Cenozoic Tectonic Evolution Of The Xingning Depression In The Northeastern Part Of The South China Sea

Xingning sag in the south of zhu-2 depression in Pearl River Mouth Basin of the northeastern South China,is a Cenozoic Faulted-depression type negative structural units and developed in the Mesozoic folded basemen.In response to multi-period tectonic movements and continental shelf evolution in the northern margin of the South China Sea,Xingning sag is NW-SE treeding,which is different from Pearl River Mouth Basin and even general Cenozoic basins in the southest south China plate.Systematically,this thesis studies the tectonic-sedimentary evolution characteristics and genetic mechanism of two-dimensional field in Xingning sag by using the related theories and technical methods of structural geology,sedimentary basin analysis and seismic sequence,making reference to achievement of previous studies.Through identification of the main Seismic reflection interface of Xingning sag,Xingning Cenozoic tectonic sequence divided into rifting tectonic sequence,tectonic sequence transition,depression tectonic sequence.The tectonical evolution of Xingning sag is divided into four forming stages.The four forming stages are the fault phase,the fault and depression phase,the slowly depression phase and the fast depression.The tectonic background from Mesozoic compressive orogenic to Cenozoic continental margin expansion,the NW-SE direction tensile stress to form a series of early of concave faults and positive flower structure of strike-slip faults in Xingning sag during Fault phase.The sag mainly characterized by multiple half grabens and grabens.Xingning sag affected by the S-N direction tensile stress result from the expansion of the south China sea during the fault and depression phase,to form a series of east-west normal fault and negative flower structure,and to form a series of east-west normal fault and negative flower structure.With continental slope of the South China Sea northward transition,tectonic activity weakened,Xingning sag accepted stable marine deposits during the slowly depression phase and the fast depression.The magma along the boundary fault continues eruption in the study area,which strengthens the control function of the boundary fault to the sag.The background of Xingning sag of Cenozoic tectonic evolution was expansion.Geodynamics for the basin evolution might come from changes in oceanic plate subduction in the Pacific Ocean and the expansion of the south China sea in different periods.Evolution law of Xingning sag was consistent with the continental slope basin of northern South China sea.