Uplift of the Longmenshan and the Tibetan Plateau

The Longmen Shan mountain range, site of the devastating 12 May 2008 Wenchuan (Mw7.9) earthquake, defines the eastern margin of the Himalayan orogen and exhibits greater topographic relief than anywhere else in the Tibetan plateau. However, before the earthquake, geodetic and geologic surveys measured little shortening across the range front, inspiring a vigorous debate about the process by which the topography of the mountain belt is produced and maintained. Two endmember models have been proposed: (1) brittle crustal thickening, in which thrust faults with large amounts of slip that are rooted in the lithosphere cause uplift, and (2) crustal flow, in which low-viscosity material in the lower crust extrudes outward from the Tibetan plateau and inflates the crust north and east of the Himalayas. We use balanced geologic cross-sections based on industry seismic reflection data to show that crustal shortening, structural relief, and topography are strongly correlated in the range front. This suggests that crustal shortening is a primary driver for uplift and topography of the Longmen Shan on the flanks of the plateau.

 

Figure: Alternative conceptual models for the uplift of the Tibetan plateau and development of the Longmen Shan range front. Top panel, uplift is produced by thrust faulting and crustal shortening. Bottom panel, uplift is produced by inflation of the ductile lower crust.