Zircon U-Pb age of Paleoproterozoic granite gneiss from the Ogcheon Belt in the Geumsan area, South Korea

A Paleoproterozoic granite gneiss body was discovered in the Jurassic Daebo granite of the Ogcheon Belt, Geumsan area, South Korea. The granite gneiss is a two-mica variety with a small amount of garnet, and has a peraluminous bulk-rock composition. U-Pb isotope analysis of zircon grain cores by LA-ICP-MS yields a 207Pb/206Pb magma crystallization age of ca. 2.5 Ga. The granite gneiss body is therefore one of the second oldest rocks in South Korea. Zircon grain mantle and rim data yield an upper intercept age of ca. 1.89 Ga and a lower intercept age of 174±74 Ma along the discordia line, which are interpreted to be metamorphic ages related to Paleoproterozoic and Jurassic magmatism, respectively.