The Shortening Rate of North Danghe Nanshan Thrusts at Its Junction with The Altyn Tagh fault, Constrained by Cosmogenic Isotope and OSL Dating of Serial Offset Terraces

Abstract:

The North Danghe Nanshan thrusts extend along the northern piedmont of the Danghe Nanshan, merges into the Altyn Tagh fault to the west. Two strands of the North Danghe Nanshan thrusts vertically offset multiple terraces, most of which are capped by Holocene loess. Previous study suggested fast thrusting of the North Danghe Nanshan thrusts based on young age and high offset. We adopt Terrestrial Cosmogenic Nuclides and Optically Stimulated Luminescence dating methods to constrain exposure ages of uplifted terraces. The exposure ages of 5.4 ± 0.2 ka, 7.8 + 0.8/- 1.5 ka, 44.4 ± 3.2 ka and 108 ± 34 ka for terraces T1, T2, T3 and T4 respectively. The differential GPS and Unmanned Aerial Vehicle-based Laser Scanning are used to measurement the vertical displacements, which range from 0 to 115 m. These vertical offsets and age constraints combined yield a vertical slip rate of 0.8-2.0 mm/yr. Considering the dipping angles of two thrust strands from outcrop and trench exposures, we estimate the shortening rate to be 1.0-5.5 mm/yr. This 100-ka time scale shorting rate is similar to the rate of 0.7-1.5 mm/yr during the last 10 Ma, which implies a possible constant shortening rate of 1.0-1.5 mm/yr since late Miocene for the North Danghe Nanshan thrusts.