The Magnetotelluric Research On Granite In South China

Cathaysia Block and the continental shelf of the East Sea in the southeast of the Eurasia are located on the edge of the western Pacific Ocean,to the east of Qinghai-Tibet Plateau,to the south of the North China Plate,to the north of the Indosinian Plate and the Northern continental shelf of South China sea and to the Northwest of the Philippine Sea plate.South China region has a very long history and complicated structure.With almost every main and severe orogenic event,there were granite emerged.So there are varies types of granite in South China and they are complex and genetic types and the forming processes of the granite are complex.This study is based on four magnetotelluric sounding profiles in South China which are obtained by the Project of Sinoprobe.After systemically analyzed and fine processed the 192 measured magnetotelluric sounding points and the 2D inverse of each survey line,the 2D electronic model of the subsurface medium in South China is built.Combined with the known geological,geophysical and geochemical data,the 2D model diagram is studied to investigate the distribution characteristics of granite in Southern China more accurately and more comprehensively,and to understand the crust-mantle electrical structure and kinetic background in the view of geophysics.The result of the study shows that in South China,granites distribute very widely and always found as planner and block.The resistivity of granites in different regions is different.In South China,the crust presents a trend of thick to thin from west to east.In the west,east and middle of the study area,the thickness of the crust is separately about 60 km,30 km and 20-30 km.The speculation is that the crust in the west of the study area becomes thicker due to the west plate collision and convergence effect while it sharply becomes thinner due to the Pacific plate subduction effect in the east.The western lithosphere thickening is mainly caused by the intracontinental compressive orogenic or intracontinental collision and convergence orogenic effect,but the eastern lithospheric thickening may be caused by the residue of the subduction of the Pacific Plate stacking underneath the lithosphere.The central lithosphere thinning is caused by the invasion of asthenolithic material of which the driving force comes from the deep thermal disturbance caused by the subduction of the Pacific Plate.