Quantitative geomorphological analyses reveal late Cenozoic uneven tectonic expansion at the North Qilian Shan

The North Qilian Shan, located in the northeastern Tibetan Plateau, serves as a tectonic boundary zone both for active blocks and plateau expansion, and is characterized geomorphologically by intense shortening and uplift. To quantify the geomorphic expression of the outward expansion, we selected the Dongda River Watershed as the study area, divided it into three tectonic regions (A, B and C) to conduct quantitative geomorphological analyses. We then calculated the geomorphic indices—normalized channel steepness (ksn), slope, relief and hypsometric integral (HI)—for 212 sub-basins in the Dongda River Watershed using TopoToolbox and the Topographic Analysis Kit (TAK). The distribution of parameters showed that the tectonic activity in the study area is Region A > Region C > Region B, which indicated that the North Qilian Shan exhibits geomorphic evidence of uneven tectonic uplift, reflecting differential tectonic activity along the North Qilian Shan fault zones during the Late Cenozoic. When combined with previously established tectonic evolution models for the North Qilian Shan, the results in this study suggest that tectonic activity here is driven both by the northward expansion of the plateau boundary and by stress transmission within block boundary zones.