Constraints of new apatite fission-track ages on the tectonic pattern and geomorphic development of the northern margin of the Tibetan Plateau

Abstract

The northern margin of the Qilian Shan is the northernmost edge of the Tibetan Plateau. The deformation timing and geomorphic development along the northern margin of the Qilian Shan are critical to understanding the dynamics of plateau growth. Although previous studies have suggested that thrusting along the middle and westernmost sections of the northern margin of the Qilian Shan began in the middle Miocene, the >600 km mountain range front may have experienced differential thrusting and exhumation history. We collected 11 apatite fission-track samples along an elevation transect to the south of Jiayuguan to unravel the cooling history and erosion variation of the northern margin of western section of the Qilian Shan. The apatite fission-track ages, fission-track lengths, and thermal modeling suggest a period of rapid exhumation initiated at ∼15–10 Ma along the northern margin of the Qilian Shan. The new fission-track ages can be divided into three domains with different mean ages. As the distribution of the fission-track ages is tightly confined by tectonic structures among them, we infer that tectonics plays the first-order control on erosion variations. Meanwhile, the strong linkage between erosion rates and glacier distribution may indicate that glacial buzzsaw exerts an important role in mountain building in the northern Qilian Shan. Additionally, combining this result with published data, we suggest that the northern margin of the Qilian Shan experienced a phase of synchronous deformation in the middle Miocene.