Experimental study of magmatic melt oxidation by CO2

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?C3.5). 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).