• The Journal of the Petrological Society of Korea
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• v.16 no.3
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• pp.180-188
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• 2007

We carried on CHIME zircon age dating for the Gamaksan alkaline meta-granitoid (GAM) from the northwestern margin of the Gyeonggi massif, and obtained a timing of regional metamorphism at $247{\pm}14Ma$ (n=103, MSWD=0.92). The age is compatible with Permo-Triassic regional metamorphic ages from the Imjingang Belt which has been regarded as possible eastward extension of Triassic collisional belt in China. Considering an extensional ductile shearing of the Gyeonggi (Kyonggi) Shear Zone which deformed GAM occurred at 226 Ma with temperature condition about $500^{\circ}C$ (Kim et al., 2000), and the Late Triassic to Early Jurassic Daedong Group unconformably overlies on top of the ductile shear zone, cooling rate of GAM over the period can be estimated as $18{\sim}10^{\circ}C/Ma$. Since new zircon begin to pow at temperature higher than upper-amphibolite facies condition (${\sim}700^{\circ}C$), cooling rate of GAM from peak metamorphism (247 Ma) to deposition of the Daedong G.oup (${\sim}$Early Jurassic) would be higher than $10^{\circ}C/Ma$. Such rapid cooling rate is compatible with that reported from exhumation stage of the Dabie-Sulu Belt, and supports an idea that the Gyeonngi massif is a part of Permo-Triassic orogenic belt in East Asia.