Low Density Carbonic Fluids in the Archean Granulite Facies Terrain of the Jequié Complex, Bahia, Brazil

The 2.7 Ga old high-grade metamorphic rocks of the Jequi Complex of Bahia include charnockites, enderbites, and late pink potassic granites. Mineralogic P-T determinations for the granite terrain yield 4-5 kb/750-850C for the peak of metamorphism. Microthermometry of fluid inclusions in quartz was performed on different rock types. Early$CO_{2}$-rich fluids have densities around 0.85$g/cm^{3}$and may represent synmetamorphic fluids, since the isochores cross the inferred P-T box. Late fluids are of lower density and correspond to the waning phase of metamorphism. The correspondence in the Jequte Complex of the relatively low P-T conditions with the low density$CO_{2}$-rich fluids provides evidence that the trapped fluids are to some degree representative of the granulite facies metamorphism, though they may have been modified by post-metamorphic processes.