Decoding the Emeishan Permian mantle plume in the southeastern margin of Tibet from the seismic signature of the local lithosphere

Abstract

SUMMARY The Emeishan large igneous province (ELIP), which is located along the southeastern margin of Tibet, is widely regarded as the erosional remnants of voluminous Permian mafic volcanic successions that were associated with mantle plume activity. In addition, evidence for the eruption of the mantle plume and its signature of lithospheric modification should have been retained in the lithosphere after cooling of the plume. Here we use calculated compressional- and shear wave receiver functions (PRFs and SRFs, respectively) from >750 broad-band stations, together with heat flow and Bouguer gravity anomaly data, to investigate the seismic signature within the lithosphere beneath the southeastern margin of Tibet. Our results from the inner zone (INZ) of the ELIP indicate that the ∼60 km depth of the Moho interpreted from depth-migrated PRF images is consistent with that inferred from SRFs and is deeper than that in the region surrounding the INZ, which shows a continuous positive converted phase at ∼35–40 km depth. The crustal geometry and physical properties show a 15–20-km-thick mafic underplated layer that extends for 150–200 km in the E–W direction and ∼400 km in the N–S direction along the base of the crust in the northeastern INZ and its surrounding region. We interpret the underplated layer as the concealed Emeishan plume hotspot track and suggest that the head of the postulated mantle plume is centred approximately beneath Panzhihua City and its surroundings. We propose a new geodynamic model for the formation of the ELIP, in which the lower–middle crust has been strengthened by voluminous mafic intrusions and underplating, whereas the Yangtze Craton in the plume region has been destroyed by removing the base of the lithosphere.