Magmatic underplating beneath the Emeishan large igneous province (South China) revealed by the COMGRA-ELIP experiment

Abstract

Because of the abundant geological, geochemical and geophysical studies conducted on the Emeishan large igneous province (ELIP) in South China, the Permian mantle plume model associated with this region is widely accepted. Furthermore, the dome-shaped structure related with this plume has been determined with success by sedimentological data and gravity stripping. Although the sediment thickness, upper crust, Moho depth and the lithosphere–asthenosphere boundary (LAB) are well constrained by active- and passive-source seismological results, the density anomaly in ELIP is still a poorly constrained issue that needs further attention. With the aim especially to understand the impact on surface of the magmatic processes that originated in the deep mantle, we performed the COMGRA-ELIP gravity experiment across this region. Using a stripping method, we determined the residual gravity in ELIP and surrounding areas. The residual gravity reaches a maximum value of +150mGal in the inner zone of ELIP and its strength decreases gradually when measuring from the inner zone to the middle and outer zones. Combining active and passive seismic results and the least-squares variance analysis method, we propose a strong density contrast of 0.2g/cm3 (density of 3.14g/cm3) for the 15- to 20-km-thick igneous layer accreted at the base of the crust, as evidence of crustal underplating in ELIP, to explain the present-day residual gravity anomaly.