Late Quaternary river incision rates and rock uplift pattern of the eastern Qilian Shan Mountain, China

Abstract

The uplift rate and pattern of the Qilian Shan Mountain, which lies in the northeast margin of the Tibetan Plateau, are key to understanding the dynamics of crustal deformation in the northeastern Tibetan Plateau. In this work, late Quaternary terraces in seven river valley sections in the eastern Qilian Shan Mountain are studied to determine terrace abandonment ages by OSL (optical simulating luminescence) and terrace heights by GPS (global positioning system) surveys. River incision rates since ~76kaBP are calculated ranging from 0.37mm/a to 1.49mm/a. Distribution of river incision rates shows that higher river incision rates (0.85–1.49mm/a) are located at the rivers' upstream reaches where mean mountain elevation is ~4000m, and relatively lower incision rates (0.32–0.62mm/a) are located at the mountain front where the mean mountain elevation is <3200m. This difference of the river incision rate reflects spatial difference in rock uplift patterns within the eastern Qilian Shan Mountain. The high mountain range is characterized by a high river incision rate (on average of 1.2±0.4mm/a) and high relief, suggesting high rock uplift rate; whereas the low mountain range is characterized by low river incision rate (on average of 0.5±0.2mm/a) and lower relief, suggesting relatively low rock uplift rate. Based on fault distributions and slip rates, we propose that the differential rock uplift of eastern Qilian Shan is mainly controlled by the thrusting along active thrust faults separating different mountain ranges and by oblique thrusting along strike-slip faults near the mountain crest.