Mantle origin of the Emeishan large igneous province from an analysis of residual gravity anomalies

The Emeishan large igneous province (ELIP) is the only verified large igneous province in China. It covers an area of 250,000 km2 from the eastern margin of the Tibetan Plateau to the western margin of the Yangtze block. Most studies on ELIP are from geochemistry and tectonics, but the deep origin of the ELIP is still unclear. In this study, we investigate the residual gravity anomaly in South China and its relationship to the Emeishan large igneous province with constrains of lithospheric structure from deep seismic sounding profiles, deep seismic reflection surveys, and a variety of broadband seismic observations acquired in South China in the last several decades. Our working scheme consists of removing the respective gravitational effects due to: (1) the sediments, and undulations of the (2) crystalline basement, (3) upper crust; (4) Moho and (5) lithospheric thickness. We have thus obtained the residual gravity anomaly of the ELIP and surrounding region, striking positive residual anomaly with maximum value of 140 mGal is observed at the ELIP region. We use the conjugate gradient method to locate the deep origins of the residual gravity data. As a result, our preferred model consists of a positive cylindrical density anomaly that provides a fit to the residual gravity anomaly observed in ELIP. As the distance increases from the inner zone of the ELIP to the outer zone, the positive residual gravity decreases. Hence, in our model, the density anomaly decreases from about 0.06 g/cm3 beneath the inner zone to about 0.03 g/cm3 beneath the outer zone. The residual gravity and our preferred density anomaly provide new evidence, along with the seismic data and geochemical data, to confirm the domal structure of the Permian mantle plume that gave rise to the Emenshan Large Igneous Province.