Impact of tectonics on alluvial landforms in the Hexi Corridor, Northwest China

Abstract

The Hexi Corridor is a Cenozoic foreland basin system on the northeast margin of the Qinghai–Tibet Plateau. The structure is characterised by reverse faults trending NNW or WNW. Rivers have been affected by sinistral offset by WNW trending faults and dextral offset by NNW trending faults. The Cenozoic sinistral offset reaches 24 km on the north front fault (trending WNW) of the Qilian Mountains. On the northeast front fault (trending NNW) of the Yumu Mountains, a bluff of the Hei River terrace has been dextrally offset by 12 m with a rate of 1.2 m/ka. The vertical movement of the faults has caused the deformation of river terraces and controlled the distribution and migration of the alluvial fans. Three terraces of the Hei River have been vertically dislocated 9 m, 4 m, and 2 m, respectively, by a reverse fault with uplift rates of 0.4–1.7 m/ka. Two reverse faults have caused the older alluvial fans to be dissected, and the younger fans to be deposited more towards the centre of the Jiuquan Basin. The dislocation of terraces and the migration of alluvial fans suggests that tectonic activity was more intense around 160 and 40 ka BP.