Abstract The formation and evolution of the Central Asian Orogenic Belt (CAOB) are intimately related to the opening and closure of the Paleo-Asian Ocean. The final closure led to amalgamation or collision between the CAOB and North China Craton. However, the issue about the subduction polarity and final closure of the Paleo-Asian Ocean has long been debated. In order to resolve this issue, we carried out a detailed geochemical and age study on the Delinggou Intrusion from the Siziwangqi area of central Inner Mongolia, at the northern margin of the North China Craton. The Delinggou Intrusion consists predominantly of diorite and quartz diorite, with minor gabbroic diorite. U–Pb zircon dating indicates that the intrusion was emplaced during early Carboniferous (330 to 343 Ma). Geochemically, the rocks are metaluminous and belong to the calc-alkaline series. They are enriched in large ion lithophile elements (LILE, e.g., Rb, Sr and Ba), and depleted in high field strength elements (HFSE, e.g., Zr, Nb, Hf, Ta and Ti). The Delinggou rocks were probably generated by partial melting of an enriched subcontinental lithospheric mantle, further contaminated by crustal material during the magmatic differentiation in a continental arc setting. We conclude that the Paleo-Asian Ocean underwent southward subduction beneath the North China Craton, and the subduction initiated in the Carboniferous (343–330 Ma), but the final ocean closure time is not yet constrained.