We have developed a novel technique that allows for direct inversion of P-wave receiver functions for a detailed 3-D S-wave velocity model. By applying this technique to a dense seismic array located in the southeastern margin of the Tibetan Plateau, we can resolve detailed crustal and uppermost mantle structures with strong lateral variations. The results indicate that the boundary faults of the geological blocks play a critical role in controlling the lateral variations of the crustal and upper mantle structures. Our findings provide new insights into the dynamics of lithosphere-asthenosphere interactions and continental collision processes in this region.

The genesis of the Cenozoic intraplate volcanism in Central Mongolia, characterized by sustained and low-volume eruptions remains debated due to the lack of a comprehensive model to interpret the Cenozoic volcanic activities. Here, we introduce a high-resolution 3D velocity model of the Hangay Dome, using a novel joint method which combines receiver function adjoint tomography and ambient noise adjoint tomography. The small-scale low-velocity zones in the crust and uppermost mantle reveal a crustal magma reservoir and partially molten subcontinental lithospheric mantle (SCLM). Melt fraction estimation indicates low-degree partially molten crust and SCLM. Combining previous geophysical and geochemical observations, we suggest that the volcanism in the Hangay Dome is driven by multilevel mechanisms. The remnant Mesozoic volatiles triggered upper mantle upwelling. This upwelling accumulated in the asthenosphere, heating the SCLM, and prompted its low-degree partial melting. The molten SCLM caused local lithospheric thinning and facilitated the magmatic underplating in the lower crust, eventually leading to the formation of the crustal magma reservoir.