The behavior of argon in H2O-CO2 bearing basaltic melts was experimentally investigated in the pressure range 1–5 GPa 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 1 GPa the variation of H2O from 0.35 to about 2 wt.% (at constant CO2 content) does not induce any systematic variation of argon dissolved in basaltic melt. For higher water contents (> 2 wt.%) we observe a positive effect of water on argon solubility.- In the range of 3–5 GPa, we did not observe any systematic variation of the argon content in the basalt melt for water concentration from 0.35 to 5.3 wt.% and at CO2 content < 0.5 wt.%. For CO2 content > 0.5 wt.%, argon concentration in basalt melt decreases from about 3800 to 2400 ppm when the CO2 content increases from 0.5 to 0.8 wt.%.- At all pressures investigated in the present study, a negligible effect of CO2 for concentration < 5000 ppm on argon content in the silicate melt is observed.- More importantly (despite all these variations) it seems that the effect of pressure in the range of 1 to 5 GPa is the dominant parameter on argon solubility in basaltic melt. Pressure has a positive effect on argon incorporation in the H2O-CO2 bearing basaltic melt reaching at 3 GPa a concentration of ~ 0.38 wt.%. This maximum of ~ 0.38 wt.% corresponds to 6.8 × 10− 5 cm3 g− 1 bar− 1 at standard temperature and pressure, a value of the same order of magnitude as that derived from volatiles free basaltic melts equilibrated with argon. The experimental data can be well described by a thermodynamic model assuming mixing of volatile species and oxygen in the silicate melt. The results can be applied for a better understanding of the fractionation noble gas/noble gas and noble gas/CO2 occurring in degassing processes during magma ascent.
Fabbrizio, A., Bouhifd, M., Andrault, D., Bolfan-Casanova, N., Manthilake, G., Laporte, D. (2017). Argon behavior in basaltic melts in presence of a mixed H2O-CO2 fluid at upper mantle conditions. CHEMICAL GEOLOGY, 448, 100-109 [10.1016/j.chemgeo.2016.11.014].
Argon behavior in basaltic melts in presence of a mixed H2O-CO2 fluid at upper mantle conditions
Fabbrizio, A
Primo
;
2017
Abstract
The behavior of argon in H2O-CO2 bearing basaltic melts was experimentally investigated in the pressure range 1–5 GPa 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 1 GPa the variation of H2O from 0.35 to about 2 wt.% (at constant CO2 content) does not induce any systematic variation of argon dissolved in basaltic melt. For higher water contents (> 2 wt.%) we observe a positive effect of water on argon solubility.- In the range of 3–5 GPa, we did not observe any systematic variation of the argon content in the basalt melt for water concentration from 0.35 to 5.3 wt.% and at CO2 content < 0.5 wt.%. For CO2 content > 0.5 wt.%, argon concentration in basalt melt decreases from about 3800 to 2400 ppm when the CO2 content increases from 0.5 to 0.8 wt.%.- At all pressures investigated in the present study, a negligible effect of CO2 for concentration < 5000 ppm on argon content in the silicate melt is observed.- More importantly (despite all these variations) it seems that the effect of pressure in the range of 1 to 5 GPa is the dominant parameter on argon solubility in basaltic melt. Pressure has a positive effect on argon incorporation in the H2O-CO2 bearing basaltic melt reaching at 3 GPa a concentration of ~ 0.38 wt.%. This maximum of ~ 0.38 wt.% corresponds to 6.8 × 10− 5 cm3 g− 1 bar− 1 at standard temperature and pressure, a value of the same order of magnitude as that derived from volatiles free basaltic melts equilibrated with argon. The experimental data can be well described by a thermodynamic model assuming mixing of volatile species and oxygen in the silicate melt. The results can be applied for a better understanding of the fractionation noble gas/noble gas and noble gas/CO2 occurring in degassing processes during magma ascent.
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