Characteristics Of Faults And Distribution Of Pre-Cenozoic Basement Lithology In Southern South China Sea

The South China Sea is the largest marginal sea on the continental margin of East Asia.It is located at the intersection of the Eurasian Plate,the Pacific Plate and the Indo-Australian Plate.It is one of the most active tectonic activities in the present.In the South China Sea,there are strong interactions between multiple plates,tensile cracking,crustal growth and thinning deformation.Mantle fluctuation range is large,resulting in lithospheric faults,wide distribution of basement and caprock fractures,and many periods.Complex movements are the geological features of the area.Fault system in the southern South China Sea and northern Borneo areas are the main research contents comprehensively,the gravity and seismic characteristics of the South China Sea,and the magnetic susceptibility characteristics of the South China Sea area.It clarifies the characteristics of the fault system in the southern and southern margins of the South China Sea,and the physical characteristics and distribution characteristics of the Paleozoic basement rocks in the southern South China Sea.It is of great significance for oil and gas exploration in the deep waters of the southern South China Sea.According to the classification of faults in the southern part of the South China Sea,the field distribution and geophysical data were used to study the distribution characteristics,formation mechanism and relationship between the fault and the internal basin of the South China Sea.Using the collected drilling,trawling data,geophysical data combined with seismic data,taking the geological constraints between the basin edge and the land,the free space gravity anomaly,the polar magnetic anomaly,and the seismic joint interpretation,clarify the Mesozoic distribution range in the southern part of the South China Sea;The authors sampled 227 sample density datas and 2128 magnetic susceptibility datas in Sabah and Sarawak of Malaysia.Combining the sample data of the northern part of the South China Sea,the age,density and magnetic susceptibility characteristics of the samples are compared and summarized.The following results and understanding are obtained:1.Characteristics of faults system in southern South China SeaThe fault system in the southern South China Sea can be divided into four types.NW strike-slip faults,NE tensile structure associated faults,SN strike-slip faults and southern arc faults.The NW strike-slip faults have indications on the zoning of the southern South China plate.When the basin is formed,most of the NE faults are related to the boundary-controlled faults of the semi-mantle basin and the extension of the basin edge.The fracture in the SN,that is,the Yuedong-Wanan fault is the western boundary of the South China Sea plate.The Lupar line and the Mersing line on the southern land of South China Sea are the remnants of the ancient South China Sea oceanic crust that subducted under Borneo and then rose to the surface.2.Magnetic susceptibility-density characteristics in the southern South China SeaFrom the former Mesozoic to the Cenozoic,the magnetic susceptibility and the density decrease gradually.Different lithology leads to different susceptibility.The higher the dark minerals content in the same lithology,the higher the magnetic susceptibility.The main factors affecting density are lithology and compaction strength.3.Distribution characteristics of the Paleozoic basement in the southern South China SeaThe Mesozoic lithology distribution characteristics in the southern part of the South China Sea.Generally speaking,the sedimentary rocks are distributed in the east,the west and the south,and the metamorphic rocks are widely distributed.Due to the large depth of the parts in the South China Sea,most of them are dynamic metamorphic rocks.And regional metamorphic rocks,igneous rocks are more like patchs or distributed along the fault.