Exhumation history of the Qilian Shan, constrained by apatite U-Pb & fission track thermochronology

Abstract

The NW-SE trending Qilian Shan defines the NE border of Tibet and SE China. This study applies apatite U-Pb and low temperature thermochronology to constrain the exhumation history of the Qilian Shan through the Mesozoic-Cenozoic. AU-Pb and AFT analysis indicate that the eastern Qilian Shan has experienced a 3 stage cooling history since the early Mesozoic, consisting of: (i) rapid initial cooling during the late Triassic-early Jurassic (~240-170 Ma); (ii) either rapid cooling in the middle-late Cretaceous (~130-75 Ma) or a stage of quasi isothermal quiescence, depending on sample elevation and proximity to major E-W faults; and (iii) rapid subsequent cooling during the late Cenozoic (~30-10 Ma). Cooling in the late Triassic-early Jurassic is likely related to the closure of the Palaeo-Asian Ocean and/or the early Triassic Qiangtang collision to Eurasia. The middle-late Cretaceous cooling can be attributed to the collision of the Lhasa Block with southern Eurasia and/or subsequent extension within the Tethys Ocean due to slab roll-back. Finally, the late Cenozoic cooling can be related to the India-Eurasia Collision. Hence, the cooling histories obtained in this study indicate the Qilian Shan has undergone 3 main stages of exhumation in response to far-field tectonic events. Results obtained from this study support previous work done in the Qilian Shan area, improving the overall understanding of strain propagation through Central Asia.