Magmatic CO2 plays an important role in connection with volcanic degassing and for the transport of carbon from the mantle to the crust. CO2 contents in silicate melts depend on pressure, temperature, oxygen fugacity and composition. Previous investigations have focused on the effects of P, T and f(O2). In our experiments, we have investigated CO2-solubility as function of melt composition.
We have synthesized five different starting materials: Basanite, Ca-rich leucitite and three intermediate compositions. Initial CO2 contents were between 7.3 and 8.7 weight percents. To assure oxidizing conditions during runs, we adjusted the Fe2O3/FeO ratios to an oxygen fugacity of 1.0 log unit above the Ni-NiO buffer.
All experiments were carried out in non-end loaded piston- cylinder apparatuses and conducted at 1.5 GPa and at temperatures of 1500C and 1400C, respectively. For the 1500C runs, we used Fe-doped platinum capsules, for the 1400C runs Pd-Au capsules. Depending on temperature, the runs lasted between 40 min. and 150 min.
CO2 contents in the run products were analysed by Secondary Ion Mass Spectroscopy. At 1500C (and 1.5GPa) CO2 solubilities range from 0.6 weight% in basanite over 1.2 wt% for the basanite50-leucitite50 composition to 3.2wt% in leucitite. At 1400C, basanite dissolves 1.9 wt% CO2, basanite50-leucitite50 2.8 wt% and leucitite 5.2 wt%. The analytical error is ± 5 % relative. We have determined 12 new solubility-composition points. Our results suggest that CO2-solubilty in silicate melts increases with increasing Ca2+ concentrations.