Paleomagnetic data from the Qaidam Block quantify post-middle Triassic convergence preceding eastern Eurasian assembly

Ruiyang Chai, Yanan Zhou, Douwe J.J. van Hinsbergen , Teng Wang, Qiang Fu, Zhenwei Chen, Chunxi Qu, Shuqi Lan, Xin Cheng, Hanning Wu

Amalgamation of East Asian blocks with Eurasia involved progressive closure of several oceanic basins preserved as sutures. Since the Permian, the North China Block has undergone ~2500 km of paleolatitudinal motion relative to Eurasia, forming Mongol–Okhotsk suture in the north. Surprisingly, no evidence in its western part has been found to coordinate this motion, which is essential for a triple conjunction with the suture. Here we report a new Middle Triassic paleomagnetic pole from the Qaidam Block, which connected the Tarim and North China Blocks, indicating a paleolatitude of ~35°N. This result is indistinguishable from coeval paleolatitudes of the North China Block, suggesting that both northward moved in unison as a coherent tectonic plate. Since the Tarim Basin had already been part of Eurasia, we propose that a cryptic, perhaps buried suture that accommodated post-Triassic convergence might be buried below the Tarim Basin or the NW Tibetan Plateau.