High-pressure, halogen-bearing melt preserved in ultrahigh-temperature felsic granulites of the Central Maine Terrane, Connecticut (U.S.A.)

Abstract Inclusions of relic high-pressure melts provide crucial information on the fate crustal rocks in deep roots orogens during collision and thickening, including at extreme temperature conditions exceeding 1000 °C. However, discoveries melt inclusions are still a relative rarity among case studies metamorphic minerals. Here we present results experimental microchemical investigations nanogranitoids garnets from felsic granulites Central Maine Terrane (Connecticut, U.S.A.). Their successful re-homogenization ~2 GPa confirms that they originally were trapped portions makes them first direct evidence high pressure peak metamorphism melting for these granulites. The has hydrous, granitic, peraluminous character typical metapelites. This is higher mafic components (FeO MgO) than most investigated previously, likely result temperatures—well above natural positive correlation between melt; trend previously supported only by evidence. Moreover, it poses severe caveat against common assumption partial metasediments depth always leucogranitic composition. NanoSIMS measurement re-homogenized show significant amounts CO2, Cl, F. Halogen abundance considered to be proxy presence brines (strongly saline fluids) depth. Brines known shift temperatures system toward values may have been responsible delaying production via biotite dehydration until reached more °C, rather 800–850 °C as commonly observed reactions.