HR: 14:25h
AN: P53A-04    [Abstracts]
TI: Formation of methane on Mars by fluid-rock interaction in the crust
AU: * Lyons, J R
EM: jrl@ess.ucla.edu
AF: IGPP University of California, Los Angeles, 595 Charles Young Dr. East, Los Angeles, CA 90095-1567
AU: Manning, C E
EM: manning@ess.ucla.edu
AF: Earth and Space Sciences University of California, Los Angeles, 595 Charles Young Dr. East, Los Angeles, CA 90095-1567
AU: Nimmo, F
EM: fnimmo@es.ucsc.edu
AF: Earth Sciences University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064
AB: Recent spectroscopic detections (Mumma et al. 2003; Krasnopolsky et al. 2004; Formisano et al. 2004) of methane in the atmosphere of Mars are the first observations of an organic compound on that planet. The relatively short photochemical lifetime of methane (about 300 years) argues for a geologically young source. We have recently shown (Lyons et al. 2005) that low-temperature alteration of basaltic crust by carbon-bearing hydrothermal fluid can produce the minimum required methane flux of 10 million moles per year, assuming conservative values for crustal permeability and oxygen fugacity as implied by martian basaltic meteorites. The crustal thermal disturbance due to a single dike 1 x 1 x 10 km intruded during the past 10,000 years is capable of driving the alteration, if all carbon is supplied by magmatic degassing from a dike with only 50 ppm carbon. Serpentinization is another possible abiogenic source of methane on Mars (Oze and Sharma 2005). During serpentinization, oxidation of olivine by water yields hydrogen and magnetite, and reduction of crustal carbon (most likely as carbonate) by hydrogen forms methane. The detection of surface olivine by MGS and Mars Odyssey and the likelihood of subsurface liquid water argue for the potential of serpentinization on present-day Mars. Future isotope measurements of methane should be able to distinguish a basalt alteration source (magmatic carbon) from a serpentinization source (crustal carbon), although the very large range in carbon isotope ratios in SNC carbonates may complicate the interpretation. Different suites of minerals are predicted for basalt alteration and serpentinization. Carbonate-bearing assemblages typical of altered basalt include epidote, actinolite, calcite and quartz. Serpentinization produces serpentine, talc, magnetite, brucite, and silica. Hydrothermal mineral assemblages have not been reported by the Mars Odyssey THEMIS instrument, but thus far only a fraction of the planet has been mapped under conditions optimal for mineral indentification. It is our contention that atmospheric methane strongly suggests ongoing hydrothermal processes on Mars. Formisano, V., et al. (2004), Science 306, 1758-1761. Krasnopolsky, V., J. P. Maillard, T. C. Owen (2004), Icarus 172, 537-547. Lyons, J. R., C. Manning, F. Nimmo (2005), Geophys. Res. Lett. 32,doi:10.10292004GL022161. Mumma, M., et al. (2003), Bull. Am. Astron. Soc. 35, 937. Oze, C. and M. Sharma (2005), Geophys. Res. Lett. 32, doi:10.1029/2005GL022691.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 3616 Hydrothermal systems (0450, 1034, 3017, 4832, 8135, 8424)
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: Fall Meeting 2005