Zircon U-Pb Dating of Metamorphic Rock from Guanghua Group in Tonghua Area and Its Geological Significance

Zhou Xiwen; Geng Yuansheng; Zheng Changqing

Abstract：Metamorphic rock series of the Guanghua Group occurs as a block in Archean TTG gneiss in Tonghua area of Jilin Province,whose forming age remains controversial for a long time.Using SHRIMP and LA-ICPMS zircon U-Pb dating techniques,representative rock samples from the Guanghua Group were analyzed,including garnet biotite schist,biotite monzogneiss,garnet hornblende schist and potassium granite intruding into the bottom of the Guanghua Group.The results show that four metamorphic rock samples have similar detrital zircon ages (concordant ages are between 2.6 Ga and 2.5 Ga) though they were collected from different strata.Most detrital zircons from four samples yeild concordant mean ages of 2 529 ± 7 Ma,2 568±4 Ma,2 526±11 Ma and 2 530±6 Ma,respectively,suggesting a derivation from Neoarchean magmatic unit.Some zircons from metamorphic rocks record 3 stages metamorphic age (2 525±10 Ma,1 926±40 Ma and 1 878±16 Ma),indicating that the Guanghua Group experienced both Neoarchean and Paleoproterozoic thermo-tectonic events.Zircons from the potassium granite yield a concordant mean age of 2 154±7 Ma,which is interpreted as intruding time of the ploton.The potassium granite has not suffered any deformation,suggesting a intracontinental rift tectonic setting.