Abstract

Garnets from an early granulite event that have partially broken down to orthopyroxene-bearing assemblages during a second regional granulite-facies metamorphism were used to test the closure temperature of the Sm-Nd system in garnet. The garnets from Søstrene Island, Prydz Bay, Antarctica, retain a memory of both the physical conditions of their formation and their Sm-Nd age, notwithstanding an effective diameter for diffusion of only 1 mm. Because only minor isotopic resetting of these garnets has taken place during the overprinting granulite event, the closure temperature for the Sm-Nd system in garnet in the present case must be >700–750 ° C. The results show that chronological constraints are essential for the unambiguous interpretation of reaction textures in terms of thermotectonic evolution. The garnet Sm-Nd dating method is particularly well suited for this purpose.

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