Tectonic strain causes the inclination divergence of paleomagneticdata from the Upper Cretaceous redbeds in the Lhasa terrane,insight from (AMS), (hf-AIR) and (CPO)

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 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) measurement on the redbeds of the Shexing Formation. Regardless of the structure displayed in the AMS data, the hf-AIR results demonstrate a weak cleavage to deformational magnetic fabric, with minimum axes corresponding roughly with the c-axis of hematite in the bedding plane. Consequently, we propose that the inclination divergence observed between the two limbs of an anticline in the Late Cretaceous paleomagnetic data from the Lhasa terrane is attributable to the deflection 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 suggest the adoption of anisotropy of magnetic remanence (AMR) as a more suitable alternative to AMS for assessing the reliability of paleomagnetic data in sedimentary rocks.