Tectonic-climatic coupling drove a mid-pleistocene river piracy in the Northern Qilian Shan, northeastern Tibetan Plateau: Evidence from Isochron 26Al/10Be Burial Dating and χ analyses

Abstract

River piracy, a dynamic process reshaping drainage networks, plays a pivotal role in landscape evolution, yet its timing and driving mechanisms in active orogens remain poorly constrained. This study focuses on the piracy between the Hongshuiba River and the Zhulongguan River in the northern Qilian Shan (Shan means “mountain” in Chinese), northeastern Tibetan Plateau, to resolve its chronology and geomorphic implications. Utilizing isochron ²⁶Al/¹⁰Be burial dating of fluvial sediments from the abandoned water divide, we determine the piracy occurred at 0.79 ± 0.24 Ma, marking the first radiometric age for such an event in this region. χ analyses reveal pre-piracy disequilibrium in the Zhulongguan River profile, attributed to an earlier piracy by the Beida River, which preconditioned the landscape for subsequent Hongshuiba-Zhulongguan piracy. Integrated results demonstrate that the Hongshuiba-Zhulongguan piracy was driven by tectonic uplift that amplified topographic gradients and the mid-Pleistocene climate transition, which enhanced erosional efficiency. These findings highlight the coupling between northward extension of the Qilian Shan and orbital-scale hydroclimatic variability in triggering threshold-driven drainage reorganization, offering insights into transient landscape responses in active orogens.