The catalysis of mineral reactions by water and restrictions on the presence of aqueous fluid during metamorphism

摘要: The problems of characterizing inter- granular regions and estimating rates intergranular diffusion in metamorphic rocks are discussed. Inter- can be anhydrous, hydrated but under- saturated with H20, or only the latter case a free aqueous fluid phase present. Estimates coefficients (D mR) at 550 ~ derived from variety published experimental work, vary 10 -8 m 2 s -1 for species through an film to ~< 4  10- 24 1 SiO2 O anhydrous grain boundaries quartzite. D mR -13 -zl 1; concentration H20 identity diffusing (generally un- known) may important controlling factors, there exists possibility spectrum values between these two extremes. Using available kinetic data it is shown that could never have been present parts basement terrane Sesia Zone (Western Alps) during uplift eclogite facies, except possibly late cooling history. breakdown sodic pyroxene+ quartz occurred response localized infiltration catalytic fluid, over time interval as short 6-6000 a, under conditions remote equilibrium. H20-present dehydration reaction metapelites Adula nappe (central also duration. These examples consistent model which deep crustal levels dry long periods development equilibrium mineral assemblages microstructures generally occurs relatively transitory fluid-present (caused by de- volatilization and/or infiltration).