Three Dimensional Crust Mantle Velocity Structure And Deep Metallogenic Structure In South China

The South China plate is located in the southeastern margin of Eurasia,adjacent to the Philippine Sea plate in the East,and subjected to the remote compression of the Western Pacific plate and the Indian Australian plate,which is mainly composed of Yangtze block and Cathaysian Block.Due to the complex tectonic setting and rich mineral resources of the South China plate,it has always been a hot research field of Geology and geophysics.The latitude and longitude of the study area are 20°N-35°N,104°E-123°E.The research data are mainly from the fixed stations of the China Seismic Network Center and the filed mobile stations set by the research group.The research data are mainly from the waveform data of 934 teleseismic events recorded by 479 stations,from which 77969 teleseismic P-wave arrival time data are selected,and grids(50-800 km)are set at different depths.By using P-wave travel time tomography,the P-wave velocity transverse structure and profile structure images of each depth layer are obtained,so as to further study the characteristics of crust mantle movement in the deep part of South China continent and its metallogenic tectonic background and dynamic process.According to the results of P-wave tomography,the following conclusions are obtained:(1)Two obvious high velocity anomalies in the study area are located in the upper mantle of the Yangtze block and in the mantle transition zone of the eastern segment of the Jiangnan orogenic belt.The former reflects the thick lithospheric root of the craton,while the latter reflects the deep subduction of the paleo Pacific plate.(2)The low velocity anomalies in the crust and mantle of Cathaysia Block are generally located above the high velocity anomalies,and their distribution characteristics are related to the large-scale magmatic activities in the late Mesozoic;(3)Comprehensive analysis shows that the South China block is influenced by the subduction of the Pacific plate and the Philippine Plate.The subducted block has reached the lower mantle,and then the Pacific plate retreats eastward.With the retreat of the Pacific subduction plate,the low velocity anomalous body beneath the Cathaysian Block upwelling along the magmatic channel and fault zone,rising to the shallow asthenosphere,which eroded the overlying lithosphere and separated the lithosphere beneath the Yangtze block.At the same time,the upwelling asthenosphere thermal material mineralized in the shallow part,forming a number of metallogenic belts in South China.In conclusion,the lithospheric delamination and magmatic activities in South China are related to the westward subduction and retreat of the paleo Pacific plate.The upwelling of asthenosphere beneath the Cathaysian Block erodes the overlying lithosphere and makes the delamination more likely to occur.The material exchange among asthenosphere,upper mantle and lithosphere led to a series of tectonic activities,such as magmatism,mountain uplift and plate fracture,which eventually made the South China continent present the basic structural characteristics after several tectonic movements.