GENETIC MECHANISM OF THE YINGGEHAI BASIN, NORTHERN SOUTH CHINA SEA: A COMPARATIVE STUDY TO THE WEIHE BASIN

The Yinggehai Basin is a Cenozoic depositional basin located on the Northern Continental Margin of the South China Sea, a unique and important tectonic position at the convergent hinge among the Eurasian, Pacific and Indo-Australian plates. The complicated geotectonics of the basin has made the genetic mechanism of the basin a hotspot. In this paper, the Weihe Basin, a basin with similar tectonic subsidence and sedimentary evolution history and genetic mechanism, is selected for purpose of comparative study. The Yinggehai Basin and the Weihe Basin are on the Southern and Northern margins of the South China plate respectively. Both of them are located at a juncture of plates as typical strike slip basins with long terms of rapid subsidence and sedimentation histories. Taking the Weihe Basin as an example, a comparative study is carried out on the history of tectonic subsidence and sedimentation, upon the consideration of specific tectonic location of the Yinggehai Basin and the tectonic background of the expanding South China Sea. The comparison reveals that the formation and evolution of the Yinggehai Basin is closely related with the collision between the India plate and the Qinghai-Xizang plate, escape and the self rotation of Indo-China block, eastward extrusion of the Southern China block and the subduction of the Pacific plate. Affected by the multi-stage plate tectonic activities, the basin has experienced several evolutionary stages. Since Cenozoic, it has suffered a sinistral strike stage, a slip stretch-thermal subsidence stage and an extral strike slip extension stage. In addition, high temperature and pressure geological records, mud diapir and other special geological phenomena are observed in the Yinggehai Basin under the control of thermal subsidence related to the expansion of the South China Sea since Oligocene(33~15 Ma).