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

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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 1 2010

ASJC Scopus subject areas

  • Geochemistry and Petrology

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