Paleomagnetic constraints on the Early Permian pause of the northward drift of the Indochina block and its implications for the evolution of the Paleo-Tethys Ocean

The Indochina block is one of the major blocks separating the northern and southern branches of the east Paleo-Tethys Ocean. Paleomagnetic studies on the late Paleozoic drift history of the Indochina block are crucial for quantitatively constraining the evolution of the east Paleo-Tethys Ocean. In this study, we conducted paleomagnetic analyses on the Wusu basalts in the Simao Basin (southwestern Yunnan Province, China), located in the northern part of the Indochina block. Paleomagnetic analysis of the Wusu basalts reveals a clockwise rotation in remanent magnetization directions. We interpret this observed rotational pattern as the tectonic result of bookshelf faulting within a dextral intra-arc shear zone, which was active during the oblique subduction of the east Paleo-Tethys Ocean. Paleomagnetic analysis passed an inclination-only fold test, indicating a paleolatitude of 14.2°S ± 3.2° for the sampling area (23.3°N, 101.6°E) during the Early Permian (287 ± 5 Ma). This new paleolatitude, combined with existing data, confirms a three-phase drift history for the Indochina and North Qiangtang blocks. They initially drifted northward slowly from the Late Carboniferous to the Early Permian, then remained relatively stable during the Early to Middle Permian, and underwent accelerated northward drift after the Middle Permian. Based on paleomagnetic analyses and regional magmatic records, we propose that the opposing subduction of the southern and northern branches of the east Paleo-Tethys Ocean during the Early to Middle Permian may have contributed to this period of relative stability.