Geology of the Proterozoic basement rocks and Permo-Triassic allochthons in the Geonggi massif, Korean Peninsula

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The Gyeonggi massif in the Korean Peninsula comprises granulite-and amphibolite-facies units that are separated by an extensive mylonite zone. Granulites distant from the mylonite zone yield CHIME ages of c. 1860Ma. Granulites near the mylonite zone show growth of cordierite and biotite aggregates around garnet grains after the ductile shearing, and yield 247-240Ma monazite domains on and within c. 1860 Ma monazite grains. The paragneisses in the amphibolite-facies unit contain Neoproterozoic detrital zircon grains and monazite grains with unequivocal metamorphic ages of 251-243Ma. Two crustal units underwent differing evolutional histories prior to amalgamation. The Permo-Triassic amphibolite-facies unit detached from the Yangtzu block and was thrust over the granulite-facies unit of the North China block during the Sulu orogeny. Permo-Triassic metamorphic overprints on the latter are attributed to contact metamorphism from the hot allochthon.