Study On The Deep Crust-mantle Velocity Structure Of Nanling Tectonic Belt And Cathaysia Block

Cathaysia block is an important metallogenic and granite producing area in China.The source of metallogenic deposits and deep metallogenic mechanism in this area have been controversial.In addition,the academic community has not formed a unified understanding of the tectonic evolution of Cathaysia block.In this study,the upper mantle morphology distribution and velocity structure of Cathaysia block were discussed based on the deep mineralization process and deep dynamic mechanism.Firstly,451 teleseismic events were recorded across the central part of the Cathaysia block by broadband seismic lines(81 stations,5?8 km apart),and a total of 7231 relative traveltime residuals were obtained for teleseismic tomography,and the two-dimensional crust-mantle velocity structure with high resolution(lateral 0.2°)above the survey line was obtained.The conclusions are as follows:(1)A low-velocity anomaly gradually deepens from west to east in the upper mantle of the central Cathaysia block;(2)The velocity structure in the lithosphere of Cathaysia block has a strong lateral velocity difference,and has a certain spatial correlation with the distribution of fault zones.According to the results of previous studies,the low-velocity anomalies in the upper mantle of Cathaysia block may be attributed to the uprising hot asthenospheric materials,which arrive at the bottom of the lithosphere and initiate lithospheric delamination,and may continue to invade the crust along deep and large faults to provide energy for the formation of metal mineral deposits.However,the cold material of the delaminated lithosphere sinks and the trace left by it is the high velocity anomaly in the asthenosphere.Then,the velocity structure of the upper mantle in the Cathaysia block was obtained by using 25128 travel time residual data of 330 earthquakes received from 82 fixable stations and81 portable stations in Guangdong and Fujian provinces.The conclusions are as follows :(1)the velocity of the upper mantle in the Cathaysia block is affected by the possible Hainan plume;(2)The upwelling of asthenospheric material caused by the subduction of the Eurasian plate also has an influence on the low velocity of the upper mantle of Cathaysia block.The Cenozoic asthenospheric material keeps the low velocity beneath the Zhenghe-Dapu fault zone formed in the Mesozoic.(3)The high velocity anomalies in the mantle transition zone of Cathaysia block may be the remnants of the subduction of the ancient Pacific plate.