Stratified crustal shortening under the Longmenshan thrust belt, Tibetan plateau

Abstract:

Stratified crustal shortening under the Longmenshan thrust belt, Tibetan plateau

Xiwei Xu^1&2, Baojin Liu³, John H. Shaw², Guihua Yu¹

1. Key Lab of Active Tectonics & Volcano, Institute of Geology, CEA, Beijing 100029, China

2. Department of Earth & Planetary Science, Harvard University, Cambridge, MA 02138, USA

3. Geophysical Prospecting Center, CEA, Zhengzhou 450002, China

Crustal velocity structure and new seismic reflection profiling across the foothills of the Longmen Shan and Sichuan Basin reveals a distinct pattern of crustal structure under Longmenshan thrust belt: brittle thrust faults with multiple detachments in the upper crust that are localized above, but decoupled from, a steep contact (FL) in the lower crust and upper mantle across which the lower crust thickens abruptly. Then two models are presented: 1) Model showing breakthrough thrusting of the plateau crust over the Sichuan Basin above the basal detachment (FD2); 2) Model showing indentation of a strong structural wedge of the Yangtze Craton into the weak plateau, but no sliding on the contact FL or sliding on the contact FL. This observation provides insights that help us to understand the mechanisms of crustal shortening, thickening, and uplift of the Tibetan Plateau.