Late Pleistocene slip rate of the northern Qilian Shan frontal thrust, western Hexi Corridor, China

摘要

We derive a slip rate for a frontal thrust in the western Hexi Corridor along the northern Qilian Shan by combining topographic profiling and Be-10 exposure dating. The active Yumen-Beidahe thrust fault offsets late Pleistocene alluvial-fan deposits, and a prominent north-facing scarp is well preserved. To quantify the slip rate, we surveyed the uplifted terraces and sampled quartz-rich pebbles on terrace surfaces and river channels to determine surface exposure ages and pre-depositional inheritance. The minimum vertical slip rate of the fault is 0.73 +/- 0.09mm a(-1). This represents a horizontal shortening rate of 1.26 +/- 0.31mm a(-1) for a fault dip of 30 +/- 5 degrees. This estimated slip rate supports the inference made from previous geological and GPS constraints that NNE-directed shortening across the western Qilian Shan and the Hexi Corridor is distributed on several active faults with a total shortening rate of 4-10mm a(-1).