College of Earth Sciences, Jilin University, Changchun 130061, China

The zircon LA-ICP-MS U-Pb isotopic dating of sandstones in Buyant Group in Holingola area of Inner Mongolia has been presented. The results from 112 sampling points show that the main peaks of yield ages are 257 Ma, 283 Ma, 313 Ma and some older ages(>1 700 Ma). The zircons with a peak age of 257 Ma indicate that the depositional age of the sedimentary rocks was Early Triassic, which means that Buyant Group should be assigned into Lower Triassic, rather than Lower Proterozoic. The provenance of the sandstones are mainly the volcanic rocks of Dashizhai Formation, the Sunidzuoqi-Xilinhot-southern Xi Ujimqin volcanic arc and the metamorphic basement of the adjacent block, and partly from the northern margin of the North China Plate. It is indicated that the collision between the northern margin of North China Plate and the blocks to the north began in Early Triassic.