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First report of zircon SHRIMP U-Pb dating from the Dufek granite in the Sør Rondane Mountains, East Antarctica

We report here the first zircon SHRIMP U-Pb chronological result yielding age of (619±7) Ma (11 spots) for the Dufek granite, the largest one of the Early Paleozoic granitoids in the Sør Rondane Mountains, East Antarctica. The analyzed zircon crystals are euhedral, have zonal patterns and Th/U ratios of 0.22∼1.04, indicating magmatic genesis. The single zircon crystal has the 206Pb/238U age of 664 Ma to 600 Ma with the analyzed spots being from the core parts and mantle-rim part of the zircon grains. The result of 619 Ma analysis shows beyond doubt that the Dufek granite formed during 620 Ma is much older by at least 70 Ma than that of the previously widely believed (500∼550 Ma) obtained by Rb-Sr, Sm-Nd and K-Ar isotopic analyses of the Sør Rondane Mountains Pan-African granitoids. Previous chemical characteristics and isotopic data supported that the Dufek granite has chemical affinity with A-type granites under within-plate setting. The U-Pb age of 620 Ma for magmatic zircons in the Dufek granite therefore may represent the age of earlier melt crystallization that occurred at the Late Neo-Proterozoic during the extensional tectonic setting during/after Gondwanaland formation.