Magnetic fabric study of the Late Jurassic-Early Cretaceous strata in Baoji area of Lhasa block

The Lhasa and Qiangtang blocks are at the heart of the Tibetan Plateau. However, the time for the specific combination of the two blocks is still in heated controversy. To further find geological evidence that can constrain the time limit between the two blocks, the authors studied the characteristics of the magnetic fabric of the Late Jurassic-Early Cretaceous strata in Lhasa block. According to the results obtained, the magnetic structure of Late Jurassic strata encountered strong tectonic stress, and the principal axis k₁ of the magnetic susceptibility of the Tukari Formation was oblique to the ground plane. After the stratigraphic correction, the k₁ azimuth and regional fold direction consensus indicate that the stress azimuth was NNE-SSW; the k₁ orientation of the Sabozhibule Formation was parallel to the plane (NNE-SSW) before the stratigraphic correction, indicating the direction perpendicular to the principal compressive stress and inferring the late tilting. The Late Jurassic formation magnetic structure recorded the same period of stress, and the stress direction was NNE-SSW. The Early Cretaceous Duoni Formation magnetic structure shows that the subsequent tectonic stress field intensity was weak, and was not in the same period as the Late Jurassic stress. Therefore, by comparing the magnetic fabric characteristics of the Late Jurassic and Early Cretaceous strata, the authors concluded that the magnetic fabric of the Late Jurassic in Baoji area recorded a strong tectonic stress in NNE-SSW, and that the stress in this period originated from the LhasaQiangtang block collision event, while the Duoni Formation was not affected by the stress field, only the stress field of the regional fold uplift was recorded.