Computer Science
Scientific paper
Jul 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982e%26psl..59..420k&link_type=abstract
Earth and Planetary Science Letters, Volume 59, Issue 2, p. 420-428.
Computer Science
32
Scientific paper
The temperature dependence of water diffusivity in rhyolite melts over the range 650-950°C and [PT((H2O] = 700 bars is evaluated from water concentration-distance profiles measured in glass with an ion microprobe. Diffusivities are exponentially dependent on concentration over this temperature range and vary from about 10-8 cm2/s at 650°C to about 10-7 cm2/s at 950°C at 2 wt.% water. Water solubility also varies with temperature at a rate of -0.14 wt. per 100°C increase. The avtivation energy (Ea) appears to be constant at 19 +/- 1 kal/mole for 1, 2,and 3 wt.% H2O. Comparison of these data with results for cation diffusion indicates that this value is a minimum Ea for diffusion of any species in a rhyolite melt.
Compensation plots of log10D0 (the frequency factor) versus Ea indicate that hydrous rhyolite melts follow the same trend as anhydrous basalts. D0 increases for H2O and Ca2+ [1] as Ea decreases. This suggests that these molecules may diffuse by different mechanisms than do monovalent cations, and that hydration of the melt affects diffusion of Ca2+ and H2O differently than it does monovalent cation diffusion. The results imply that dramatic increases in cation diffusivities by hydration [1] may occur with additions of less than 1 wt.% H2O.
Delaney John R.
Holloway John R.
Karsten Jill L.
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