The effect of anhydrous composition on water solubility in granitic melts
-
Harald Behrens
and
Nicole Jantos
Abstract
The effect of anhydrous composition on the solubility of water in granitic melts was investigated experimentally at 800 °C and pressures from 50 to 500 MPa. Starting materials were ten natural obsidians from various localities worldwide and one re-melted leucogranite from the Himalayas.
Most of the experiments were performed in externally heated pressure vessels using Ni-NiO to buffer fO₂. All samples were quenched isobarically after reaction for 120-336 h. Water contents of the resulting glasses were determined by Karl-Fischer titration.
The solubility data indicate that Na/K ratio and normative Qz content have only a minor effect on water solubility, whereas the (MCLNK-A)/O parameter, defined as 100·(2Mg + 2Ca + Li + Na + K- Al)/total oxygen, has a major effect. A parabolic law expressed as the mole fraction of H2O in the melt on a one-oxygen mole basis is proposed to describe the compositional dependence of water solubility in the range 50-200 MPa:
XH₂O = XH₂O0 · (1 + 0.05 ·{[(MCLNK-A)/O] - 0.5}2)
Minimum mole fractions of water in the melt (XH₂O0) are 0.0521 at 50 MPa, 0.0757 at 100 MPa, and 0.1069 at 200 MPa. The equation fits water solubility data for granitic and phonolitic melts at 100 MPa and 200 MPa to within ±4% relative. The effects of anhydrous composition on water solubility are much more pronounced at 500 MPa than at lower pressures. Thus, the following expression was derived to represent the effects of anhydrous melt composition on water solubility at 500 MPa:
XH₂O = 0.1681·(1 + 0.13·{[(MCLNK-A)/O] - 0.5}2).
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Self diffusion of Si and O in dacitic liquid at high pressures
- The effect of anhydrous composition on water solubility in granitic melts
- Stability and phase relations of Ca[ZnSi3]O8, a new phase with feldspar structure in the system CaO-ZnO-SiO2
- Magmatic Na-rich phlogopite in a suite of gabbroic crustal xenoliths from Volcán San Pedro, Chilean Andes: Evidence for a solvus relation between phlogopite and aspidolite
- The influence of T, aSiO₂, and fO₂ on exsolution textures in Fe-Mg olivine: An example from augite syenites of the Ilimaussaq Intrusion, South Greenland
- An experimental study of the external reduction of olivine single crystals
- Determination of site population in olivine: Warnings on X-ray data treatment and refinement
- Structural properties of ferromagnesian cordierites
- A calorimetric study of zoisite and clinozoisite solid solutions
- Mineralogy of lead in a soil developed on a Pb-mineralized sandstone (Largentière, France)
- Experimental mixtures of smectite and rectorite: Re-investigation of “fundamental particles” and “interparticle diffraction”
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- Hydrothermal reactivity of Lu-saturated smectites: Part II. A short-range order study
- Pulsed field gradient proton NMR study of the self-diffusion of H2O in montmorillonite gel: Effects of temperature and water fraction
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- Reply to Comment on “Molecular dynamics simulation of phase transitions and melting in MgSiO3 with the perovskite structure”
