Study On Velocity Structure Of The Xiangshan Volcanic Basin Based On Ambient Noise Tomography

The Xiangshan Volcanic Basin in Jiangxi Province is located at the southwest end of the Gan-hang volcanic rock uranium metallogenic belt,which is located in the collision junction of Yangtze plate and Cathaysian plate.Xiangshan uranium ore-field is an important volcanic uranium ore field in China.To further analyze the relationship between tectonic activities such as concealed faults in the Xiangshan volcanic Basin and adjacent areas and uranium mineralization,based on 142 short-period seismic stations located in the Xiangshan Volcanic Basin and adjacent areas,this paper obtained the ambient noise data for a continuous month,calculated the waveform correlation function,and extracted 3100 Rayleigh wave phase velocity dispersion curves of 1～6s period.The phase velocity and group velocity imaging results were obtained based on the Fast Marching Method(FMM)surface wave tomography method,and the three-dimensional S-wave velocity structure within the depth range of 1-6km in Xiangshan and its adjacent areas was obtained by using the neighborhood algorithm inversion,and the inversion results of the "one-step method" are generally consistent.However,in order not to over-analyze the abnormal characteristics,the smoother ’two-step method ’ inversion results are selected for subsequent interpretation.The velocity structure results show that the lateral inhomogeneity of the shallow crust is strong,and the velocity anomaly morphology and the tectonic distribution in the study area present a good correspondence.The high-speed anomaly at a depth of 2 km corresponds well with the exposed metamorphic rocks.The NE low-velocity anomaly zone in the middle of the study area is generally consistent with the spatial distribution of the late Cretaceous red Basin.Below the depth of 3 km in the crust,the range of low-speed zone in the red basin gradually decreases,which is presumably related to the top boundary of the metamorphic rock basement.The boundary of high and low velocity anomalies in the center of the study area is parallel to the trend of the Fuzhou-Yongfeng fault,indicating that the basement fault has a certain control over the formation and evolution of the basin.A new basement fault in the Xiangshan area is found with the same strike as the deep fault in this area.It is speculated that this fault is a secondary strike-slip fault derived from the long-term strike-slip shear action of the Fuzhou-Yongfeng fault.There are obvious differences in velocity structure between the Xiangshan and the Yuhuashan volcanic Basins,indicating that they have been subjected to different tectonic-magmatic activities,which may be an important factor for the differences in uranium deposits between the two volcanic Basins.This study reveals the structural background of the Xiangshan and its adjacent areas,which provides a basis for the deep second space ore prospecting in the later stage,and shows that the seismic ambient noise tomography method has a good application prospect in the research of volcanic activity structure survey,mineral mineralization structure exploration and other aspects.