Mapping the deep lithospheric structure beneath the eastern margin of the Tibetan Plateau from gravity anomalies

Abstract

Various authors have investigated the mechanism of lateral support of the lithosphere in maintaining the uplift of the Tibetan Plateau, based on gravity data and elastic flexural modeling, in the south of the plateau across the Himalayas and in the north and the northwest across the Altyn Tagh and West Kunlun Shan. However, the degree of the regional compensation and lateral support to the east of the Tibetan Plateau has remained unknown. In this paper we present a lithospheric flexure model by interpreting gravity and topography to understand the first‐order problem of lateral support of the lithosphere at the eastern margins of the Tibetan Plateau. The flexural modeling constrains the geometry and strength variation of the lithosphere from the eastern margin of Tibet past the Longmen Shan ranges on to the Sichuan Basin. A lithosphere of intermediate strength (Te = 45 km) beneath the Sichuan Basin is weakened (Te = 36 km) by the thrusting underneath the eastern margin of the Tibetan Plateau. The strength variations indicate that about 10 km of the crustal material of the lithosphere has been ripped off and integrated into the thickened, upper crust of the Tibetan Plateau, which, however, has no appreciable strength. The stiffness of the lithosphere keeps the Tibetan Plateau relatively stable at its eastern margin and enables the weight of the plateau to be supported in the east by the Sichuan. Lithospheric deformation in the southern Longmen Shan area is more pronounced than in the northern region.

A geological and geophysical context for the Wenchuan earthquake of 12 May 2008, Sichuan, People's Republic of China

“…Gravity data across the Longmen Shan also suggest that little flexural loading of the Sichuan Basin occurred in Late Cenozoic time, and the crust here is (nearly) Airy-compensated ( Fig. 3; but see Jiang and Yu, 2005).…”

“…This older and computed (line) Bouguer gravity anomalies for Airy compensation of the Longmen Shan for a density contrast between crustal root and mantle of 400 kg/m 3 . Gravity data from Jiang and Yu (2005). deformation provides the starting geometry for later Cenozoic deformation (see Burchfiel et al, 1995).…”

Architecture of basin-mountain systems and their influences on gas distribution: A case study from the Sichuan basin, South China

“…However, the formation and uplift of the Tibetan plateau chiefly resulted in the formation and evolution of the southwestern segment of the basin-mountain system Meng et al, 2006;Hubbard and Shaw, 2009). It has been suggested that the lithosphere strength and the shape of the western margin of the Yangtze plate are the basic controlling attributes of the formation and evolution of the system (Jiang and Jin, 2005).…”

Crustal P-wave velocity structure of the Longmenshan region and its tectonic implications for the 2008 Wenchuan earthquake

“…Therefore, a simple one-dimensional crustal model is not appropriate for this area, because large residuals and bias of the velocity structure inversion could be introduced. The Moho discontinuities ( Figure 3) were inverted using the harmonious series method with Bouguer gravity data [17][18][19]. In the initial model, the Moho discontinuities are represented by a linearly continu- ous transition layer.…”