Redox and temperature conditions governing chemical and isotopic equilibration of CO2 and CH4 in volcanic-hydrothermal environments
Final Report Abstract
We analyzed the chemical and isotopic composition of hydrothermal gases emanating from Mediterranean volcanic systems to investigate the genetic relationship between the discharged carbon-bearing species CO2 and CH4. Our data gave unambiguous evidence that CO2 is abiogenically reduced to CH4 under bi-phase hydrothermal conditions. The reductive power seems to derive from ferrous iron. For the reduction itself, no special redox conditions are required. Rather, the presence of saturated water vapor seems to be important. The observation that natural occurrences of methane can be generated abiogenically from CO2 in the presence bi-phase hydrothermal conditions and ferrous iron has important implications for a broad number of disciplines in the Earth and Planetary sciences. First, under the volcanic-hydrothermal conditions met in the early Archean, abiogenic methane fluxes might have been as high as SOMt/yr. This would have been sufficient to enable the origin of life via HCN synthesis. Second, the occurrence of methane in the atmosphere of extraterrestrial planets cannot be used as a bioindicator unless abiogenic fluxes can be determined. Third, the isotopic geothermometer CH4-CO2 seems to be a powerful tool to constrain the temperature and the depth of bi-phase zones of volcanic aquifers.
Publications
- (2005) Fluid geochemistry of the magmatic-hydrothermal system of Nisyros (Aegean arc, Greece). In: The geology, geochemistry and evolution of Nisyros volcano (Greece); implications for the volcanic hazards (eds. J.C Hunziker, L. Marini), Memoires de Geologie (Lausanne) 44, 121-163.
Marini, L., and Fiebig, J.
- (2007) Natural evidence for rapid abiogenic hydrothermal generation of CH4. Geochim. Cosmochim. Acta 71, 3028-3039.
Fiebig, J., Woodland, A.B., Spangenberg, J., and Oschmann, W.
- (2007) The origin of the fumaroles of La Solfatara. Geochim. Cosmochim. Acta 71, 3040- 3055.
Caliro, S., Chiodini, G., Moretti, R., Avino, R., Granieri, D., Russo, M,, and Fiebig, J.
