Chemical interaction of aqueous solutions with epidote-feldspar mineral assemblages in geologic systems. II. Equilibrium constraints in metamorphic/geothermal processes.

Abstract

Constraints imposed by equilibrium among epidote, garnet, and feldspar solid solutions in geological systems are characterized on the basis of calculation of the thermodynamic properties of aqueous, mineral, and gas phases at high P and T (M.A.81-2677). The calculations involved identification of phase relations among aqueous solutions and minerals in the system CaO-FeO-Fe2O3-Al2O3-SiO2-H2O-HCl-CO2 at P and T to 5 kbar and 600oC with the aid of P - T, temperature - composition, and logarithmic activity and fugacity diagrams which include provision for both solid solution and substitutional order/disorder in minerals. Compositions and compatabilities of coexisting minerals in the system reflect complicated functions of P, T, and fluid composition.M.S.