HR: 14:55h
AN: V23D-06    [Abstracts]
TI: Oxygen Fugacity Variation in Martian Meteorites: Carbon Buffering in the Martian Mantle?
AU: * Righter, K
EM: kevin.righter-1@nasa.gov
AF: NASA Johnson Space Center, Mailcode KT, 2101 NASA Pkwy, Houston, TX 77058, United States
AB: Calculations of fO₂ in the martian meteorites result in a 5 log fO₂ unit range in values relative to the FMQ buffer. If graphite is present in a planetary mantle, the effect of pressure on C-CO-CO₂-CH₄ equilibria is such that relative oxygen fugacity would increase with pressure. Given the range of fO₂ estimates for martian meteorites, it is worthwhile considering whether this could be achieved by polybaric C-CO- CO₂-CH₄ equilibria in the martian mantle. Only 40-80 ppm C is required to keep peridotite mantle buffered at the C-O surface. Indeed, studies of martian meteorites have shown that Mars is a volatile-rich planet, and C may be an important constituent of the volatile budget. If C buffering at variable pressure is controlling oxygen fugacity in the martian mantle, it would require formation of ALH 84001 at lowest pressures, shergottites at intermediate pressures, and nakhlite and Chassigny parent melt formation at highest pressures, all of which is consistent with knowledge of these meteorites. Carbon buffering is thus a simpler explanation for oxygen fugacity variations in the martian mantle and crust, than by hydrous reservoirs or by crustal assimilation. Furthermore, a small activity of CH₄ would be associated with a C-CO-CO₂2-CH₄ gas in the martian mantle, and volcanic degassing of this species could account for the small amount of methane detected recently at the surface of Mars.
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1036 Magma chamber processes (3618)
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 3630 Experimental mineralogy and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting