Computer Science
Scientific paper
Jan 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53...89s&link_type=abstract
Geochimica et Cosmochimica Acta (ISSN 0016-7037), vol. 53, Jan. 1989, p. 89-95. Research supported by the City University of New
Computer Science
3
Chemical Composition, Earth Mantle, Geochemistry, Oxidation, Fayalite, Magnetite, Olivine, Quartz, Saturation, Thermochemistry
Scientific paper
The oxidation state of the earth mantle was investigated in experiments designed for establishing phase equilibrium relations in an Mg-Fe-Si-O-H system, with and without C, at high pressures and temperatures. The computed equilibrium data show that, in a carbon-free system, an olivine of appropriate mantle composition is stable over a wide range of temperature and oxygen fugacities. In a carbon-containing environment, the fluid phase in the peridotite + water system consists mostly of H2O and small amounts of CO2 and CH4. However, if Fe is increased from undersaturation to that of saturation, the CH4 content of the fluid increases from a low of 1 percent to a high of 89 percent. Thus a fluid with as much as 75 percent CH4 could be in equilibrium with olivine without metallic Fe as a coexisting phase. In such case, the oxygen fugacity of the primitive-mantle bulk would be several log units below that of the fayalite-magnetite-quartz (FMQ) buffer, although the top upper-mantle rocks may be as oxidized as the FMQ buffer.
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