Please use this identifier to cite or link to this item:
AuthorsPaonita, A.* 
Favara, R.* 
Nuccio, P. M.* 
Sortino, F.* 
TitleGenesis of fumarolic emissions as inferred by isotope mass balances: CO2 and water at Vulcano Island, Italy
Issue Date2002
Series/Report no.5/66(2002)
Keywordsisotope geochemistry
volcanic gases
mixing modeling
Subject Classification04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry 
04. Solid Earth::04.08. Volcanology::04.08.01. Gases 
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas 
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring 
05. General::05.02. Data dissemination::05.02.01. Geochemical data 
AbstractWe have developed a quantitative model of CO2 and H2O isotopic mixing between magmatic and hydrothermal gases for the fumarolic emissions of the La Fossa crater (Vulcano Island, Italy). On the basis of isotope balance equations, the model takes into account the isotope equilibrium between H2O and CO2 and extends the recent model of chemical and energy two-end-member mixing by Nuccio et al. (1999). As a result,the H2O and CO2 content and the dD, d18O, and d13C isotope compositions for both magmatic and hydrothermal end-members have been assessed. Low contributions of meteoric steam, added at a shallow depth, have been also recognized and quantified in the fumaroles throughout the period from 1988 to 1998. Nonequilibrium oxygen isotope exchange also seems to be occurring between ascending gases and wall rocks along some fumarolic conduits. The d13CCO2 of the magmatic gases varies around -3 to 1‰ vs. Peedee belemnite (PDB), following a perfect synchronism with the variations of the CO2 concentration in the magmatic gases. This suggests a process of isotope fractionation because of vapor exsolution caused by magma depressurization. The hydrogen isotopes in the magmatic gases (-1 to -35‰ vs. standard mean ocean water [SMOW]), as well as the above d13CCO2 value, are coherent with a convergent tectonic setting of magma generation, where the local mantle is widely contaminated by fluids released from the subducted slab. Magma contamination in the crust probably amplifies this effect. The computed isotope composition of carbon and hydrogen in the hydrothermal vapors has been used to calculate the dD and d13C of the entire hydrothermal system, including mixed H2O-CO2 vapor, liquid water, and dissolved carbon. We have computed values of about 10‰ vs. SMOW for water and -2 to -6.5‰ vs. PDB for CO2. On these grounds, we think that Mediterranean marine water (dDH2O 10‰) feeds the hydrothermal system. It infiltrates at depth throughout the local rocks, reaching oxygen isotope equilibrium at high temperatures. Interaction processes between magmatic gases and the evolving seawater also seem to occur, causing the dissolution of isotopically fractionated aqueous CO2 and providing the source for hydrothermal carbon. These results have important implications concerning fluid circulation beneath Vulcano and address the more convenient routine of geochemical surveillance.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
Paonita et al., Geoch. Cosmoch. Acta 2002.pdfMain article579.71 kBAdobe PDFView/Open
Redirect Elsevier.htmlRedirect-Elsevier539 BHTMLView/Open
Show full item record

Page view(s)

Last Week
Last month
checked on Jul 22, 2017


checked on Jul 22, 2017

Google ScholarTM