Lithospheric structure of the Emeishan Large Igneous Province: Implications for plume-lithosphere interaction.

Emeishan Large Igneous Province (LIP)is located at the western margin of the Yangtze Craton and is generally believed as the melting product of the Emeishan mantle plume head at the middle.late Permian. To better understand plume-lithosphere interaction processes,we used the S-wave receiver function method to image the lithospheric discontinuities across the Emeishan LIP, based on the broadband seismic data from the COMPASS-ELIP experiment. Combined with the S-wave velocity structures constructed by the teleseismic S-wave finite-frequency tomography based on the data of the same experiment,and extracted from the surface wave tomography in East Asia,we obtained the lateral variations of the lithospheric structure beneath the Emeishan LIP. Our results reveal crustal thickening by 15 similar to 20km and lithospheric thinning of similar to 50km beneath the inner zone (INZ) of the Emeishan LIP. The lithospheric mantle beneath the INZ is characterized by the layered high-velocity anomaly,but with non-obviously converted phase of S-. wave receiver functions at the base of the lithosphere. The thickest lithosphere of similar to 170km is imaged beneath the intermediate zone (IMZ)and that beneath the outer zone (OTZ)is similar to 150km. Moreover,our results show that the mid.lithospheric discontinuity (MLD) is well-developed beneath the IMZ and OTZ,and the lithosphere-asthenosphere boundary (LAB)is locally undetectable where the low. velocity anomaly exists in the upper mantle of the IMZ. These,together with petrological and geochemical analyses and geodynamic modeling,allow us to propose a plume-lithosphere interaction model to account for variable lithospheric deformation across the Emeishan LIP. The INZ-s lithosphere was once rapidly thinned due to the thermal-mechanical impact of the mantle plume head. Meanwhile,the high-degree decompression melting of the mantle plume head generated large-volume magma,some of which had penetrated the lithospheric mantle and the crust,while some erupted as the Emeishan basalts. The INZ-s lithosphere thus mainly shows a vertical deformation pattern. In the IMZ,the basal shear of the mantle plume periphery was responsible for the lateral extension of the lithospheric mantle and even has caused localized tearing by thermal-chemical erosion. The OTZ-s lithosphere was mainly dragged vertically,leading to certain detachment and thinning of the lithosphere. In addition,the layered high-velocity anomaly imaged beneath the INZ indicates that the thinned lithosphere associated with the plume activity would have been partly re-healed by trapping the residuals left by the melt extraction of the plume. Consequently,the plume-modified lithosphere of the INZ became more depleted and thus was largely strengthened. The distinct structure of the lithosphere across the Emeishan LIP therefore provides new insights into mantle plume-lithospheric interaction