Paleomagnetic constraints on Paleogene-Neogene rotation and paleo-stress in the northern Qaidam Basin.

Knowing the rotation and paleo-stress history in Qaidam Basin is a fundamental parameter to quantify the mechanism of intracontinental deformation in Tibetan Plateau. However, few studies have been conducted on tectonic rotation and stress evolution over long timescales in the Qaidam Basin. Here, we report new magnetic declination and the anisotropy of magnetic susceptibility (AMS) from a ∼52–7 Ma sequence of fluvial and lacustrine sediments in the Dahonggou (DHG) section in the northern Qaidam Basin. The magnetic declination revealed that the northern Qaidam Basin underwent a clockwise rotation 25.1° ±8.6° during ∼33–17 Ma, followed by a counterclockwise rotation 16.9°±6.8° during ∼17–13.5 Ma. The AMS results showed that the "earliest deformation" fabrics were interrupted by the "pencil structure" fabrics in the intervals of ∼52–45 and ∼21–15 Ma. The interruption, synchronous with the marked deceleration of the India-Asia convergence rate, indicates pulse of strong tectonic compressive stress. In addition, the AMS results documented a transition in stress direction from S-N to SW-NE at ∼15 Ma, suggesting a kinematic shift in the northeastern TP. Our constraints on the rotation and stress from the northern Qaidam Basin support the two-stage evolution of the Altyn Tagh Fault (ATF). The fast-rate slip motion on the ATF during the early Oligocene caused the clockwise rotation in the northern Qaidam Basin; the second stage with enhanced thrusting since the middle Miocene caused extensive crustal shortening and dispersive NW-trending folds and faults in the Qaidam Basin and the northeastern TP. [ABSTRACT FROM AUTHOR]