Crustal shear-wave velocity structure and its geodynamic implications beneath the Emeishan large igneous province

As the first large igneous province in China that is widely recognized by the international geosciences community, the Emeishan Large Igneous Province (ELIP) is of great significance for understanding the formation and mechanism of mantle plume, the co-evolution of biology and environments, and the resource enrichment and mineralization. Although the structural geometry and physical properties recorded in the crust and lithospheric mantle are well constrained by comprehensive geophysical investigation, the shear wave velocity structure in the ELIP remains poorly known. In this paper, based on the data of the COMPASS-ELIP experiment and the Regional Digital Seismic Networks in Yunnan and Sichuan Provinces, the crustal shear-wave velocity structure along the profile is reconstructed using a joint inversion of receiver functions and ambient noise surface waves. A weighted stacking strategy is used to match the information source and spatial resolution between receiver functions and surface waves. The results show that from west to east, the average crustal shear-wave velocity is featured by zonation along the profile, and the average crustal Vs within the inner zone is the relatively highest with a range of 3. 6 similar to 3. 8 km . s(1). A major contribution to this feature of the high velocity within the inner zone comes from the middle and lower crust, especially from the significant high-velocity anomaly (about 3. 8 similar to 4. 2 km . s(-1)) exiting at the base of the lower crust. The low-velocity zone in the upper and middle crust can be observed on both sides of the Lijiang-Xiaojinhe fault and Shuicheng-Ziyun fault, which is more prominent in the middle crust nearby the Shuicheng-Ziyun fault. Combined with other evidence from previous geophysical investigations conducted in the ELIP, the middle and lower crustal high-velocity anomalies we observed within the inner zone strongly further suggest they are the seismic signatures of the large-scale magmatic underplating and subsequent magmatic intraplating related to the late Permian mantle plume activities. Such ancient plume activities not only modified the crustal structure and composition within the central Yunnan block, but also changed the crustal strength there, and eventually affected the present deep process beneath the southeastern margin of the Tibetan Plateau