Inclination Divergence of Paleomagnetic Data Caused by Tectonic Strain in Cretaceous Redbeds From the Lhasa Terrane (Tibetan Plateau): Insights From AMS, hf-AIR, and CPO Analyses

Abstract

Paleomagnetic data from the Lhasa Terrane have been commonly utilized to constrain the paleo-position and shape of the southern margin of Asia prior to the India-Asia collision. However, there has been an ongoing debate regarding the reliability of the paleomagnetic data derived from Upper Cretaceous sedimentary rocks in the Lhasa Terrane. Here, we employ combined anisotropy of magnetic susceptibility (AMS), high-field anisotropy of isothermal remanent magnetization (hf-AIR), and crystal preferred orientation (CPO) measurements on the redbeds of the Shexing Formation. Regardless of the structure displayed by the AMS, the hf-AIR demonstrates a weak cleavage to deformational magnetic fabric, with minimum axes corresponding roughly with the c-axis of hematite in the bedding plane. Consequently, we argue that the inclination divergence observed between the two limbs of anticlines in the Late Cretaceous paleomagnetic data from the Lhasa Terrane is attributable to the rotation of hematite under weak post-depositional tectonic strain. We caution against using Upper Cretaceous redbeds from the Lhasa Terrane for paleogeographic reconstruction without an efficient correction of tectonic strain. Furthermore, we propose the adoption of anisotropy of magnetic remanence as a more suitable alternative to AMS for assessing the reliability of paleomagnetic data in sedimentary rocks.