Shallow anatomy of a continent-ocean transition zone in the northern South China Sea from multichannel seismic data

摘要

The Cenozoic tectonic evolution of the South China Sea is reflected in diverse tectonic processes including continental rifting, seafloor spreading, subduction, terrane collision and strike-slip fault movement. A continent-ocean transition zone in the northern South China Sea caused by the lithospheric extension when the continent underwent break-up, rifting and later seafloor spreading, is clearly imaged in the multi-channel seismic data presented in this study. The morphological units of the continent-ocean transition zone are the rift-depression, the volcanic zone and tilted fault blocks. The volcanic zone represents a highest extension zone within the continent-ocean transition zone and is mainly distributed in the southern slope uplift zone along the northern passive margin of the South China Sea. The large listric-normal faults bounding the Dongsha Rise and Baiyun Sag are evidenced in the seismic image. The passive margin in the northern South China Sea underwent the wide-rift to narrow-rift process in the transition zone as inferred from the relation between the surface heat flow and initial rifted crustal thickness. The continent-ocean transition zone in the continental margin of the South China Sea is consistent with high heat flow zone (average 90mW.m ~(-2)) observed in the previous heat flow measurements and at ODP Site 1148, and is manifested in a sharp change of the P-wave velocity. The rifted margin of the South China Sea is a non-typical magma poor passive margin or an intermediary form between the Iberian-type non-volcanic and the Greenland-type volcanic margin compared to the world's typical passive margins.