Spatial distribution of seismic layer, crustal thickness, and Vp/Vs ratio in the Permian Emeishan Mantle Plume region

Abstract

Seismological studies of lithospheric structure and rheology can provide important information regarding the lithosphere's interaction with the mantle plume and its successive deformation characterization. The Emeishan Large Igneous Province (ELIP) in eastern Tibet was probably produced by a Late Permian Emeishan mantle plume and experienced tectonically driven modifications during Mesozoic–Cenozoic, such as the eastward subduction of the Indian Ocean plate and roughly north-southward tectonic escape or middle crustal flow. The crustal responses to the Emeishan mantle plume and its modification from successive tectonic activities are still unclear. Here, we present the lithosphere rheology structure derived from seismic activity and the spatial distribution of seismic energy release, which records the lithospheric deformation from the Late Permian mantle plume activity and the Mesozoic–Cenozoic modifications. In addition, we estimate the crustal thickness and the average crustal Vp/Vs ratio from wide-angle seismic profiling and receiver function imaging. Our results demonstrate that the seismogenic layer thins away from the proposed center of the Emeishan mantle plume. The layer is approximately 24km in depth beneath the center of the Emeishan mantle plume and approximately 10km in depth beneath the margin of the plume, with corresponding crustal thinning and spatial variations of the average crustal Vp/Vs ratio. Distinctive patterns among crustal thickness, seismogenic layer and the average crustal Vp/Vs ratio are observed both east and west of the Xiao Jiang Fault (XJF). These remarkable features are interpreted to result from the modification of the Late Permian mantle plume, probably by tectonic escape in the west of the XJF and by a north-southward middle crustal flow in the east of the XJF.