NEW PALEOMAGNETIC RESULTS FROM NORTHERN CHINA - COLLISION AND SUTURING WITH SIBERIA AND KAZAKHSTAN

We report new results from our paleomagnetic studies of the Inner Mongolia autonomous region in northeastern China and the Xinjiang autonomous region in northwestern China. Primary magnetizations are isolated in Tertiary, Cretaceous, Late Jurassic and Late Permian rocks and secondary components of magnetization of Late Jurassic and Recent ages are seen in strata of Inner Mongolia. Western Junggar Basin and part of the Tarim block, suffered widespread complete tectono-thermal remagnetization at about 280 Ma (Permian). The paleomagnetic evidence suggests that the sampled areas in Inner Mongolia have been part of the North China Block at least since Late Permian time and the Junggar block collided with the Tarim block by Late Permian time. Our own paleomagnetic results together with available data from other parts of eastern Eurasia, suggest a tectonic model in which Kazakhstan, Europe and Siberia collided with each other and formed the Europe-Siberia-Kazakhstan plate (EUR-SIB-KAZ) in Late Permian time. To the east, Mongolia (= Outer Mongolia), Inner Mongolia and the North China Block were also wedged together forming the Mongolia-North China plate (MON-NC) by this time. These two composite continental plates were not a stable unit in the Late Permian. The geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the Late Permian near the western end (50°N, 75°E) of the Southern Siberian Fold Belt and progressed eastward as the MON-NC plate rotated and clockwise about 117° relative to the EUR-SIB-KAZ plate during the Early Mesozoic. Suturing and rotation were probably complete by the Late Jurassic. Significant relative motion between the Tarim and Siberia blocks continued from Early Triassic to Late Jurassic, as Tarim moved northeastward 1400 km relative to Siberia. © 1990.