Moho depth inversion in the Tibetan Plateau from high-precision gravity data

Abstract

The Tibetan Plateau (TP) is the youngest orogenic belt formed by continental collision on the Earth. It is a natural laboratory for studying continental dynamics such as continental convergence, plate subduction, and plateau uplift. Studying its deep structure has always been a hot issue in geological research. The Moho is the interface between the crust and the mantle and is an important interface in the structure of the Earth's circle. Its depth, lateral variation, and fine structure of the crust-mantle interface are important parameters to reveal the process of lithospheric dynamics in the TP. The study of the Moho surface generally has two methods: seismic and gravity. Seismic detection has the characteristics of high precision, but they are limited along a few cross-sectional lines and have a high cost. It is not suitable and cannot be carried out in a large area of the TP; Gravity inversion can obtain large-area Moho depth, but affected by gravity data and inversion methods, the accuracy is lower than that of seismic. In this paper, a high-precision gravity field model is selected. With the constraint of seismic observation, the Parker-Oldenburg interface inversion method is used, and the Bott iteration method is introduced to improve the inversion efficiency. The high-precision Moho depth in the TP is obtained, consistent with the seismic detection results. The research results show that the shape of the Moho in the TP is complex, and the variation range is large, reaching 60-80 km. In sharp contrast with the adjacent area, there is a clear sharpness zone at the plateau's edge. In the TP's interior, the Moho's buried depth is characterized by "two depressions and two uplifts". The Moho in the south of the Yarlung Zangbo River (YZR) inclines to the north, and the Moho in the north depresses downward, interpreted as the Indian plate subducts to the north below Tibet. The Moho depression on the north side of the Qiangtang block (QTB), up to 72 km deep, may be related to the southward subduction of the lithosphere. The Moho uplift of the QTB has the same strike as the Bangong-Nujiang suture zone (BNS), which may reflect that the area is compensated by a low-density and low-velocity mantle.