Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/346
AuthorsFiebig, J.* 
Chiodini, G.* 
Caliro, S.* 
Rizzo, A.* 
Spangenberg, J.* 
Hunziker, J. C.* 
TitleChemical and isotopic equilibrium between CO2 and CH4 in fumarolic gas discharges: generation of CH4 in magmatic-hydrothermal systems
Issue Date2004
Series/Report no.10/68(2004)
DOI10.1016/j.gca.2003.10.035
URIhttp://hdl.handle.net/2122/346
Keywordsfumarolic gases
hydrothermal systems
chemical and isotopic equilibrium
Subject Classification03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems 
04. Solid Earth::04.08. Volcanology::04.08.01. Gases 
AbstractThe chemical and isotopic composition of fumarolic gases emitted from Nisyros Volcano, Greece,and of a single gas sample from Vesuvio, Italy, was investigated in order to determine the origin of methane (CH4) within two subduction-related magmatic-hydrothermal environments. Apparent temperatures derived from carbon isotope partitioning between CH4 and CO2 of around 340°C for Nisyros and 470°C for Vesuvio correlate well with aquifer temperatures as measured directly and/or inferred from compositional data using the H2O-H2-CO2-CO-CH4 geothermometer. Thermodynamic modeling reveals chemical equilibrium between CH4, CO2 and H2O implying that carbon isotope partitioning between CO2 and CH4 in both systems is controlled by aquifer temperature. N2/3He and CH4/3He ratios of Nisyros fumarolic gases are unusually low for subduction zone gases and correspond to those of midoceanic ridge environments. Accordingly, CH4 may have been primarily generated through the reduction of CO2 by H2 in the absence of any organic matter following a Fischer-Tropsch-type reaction. However, primary occurrence of minor amounts of thermogenic CH4 and subsequent re-equilibration with co-existing CO2 cannot be ruled out entirely. CO2/3He ratios and 13CCO2 values imply that the evolved CO2 either derives from a metasomatized mantle or is a mixture between two components, one outgassing from an unaltered mantle and the other released by thermal breakdown of marine carbonates. The latter may contain traces of organic matter possibly decomposing to CH4 during thermometamorphism.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
Fiebig et al. Geoch. et Cosmoch. Acta 2004.pdfMain article809.92 kBAdobe PDFView/Open    Request a copy
Redirect Elsevier.htmlRedirect-Elsevier539 BHTMLView/Open
Show full item record

Page view(s)

306
checked on Apr 29, 2017

Download(s)

61
checked on Apr 29, 2017

Google ScholarTM

Check

Altmetric