Geological Structure and Dynamics of the Yinggehai Active Rift Basin,South China Sea

The Yinggehai Basin is a unique NNW-trending petroliferous basin in the northwestern South China Sea.This paper mainly utilized stratigraphic,tectonic and seismic data by characterizing the geological structures and conducting the geo-mechanical analysis to study the formation,evolution and dynamics of the Yinggehai Basin.The study indicates that the Ailaoshan-Truong Son extruded terrane is composed of multiple secondary extruded bodies.The Red River fault zone,located within the Qiangtang-Simao-Yinggehai mantle flow channel and basin zone,experienced transform-type sinistral strike-slip motion before the basin forming stage and formed a NW-trending extruded mantle uplift,which activated the Yinggehai basin.After experiencing the rift depression,fault depression,and fault subsidence,the basin eventually formed large-scale,thick sedimentation features with ideal hydrocarbon-forming conditions at the end of the Miocene.Later,the basin dynamically transformed and entered a period of tectonic superposition,reworking,and thermal subsidence.Superposition of the NNW thrust sinistral strike-slip fault zone on the northern Hanoi sub-basin complicated the basin structure.Since the Pliocene,the southern Yinggehai main basin has been transformed into an extensional dextral strike-slip environment that hosted numerous mud diapirs.The thin crust and high geothermal gradient provide favorable conditions for the large-scale accumulation of natural gas.