EXPERIMENTAL-DETERMINATION OF THE REACTION PARAGONITE=JADEITE+KYANITE+H2O, AND INTERNALLY CONSISTENT THERMODYNAMIC DATA FOR PART OF THE SYSTEM NA2O-AL2O3-SIO2-H2O, WITH APPLICATIONS TO ECLOGITES AND BLUESCHISTS

Hydrothermal reversal experiments have been performed on the upper pressure stability of paragonite in the temperature range 550-740 ° C. The reaction {Mathematical expression} has been bracketed at 550 ° C, 600 ° C, 650 ° C, and 700 ° C, at pressures 24-26 kb, 24-25.5 kb, 24-25 kb, and 23-24.5 kb respectively. The reaction has a shallow negative slope (- 10 bar °C-1) and is of geobarometric significance to the stability of the eclogite assemblage, omphacite+kyanite. The experimental brackets are thermodynamically consistent with the lower pressure reversals of Chatterjee (1970, 1972), and a set of thermodynamic data is presented which satisfies all the reversal brackets for six reactions in the system Na2O-Al2O3-SiO2-H2O. The Modified Redlich Kwong equation for H2O (Holloway, 1977) predicts fugacities which are too high to satisfy the reversals of this study. The P-T stabilities of important eclogite and blueschist assemblages involving omphacite, kyanite, lawsonite, Jadeite, albite, chloritoid, and almandine with paragonite have been calculated using thermodynamic data derived from this study. © 1979 Springer-Verlag.