New Late Jurassic to Early Cretaceous Paleomagnetic Results From North China and Southern Mongolia and Their Implications for the Evolution of the Mongol-Okhotsk Suture

摘要

To better constrain the evolution of the Mongol-Okhotsk suture, we carried out new paleomagnetic studies on Sharilyn Formation (similar to 155Ma) and Tsagantsav Formation (similar to 130Ma) in southern Mongolia, Amuria Block (AMU), and Tuchengzi Formation (similar to 140Ma) and Dadianzi/Yixian Formation (similar to 130Ma) in the Yanshan belt, North China Block (NCB). A total of 719 collected samples (from 100 sites) were subjected to stepwise thermal demagnetization. After a low-temperature component of viscous magnetic remanence acquired in the recent field was removed, the stable high-temperature components were isolated from most samples. The high-temperature components from each rock unit passed a fold test and a reversal test, indicating their primary origins. The corresponding paleomagnetic poles were thus calculated. For AMU, the similar to 155Ma pole is at 74.7 degrees N/232.5 degrees E (A(95)=3.7 degrees), the similar to 130Ma pole at 74.6 degrees N/194.7 degrees E (A(95)=2.9 degrees); for the NCB, the similar to 140Ma pole is at 82.7 degrees N/208.6 degrees E (A(95)=4.3 degrees), the similar to 130Ma pole at 80.5 degrees N/197.4 degrees E (A(95)=2.3 degrees). By combining our new results with the published data, we refined the 155-100Ma segment of the apparent polar wander paths for AMU and NCB, which can demonstrate that these two blocks have been tectonically coherent (AMU-NCB) during 155-100Ma. Comparison of the apparent polar wander paths, however, revealed a latitudinal plate convergence of 14.3 degrees 6.9 degrees and similar to 19.0 degrees relative rotation between Siberia and the AMU-NCB after similar to similar to 155Ma. Large-scale latitudinal convergence likely ceased by similar to 130Ma, although some relative rotation between them continued along the Mongol-Okhotsk suture until similar to 100Ma.