Metasomatic interaction between rock and solution under varying pressure-temperature conditions

Abstract

Variations in the activity of major components in a rock and solution initially equilibrated with the activity were evaluated under thermal and pressure gradient conditions by the example of the system granite-chloride solution. These variations are controlled by the shifts of mineral hydrolysis reactions in the rock and dissociation equilibria of salts, acids, and bases in the solution. The resulting relationships between \(a_{Me^ + } /a_{H^ + }^{sol} \) and \(a_{Me^ + } /a_{H^ + }^{rock} \) control the direction of infiltration metasomatism. There is a high-temperature region, where the behavior of Mg and Fe is very different from that of Na and K and the behavior of Ca is transitional, and a low-temperature region, where these components are similar to each other. The processes of acidic and alkalic metasomatism may be accompanied in various combinations by the processes of basification and debasification, as well as rock silicification and desilication. The type of these combinations is controlled by the character of the gradient field, involving either a decrease or an increase in temperature and pressure, and can be correlated with a particular metasomatic association.