Remnants of magma underplating by the Emeishan mantle plume within the lithosphere beneath southeastern margin of the Tibetan Plateau

Abstract

The Emeishan Large Igneous Province (ELIP) is located along southeastern margin of the Tibetan Plateau, where long-wavelength crustal thickening and surface uplift have been attributed to the influx of weak crustal material from central Tibet into the lower crust beneath the Yangtze Craton. We have developed a new shear-wave velocity model for the lithosphere beneath eastern Tibet, based on a two-step linearized joint inversion technique of P-wave receiver functions (PRFs) with Rayleigh wave dispersion (10–60 s period) and Love wave dispersions (8–30 s period) for three dense seismic arrays. We applied bootstrap resampling technique to calculate the results of inversion. The resulting shear velocity model revealed two major low-velocity features in the middle–lower crust beneath southeastern Tibet. The horizontally extensive low-velocity zone (LVZ) beneath the northern Sichuan–Yunnan diamond-shaped block (SYDSB) can be interpreted as possible lower crustal flow from central Tibet, whereas the low-velocity anomaly observed beneath the Xiaojiang Fault is consistent with the presence of a partially molten layer enhanced by shear deformation along large faults. These two LVZs are separated by a lithospheric-scale high-velocity zone (HVZ) that is situated beneath the geologically inferred core of the ELIP. Based on other geophysical and geological evidence, we interpret this high-velocity anomaly body as remnants of the Emeishan plume-strengthened lithosphere that originally formed during the Permian volcanism, and we speculate that it has acted as a barrier to the hypothesized flow of lower crustal material from central Tibet since the late Cenozoic.