Oxidation state of the mantle

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90275-5· OSTI ID:7243018

Saxena, S K ^[1]

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1. Brooklyn College, NY (USA) Graduate Center, New York, NY (USA)

Phase equilibrium relations are established in a system Mg-Fe-Si-H-O, with and without C, at high pressures and temperatures. High pressure-temperature equations of state for the fluids including non-ideal mixing are used in the calculations. The computed equilibrium data show that an olivine of appropriate mantle composition is stable over a wide range of temperature and oxygen fugacities in the carbon-free system. If C is introduced, such that the equilibrium assemblage may contain graphite or diamond, the fluid phase in the peridotite + water system consists mostly of H{sub 2}O and little CO{sub 2} and CH{sub 4}. However, the fluid composition is strongly affected by the Fe content of the system. If Fe is increased from undersaturation to that of saturation the CH{sub 4} content of the fluid changes from a low of 1% to a high of 89%. The calculated results show a fluid with as much as 75% methane could be in equilibrium with olivine without metallic Fe as a coexisting phase. The fO{sub 2} of the primitive mantle with such a fluid composition would be several log units below that of the quartz-fayalite-magnetite buffer.

• OSTI ID: 7243018
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 53:1; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
EARTH MANTLE
ELEMENTS
EQUILIBRIUM
GEOCHEMISTRY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
MAGMA
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MAGNESIUM SILICATES
MATHEMATICAL MODELS
MINERALS
NONMETALS
NUCLEAR MODELS
OLIVINE
OXIDE MINERALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PERIDOTITES
PHASE STUDIES
PLUTONIC ROCKS
PRESSURE EFFECTS
PYROXENES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SPINELS
TEMPERATURE EFFECTS
THERMODYNAMIC ACTIVITY
TRANSITION ELEMENT COMPOUNDS
VALENCE
VALENCY MODEL