Early Cretaceous Terminal Convergence Between the North China‐Mongolia and Siberia Continents: Imprints from the Chagan Obo Shear Zone in Central Inner Mongolia, North China

The ENE-striking Chagan Obo shear zone in central Inner Mongolia is critical to constrain the termination of convergence between the North China-Mongolia and Siberia continents. We recognized three ENE-striking zones with strong deformation in the Permian biotite monzogranite within the shear zone and investigated the structural and kinematic characteristics. The strong deformation zones developed dense ENE-striking and NNW-dipping foliations. The widespread shear sense indicators such as S-C foliations, mica fish, sigma-type, structures, and typical tight-to-isoclinal asymmetric folds show top-to-the-SSE thrusting through NNW-SSE compression. Two Ar-40-Ar-39 ages of muscovites from the muscovite quartz schists in this shear zone show 144.1 +/- 1.2 Ma and 142.1 +/- 0.9 Ma, respectively, providing the peak compression to be Early Cretaceous (144-142 Ma). Combined with the regional syn-/post-collisional magmatic rocks (166-155 Ma) related to the closure of the Mongol-Okhotsk Ocean, this shear zone's ages (144-142 Ma) suggest that the continental convergence between the North China-Mongolia and Siberia continents lasted from Late Jurassic to Early Cretaceous. The Early Cretaceous shoshonitic volcanism (137-133 Ma) and rift basins in this region indicate the onset of orogenic collapse in the eastern Central Asian Orogenic Belt.