The Cenozoic thrusting sequence of the Longmen Shan fold-and-thrust belt, eastern margin of the Tibetan plateau: Insights from low-temperature thermochronology

Abstract

The 2008 MW 7.8 Wenchuan earthquake in China led to intensive studies on the development and dynamic mechanisms of the Longmen Shan fold-and-thrust belt. To construct the uplift history of the Longmen Shan, previous works had undertaken numerous low-temperature thermochronological studies in mountainous area, in particular apatite and zircon (U–Th)/He dating, which provided valuable evidence for understanding phases of uplift in the Longmen Shan during the Cenozoic. However, few (U–Th)/He ages have been obtained from the Sichuan Basin, which leaves a blank in our understanding of the link between the Wenchuan earthquake and the out-of-sequence Longmen Shan. In this study, we carried out (U–Th)/He dating on apatite and zircon separated from samples collected in the Sichuan Basin and the frontal southern Longmen Shan. Together with previous low-temperature thermochronological studies, we reconstructed the thrusting sequence of the Longmen Shan. The results of dating of apatite suggest that thrusting in the Longmen Shan is temporally and spatially variable. After continuous thrust propagation into the Sichuan Basin (over several to tens of Myr), deformation migrated back into the mountain range, which in this case termed “out-of-sequence” style of deformation.