The northern Darhan Muminggan Joint Banner of Inner Mongolia, geotectonically crossing two geological-structural units, is divided into two parts by Bayan Obo-Chifeng deep fault (plate boundary fault). To the south of the deep fault is the North China block, and to the north is the accretion zone at the northern edge of North China plate. An important magmatic arc belt mainly composed of diorite, quartz diorite, tonalite and granodiorite is developed near Bart-Obao on the north side of Bayan Obo-Chifeng deep fault. In this paper, precise SHRIMP zircon U-Pb dating and hornblende 40Ar/39Ar dating defining the emplacement age of the intrusion and its thermal evolution history were conducted for inclusions of diorite and hornblendite hosted in granodiorite, and the constraints on Early Paleozoic subduction-collision event of the Paleo-Asian Ocean in central Inner Mongolia were provided from isotope geochronology. SHRIMP U-Pb zircon ages of the two diorite samples are 453±3 Ma and 446.8±5.3 Ma, and hornblende 40Ar/39Ar plateau ages are 459.2±2.4 Ma and 442.9±4.2 Ma. SHRIMP zircon U-Pb dating results indicate that the island arc intrusive rocks were formed around 450 Ma, resulting from the Middle-Late Ordovician (or earlier) oceanic subduction event. The results of SHRIMP zircon U-Pb dating are basically in accordance with those of hornblende conventional 40Ar/39Ar dating method, which suggests the crystallization and rapid cooling after the emplacement of the magma and may reveal collision between the Baoerhantu-Bainaimiao island arc zone and the North China plate. The dating results of the diorite imply that tectonic heat events after the emplacement and the cooling of the intrusive body did not affect the hornblende Ar-Ar closed system, and hence strong tectonic heat events did not occur later.