Crustal structure and its tectonic implications beneath the middle-lower Yangtze metallogenic belt in Anhui Province: 3D deep seismic sounding results from airgun source in inland waters

To evaluate the effectiveness of using airguns as seismic sources in inland waters to detect the regional crustal structure, a mobile large-capacity airgun excitation experiment was conducted in October 2015 in the Anhui section of the middle-lower Yangtze metallogenic belt. In this study, we extracted 1,957 first-arrival phases (Pg) and 2,179 Moho reflection phases (PmP) from the airgun seismic signals, and performed joint inversion of the traveltimes. The inversion results reveal the P-wave high-velocity anomalies above 7 km depth in the upper crust beneath the ore clustering areas, suggesting the source of mineralized materials. The crustal velocity structure characteristics substantially differed above and below a depth of 7 km, indicating the existence of a regional basement detachment surface. The velocity structure in the middle-lower crust, especially in the lower crust show lateral uniformity characteristic, which could be related to that the middle-lower Yangtze metallogenic belt had undergone a MASH metallization process. The Moho is 30-36 km deep, and its uplift zone extends from southwest to northeast in a "V" shape, which is consistent with the planar spreading characteristics of the metallogenic belt, indicating that the asthenosphere uplift and crustal thinning have had a controlling effect on the formation of the metallogenic belt. This study suggests the present-day crust in the region along the Yangtze River in Anhui retains the traces of lithosphere delamination-thinning and basaltic magma underplating during the Yanshan period. Our results indicates that airgun source detection in inland waters can effectively determine the continental crustal structure.