CENOZOIC MULTI-PULSE RANGE GROWTH IN THE QILIAN SHAN, NORTHERN TIBET PLATEAU, AS CONSTRAINED BY GEOLOGIC MAPPING AND APATITE FISSION TRACK THERMOCHRONOLOGY

The most significant consequence of India-Asia continental collision is the formation of Himalayan-Tibetan orogen and related Tibetan Plateau. The Cenozoic Qilian Shan thrust belt and the Haiyuan left-slip fault define the northeastern margin of Tibet Plateau. Thrust and strike-slip fault systems play a critical role in accommodating continental convergence, but age estimates for the initiation of Cenozoic structures, and the styles and processes of range growth are still debated. In this study, we integrate detailed field observations, geologic mapping, and apatite fission track thermochronology to constrain the exhumation history of the central and northern Qilian Shan, initiation ages of thrust and strike-slip faults in the region, and the multi-pulse Cenozoic growth history of the northern of Tibet Plateau. Our analyses show that the central and northern Qilian Shan underwent rapid cooling history during Cretaceous resulting from a far-field tectonic event, followed by Eocene-Oligocene thrust faulting across the Shule Nan Shan, Tuolai Nan Shan, and Tuolai Shan ranges, and final accelerated cooling and denudation at ca. 10-5 Ma during the initiation of the western termination segment of the Haiyuan strike-slip fault and the reactivation of Tuolai Shan thrust fault. We suggest that the Qilian Shan thrust belt experienced out-of-sequence deformation starting in the Eocene as a result of far-field stress transmitted from initial early Cenozoic India-Asia collision, and the basins and ranges across the northern Tibetan Plateau have since experienced multiple pulses of growth.