Hydrogen and the melting of silicates: the system SiO/sub 2/-H/sub 2/O-H/sub 2/

Conference · Mon Dec 31 23:00:00 EST 1984 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6460101

Luth, R; Boettcher, A

The authors previously demonstrated the important role of hydrogen on melting in the system CaMgSi/sub 2/O/sub 6/-H/sub 2/O-H/sub 2/ and NaAlSi/sub 3/O/sub 8/-H/sub 2/O-H/sub 2/. To augment this, they determined the vapor-saturated solidi in the system SiO/sub 2/-H/sub 2/O-H/sub 2/ as a function of P, T, and activity of H/sub 2/ in vapors (aH/sub 2//sup v/) buffered by HM-H/sub 2/O, IW-H/sub 2/O, and pure H/sub 2/O. Increasing the aH/sub 2//sup v/ increases melting temperatures relative to those in SiO/sub 2/-H/sub 2/O (see below), but the change is far greater than calculated for ideal lowering of aH/sub 2//sup b/O by the H/sub 2/. For example, changing the value of aH/sub 2//sup v/ (calculated) from approx.10..gamma../sup 7/(pure H/sub 2/O) to approx.10/sup -5/ (HM) increases the solidus 60/sup 0/C at 5 kbar. This effect and the abrupt changes in slope of the IW solidus suggest that pressure-induced structural changes occur in the hydrogen-bearing liquids, which affects the solubility of H/sub 2/ and H/sub 2/O. Comparison of melting in SiO/sub 2/-H/sub 2/O-H/sub 2/ with that in SiO/sub 2/-H/sub 2/O-CO/sub 2/ demonstrates that large proportions of H/sub 2/ increase solidus temperatures of the hydrous liquids less than isomolar proportions of CO/sub 2/, suggesting that H/sub 2/ is more soluble than is CO/sub 2/ or that the activity coefficient for H/sub 2/ in the vapor is larger than that for CO/sub 2/. Additional evidence for the greater solubility of H/sub 2/ is that 40 mole% in the vapor shifts the critical end-point from approx. 10 kbar for SiO/sub 2/-H/sub 2/O to a critical point at approx.29 kbar, whereas 5% CO/sub 2/ shifts the point to approx.30 kbar because of the relatively diminished solubility of SiO/sub 2/ in the vapor and the relatively low solubility of CO/sub 2/ in the liquid. Hydrogen interacts strongly with silicate liquids and must be considered in all petrologic situations.

• Research Organization: Univ. of California, Los Angeles (USA)
• OSTI ID: 6460101
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
ACTIVATION ENERGY
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL ACTIVATION
CHEMICAL REACTION KINETICS
CHEMISTRY
ELEMENTS
ENERGY
GEOCHEMISTRY
GEOLOGY
GEOTHERMAL SYSTEMS
HYDROGEN
HYDROGEN COMPOUNDS
KINETICS
MAGMA SYSTEMS
MAGMATISM
MINERALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PETROLOGY
PRESSURE EFFECTS
REACTION KINETICS
SILICATE MINERALS
SOLUBILITY
TEMPERATURE EFFECTS
WATER