The Xiwuqi area of Inner Mongolia is tectonically situated at the suture zone between Hegenshan and Xar Moron faults. Magmatic rocks occur widely in the area. LAICPMS dating for zircon separated from the Daqinhundi and Jinxing quartzdiorite plutons indicates that both plutons formed at 325±3Ma and 322±3Ma respectively. Lithological and geochemical analysis show that two plutons belong to lowK tholeiitic and calkalkaline series, and are enriched in large ion lithophile elements (LILE) such as Rb, Ba and K, and depleted in high field strength elements (HFSE) such as Nb, Ta, Ti and P. Geochemical compositions also show that the plutons are characterized by subduction genesis. Combined with regional data, a suite consisting of hornblende diorite, quartzdiorite, tonalite and granodiorite is developed in the Suzuoqi and Xiwuqi areas and similar to the complex in island arc and active continental margin. This set of rocks form early and late Carbonifous magmatic arc, presence of which may be related to the northward subduction of paleoAsian ocean slab.