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Abstract
The solubility and solubility
mechanisms of H2O have been determined for melts in
the system K2O-SiO2-H2O
from 0.8 to 2.0 GPa in the 700-1100°C temperature range.
Solubility and solubility mechanisms of the silicate in coexisting
aqueous fluids were also determined. Solubility mechanisms of
water and silicate in coexisting melts and aqueous fluids were
determined by in-situ, high-temperature/high-pressure Raman spectroscopy.
Solubility of silicate and H2O was determined chemographically.
The water solubility in the
melts displays a weak negative correlation with K/Si, whereas
the silicate solubility in the coexisting fluid is a strong positive
function of K/Si so that for the most potassic composition studied,
K2Si2O5 , nearly complete miscibility between
hydrous melt and silicate-saturated aqueous fluids were observed
at 2.0 GPa. The H2O solubility shows a small linear
and negative correlation with temperature. The silicate solubility
in aqueous fluid increases with increasing temperature. Both
solubilities are strong non-linear and positive functions of
pressure. The temperature-dependence becomes more pronounced
with increasing pressure and with increasing K/Si.
From high-pressure/high-temperature
in-situ Raman spectroscopy the silicate speciation in both melts
and coexisting aqueous fluids resemble one another with Q3 and
Q2 species associated with adjacent K+ in the structure, and
with H2O bonded as K-OH and HH2SiO4
type complexes.
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