Paleomagnetic evidence from the southern Lancangjiang volcanic belt in western Yunnan (SW China) and its implication to the linkage of the Indochina and North Qiangtang during the evolution of Paleo-Tethys

We report a paleomagnetic and U-Pb geochronological study on the early Late Triassic volcanic rocks in the southern Lancangjiang suture belt in western Yunnan of southwest (SW) China. The age of the sampled sections was constrained to be the Carnian Stage of Late Triassic times. Stable Characteristic Remanent Magnetizations (ChRMs) were isolated from 21 sites ( 11 sites of rhyolites and 10 sites of volcano clastic rocks) at high temperatures following step-wise thermal demagnetization. The data pass fold, reversal and conglomerate tests, and are interpreted to be primary thermal remanent magnetizations (TRMs). The new Late Triassic paleomagnetic pole (46.1°N/176.2°E, K=44.9, A₉₅=4.8, N=21) yields a paleolatitude of 26.0 ± 4.8°N at the reference site (23.0 °N/100.4°E) in the southern Lancangjiang area. This new paleolatitudinal constraint on the Paleo-Tethys suture zone in western Yunnan indicates that the north branch of the Paleo-Tethys Ocean closed no later than the early Late Triassic, and confirms a geographic linkage between the North Qiangtang and Indochina blocks at least during the Early Permian to Late Triassic. A comprehensive analysis of paleomagnetic and geological data supports the view that the Qiangtang Block should be further subdivided into the North and South Qiangtang, as suggested by previous models.