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Recognition of the Phanerozoic “Young Granite Gneiss” in the central Yeongnam Massif
송용선,이호선,박계헌,Ian C.W. Fitzsimons,Peter A. Cawood 한국지질과학협의회 2015 Geosciences Journal Vol.19 No.1
Up to now, all the high-grade gneisses of the Koreanpeninsula have been regarded as Precambrian basement rocksand presence of the Phanerozoic high-grade metamorphic rockshave remained unknown. However, such granite gneiss is discoveredthrough this study from the central Yeongnam massif nearGimcheon. SHRIMP zircon U-Pb age determinations on the granitegneiss, having well-developed gneissic foliations and migmatitictextures, reveal concordant age of ca. 250 Ma indicating the EarlyTriassic emplacement of this pluton, which is in contradict to theprevious belief that it is a Precambrian product. Even though thegranite gneiss reveals well-developed gneissic foliations and somezircons show rather low Th/U ratios, the metamorphic age hasnot been determined successfully. However, the age of metamorphismcan be constrained as middle Triassic considering theabsence of any evidences of metamorphism from the nearbygranitic plutons having emplacement ages of ca. 225 Ma. EarlyTriassic emplacement and subsequent Middle Triassic metamorphismof the granite gneiss from the Yeongnam massif bear aremarkable resemblance to the case of South China block. Wesuggest the possibility that Early to Middle Triassic metamorphismof the Korean peninsula might be products of the intracontinentalcollisional events not directly related with the EarlyTriassic continental collision event.