Mass transfer and replacement of minerals in the course of infiltration metasomatism

Abstract

The direction of Na, K, Ca, Mg, and Fe transfer was determined in the granite-chloride solution system during the metasomatic replacement of granite in response to a temperature and pressure change. The analysis of modeled metasomatic zoning (metasomatic columns) indicates that metasomatic processes of alkaline/acidic and basification/debasification types are controlled by differences in the chemical potentials of components in the solution and rock and by the addition/removal of material due to its excess/deficit in the solution. The former are manifested in the mineralogy of the rear zones of metasomatic columns, while the latter control the total variations in the contents of components in all zones. One of the consequences of this difference is the occurrence of extrema in the distribution of components in zones. Information on the chemical composition of rocks in any given zone does not provide a clue to either the character of the metasomatic processes or the proportions of component concentrations in the solution. In contrast to isobaric-isothermal columns, their thermogradient analogues are characterized by the continuous replacement of minerals and mass transfer in all zones. This predetermines the possibility of the identification of the gradient character of certain columns.