Abstract:
Objectives The northward drift history of the North Qiangtang Block during the Permian and Triassic is of great significance for understanding the movement process and geodynamics of the Tethyan blocks from Gondwana to Eurasia. However, the Early Triassic paleolatitudinal position of the North Qiangtang Block, as revealed by paleomagnetic data, remains inconclusive, leading to controversies regarding the key processes of its northward drift.
Methods Therefore, this study conducted detailed petrographic, rock magnetic, anisotropy of magnetic susceptibility (AMS), and demagnetization experiments on representative limestone samples from the Lower Triassic Yingshuiquan Formation in the North Qiangtang Block. The aim was to understand the types and content of magnetic minerals in the rocks, assess the degree of tectonic influence on the strata, evaluate whether the characteristic remanent magnetization (ChRM) obtained from the samples represents a primary remanence, and thereby determine the paleolatitude of the North Qiangtang Block during the Early Triassic.
Results The experimental results show that the main magnetic minerals in the Yingshuiquan Formation limestones are pseudo−single−domain (PSD) magnetite and hematite. The AMS exhibits typical sedimentary fabrics. Demagnetization reveal two−component magnetizations, allowing for the isolation of a stable ChRM carried by both magnetite or/and hematite. The ChRM directions pass both the fold test and the reversal test. The Elongation/Inclination (E/I) correction indicates no significant inclination shallowing in the samples. The corresponding paleomagnetic pole position of the Northern Qiangtang Block in the Early Triassic is λ=−45.4°, \textitΦ =41.7°, A95=4.2°.
Conclusions Consequently, this study argues that the Yingshuiquan Formation limestones have not been subjected to intense subsequent tectonic deformation, and the primary remanence carried by the magnetic minerals records the information from the time of rock formation. The Early Triassic paleogeographic position of the North Qiangtang Block revealed by the paleomagnetic data from the Yingshuiquan Formation is reliable. The North Qiangtang Block was located at a near−equatorial paleolatitude (1.1°±4.5°S) during the formation of the Yingshuiquan Formation (approximately 249 Ma). The results support the scenario that the North Qiangtang Block underwent rapid northward drift during the Triassic. This work also provides a fundamental basis for conducting more detailed paleomagnetic studies on this stratigraphic unit in the future, contributing to a deeper understanding of the drift history of the North Qiangtang Block from Gondwana to Eurasia and the geodynamics of the Tethys.
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