We provide new geochronological and geochemical constraints on the formation and evolution of an early to midPaleozoic arc pluton, from north of Damaoqi, Inner Mongolia. This pluton has a transitional normal arc/adakite geochemical affinity. SHRIMP zircon U-Pb ages suggest that diorites was emplaced at 452±3 Ma and 440±2 Ma, quartz diorite at 446±2 Ma, and granodiorite at 440±2 Ma, which represents an Ordovician oceanic subduction event. Precambrian zircon inheritance (ca.1967 Ma) occurs in a finegrained diorite which indicates that the arc was built on a Precambrian continental crust.