1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. Geological Survey Institute of Jilin Province, Changchun 130061, China

Zircon LA-ICP-MS U-Pb geochronology and geochemical analyses are undertaken for the garnet-bearing muscovite monzogranite in Yitong area, central Jilin Province. The formation age and petrogenesis of the granite are determined, and the regional tectonic background is discussed. Zircons from the granite are euhedral-subhedral in shape, and display fine-scale oscillatory growth zoning, indicating a magmatic origin. LA-ICP-MS zircon U-Pb dating result indicates that the garnet-bearing muscovite monzogranites formed in the middle Triassic (243 Ma). The garnet-bearing muscovite monzogranites have high SiO₂ (SiO₂=74.1%-76.49%), rich aluminum (Al₂O₃=14.47%-14.68%) and alkali (Na₂O+K₂O=4.31%-7.9%), low Fe₂O₃T and MgO (MgO=0.1%-0.13%, Fe₂O₃T=0.46%-1.02%). The ratio of CaO/Na₂O is between 0.17-0.21. The garnet-bearing muscovite monzogranites in Yitong region are relatively enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and depleted of heavy rare earth elements (HREEs) and high field strength elements (HFSEs). They are characterized by high Sr and Ba, poor Rb and Y, and negative Eu abnormally (δEu=0.48-0.62), with Rb/Sr<1. The ε_Hf(t) values and T_DM2 of zircons range from +6.10 to +8.00 and from 725 Ma to 814 Ma, respectively. The above features indicate that garnet-bearing muscovite monzogranites in Yitong area were derived from partial melting of metasedimentary rock. These granites have high Sr/Y ratios, which suggest they formed in a thickened continental crust. Combined with the coeval granitic rocks in central Jilin Province, we suggested that a significant collisional and thickening event took place during the Middle Triassic.