Differential tectonic activity along the southern boundary of the Qilian Mountains: Insights from low-temperature thermochronology, seismic data, and fluvial geomorphology

The Cenozoic development of the Tibetan Plateau is one of the most remarkable events in the geosciences. The southern boundary of the Qilian Mountains is a spectacular basin-mountain boundary in the northern Tibetan Plateau offering a valuable opportunity to investigate the growth processes and mechanisms of the Tibetan Plateau. Structural activity is significantly variable across the northern Qaidam basin, and the underlying reason for these differences remains uncertain. To address this issue, we undertook an analysis of two main watersheds—the Tataleng and Yuqia River watersheds—encompassing the middle section of the northern Qaidam basin. This study utilized a multidisciplinary approach combining fluvial geomorphology, low-temperature thermochronology, and seismic data to comprehensively investigate the structural activity within the northern Qaidam basin. The high channel steepness index, young low-temperature thermochronologic ages, concentrated earthquakes, and numerous knickpoints along the piedmont area of the Qaidam Shan collectively suggest that this region is among the most structurally active areas along the southern boundary of the Qilian Mountains. The varying levels of structural activity in the northern Qaidam basin could be linked to the intense glacial erosion in the Qaidam Shan during the Quaternary. Moreover, the flow orientation observed in the bedrock mountains is consistent with the N-S compressional stress field in the northern Qaidam basin during the early Cenozoic, representing a stark contrast to the modern NE-SW stress field. In this way, this research supports the understanding that river geomorphic parameters, including river steepness index and flow direction, are valuable tools for unveiling the regional tectonic evolution in bedrock mountain areas.