Abstract
We report here the occurrence of trapped fluid phases within upper amphibolite and granulite facies minerals in the gneiss-charnockite progression of the Lützow-Holm Bay (LHB) region in East Antarctica. The dominant fluid species in garnet, feldspars and quartz from charnockites comprises dense carbon dioxide, as confirmed by microthermometric experiments and laser-induced micro Raman analyses. The abundance of carbonic inclusions shows as much as five times increase when passing from gneiss to charnockite, suggesting the external influx of carbon dioxide which lowered the water activity through carbonic metamorphism. From the various phase-types of inclusions present in different minerals and their relative chronology of entrapment, we trace the fluid evolution in the LHB from an early high dense pure carbonic regime through mixed carbonic aqueous to a late aqueous regime. The scarcity of aqueous inclusions in the granulite minerals testifies to low PH2O and high PCO2 conditions for the crystallization of the charnockite assemblage, which is in keeping with the solid phase equilibria observed in these rocks. Similar findings from granulite terrains in other Gondwana crustal segments suggest that CO2 advection in the deep crust has been fundamental to the Earth’s crustal evolution history.
