Paleomagnetic Evidence for a Late Permian Qaidam-North China Connection, and the Cryptic Final Mesozoic Intra-Asian Suture

Abstract

Paleomagnetic data have long shown that the final assembly of eastern Eurasia occurred in the latest Jurassic, after the North China Block moved 1,000 s of km toward Eurasia throughout the late Paleozoic and Mesozoic. This was accommodated along the Solonker and Mongol-Okhotsk subduction zones whose sutures are well documented in (inner) Mongolia. During this time, one or more plate boundaries must have existed west of China to connect the (inner) Mongolian suture with the Paleotethyan plate boundaries. Paradoxically, no candidate Mesozoic plate boundary is known between North China and Eurasia to its west, in northern Tibet, the Tarim Basin, or the Tien Shan region. In this study, we show paleomagnetic pole from Upper Permian (255.7 ± 3.8 Ma) red beds from the Qaidam Block of northern Tibet, adjacent to the Tarim Basin, with positive fold test and corrected for inclination shallowing, with D = 348.7° ± 2.3°, I = 47° ± 2.5°, λ = 77.6°N, ɸ = 332.8°E, A95 = 2.1°, K = 24.7, N = 199. These data reveal that Qaidam Block's paleolatitude was indistinguishable from that expected if it was part of North China but must have undergone ∼21° ± 2° (>2,300 ± 220 km) paleolatitudinal motion relative to Eurasia since late Permian time. This suggests that the missing plate boundary (or boundaries), in the form of a transform or a subduction zone, must be sought around or within the Tarim Basin. This may form a starting point in a search for the cryptic, last intra-Asian suture(s) and calls for systematic regional restoration of circum-Tarim tectonic history.