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Moonsup Cho,김현철,이유영,Kenji Horie,Hiroshi Hidaka 한국지질과학협의회 2008 Geosciences Journal Vol.12 No.1
We discovered the oldest rock in South Korea, and dated this migmatite using a Sensitive High-Resolution Ion Microprobe (SHRIMP). Zircon grains from a tonalitic migmatite, Daeijak Island, western Gyeonggi massif, are distinctly zoned and commonly characterized by oscillatory-zoned cores and structureless rims. The U–Pb zircon ages estimated from six spot analyses of the rims in five grains define a concordant age group with the weighted mean 207Pb/206Pb age of 2508 ± 18 Ma, interpreted as the age of migmatization. On the other hand, the cores yield an older 207Pb/206Pb age of ca. 2.58 Ga, interpreted as the crystallization age of tonalitic protolith. These results demonstrate not only the presence of Neoarchean granitoids but also high-grade migmatitic metamorphism at ca. 2.51 Ga in the Gyeonggi massif, which are correlative with those reported from the North China craton. We discovered the oldest rock in South Korea, and dated this migmatite using a Sensitive High-Resolution Ion Microprobe (SHRIMP). Zircon grains from a tonalitic migmatite, Daeijak Island, western Gyeonggi massif, are distinctly zoned and commonly characterized by oscillatory-zoned cores and structureless rims. The U–Pb zircon ages estimated from six spot analyses of the rims in five grains define a concordant age group with the weighted mean 207Pb/206Pb age of 2508 ± 18 Ma, interpreted as the age of migmatization. On the other hand, the cores yield an older 207Pb/206Pb age of ca. 2.58 Ga, interpreted as the crystallization age of tonalitic protolith. These results demonstrate not only the presence of Neoarchean granitoids but also high-grade migmatitic metamorphism at ca. 2.51 Ga in the Gyeonggi massif, which are correlative with those reported from the North China craton.