HR: 0800h
AN: B31B-0985    [Abstracts]
TI: Possible Evidences for Abiogenic Hydrocarbons in Hydrothermal Fluids of Everman Volcano, Socorro Island, Mexico
AU: * Taran, Y
EM: taran@geofisica.unam.mx
AF: UNAM, Ciudad Universitaria, Mexico, D.F 04510 Mexico
AB: Geochemists believe that the Fischer-Tropsch reaction may be responsible for the abiogenic production of hydrocarbons (HC) in nature. Among environments where this is possible, terrestrial and submarine hydrothermal systems are main candidates. Among geochemical criteria for a natural FT process there are two most popular: Shultz-Flory distribution of alkanes and the decrease of δ¹³C of alkanes with increasing carbon number: the heavier alkanes should be isotopically ligher. The application of the first criterion is often wrong, because for the FT synthesis it makes sense only for n>4. The light HC products of a real FT synthesis have a maximum at C3-C4. The second rule is also not absolute, because after a heating of organic matter at >700°C the set of light alkanes formed as the result of such high-temperature thermo-degradation shows the same inverse, ``synthetic'', δ¹³C distribution. In the fumarolic steam of Everman volcano at Socorro island both criteria were fulfilled. Vapors from Socorro have 96° C, very high hydrogen and methane concentrations and a local minimum at ethane in the HC concentration distribution. Methane of Socorro is isotopically heavy (-9 > δ¹³C1 > -15 ‰ PDB) and δ¹³C2 > δ¹³C3 > δ¹³C4 (-21, -24, -25 permil, respectively). The source of high H₂ and CH₄ in Socorro gases is thought to be the serpentinization of Mg-rich gabbroid intrusive bodies inside and beneath the volcano edifice by infiltrated seawater in presence of magmatic CO₂. The methane can be a mixture of isotopically heavier abiogenic CH₄ and isotopically lighter thermogenic CH₄. In that case, the inverse isotopic distribution could be an artifact, if most of C2+ are of thermogenic origin.
DE: 1055 Organic and biogenic geochemistry
DE: 4811 Chemosynthesis
DE: 5215 Origin of life
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Biogeosciences [B]
MN: Fall Meeting 2005