may be explained by the simple-shear model proposed by Wernicke (1981). The tectonic development of the South China Sea was the consequence of various interactions of three major plates, and may be summarized into three stages with dominating influences of, respectively, the retreat of the West Pacific subduction zone in the Late Cretaceous, the hard collision and impinging of India to Tibet since the Late Eocene, and the fast northward subduction of the Indian Ocean-Australian plate since the late Early Miocene.