Geomorphic expressions of collisional tectonics in the Qilian Shan, north eastern Tibetan Plateau

Abstract

The Qilian Shan, north eastern Tibetan Plateau, is an area of active deformation caused by convergence in the India-Eurasia collision zone. Geomorphic indices capture the landscape response to competition between tectonics and climate, reflecting the spatial distribution of erosion. We use geomorphic indices (hypsometric integral (HI), normalised channel steepness (ksn), elevation-relief ratio (ZR) and surface roughness (SR)) to identify areas of active deformation and erosion, highlight landscape variations and we interpret the results for potential tectonic and climatic drivers. High HI (> 0.15), ksn (> 100) and low ZR (< 2) occur in the hanging wall of thrust faults, consistent with active uplift of these structures. Relatively high HI (> 0.15) and ksn (> 100) values in the eastern region are attributed to thrust parallel rivers in this region excavating wide valleys between the faults. The east-west precipitation variation across the Qilian Shan (>500 mm/yr to <100 mm/yr) is not a first order control on the regional landscape. There is an abrupt northwards transition from low to high HI, ksn and SR and high to low ZR partially coincident with the left-lateral Haiyuan Fault. We suggest that this transition is due to a difference in deep structure. A south-to-north transition from creeping to locked behaviour on an underlying detachment thrust has previously been suggested to occur along the intersection of this thrust detachment with the overlying Haiyuan Fault, providing a potential explanation for the location of the geomorphic change. Our results show these geomorphic indices to be sensitive to the underlying tectonic structure of the area. These methods could be applied to other fold-and-thrust belts and tectonic settings, to help understand the underlying structure, and the processes responsible for deformation.