Argon behavior in basaltic melts in presence of a mixed H2O-CO2 fluid at upper mantle conditions

The behavior of argon in H2O-CO2 bearing basaltic melts was experimentally investigated in the pressure range 1–5GPa and at temperatures between 1350 and 1600°C. Our experimental data simulate the partitioning of argon between an Ar-H2O-CO2 bearing fluid and a silicate melt occurring during magma ascent and degassing. The experimental results show several features:-At a pressure of 1GPa the variation of H2O from 0.35 to about 2wt.% (at constant CO2 content) does not induce any systematic variation of argon dissolved in basaltic melt. For higher water contents (>2wt.%) we observe a positive effect of water on argon solubility.-In the range of 3–5GPa, we did not observe any systematic variation of the argon content in the basalt melt for water concentration from 0.35 to 5.3wt.% and at CO2 content 0.5wt.%, argon concentration in basalt melt decreases from about 3800 to 2400ppm when the CO2 content increases from 0.5 to 0.8wt.%.-At all pressures investigated in the present study, a negligible effect of CO2 for concentration