Paleomagnetic constraints on the tectonic response of the eastern part of the West Qinling to the eastward spreading process of the Tibetan Plateau

In order to investigate the deformation characteristics of various parts of the West Qinling Mountains at the 'cross tectonic' pivot during the eastward extensional uplift of the Tibetan Plateau, detailed paleomagnetic studies were carried out in the Lower Cretaceous and Neoproterozoic strata of Zhouqu, Wudu, Chengxian and Fengxian areas. The Early Cretaceous paleomagnetic poles were derived for the Zhouqu and Chengxian areas (85. 7 degrees N, 279. 8 degrees E, A(95) = 9. 1 degrees for Zhouqu and 72. 3 N, 226. 3 degrees E, A(95) = 6. 8 degrees for Chengxian), and the Neogene paleomagnetic pole for the Wudu area (65. 8 degrees N, 206. 1 degrees E, A(95) =12. 8 degrees). A comparison of each with contemporaneous paleomagnetic poles in northern China shows that: (1) A counterclockwise local tectonic rotation of 14. 7 +/- 5. 8 degrees occurred in the Zhouqu area relative to northern China after the Early Cretaceous. (2) The Early Cretaceous paleomagnetic pole in the Chengxian area is consistent with the North China reference pole. (3) After the Neoproterozoic, the Wudu area underwent a local clockwise tectonic rotation of 25. 1 +/- 5. 6 degrees with respect to the North China reference pole. Based on previous research achievements, it is believed that the tectonic response of the eastward expansion and evolutionary process of the Tibetan Plateau in the Western Qinling region exhibits different activity characteristics in each tectonic site. The north-western area is characterized by left-slip faulting, and the land masses on both sides of the controlling fault show in situ clockwise rotation, which is consistent with the dynamic mechanism in the northeastern part of the Tibetan Plateau. The primary body of the south-western region is controlled by the north-eastward extrusive recoil of Songpan-Garze. It is accompanied by drag deformation in the vicinity of the fracture in a north-easterly secondary strike-slip fracture that is translational and misaligned, resulting in local counterclockwise rotation. The early strike-slip fractures in the eastern region formed a pull-apart basin, which was modified by extrusive stresses in the late stage, with tectonic overturning of the boundary fractures and weak deformation within the basin.