An Inclination Shallowing-Corrected Early Triassic Paleomagnetic Pole for the North China Craton: Implication for the Mesozoic Geography of Proto-Asia

The Early Mesozoic is a key period for the formation of the Asia continent. In this study, in order to reconstruct the Early Mesozoic paleogeography of Proto-Asia, we carried out a paleomagnetic study on the Early Triassic strata from the Chengde Basin in the northeastern North China Craton (NCC). Rock magnetic investigations reveal magnetite and hematite as the main magnetic carriers. Characteristic remanent magnetization directions from 21 sites show normal and reversed polarities and site-mean directions pass fold tests. After inclination shallowing (IS) correction with the elongation/inclination method, a mean direction is calculated at D-s/I-s = 322.5 degrees/39.5 degrees (k(s) = 32.6, alpha(95s) = 5.7 degrees) in stratigraphic coordinates. The corresponding Early Triassic paleomagnetic pole (lambda/phi = 53.5 degrees N/9.5 degrees E, A(95) = 5.3 degrees) overlaps with coeval poles that have also been corrected for IS reported from the western part of the NCC. This result indicates that there is no relative movement between the eastern and western parts of the NCC. With all IS-corrected paleomagnetic poles, a mean Early Triassic pole is recalculated for the NCC at lambda/ phi= 59.4 degrees N/13.4 degrees E (A(95) = 4.7 degrees). We use this pole to reconstruct the paleogeography of Proto-Asia and confirm previous studies that did not use IS corrections, in which two triangle bay-shaped oceans, the Paleo-Tethys Ocean and the Mongol-Okhotsk Ocean, existed along the southern and northern margins of the unified NCC-Mongolian Block (MOB). Clockwise rotations of the South China Craton and Siberia Craton relative to the NCC-MOB during the Early Mesozoic led to the final closure of both oceans.