Closure time of the Mongolia-Okhotsk Ocean: constraint of angular unconformity between the Lower Cretaceous and the lower geological body in the Tuquan area of the Greater Hinggan Mountains

The closure time of the Mongolia-Okhotsk Ocean has always been the focus of geological debate.Detailed survey shows that there is an angular unconformity between the Lower Cretaceous and the lower geological body in Tuquan area of the Greater Hinggan Mountains, The overlying stratum is the tuff of the Lower Cretaceous Baiyingaolao Formation with the stratification of 332°∠15°.The structural deformation of the underlying strata is strong, and genicular folds are developed, and 10 cm ancient weathering crust is seen at the top.Combined with the comprehensive study of regional data, the unconformity is a regional angular unconformity, which is one of the marks to identify the orogenic movement.The unconformity may not only represent the closed collision orogeny of the Mongolia-Okhotsk Ocean before the Early Cretaceous, but also suggest that the evolution stage of eastward creep and extension of the eastern continental margin began from the Early Cretaceous.