INTEGRATED APPROACHES TO UNDERSTANDING PROCESSES AND EVENT HISTORIES IN HIGH-TEMPERATURE METAMORPHIC TERRANE
Recent work on granulite facies migmatites from Prydz Bay, east Antarctica, has been shedding more light on the local-scale controls of reaction processes involving accessory minerals during the generation and extraction of melts. Detailed textural characterization and integrated REE analysis has suggested that zircon in a number of terranes grew in equilibrium with garnet during partial melting, and not only during late-stage cooling and crystallization of melts. In a test of this hypothesis, simplified thermodynamic models of zircon behavior in melts generated through anatexis of metapelitic granulites have been generated using THERMOCALC. The models show that accessory minerals can theoretically grow during melt extraction and transport if melts pond and begin to react with wall rocks. These results have major implications for the interpretation of zircon ages in high-grade terranes because they suggest that zircon in migmatites need not date terrane-wide cooling below the solidus. Moreover, scatter in age data between and within samples may relate to local-scale differences in growth environment and date real crystallization stages throughout the thermal history of the migmatite.