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http://hdl.handle.net/2122/343
Authors: | Grassa, F.* Capasso, G.* Favara, R.* Inguaggiato, S.* Faber, E.* Valenza, M.* |
Title: | Molecular and isotopic composition of free hydrocarbon gases from Sicily, Italy | Journal: | Geophysical Research Letters | Series/Report no.: | 31 (2004) | Publisher: | American Geophysical Union | Issue Date: | 2004 | DOI: | 10.1029/2003GL019362 | URL: | http://www.agu.org/ | Keywords: | Isotopic composition/chemistry Organic geochemistry |
Subject Classification: | 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems 04. Solid Earth::04.08. Volcanology::04.08.01. Gases 05. General::05.02. Data dissemination::05.02.01. Geochemical data |
Abstract: | Chemical and isotopic data have been used as geochemical tracers for a genetic characterization of hydrocarbon gases from a total of eleven manifestations located in Eastern and Central-Southern Sicily (Italy). The molecular analysis shows that almost all the samples are enriched in methane (up to 93.2% Vol.), with the exception of four gas samples collected around Mt. Etna showing high mantle-derived CO2 content. Methane isotope signatures suggest that these are thermogenic gases or a mixture between thermogenic gases and microbial gases. Although samples from some mud volcanoes in Southern Sicily (Macalube di Aragona) show isotope signatures consistent with a mixing model between thermogenic and microbial, by combining the molecular compositions (C1/(C2 + C3))and the methane isotope ratios (d13C1), such a process seems to be excluded. Therefore, the occurrence of secondary post-genetic processes should be invoked. Two main hypotheses have been considered: the first hypothesis includes that the gas is produced by microbial activity and altered post-genetically by microbial oxidation of methane, while according to the second hypothesis thermogenic gas have modified their molecular ratios due to vertical migration. |
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