U-Pb Ages of zircons from the Xi Ulanbulang hypersthene-plagioclase granulite in the North Daqing Mountains, Central Inner Mongolia

Abstract：The Xi Ulanbulang hypersthene-plagioclase granulite in central Inner Mongolia is regarded as an old granitic intrusion separated from the Caledonian plagiogranite and Variscan granodiorte, as has been determined by regional surveys of the 1∶50 000 and 1∶250 000 Shilanhada Sheet and Bayan Obo sheet. Single-zircon U-Pb dating of the hypersthene-plagioclase granulite gave discordia and concordia upper and lower intercept ages of （2 511.4±4.9） Ma and （818±159） Ma respectively. These ages, combined with the results of regional survey, suggest that the former age represents the age of emplacement of the older granitic intrusion； while the latter represents the age of the superimposed deformational-metamorphic thermal event in the late stage .The two ages give direct evidence for crustal evolution in the Central Daqing Mountains.