Water solubility in haplobasaltic melts
Water solubility in haplobasaltic melts (in Ninth international symposium on Experimental mineralogy, petrology and geochemistry, Peter Ulmer (convener))
European Journal of Mineralogy (October 2003) 15 (5): 803-814
- anorthite
- basaltic composition
- chain silicates
- clinopyroxene
- density
- diopside
- experimental studies
- feldspar group
- framework silicates
- hydroxyl ion
- infrared spectra
- magmas
- melts
- physical models
- plagioclase
- pyroxene group
- silicate melts
- silicates
- solubility
- spectra
- thermodynamic properties
- titration
- water
The solubility of water in melts of the haplobasaltic system (NaAlSi (sub 3) O (sub 8) -CaAl (sub 2) Si (sub 2) O (sub 8) -CaMgSi (sub 2) O (sub 6) , Ab-An-Di) was investigated at pressures of 50, 200 and 500 MPa and at temperatures between 1200 degrees C and 1420 degrees C using an internally heated gas pressure vessel. Compositions close to the binary joins Ab100-An100 and Ab (sub 50) Di (sub 50) -An (sub 50) Di (sub 50) were studied. The water content of the glasses was analysed using Karl-Fischer-titration and near-infrared (NIR) spectroscopy. Linear molar absorption coefficients for the NIR combination bands of OH groups at 4500 cm (super -1) (epsilon (sub OH) ) and molecular H (sub 2) O at 5200 cm (super -1) (epsilon (sub H2O) ) were determined for Ab (sub 50) An (sub 50) , An (sub 56) Di (sub 44) , and Ab (sub 54) Di (sub 46) compositions. Concentration of OH groups is found to be significantly higher in Ab (sub 50) An (sub 50) glasses than in other glasses quenched at similar rate. This is attributed to the depolymerisation of the network structure enabling the formation of stable Ca-complexes in the glasses. An increase in pressure from 50 to 200 or from 200 to 500 MPa approximately doubles the water solubility in haplobasaltic melts. Depending on compositions 2.0-3.0 wt% water can be dissolved at 50 MPa, 3.7-6.1 wt% at 200 MPa and 7.6-12.4 wt% at 500 MPa. In general, the lowest H (sub 2) O solubility was found in the An (sub 56) Di (sub 44) melt. At 50 MPa, the variation of water solubility with composition appears to be complex but the precision of the data does not allow to extract reliably compositional trends. In general, data at 200 and 500 MPa show a strong decrease in H (sub 2) O solubility with increasing Di content, e.g. from 5.99 wt% (Ab (sub 100) ) to 4.94 wt% (Ab (sub 54) Di (sub 46) ) and from 5.81 wt% (Ab (sub 50) An (sub 50) ) to 5.21 wt% (Ab (sub 27) An (sub 29) Di (sub 44) ) at 1200 degrees C/200 MPa. The effect of Ab/An ratio on water solubility appears to be small at 200 MPa. In contrast, at 500 MPa the water solubility decreases strongly with increasing An content of the melt.
