3-D Crustal Shear-wave Velocity Structure In Southeast China And Its Tectonic Implications

Southeast China is located at the southeastern margin of Eurasia plate,and it is one of the most enriched areas in China for non-ferrous metals,rare metals,rare earths,uranium and other mineral resources.The deep processes and mechanisms of the Nanling and the Wuyi metallogenic belts in this region have been in research and exploration for a long time,and so far there has not been a good explanation.Revealing the crust-mantle structure and the tectonic relationship between the deep and shallow in the study area is of great significance for understanding the deep tectonic background and metallogenesis of the two metallogenic belts.This paper studies the 3-D crustal shear-wave velocity structure in southeast China,and the main work and achievements of this paper are as follows:(1)In this paper,the vertical components of the continuous waveform data of 187 fixed stations in southeast China are used to perform ambient noise cross-correlation calculation and stacking after 5s-50 s period band-pass filtering,normalization,and spectral whitening preprocessing,and then we measure and select dispersion data of every station-pair.Finally,we apply the direct inversion method of surface wave dispersion which is based on ray tracing to obtain the 3-D crustal shear-wave velocity structure in southeast China.The horizontal sampling interval of the model's quality is evaluated.(2)The middle-upper crust structure in the study area presents a pattern of high velocity anomaly alternating with low velocity anomaly along northeast-southwest stike.The low velocity anomalies mainly distribute in the Jiangxi Ganzhou fault basin,the Jiangxi Ji'an depression,and the Guangdong Heyuan geothermal resources area,while the high velocity anomalies mainly distribute in the Nanling and Wuyi mountain areas.It is basically consistent with the geological tectonic characteristics of the surface.In the middle-lower crust,the whole study region is characterized by the trend of high velocity anomaly in the northwest and low velocity anomaly in the southeast.Among them,the low velocity anomaly mainly distribute in the south of the Nanling mountain and the east of the Wuyi mountain,while the rest areas show relative high velocity anomaly,which is basically consistent with the regional tectonic trend.(3)The Ganjiang fault zone shows high velocity anomaly in the middle-upper crust,and low velocity anomaly in the middle-lower crust.The Heyuan segment of Shaowu-Heyuan fault zone presents low velocity anomaly in the whole crust,which may be related to the existing of geothermal resources in this area;while the middlenorth segment shows high velocity anomaly in the middle-upper crust and low-velocity anomaly in the middle-lower crust,indicating it may be a transport channel of deep matter.The Zhenghe-Dapu fault zone shows a band-shaped low velocity anomaly in the middle-lower crust.The above-mentioned velocity anomaly characteristics indicate that these three fault zones are all deep faults.(4)The crustal velocity distribution of the Nanling metallogenic belt is lateral heterogeneity.The two sides of the Ganjiang fault zone show a difference anomaly feature,with high velocity anomaly on the west side and low velocity anomaly on the east side,and this feature may be caused by different level of diagenesis and metallogenesis.The upper-lower crust of Wuyi metallogenic belt generally shows high velocity anomaly,corresponding to the Wuyi mountain range,while there are low velocity anomalies in the middle-lower crust which are linked to the upper mantle of southeast coastal area,which are speculated to be related with western subduction of the Pacific plate.