Vertical axis rotations inferred from paleomagnetic data in northeastern Tibetan plateau and its implications for geodynamic models

To help understand the deformational history of the northeastern Tibetan Plateau, paleomagnetic samples were collected from 38 sites in the early cretaceous to pliocene rocks distributed in four general regions adjacent to the Altyn Tagh fault at the northeastern edge of the Tibetan Plateau. In the Changma area, 10 sites in the Early Cretaceous sediments and basalt flows yield a mean paleomagnetic direction (Ds=32.8°,Is=59.4°, κs=36.2, α95=8.1°) , and 8 sites in Early Cretaceous basalt flows of the Beidayao area provide a concordant paleomagnetic direction (Ds=335.4°,Is=55.1°, κs=34, α95=9.6°). The Early Cretaceous paleomagnetic directions from 15 sites in the Early Cretaceous sediments and basalt flows have a concordant mean paleomagnetic direction (Ds=26.1°, Is=49.5°, κs=28.6, α95=7.3°). 4 sites in Pliocene strata at Hanxia area yield a paleomagnetic direction (Ds=355.4°, Is=48.3°, κs=135.8, α95=7.9°). Fold or reversal tests imply primary magnetizations. Together with previously published paleomagnetic data in the Qaidam basin and its surroundings, these new results indicate that (1) the Qaidam block has not undergone wholescale vertical axis rotation since the Early Cretaceous time with respect to the stable Eurasia due to the penetration of India into Asia; (2) occurrence of vertical axis clockwise rotations in areas adjacent to the eastern edge of the Altyn Tagh fault may be an important tectonic model to absorb the left-slip movement of the Altyn Tagh fault at the northeastern edge of the Tibetan Plateau after the initial collision of India with Asia.