Cenozoic two-phase topographic growth of the northeastern Tibetan Plateau derived from two thermochronologic transects across the southern Qilian Shan thrust belt

The formation of high topography on the northeastern margin of the Tibetan Plateau (the Qilian Shan) constrains the evolutionary history of the plateau. Although prominent exhumation occurred in the middle???late Miocene, the time at which deformation and relief development began in the Qilian Shan during the Cenozoic remains highly debated. Here, we use low-temperature thermochronology to reveal the histories of topographic growth in the Qilian Shan. Two transects were sampled in two primary thrust belts (Qaidam Shan and Danghenan Shan) in the southern Qilian Shan. New apatite fission track ages range from 16.6 to 113 Ma, and apatite (U-Th)/He ages range from 8.4 to 63.5 Ma. Age???elevation relationships and thermal modeling show enhanced rock exhumation in the late Paleocene???early Eocene and middle???late Miocene in both transects. The results indicate two pulses of enhanced thrusting on the major thrust belts in the southern Qilian Shan in the late Paleocene???early Eocene and middle???late Miocene. Our findings imply an early Cenozoic onset of topographic growth in the northeastern Tibetan Plateau, which was quasi-synchronous with the India???Asia collision.