Analytical and numerical simulations of uplift processes at the Tibet-Sichuan boundary

Abstract

Previous studies have shown that the uplift of Tibetan plateau started in response to the collision of Indian plate and Eurasian plate. During this process, the crust of Tibetan plateau has been greatly thickened which leads to significant elevations. The elevation gradient is extremely large at the east boundary of Tibetan plateau where Longmenshan fault exists, dropping from 4500 to 500 m within a distance of 100 km, while it is more gentle at the south and north sides of Sichuan basin. Such a difference of elevation gradient has been explained with a crustal channel flow model. However, previous crustal flow models consider the thickness of the lower crust as a constant which is highly simplified. Therefore, it is essential to build a more realistic crustal flow model, in which the thickness of the lower crust is variable and dependent on the inflow velocity of crustal materials. Here we build up both analytical and numerical models to study the mechanism and process of the uplift of Tibetan plateau at the eastern boundary. The results of the analytical model show that if the thickness of the lower crust can vary during the uplift process, the lower crustal viscosity of the Sichuan basin needs to be 10 22 Pas to fit the observed elevation gradient. Such a viscosity is one-order magnitude larger than the previous results. Numerical model results further show that the state of stresses at the plateau boundary changes during uplift processes. Such a stress state change may cause the formation of different fault types in the Longmenshan fault area during its uplift history.

Upper Crustal Collapse Reconstructed the Topography and Remodeled the Fault System of the Chuandian Fragment in the Southeastern Edge of the Tibetan Plateau, Evidenced by Anisotropy of Magnetic Susceptibility Data Sets

“…Finally, gravity drove the upper crustal subsidence, inducing the collapse of the uplifted CDF along the preexisting strike‐slip fault system. This dynamic mechanism is supported by improved numerical simulations of the uplift processes of the eastern boundary of the Tibetan Plateau, which suggested that the thickness of the lower crustal channel would have changed depending on the velocity of the internal flow and the flux of crustal materials (Peng & Leng, 2017); and by the S receiver functions of the CDF, which show that the depths of the Moho dramatically decreased from ∼55 to 60 km beneath the northern part of the CDF to ∼36–40 km beneath the western and central parts of the CDF (Hu et al., 2012), possibly indicating the eastward thinning of the lower crust beneath the CDF.…”