Anisotropy of magnetic susceptibility study of the Jurassic rocks in the Qamdo Area, eastern Tibet, and its tectonic implications

In this paper, anisotropy of magnetic susceptibility (AMS) was measured on samples from 71 sites of the Jurassic Wangbu Formation, Dongdaqiao Formation and Xiaosuoka Formation in the Qamdo area of eastern Tibet. The AMS of the Lower Jurassic Wangbu Formation indicates that the magnetic lineation is more developed than the magnetic foliation, the anisotropy degree is very high, and the minimum axis K3 of magnetic axis ellipsoid is scattered in the layer shortening direction, which is related to the structural cause. The AMS of the Middle Jurassic Dongdaqiao Formation and the Upper Jurassic Xiaosuoka Formation implies that the magnetic foliation is more developed than the magnetic lineation, the anisotropy degree is very low, and the minimum axis K3 of magnetic susceptibility ellipsoid is near vertical to the beds. These findings indicate the primary sedimentary fabric for the Middle Jurassic Dongdaqiao Formation and the Upper Jurassic Xiaosuoka Formation. The AMS of the Lower Jurassic Wangbu Formation means that the direction of the tectonic stress field was close to NE-SW direction during the Early Jurassic. The obvious change of the paleocurrent direction between the Dongdaqiao Formation and the Xiaosoka Formation suggests that the uplifting process in the southern part of the Qamdo area was earlier than the north, and the provenance of the sediment had also undergone a corresponding transformation. © 2019, Science Press. All right reserved.