LA-ICP-MS zircon U-Pb ages and geologi-cal features of Daolundaba granite in Xilinhaote area, Inner Mongolia

The granite in the Daolundaba Cu polymetallic ore district was studied with ICP-MS zircon U-Pb isotope dating and geochemical method. A late Hercynian emplacement age of 289.6±0.7Ma was obtained, and the geochemical characteristics suggest a strongly peraluminous granite which has the affinity with the Xilinhaote rock group gneiss. The magmatic activity represents the litho-spheric extension after the peak of the collision event. During the process the lithosphere began delamination and was followed by the asthenosphere upwelling or basaltic magma underplating which led to the rapid increase of the temperature of the graywacke and bio-tite plagioclase gneiss in lower crust (> 875℃), which caused the formation of strongly peraluminous magma through partial melting. At the same time, the granite always had the geochemical features of volcanic arc and the granite had a relationship with the lag of magmatic activity, which means the composition of the subducting plate was involved in the formation of magma. Combined with the chronologic and geochemical features of Hercynian rocks and the marine strata in the nearby area, it is thought that the ocean crust in the area began to subduct during the late stage of Early Carboniferous and experienced collision during the Early Permian.