THE INFLUENCE OF WATER ON THE TEMPERATURE OF AMPHIBOLE STABILITY IN MELTS

Abstract

The influence of water concentration on the crystallization temperature of amphibole in a melt was analyzed theoretically using the model of an ideal melt. A general-type equation has been derived that can explain the presence of the isobaric temperature maximum at the amphibole stability curve by invoking the twofold influence of water on the equilibrium between amphibole and the melt: in accordance with the crystallization reaction, water increases the stability of amphibole, but at the same time it decreases the mole fractions of the other melt components that are taking part in the amphibole crystallization reaction, thereby decreasing the stability of amphibole. The pargasite-water-carbon dioxide system was used as an example to show that the model is a good fit to the experimental data. The data were used to obtain the coefficients in the equations that relate the constants of pargasite-melt and tremolite-melt equilibria to temperature and pressure. © Pleiades Publishing, Ltd. 2009.