Optical dating of an offset river terrace sequence across the Karakax fault and its implication for the late Quaternary left-lateral slip rate

Abstract

The Karakax fault is one of the largest left-lateral strike-slip faults at the rim of the northwestern Tibetan Plateau. In this study, the optical dating techniques were applied to the Taersayijilega river terraces, which were transversely cut and offset by the Karakax fault. Six fluvial sand samples from the river terraces were collected and dated. The results show that the terraces (T2-T5) have ages of 14.5±1.0ka, 21.2±1.2ka, 28.5±1.7ka and 39.7±2.5ka, respectively. By interpreting high resolution satellite images, the horizontal displacements of the four river terraces are estimated at ∼160m, ∼235m, ∼260m and ∼365m, respectively. Based on the ages and offsets of the terraces, the average left-lateral slip rate of the Karakax fault was estimated at 7.8±1.6mm/a during the late Quaternary. Such rate of the Karakax fault is significantly higher than that of the Longmu-Gozha Co fault, suggesting that the Karakax fault plays an important role in accommodating eastward movement of the Tibetan Plateau at the northwest during the late Quaternary.