ALTERATION OF THE REDOX STATE OF WATER-CONTAINING BASALTIC MAGMAS IN THE COURSE OF OUTGASSING

Abstract

Geochemical and experimental data indicate that the oxygen fugacity (fox) of basaltic magmas increases markedly as they flow toward the ground surface. In this paper, we present data obtained by numerical modeling of changes in the redox state of basaltic magmas as a result of the liberation of gaseous H2O-H2 as the magmas rise toward the ground surface. The model calculations presented above have several limitations and do not express all characteristics of the redox-state evolution of natural magmas (e.g., they do not take account of the presence of other volatiles, of changes in the composition of the melt, and the like). In addition, there is a need to add or refine data on the mechanism of joint solution of H2 and H2O and of other volatiles in magma melts. But the results indicate that outgassing has a significant effect on the redox conditions of magmas. Outgassing of initially reduced water-containing magmas, which is an effective mechanism for increasing fo2, is probably one of the factors causing oxidation of basalts as they rise to the surface.