Formation of the North-South Seismic Zone and Emeishan Large Igneous Province in Central China: Insights from P-Wave Teleseismic Tomography

The geodynamic features of the north-south seismic zone (NSSZ) and the formation of the Emeishan large igneous province (ELIP) in China remain controversial. In this study, we conducted detailed P-wave teleseismic tomography studies in the NSSZ and adjacent regions. The results revealed large high-velocity anomalies beneath the Songpan-Ganzi Block and the South China Block, possibly representing large-scale lithospheric delamination. We further identified low-velocity structures at 50-200 km depths in the western and southern parts of the NSSZ, suggesting an upwelling asthenosphere induced by delamination and the absence of a rigid lithosphere. Two high-velocity structures beneath the Sichuan basin and the Alashan block were also revealed, which may represent the lithospheric roots of these structures. These rigid lithospheric roots may have obstructed the eastward extrusion of the Tibetan plateau and led to stress accumulation and release (triggering earthquakes) in the Longmenshan Orogenic Belt and the northern part of the NSSZ. Because of this obstruction, the eastward extrusion was redirected southeastward to Yunnan in the southern part of the NSSZ, which led to stress accumulation and release causing earthquakes along the Honghe and Xiaojiang faults. The results from this study reveal a high-velocity structure with a subducted slab-like appearance that may represent vestiges of the Paleo-Tethys oceanic lithosphere, which subducted beneath the ELIP and initiating large-scale mantle return flow or mantle upwelling, contributing to the formation of the ELIP.