GRANITIZATION OF AMPHIBOLITES: 2. CHARACTERIZATION OF PHYSICAL AND CHEMICAL PHENOMENA RELATED TO FLUID FILTRATION THROUGH A ROCK

Abstract

The filtration of alkali- and silica-bearing solution through amphibolites of various mineral composition and structure was studied at a temperature of 750°C and a total pressure of 5 kbar. The laboratory experiments simulated the process of granitization. The flow rate of solution through samples and their permeability were estimated. It was shown that fluid filtration through samples was accompanied by input of alkalis and silica and removal of CaO, MgO, and FeO. The structure and mineral composition of amphibolites experienced the following major changes during solution filtration (stage of feldspathization an debasification): biotite acquired a preferential orientation, the Fe/(Fe + Mg) values of mafic minerals changed, the anorthite mole fraction of plagioclase decreased from labradorite to andesine, the marginal zones of ilmenite crystals were enriched in titanium, and magnetite crystallized. The melting of debasified margins of amphibolite samples produced near-eutectic liquids of granite or trondhjemite types. It was argued that the regional development of granitization is possible mainly in tectonically active and permeable zones.