The formation of North-South Seismic Zone and Emeishan large igneous province in Western China: Insight from teleseismic tomography

Abstract. Several models have been suggested to explain the earthquake mechanism of the North-South Seismic Zone (NSSZ) and the formation of the Emeishan Large Igneous Province (ELIP). In this study, I extended the study region and carried out detailed teleseismic tomography in the NSSZ and near-by regions. Results identified by this study reveal large plate-like high-velocity anomalies beneath the Songpan-Ganzi Block and the South China Block, which may be associated with large-scale lithospheric delamination, and low-velocity structures at 50–200 km depths in the western and southern parts of this study region, which imply upwelling asthenosphere induced by delamination and the absence of the rigid lithosphere there. Two high-velocity structures beneath the Sichuan Basin and the Alashan Block are revealed, which might be the lithospheric roots of these structures. These rigid lithospheric roots obstructed the eastward extrusion of the Tibetan Plateau and led to stress accumulations and releases (earthquakes) in the Longmenshan Orogenic Belt and the northern part of the NSSZ. Due to obstruction by the Sichuan Basin’s lithosphere, eastward extrusion was redirected southeastward to Yunnan in the southern part of the NSSZ, which led to stress accumulations and releases (earthquakes) along the Honghe and Xiaojiang Faults. This study provide velocity images reveal a slab-like high-velocity structure, which might be associated with the lithospheric vestige of the Paleo-Tethys Ocean that subducted beneath the ELIP, which resulted in large-scale return mantle flow or mantle upwelling and contribute to the LIP formation in early Mesozoic.