Primary cordierite with> 2.5 wt% CO2 from the UHT Bakhuis Granulite Belt, Surinam: CO2 fluid phase saturation during ultrahigh-temperature metamorphism

摘要: The Paleoproterozoic Bakhuis Granulite Belt (BGB) in Surinam, South America, shows ultrahigh-temperature metamorphism (UHTM) at temperatures of around 1000 °C which, unusually, produced peak-to-near-peak cordierite with sillimanite and, in some cases, Al-rich orthopyroxene on a regional scale. Mg-rich cordierite (Mg/(Mg + Fe) = 0.88) in a sillimanite-bearing metapelitic granulite has a maximum birefringence of second-order blue (ca. 0.020) indicative of a considerable amount of CO2 (> 2 wt%) within its structural channels. SIMS microanalysis confirms the presence of 2.57 ± 0.19 wt% CO2, the highest CO2 concentration found in natural cordierite. This high CO2 content has enabled the stability of cordierite to extend into UHT conditions at high pressures and very low to negligible H2O activity. Based on a modified calibration of the H2O–CO2 incorporation model of Harley et al. (J Metamorph Geol …