Was there an ocean between the North China-Qaidam and Tarim blocks connecting the Mongol-Okhotsk and Paleo-Tethys oceans?

Teng Wang, Yanan Zhou, Douwe J.J. van Hinsbergen , Mark J. Dekkers, Zhenwei Chen, Ruiyang Chai, Dongmeng Zhang, Bitian Wei, Anliang Xiong, Dongwei Liu, Xin Cheng, Hanning Wu, Yunpeng Dong

The tectonic history of the final amalgamation of Eurasia is puzzling: geological and paleomagnetic data yield contrasting interpretations. Paleomagnetism shows that the North China Block and the Qaidam Basin fragment, migrated northward by several thousand kilometers relative to Eurasia until the latest Jurassic-Early Cretaceous. If true, plate tectonic principles require that a North China-Eurasia plate boundary existed. To the north, this may be the Mongol-Okhotsk suture, which contains sparse Mesozoic marine sediments. To the west, an associated geological record remains unknown. Here, we report for the first time an inclination shallowing-corrected pole from Lower Permian limestones of the Qaidam Basin passing both fold and reversal tests, that yields a northern hemisphere reversed direction of D = 32.2° ± 4.5° and I = -44.2° ± 5.1°, corresponding to a paleomagnetic pole at λ = 17.4°S and φ = 247.6°E (A95 = 4.0°, K = 12.0, N = 113). This indicates a post-early Permian Qaidam-Eurasia convergence of ~20° (＞2000 km) in latitude, like North China. When combined with existing paleomagneitc data, it shows that this convergence was mostly accommodated after the Triassic. The robustness of the paleomagnetic dataset calls for an explanation of a missing geological record of convergence. Continental crustal shortening invariably leads to high orogens. We therefore speculate that a cryptic Mesozoic oceanic suture exists between the Qaidam and Eurasia, whose remains may be buried below the Tarim Basin. How this boundary connected to the Mongol-Okhotsk suture and to the Tethyan sutures remains currently unresolved and warrants further investigation.