Constraining the Intracontinental Tectonics of the SW Central Asian Orogenic Belt by the Early Permian Paleomagnetic Pole for the Turfan‐Hami Block

Overview & Synopsis

In order to better understand the kinematics and geodynamics of the late Paleozoic to early Mesozoic transition from accretionary to intracontinental tectonics in the southwest Central Asian Orogenic Belt, we performed a paleomagnetic study on Lower Permian strata in the Turpan-Hami Basin, NW China. Magnetite and hematite are shown to be the principal magnetic remanence carriers. A typical sedimentary fabric that has not been modified by postdepositional deformation is recognized via magnetic fabric study. Stable characteristic remanent magnetizations, all of reverse magnetic polarity, are revealed by step demagnetizations. Remanence age is determined to be of Early Permian affinity, based on a fold test, remanence behavior of minerals, and geochronologic data. With inclination shallowing corrections, the first Early Permian paleomagnetic pole for the Turpan-Hami Block is acquired as λ = 75.7°N, φ = 276.3°E, A 95 = 5.7°, and N = 10 sites. Comparisons of this new pole with published ones from neighboring cratonic blocks provide kinematic constraints on the tectonic transition and subsequent intracontinental tectonics of this region. The Turpan-Hami and Yili blocks have kept their relative positions since the Early Permian. Significant latitudinal movement of 14.7°± 7.2°occurred between the Turpan-Hami and South Junggar blocks and could be mainly accommodated by late Paleozoic crustal shortening of at least~530 km across an intra-arc basin in the Bogda belt. The Turpan-Hami Block has experienced large-magnitude relative rotations of −41.1°± 7.1°a nd 21.2°± 9.4°with respect to Tarim and South Junggar since the Early Permian, respectively, corresponding to dominant intracontinental tectonics characterized by large-magnitude strike-slip displacements along megashear zones.