Analysis of Moho Structure in Central Tibet Area Revealed by Deep Reflection Seismic Method

Revealing the Moho structure in Tibet Area has important geodynamic significance for understanding the origin of the subduction of the Middle Tethys oceanic crust and the South Qiangtang Depression. Based on deep reflection seismic data across the Bangong Lake-Nujiang River Suture Zone (BNS), the depth seismic reflection migration profile, layer velocity field and high-resolution Moho structure are obtained, by using medium-to-long wavelength static correction, noise suppression, optimized stack and pre-stack depth migration (PSDM). According to the depth domain profile, Moho in the BNS is located 65–80 km below the surface and presents a trend of discontinuous northward uplift, indicating that there are lithospheric upper mantle fault steps between the Lhasa block and the South Qiangtang Block, with a maximum step of 15 km. After analyzing the Moho morphology on both sides of the suture zone, it is believed that these fault steps are jointly driven by terranes from the north and south sides, the upper mantle of the lithosphere of the Lhasa terrane is on the south side, and the upper crust of the Qiangtang Block is on the north side. The Moho structure under the BNS indicates that with the closing of the Tethys Ocean (in the Late Jurassic-Early Cretaceous period), the South Qiangtang terrane was transformed from marginal Marine sediments into a foreland basin and formed the South Qiangtang Depression.