Cenozoic clockwise rotation of the northeastern Tibetan Plateau: Paleomagnetic evidence from volcanic sequences in the West Qinling Mountain

Vertical-axis rotations recorded by paleomagnetic results from the northeastern Tibetan Plateau afford new insights into the tectonic processes related to the growth of the Tibetan Plateau. Here, geochronological and paleomagnetic investigations on the Cretaceous-Tertiary basalt sequences within the West Qinling Mountain were conducted to decipher the vertical-axis rotations of the northeastern Tibetan Plateau. Potassium-argon (K-Ar) results from the basaltic rocks reveal two time episodes of extrusive volcanism, 123-90 Ma and 21-15 Ma. Comparisons between the obtained paleomagnetic data and the equivalent age-expected directions of the Eurasia and the North China block respectively, indicate that 10-20 degrees clockwise rotation occurred in the West Qinling Mountain only after similar to 15 Ma. Combined with the previous estimation of Eocene clockwise rotation in the Xining-Lanzhou region north of the West Qinling Mountain, we conclude that two-stage clockwise tectonic rotation occurred in different parts of the northeastern Tibetan Plateau, related to different deformational kinematics. The Eocene-clockwise rotation was likely in response to N-S trending normal faulting, suggesting that inboard extension in East Asia drove the rotation within the outmost region of the Tibetan Plateau. In contrast, the mid-Miocene clockwise rotation was linked to crustal right lateral shear in the northeastern corner of the Tibetan Plateau when the plateau grew to its northern margins.