Starting of Qilianshans uplift since Cenozoic and its implications for Tibetan mantle dynamics

The Qilian Shan, located at the northeastern edge of the Tibetan Plateau, plays a crucial role in understanding the Plateau's uplift and expansion processes. There are two classical models, one proposes a progressive expansion of the thickened crust, while the other suggest that the northern extent of the Plateau was established soon after the collision between India and Eurasia around 50 Ma ago. Nevertheless, a recent study introduces a more complex scenario, proposing a pulsed uplift of the northern Tibetan Plateau starting around 30 Ma (Wang et al., 2022). These models heavily rely on the spatial and temporal evolution of the Qilian Shan. Nevertheless, the exact timing and mechanisms of its evolution remain elusive. To delve into the growth history of the southern Qilian Shan, we have obtained apatite fission track data from the Dachaidan Shan and the northern Qaidam basin. Notably, AFT ages from the Dachaidan Shan transect (ranging from 35 Ma to 10 Ma) vary significantly with elevation. An intriguing observation is a possible break in slope at 182 Ma, which is interpreted as indicating the onset of intense exhumation in the southern Qilian Shan. Furthermore, within the Qaidam basin, a total reset AFT age group of 14.83.8 Ma was found in Jurassic strata but not in Cretaceous and Cenozoic strata. This suggests a rapid cooling event occurred at that time, which we interpret as marking the initial deformation of the northern margin of the Qaidam basin. In combination with previous studies on the deformation time of the Qilian Shan, our findings suggest that the initial deformation of the Qilian Shan occurred in the Middle Miocene, followed by a multi-step outward expansion. This synchronized expansion might have been triggered by the removal of mantle beneath northern Tibet. Wang, W., Zhang, P., Garzione, C.N., et al., 2022. Pulsed rise and growth of the Tibetan Plateau to its northern margin since ca. 30 Ma. Proceedings of the National Academy of Sciences 119, e2120364119. This research was supported by the State Key Laboratory of Earthquake Dynamics (LED2021A05) and the National Natural Science Foundation of China (42272269).