Paleomagnetism of Late Triassic Volcanic Rocks From the South Qiangtang Block, Tibet: Constraints on Longmuco-Shuanghu Ocean Closure in the Paleo-Tethys Realm

Abstract

The South Qiangtang block of the Qinghai-Tibet Plateau represents an area critical to understanding the late Paleozoic and early Mesozoic history of the Tethyan realm, but its drift history remains poorly constrained. Here we report a new quantitative paleogeographic constraint for the South Qiangtang block from a paleomagnetic study of Late Triassic volcanic rocks of the Xiaoqiebao Formation. A characteristic remanent magnetization isolated from 25 sites passes both fold- and reversal tests, and likely represents a primary magnetization. On the basis of these data, we estimate that the South Qiangtang block occupied a paleolatitude of 30.1 ± 4.6°N at ca. 222 Ma. When combined with existing paleomagnetic constraints, these new results indicate that the South Qiangtang block (and other “Cimmerian” blocks) moved rapidly northward (in true latitude) between the middle Permian and Late Triassic. Our new data further suggest that the southern branch of the Paleo-Tethys (Longmuco-Shuanghu Ocean) likely closed by the mid-Late Triassic.