The oldest (ca. 2.51 Ga) rock in South Korea: U？Pb zircon age of a tonalitic migmatite, Daeijak Island,western Gyeonggi massif

다국어 초록 (Multilingual Abstract)

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.

다국어 초록 (Multilingual Abstract)

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.

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