Speciation of reduced C-O-H volatiles in coexisting fluids and silicate melts determined in-situ to ∼1.4GPa and 800°C

Bjorn O. Mysen, Shigeru Yamashita

Research output: Contribution to journalArticle

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Abstract

The structure of silicate melts in the system Na2O·4SiO2 saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800°C) and pressure (up to 1435MPa). Redox conditions in the HDAC were controlled with the reaction, Mo+H2O=MoO2+H2, which is slightly more reducing than the Fe+H2O=FeO+H2 buffer at 800°C and less.The dominant species in the fluid are CH4+H2O together with minor amounts of molecular H2 and an undersaturated hydrocarbon species. In coexisting melt, CH3 - groups linked to the silicate melt structure via Si-O-CH3 bonding may dominate and possibly coexists with molecular CH4. The abundance ratio of CH3 - groups in melts relative to CH4 in fluids increases from 0.01 to 0.07 between 500 and 800°C. Carbon-bearing species in melts were not detected at temperatures and pressures below 400°C and 730MPa, respectively. A schematic solution mechanism is, Si-O-Si+CH4Si-O-CH3+H-O-Si. This mechanism causes depolymerization of silicate melts. Solution of reduced (C-O-H) components will, therefore, affect melt properties in a manner resembling dissolved H2O.

Original languageEnglish
Pages (from-to)4577-4588
Number of pages12
JournalGeochimica et Cosmochimica Acta
Volume74
Issue number15
DOIs
Publication statusPublished - Aug 2010

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Silicates
silicate melt
melt
Diamond
Fluids
fluid
diamond anvil cell
Bearings (structural)
Depolymerization
Schematic diagrams
Hydrocarbons
redox conditions
Buffers
FTIR spectroscopy
Carbon
Spectroscopy
Temperature
silicate
probe
in situ

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Speciation of reduced C-O-H volatiles in coexisting fluids and silicate melts determined in-situ to ∼1.4GPa and 800°C. / Mysen, Bjorn O.; Yamashita, Shigeru.

In: Geochimica et Cosmochimica Acta, Vol. 74, No. 15, 08.2010, p. 4577-4588.

Research output: Contribution to journalArticle

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AB - The structure of silicate melts in the system Na2O·4SiO2 saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800°C) and pressure (up to 1435MPa). Redox conditions in the HDAC were controlled with the reaction, Mo+H2O=MoO2+H2, which is slightly more reducing than the Fe+H2O=FeO+H2 buffer at 800°C and less.The dominant species in the fluid are CH4+H2O together with minor amounts of molecular H2 and an undersaturated hydrocarbon species. In coexisting melt, CH3 - groups linked to the silicate melt structure via Si-O-CH3 bonding may dominate and possibly coexists with molecular CH4. The abundance ratio of CH3 - groups in melts relative to CH4 in fluids increases from 0.01 to 0.07 between 500 and 800°C. Carbon-bearing species in melts were not detected at temperatures and pressures below 400°C and 730MPa, respectively. A schematic solution mechanism is, Si-O-Si+CH4Si-O-CH3+H-O-Si. This mechanism causes depolymerization of silicate melts. Solution of reduced (C-O-H) components will, therefore, affect melt properties in a manner resembling dissolved H2O.

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