Geomorphic evidence for northeastward expansion of the eastern Qilian Shan, northeastern Tibetan Plateau

Abstract

The eastern Qilian Shan is a tectonically-active region consisting of a series of faults with bounded intermountain basins and is located within the transition zone between the mainland Tibetan Plateau and the Alax Block. Active deformation affecting the topography in this region can be quantified based on geomorphic indices. Therefore, we applied the geomorphic indices (hypsometry and stream-power incision model) to evaluate the tectonic deformation pattern of the eastern Qilian Shan. Hypsometric curves and S-A plots of the selected seven rivers were determined. HI values of every single sub-basins were also calculated. The results show that the local topographic evolution of the eastern Qilian Shan is in pre-steady state and will soon reach its equilibrium state. According to the analysis of regional climate condition (e.g., rainfall and glaciers distribution) and fault characteristics, it is suggested that abundant glacial snowmelt water sustains fluvial incision, and tectonic deformation from sustained northeastward expansion of the Tibetan Plateau is the main reason for the landscape growth. Combining the research of the deep electric structure beneath the Gulang Boundary Zone, we claimed that the eastern Qilian Shan (even the northeastern Tibet) has been growing and expanding northeastward since the middle Miocene, and its leading edge now is the Hexibao-Sidaoshan Fault. On the premise of synthetically considering the western and middle parts of the Qilian Shan, it is suggested that the Hexibao-Sidaoshan Fault area will rise into a mountain in 1–2 Ma.