Lithospheric controls on the formation of the Qilian Shan plateau: Evidence from apatite (U[sbnd]Th)/He and cosmogenic 21Ne results in the Central Qilian Shan

Abstract

The Qilian Shan, located on the northeastern edge of the Tibetan Plateau, shares similar topographic features with Tibet marked by a flat upland plateau flanked by highly-dissected steep margins. Therefore, the research on the topographic evolution of the Qilian Shan will not only facilitate the understanding of its uplift history but also shed light on the uplift process and formation mechanism of the Tibetan Plateau. In this study, we carried out (UTh)/He and cosmogenic 21Ne analyses on the granitoid peneplain of the Central Qilian Shan, and our results indicate that the Qilian Shan has inherited a Cretaceous low-relief landscape that formed at low elevation. Apatite (UTh)/He cooling ages and 21Ne-inferrred erosion rates record a slow exhumation process with a rate of ∼15 ± 5 m/Myr of the peneplain from the middle Cretaceous to present. Combined with previous studies on the Cenozoic tectonics of the Qilian Shan, we infer that the prolonged stable landscape of the Central Qilian Shan has been elevated to high elevation along the boundary thrusting by coeval crustal thickening of the Qilian Shan, to form a flat upland plateau. Whereas, compared to the Central Qilian block, the southern and northern Qilian Shan have relatively weak lithosphere, which consist of accretionary systems. The strong thrusting of the boundary faults enabled the southern and northern Qilian Shan uplifted to form highly-dissected margins flanking the flat interior plateau. In this context, our study may provide an analog for understanding the uplift mechanism of the Tibetan Plateau.