COMAGMAT - A FORTRAN PROGRAM TO MODEL MAGMA DIFFERENTIATION PROCESSES

The purpose of this paper is to present a general model (COMAGMAT) for the calculation of equilibrium temperatures and phase relations at a given extent of crystallization or melting in natural magmatic systems . This model is based on a set of empirical expressions that describe mineral-melt equilibria for major and trace elements in terms of press ure (up to 12 kbar), temperature, and liquid compositions for systems ranging from primitive basalts to dacites. These expressions are in th e form of empirically calibrated mineral-melt geothermometers for Oliv ine, Augite, Pigeonite (Opx), Plagioclase, Ilmenite, and Magnetite use d to develop the algorithm simulating multiply saturated magmatic melt s. The results of the program are in the form of calculated liquid lin es of descent, plus the equilibrium mineral proportions and compositio ns. The phase equilibria calculations form the core of a model that al lows the user to simulate processes ranging from simple isobaric cryst allization to in situ differentiation processes resulted from crystal settling, and polybaric fractionation.