Late Miocene accelerated exhumation in the central Tajik Basin and implications for northward indention and lateral growth of the Pamir

Abstract

The Tajik Basin, located at the west of the Pamir, is characterized by a series of thin-skinned folds and thrusts within its interior. Constraining the onset of deformation of these structures is important both for illustrating basin inversion process and for understanding growth history of the adjacent Pamir. To date, the timing of thrusting and folding within the Tajik Basin has not been well studied. In this study, we determined the timing of fault motion of the Aruntau thrust in the central Tajik Basin by using apatite (UTh)/He thermochronometry. Apatite (UTh)/He age data of sandstone samples collected from the hanging wall of the Aruntau thrust fault, combined with thermal history simulation, constrains the onset of rapid cooling of rock samples at ca. 10–6 Ma. Given the compressional tectonic regime, we propose that the observed rapid cooling was caused by thrust-induced exhumation, and thus, the cooling age of ~10–6 Ma approximately represents the timing of thrusting initiation. Integrated with previous studies, we found that the late Miocene tectonic deformation was not only circumscribed within the Tajik Basin, but also occurred in the areas north and east of the Pamir and within the Pamir. We suggest that the synchronously widespread tectonic deformation in the Pamir-Tian Shan convergence zone reflects the enhanced northward indentation and lateral growth of the Pamir since the late Miocene.