Late Quaternary thrusting in the southern margin of the Chaiwopu Basin, northern Chinese Tian Shan foreland

Thrusting and the associated folding are crucial geological processes accommodating the crustal shortening in a foreland setting. This work focuses on the late Quaternary thrusting of the Banfanggou fault (BF) in the southern Chaiwopu Basin, northern Chinese Tian Shan foreland. The outcrops at the Urumqi River in the western part of the southern margin of the basin show that the BF, dipping south with angle of 60–80 °, has thrust the Neogene mudstone onto the Quaternary gravels and has displaced the terrace surfaces. In contrast, the eastern segment of the BF exists as a blind thrust fault. By using the geomorphic surface (river terrace and alluvial fan) as the reference, the average rate of vertical slip on the western segment of the BF over the past ~12 ka is estimated to ~1.7 mm/year, and the estimated rate at the eastern segment of the fault is ~1.0–1.3 mm/year. Despite of the uncertainties of the rates deriving from the vertical offsets and the geomorphic ages, the resultant vertical slip rates might imply relatively high seismic risk in the southern Chaiwopu Basin.