U-Pb Ages of zircons from the Xi Ulanbulang hypersthene-plagioclase granulite in the North Daqing Mountains, Central Inner Mongolia
ZHANG Yu-qing, WANG Tao, JIA He-yi, ZHANG Zhi-xiang(Inner Mongolia Institute of Geological Survey, Hohhot 010020, Inner Mongolia, China)
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.