The Research Of Tectonic Featuresand Metallogensisof The Eastern Part Of South China Block By Magnetotelluric Array Data

From the Proterozoic to the Cenozoic,the South China blockexperienced many complicated geological activities,such as the mergeof ancient blocks,the Intracontinental orogenism and the subductionog oceanic lithosphere.Nowadays,the South China Block is composed of three major units,the Yangtze cratonic block in the west,the Cathaysia block in the east which was reconstructed by multi-stage magmas,and the Jiangnan Orogenic Belt formed by the collision between the formal two blocks.However,due to the special tectonic environment of the South China block,there are many controversial geological problems about the relationship between the Yangtze and Cathaysia blocks,the metallogenic background and dynamics of South China Block.The motivation of this study is to provide electrical constraints for the existing arguments with 3-D resistivity model of eastern South China Block.This paper is based on the data collected by the projects,(1)The crustal electrical structure of the qin-hang belt and its adjacent areas,and(2)Experimental Study of Standard Network of Continental Electromagnetic Parameters(Sino Probe-02-04).The area of research is in the geographical ranges of 23°N ?31°N and111°E?121°E.The main geological blocks include the small eastern part of Yangzi Block,the eastern part of Jiangnan Orogenic Belt and the most of the Cathaysia Block.Through the detailed data processing and analysis,the 2D and 3D electrical lithospheric models ofthe eastern South China block were obtained by using the Win Glink software and the Mod EM program both using NLCG as the inversion algorithm.The results show that the tectonic manifestation of the Yangtze and Cathaysia blocks collided at the southwest part of eastern section of Jiangnan Orogenic Belt,and the Yangtze block has crossed the Jiangnan Orogenic Belt and where the Jiangshao fault was formed.In the northeastern part of eastern section of Jiangnan Orogenic Belt,there are obvious mantle material intrusion,which has destroyed the contact relationship between two blocks and drastically reformed the deep structures of the Jiangshao and northeastern Jiangxi faults.It is the deep structural reason for the Northeast Jiangxi metallogenic belt of gold and silver.The eastern part of South China block is mainly composed of Cathaysia block.The study found that the upper crust of the Cathaysia block was invaded and destroyed by magmas.The lower crust and the upper mantle appear interphase and band-like low resistivity and high resistivity anomalies along the Tunxi-Yingtan-Anyuan and Shangyu-Dapu-Zhenghe faults,which indicates that the subduction of the Paleo-Pacific Plate hasretreated under the action of gravitational drag,resulting in the tensile environment in the eastern South China block,which is the cause of the formation of the A-type granites in the South China block.The time of the plate retreat is varied according to the latitudes,which shows the nonsynchronous retreat of Pacific.Therefore,from the Jurassic to the Cretaceous,magmas upwelled in the Nanling area.The magmas were "traped" by the upper crust,and the compositionexchange inthe earth formed the main tungsten-tin Nanling metallogenic belt.