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The solubility of H 2 O and CO 2 under predicted magma genesis conditions and some petrological and geophysical implications
Author(s) -
Mysen Bjørn O.
Publication year - 1977
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg015i003p00351
Subject(s) - solubility , silicate , liquidus , depolymerization , polymerization , mineralogy , geology , mantle (geology) , silicate minerals , viscosity , crystallization , thermodynamics , chemistry , analytical chemistry (journal) , geochemistry , phase (matter) , environmental chemistry , polymer , organic chemistry , physics
Available data on the solubility of H 2 O and CO 2 in silicate melts at high pressures and temperatures reveal that (1) the solubility of H 2 O is several times greater than that of CO 2 and (2) the solubility of H 2 O depends strongly on pressure and, compared to that of CO 2 , depends only to a small extent on temperature. It has been suggested that the species in silicate melts can be chosen so that the molar solubility of H 2 O may not depend on the bulk composition of the melt. The solubility of CO 2 , on the other hand, varies significantly with pressure, temperature, and bulk composition of the melt. Solution of volatiles at high pressure affects the structure of the silicate melts. Water depolymerizes the melt, the result being lowered viscosity. The same depolymerization is manifested in the enhanced stability of silicate minerals on the liquidus, which are less polymerized than the minerals precipitating from the same melt composition at the same pressure under volatile‐free conditions. Carbon dioxide, on the other hand, enhances polymerization of the melt, the result being increased viscosity and increased stability of liquidus minerals which are more polymerized than those that would precipitate under volatile‐free conditions. Because of the large difference in the solubilities of CO 2 and H 2 O in silicate melts, partial melting of an (H 2 O + CO 2 )‐bearing mantle results in enrichment of H 2 O in the liquid, whereas the residual mantle becomes, enriched in CO 2 . At P ≲ 20 at the CO 2 may be retained in a vapor phase. At higher pressures, carbonate is likely to be the stable phase. Therefore it would be expected that as the result of partial melting throughout geological history the upper mantle would be heterogeneous with respect to vapor components.