Bedrock channel form in the Madong Shan (NE Tibet): Implications for the strain transfer along the strike-slip Haiyuan Fault

Abstract

The Cenozoic tectonic deformation in the Madong Shan, especially since the Holocene, is the key to understand stress transfer at the southeastern terminus of the Haiyuan Fault, northeastern Tibetan Plateau. In this work, we explored the uplift pattern of the Madong Shan by combining the form of bedrock channel and river incision rate. The normalized channel steepness (ksn) and wideness (kwn) indices provided two comparable channel morphologic parameters. To evaluate the differences among the rock uplift, river incision rates were determined by optical stimulated luminescence (OSL) dating of the strath terraces along two rivers. The results show that channels in the northern Madong Shan are relatively steeper and narrower, and have the higher shear stress to incise than those in the south. The incision rates in the northern channels were two times higher than those in the southern channels since the late Holocene. The major changes of channel morphometry and incision rates are coinciding spatially with the stress transfer direction along the Haiyuan Fault, rather than the lithologic variations. Therefore, we speculate that the differential bedrock channel form and river incision were mainly controlled by variable tectonic uplift across the Madong Shan with secondary contribution of the lithology. Deformation of the Madong Shan has been continuously driven by the strain transfer along the Haiyuan Fault.