First Early Permian Paleomagnetic Pole for the Yili Block and its Implications for Late Paleozoic Postorogenic Kinematic Evolution of the SW Central Asian Orogenic Belt

摘要

We conducted a paleomagnetic study on the Early Permian volcanic and sedimentary rocks, and the Neoproterozoic mafic dikes in the Yili Block, NW China. Magnetite and hematite were proven to be the principal magnetic remanence carriers. Demagnetizations revealed stable characteristic remanence magnetizations with a sole reversed magnetic polarity. The magnetic remanence of only the Early Permian strata turned out to be primary based on positive fold tests; meanwhile, the magnetic remanence age of the mafic dikes is ambiguous. Accordingly, the first Early Permian paleomagnetic pole for the Yili Block is calculated at =81.5 degrees N, =256.5 degrees E, N=11, and A(95)=10.9 degrees. Comparisons of this new pole with published ones from the Yili, Tarim, and South Junggar blocks provide new quantitative constraints on late Paleozoic kinematic evolution of the SW Central Asian Orogenic Belt: (1) Between the Yili and Tarim blocks, significant relative movement took place along major strike-slip faults during the Late Carboniferous to Early Permian (580290km) and the Early to Late Permian (585340km), and the displacement rate increased from the Late Carboniferous to Early Permian (similar to 19.39.7mm/yr) to the Early to Late Permian (similar to 29.3 +/- 17.0mm/yr); (2) a significant relative rotation of 28.3 degrees +/- 18.3 degrees in the Late Permian, and a lateral displacement of 630 +/- 295km after the Late Permian occurred between the Yili and South Junggar blocks. The significant strike-slip movements played an important role in the formation of the Central Asian Orogenic Belt and should be considered with great attention in tectonic and paleogeographic reconstructions.