Lithospheric density structure beneath the Tibetan Plateau from the joint inversion of gravity and seismic data

Using the joint inversion of gravity and surface wave phase velocity data, we developed the lithospheric density structure beneath the Tibetan Plateau and revealed the characteristics of the distribution of density anomalies. Then, we discussed the possible causes of the density anomalies. The results of simulation tests show that the lateral resolution of the inversion results of surface wave phase velocities reaches 1 degrees in the eastern Tibetan Plateau, 1.5 degrees in the central Tibetan Plateau, and lower than 2 degrees in the western Tibetan Plateau. And the model from the joint inversion of gravity and seismic data has resolution of 1 degrees in both central and western Tibetan Plateau. In the case of significant differences between seismic wave velocity anomaly and density anomaly features, the results of the joint inversion of gravity and seismic data are closer to the real density structure than the results of the surface wave phase velocity inversion alone. The density model revealed by the joint inversion of gravity and seismic data shows that: (1) The middle and lower crust of the Tibetan Plateau shows remarkable low-density and low-V-S anomalies, which indicate the possibility of crustal partial melting and the existence of the crust flow. (2) The lithospheric mantle beneath the Tibetan Plateau shows high- density and low-V-S anomalies, which indicate the partial melting and underplating of the upper mantle. (3) The lithospheric mantle of the Bangonghu-Nujiang Suture and the Longmucuo-Shuanghu Suture exhibits low-density and low-V-S features, which may be caused by the hydration of peridotite in the lithospheric mantle; the low- density and low-V-S anomalies of the Kunlun Fault Belt support the tectonic theory of upwelling of the asthenosphere in this region. (4) Low-density and high-V-S anomalies are found in the lithospheric mantle beneath Yunnan-Guizhou Plateau, Sichuan Basin and Ordos Block, which are consistent with the characteristics of craton lithospheric mantle.