Late Cenozoic thrust propagation within the Keping fold-and-thrust belt along the southern foreland of Chinese Tian Shan: Evidence from apatite (U[sbnd]Th)/He results

Abstract

The Keping fold-and-thrust belt (FTB) is located along the southern foreland of the Chinese Tian Shan, consisting of 3–6 rows of E- to NE-trending thrusts. Determining the time of thrusting and folding within the Keping FTB is crucial to understand the process and characteristic of tectonic deformation along the southern Tian Shan foreland. Here, we present new deformation ages of four thrusts within the Keping FTB by using the apatite (UTh)/He thermochronometer. Based on analyses of 59 single-grain apatite (UTh)/He ages of 13 sandstone samples collected from the hanging-walls of the four thrusts, the deformation ages of two thrusts located at the northern part of the western Keping FTB were constrained to be ~12 Ma and ~ 11 Ma, respectively; while those of two thrusts located at the southern part of the eastern Keping FTB were interpreted to be ~14 Ma and ~ 13 Ma, respectively. The above deformation ages, together with previous studies, suggest that the Cenozoic deformation across the southern Tian Shan foreland initiated at ~16–12 Ma, and the propagation process of the Keping thrust system is laterally non-synchronous. Additionally, the million-year-scale crustal shortening rates of the Keping FTB were recalculated to be ~2.2–3.9 mm/yr in its western segment and ~ 1.3–3.6 mm/yr in its eastern segment, based on the new age constraints of initial tectonic deformation and published shortening estimates.