A Numerical Study of Lithospheric Deformation and Strain Partitioning Across the Longmen Shan Orogenic Belt, Eastern Tibetan Plateau

摘要

The Longmen Shan orogenic belt is the landform boundary between the eastern Tibetan Plateau and the Sichuan Basin. However, there are significant differences in lithospheric deformation across its southern and northern segments. We established numerical models to investigate the effect of rheological heterogeneity on lithospheric deformation across the eastern plateau margin. The results show that the rheological heterogeneity of the Longmen Shan controls the type of lithospheric deformation and the strain partitioning. When the Longmen Shan is weak or narrow, high strain is predicted between the plateau and the Sichuan Basin along the Longmen Shan, which helps to explain the lack of a Cenozoic foreland basin along the southwestern part of the Sichuan Basin. However, when the upper crust of the Sichuan Basin is weak, the deformation should extend into the interior of the basin, such as the Longmen Shan-Longquan Shan thrust system, which provides sedimentary space for the Cenozoic sediments. In contrast, when the Longmen Shan is strong or wide, the deformation is diffuse over a broad transition zone. The strain is mainly localized along the boundary between the Songpan-Ganzi terrane and the Longmen Shan. This result can be used to understand the uplift of the Min Shan. Compared to the observations, the high strength of the Longmen Shan corresponds to the distribution of the Precambrian crystalline basement. The rheological heterogeneity of the Longmen Shan is from the result of the amalgamation of ancient continents, which illustrates the control of the ancient continental margin on recent tectonics.