ISOTOPIC CHRONOLOGY AND GEOCHEMISTRY OF THE HERCYNIAN YONGXIN GRANITOID IN LONGJING, JILIN PROVINCE

The Hercynian Yongxin granitoid in Longjing, Jilin Province, 252.77±0.66 Ma by LA-ICP-MS zircon U-Pb dating, is formed in the Late Permian. Petrochemically, the content of SiO₂ is between 57.60% and 76.50%, averagely 68.50%, with A/CNK(Al₂O₃/CaO+Na₂O+K₂O) less than 1.1, Na₂O greater than 3.2%, and K₂O/Na₂O generally less than 1, indicating the characteristics of typical I-type granite. In the lithological classification diagram, the Yongxin granitoid falls in monzonite, quartz monzonite, granodiorite and granite areas. The trace element normalized spider diagram shows enriched LREE and LILE (Rb, Th and Ba) and depleted HFSE (Nb and Ta). The chondrite-normalized REE distribution patterns present high contents of REE, relatively enriched LREE and losses of HREE. The whole distribution patterns belong to syn-collision granites. Most of the samples are plotted in the syn-collisional and post-collisional granite field in the R1-R2 tectonic discrimination diagram. Regarding to the comprehensive judgment of the tectonic environment, the age of the Hercynian Yongxin granitoid may represent the convergence collision time of the North China Craton and Jiamusi block.