Strike-slip movement of the Altyn Tagh fault and implications for mountain formation inferred from paleomagnetic data in northeastern Tibetan Plateau

To help understand the deformational history of the northeastern Tibetan Plateau, paleomagnetic samples were collected from 38 sites in the Early Cretaceous to Pliocene sedimentary and volcanic 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 (D-s = 32.8 degrees, I = 59.4 degrees, kappa(s) = 36.2, alpha(95) = 8.1 degrees), and 8 sites in Early Cretaceous basalt flows from the Beidayao area provide a concordant paleomagnetic direction (D-s = 335.4 degrees, I-s = 55.1 degrees, kappa(s) = 34, alpha(95) = 9.6 degrees). The Early Cretaceous paleomagnetic directions from 15 sites in the Early Cretaceous sediments and basalt flows have a concordant mean paleomagnetic direction (D-s = 26.1 degrees, I-s = 49.5 degrees, kappa(s) = 28.6, alpha(95) = 7.3 degrees). 4 sites in Pliocene strata at Hanxia area yield a paleomagnetic direction (D-s = 355.4 degrees, I-s = 48.3 degrees, kappa(s) = 135.8, alpha(95) = 7.9 degrees). 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 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 India-Asia collision-induced left-slip movement of the Altyn Tagh fault at the northeastern edge of the Tibetan Plateau.