Dynamics of the Continental Margins in South China Sea: Scientific Experiments and Research Progresses

Abstract

AbstractComprehensive geophysical surveys, including the multi‐channel seismic survey with long streamer and large power source and the refraction/reflection seismic survey of ocean bottom seismology (OBS) have been deployed in the southern margin and the southwest sub‐basin of South China Sea for the first time. Based on the interpretation of these geophysical data, combined with studies on tectonics structure, geochemistry and dynamic simulation, etc, our project worked out the dynamics of the continental margins in South China Sea. Major conclusions are as follows: Two sea‐floor spreading events occurred in Cenozoic. The first episode happened between 33.5~25 Ma, and after a 1.5 Ma tectonic adjustment, the second episode started between 23.5~15.5 Ma. In both episodes, the South China Sea experienced propagation of rifting and spreading from east to west, resulting in a structural framework featured with blocks in north‐south direction and segments in east‐west direction; there is different structural transformation time, from faulting to depression, for Cenozoic sedimentary basins in the southern and northern margins, corresponding to the end time of early and late sea basin spreading respectively. The continental crust of South China Sea might have experienced depth‐dependent stretching. The lower crust and top of upper mantle have been magnetized and no obvious velocity anomalies of the mantle have been found in oceanic basin. Both the southern and northern margins belong to non‐volcanic continental margins, although lower crustal bodies of high‐velocity occur in the east of the northern margin, but without seaward reflector. The origin and evolution of sediment basins on the northern and southern continental margins are very distinct, and show ring‐like belt distribution characteristics with oil outside and gas inside. We believe that the hydrocarbonbearing prospects in southern continental marginal basins are superior to these of northern continental marginal basins. In Mesozoic, the northern and southern margins of South China Sea were parts of South China block, and were controlled by the Palaeo‐Tethys and Paleo‐Pacific tectonic domains.