Paleomagnetic Rotation Constraints on the Deformation of the Northern Qaidam Marginal Thrust Belt and Implications for Strike-Slip Faulting Along the Altyn Tagh Fault

Discordant Cenozoic paleomagnetic rotation results obtained throughout the northeastern Tibetan Plateau have yielded different tectonic models for the evolution of the Altyn Tagh Fault and the northeastern Tibetan Plateau. Here based on detailed existing magnetostratigraphic age constraints, we carried out an in-depth paleomagnetic study along the Hongliugou section in the middle northern Qaidam marginal thrust belt to address the Cenozoic rotations of this region. A total of 1,342 Jurassic-Neogene siltstone-sandstone core samples were collected from 128 sites across 18 time intervals. Rock magnetic analysis suggested that magnetite and hematite are the dominant magnetic carriers. Detailed thermal demagnetization analyses were performed, and the characteristic remanent magnetizations of 90 sites (743 samples) were obtained, which yielded positive fold and reversals tests, indicating that they likely represent primary magnetizations. Detailed paleomagnetic declination versus age analyses revealed three periods of rotations: 12.515.7 degrees statistically insignificant counterclockwise rotations during 45-33Ma, successive clockwise rotations of 32.215.4 degrees during 33-14Ma, and subsequent statistically insignificant counterclockwise rotations of 8.79.4 degrees after 14Ma. These three periods of rotations are similar to those calculated based on previously available magnetostratigraphic data from the nearby Dahonggou section. Based on the integration of these data with other lines of geological evidence, we attributed the latter two periods of rotations to fast strike-slip faulting along the Altyn Tagh Fault.