First Paleomagnetic Result From the Early Permian Volcanic Rocks in Northeastern Mongolia: Evolutional Implication for the Paleo-Asian Ocean and the Mongol-Okhotsk Ocean.

The Mongolia Block (MOB), which is now sandwiched by the Siberia Craton (SIB) and the North China Craton (NCC), plays an essential role for understanding the late stage evolution of the Paleo-Asian Ocean and the early stage evolution of the Mongol-Okhotsk Ocean. Here, a paleomagnetic study is performed for the first time on the Early Permian volcanic strata in the Bayandun region of northeastern Mongolia and the data are used to uncover the late Paleozoic paleoposition of the MOB and better understand the evolution of both oceans. Zircon U-Pb dating results reveal an emplacement age of 283 ± 3 Ma for the studied volcanic strata. Rock magnetic analyses identify that titanium-poor magnetite is the main magnetic carrier. Characteristic remanent magnetization isolated from seven sites shows consistent reverse polarity, corresponding to the Permo-Carboniferous (Kiaman) Reverse Superchron. Site-mean directions pass fold tests, and an Early Permian paleomagnetic pole is calculated for the MOB at λ/φ = -14.9°N/76.8°E (A95 = 5.7°) with N = 7 sites. Comparison with published Permian paleomagnetic poles from surrounding blocks indicates that (1) the MOB should have welded with the NCC before the Early Permian or was at least very close to it. (2) The welded MOB-NCC was separated from the SIB by the Mongol-Okhotsk Ocean with ~30° latitudinal difference during the Early Permian. (3) Significant vertical-axis strike-slip related rotations occurred within and along the margins of the unified MOB-NCC due to the far-field stress effect produced by posterior orogenic events. [ABSTRACT FROM AUTHOR]