CHEMICAL CHARACTERISTICS (COMPOSITION, PH , AND EH) OF THE ROCK-WATERSYSTEM - II - DIORITE (ANDESITE)-WATER AND GABBRO (BASALT)-WATER SYSTEMS

Computer simulation of the interaction (at temperatures of 25-800 degr ees C and pressures of 0.001-5 kbar) between water and rocks of interm ediate and basic composition (diorite and gabbro) without Cl, S, and C or with their contents at the background level demonstrates that the water phase in nonvariant equilibria in these systems is alkaline (wit h a minimum in the pH value occurring at similar to 400 degrees C). Th e total salinity of the solutions increases with increasing temperatur e. In systems with carbon, the fluid enriches in CO2 at high temperatu res and possibly separates into immiscible CO2-rich and H2O-rich phase s. in addition to the seven redox buffers described in the system gran itoids-water, a series of potential-controlling buffer reactions is co nsidered in the diorite-water and gabbro-water systems. Unlike the sit uation with acid rocks, these reactions in the latter systems are cont rolled only by the Fe(II)-Fe(III) equilibrium. A characteristic featur e of these reactions, which is important for the Earth crust as a whol e, is that they necessarily involve solid phases without elements of v arying valence (a condition required by mass balance in the systems).