LATE CENOZOIC RIGHT-LATERAL MOVEMENT ALONG THE WENQUAN FAULT AND ASSOCIATED DEFORMATION: IMPLICATIONS ON KINEMATIC HISTORY OF THE QSIDAM BASIN, NORTHEASTERN TIBETAN PLATEAU

The northeastern margin of the Tibetan plateau, bounded on the NW by the NE-trending Altyn Tagh fault, consists of four tectonic units; the Qilian Shan, west Qinling and east Kunlun fold-thrust belts and the Qsidam basin. In the area where these tectonic units come together, the NW-trending Wenquan fault lies between the Qsidam basin and west Qinling belt and contains clear evidence of active right-lateral movement. At the northern and southern ends of the fault, right-lateral movement has been transferred to NE-SW crustal shortening. Right-lateral movement was initiated in late Miocene and Pliocene time and has accumulated ~20 km of total displacement, which yields an average slip rate of ~4 mm/yr. Uplift of the Wahong Shan, bounded by the Wenquan fault on the east, resulted from en echelon thrusting and folding associated with right-lateral movement. The right-lateral movement along the Wenquan fault suggests that displacement occurs between the tectonic units within the northeastern margin of the plateau and that the Qsidam basin is underlain by a more rigid basement which has moved northward relative to the west Qinling belt to the east. The right-lateral Wenquan fault and left-lateral Altyn Tagh fault can be regarded as conjugate structures that accommodated the northward indentation of the Qsidam basin into the Qilian Shan belt. Because the Wenquan fault has a slower slip-rate than the Altyn Tagh fault, the northward movement of the rigid basement of the Qsidam basin must have a component of clockwise rotation relative to the Qilian Shan belt. The west Qinling belt pinches out westward between the Wahong Shan and Qilian Shan belt, implying that it may have undergone some eastward extrusion due to the N-S convergence between the Qsidam basin and Qilian Shan belt.