Experimental study of magmatic melt oxidation by CO2

Abstract

The process of CO2 flashing through hydrous albite-hedenbergite melt was experimentally examined at a temperature of 1100°C and a pressure of 2 kbar. Carbon dioxide was generated when the melt interacted with calcite, and wollastonite was the predominant synthesized phase. Mafic components were introduced into the hydrous albite melt via the dissolution of natural hedenbergite. Raman spectroscopic data on bubbles of the fluid phase in the quench glass indicate that the CO2/H2O proportions of the bubbles vary. IR spectroscopic data on the glass prove that the water concentration after CO2 flashing decreased from 5.5 to approximately 3 wt %. The comparison of the composition of the recrystallized clinopyroxene in contact with melt (with and without CO2 blowing) indicates that CO2 oxidizes Fe in the melt. The redox effect of CO2 is quantified by the empirical clinopyroxene tool for metering oxygen fugacity (oxometer), which was calibrated based on experimental data. The oxygen fugacity in our experiments with CO2 flashing (estimated by the clinopyroxene oxometer) was NNO + (3.0–3.5). Our estimates with the application of the clinopyroxene oxometer indicate that the maximum oxygen fugacity in the magmatic chambers of Vesuvius and Stromboli volcanoes (which are bubbled with CO2) is also close to NNO + (3.5 ± 0.5).