HR: 14:10h
AN: B23D-03 INVITED     [Abstracts]
TI: Organics in volcanic gases: a review on their distribution and applications to volcanic surveillance
AU: * Capaccioni, B
EM: b.capaccioni@uniurb.it
AF: Institute of Volcanology and Geochemistry, Loc. Crocicchia, Urbino, 61029 Italy
AU: Tassi, F
EM: francot@geo.unifi.it
AF: Department of Earth Sciences, Via G. La Pira, 4, Florence, 50121 Italy
AU: Maione, M
EM: maione@uniurb.it
AF: Department of Chemical Sciences, Piazza Rinascimento 6, Urbino, 61029 Italy
AU: Mangani, F
EM: mangani@uniurb.it
AF: Department of Chemical Sciences, Piazza Rinascimento 6, Urbino, 61029 Italy
AU: Vaselli, O
EM: orlando@geo.unifi.it
AF: Department of Earth Sciences, Via G. La Pira, 4, Florence, 50121 Italy
AB: Over the past fifteen years, a large amount of quantitative analytical data has been accumulated on light hydrocarbons in fumarolic and geothermal gas discharges from several volcanic and geothermal systems around the world. These data, which include new and published data on approximately 500 low-temperature, geothermal, and volcanic gas discharges from different geodynamical settings, have enabled a systematic understanding of the behavior and mechanisms of formation of C1-C6 hydrocarbons and heterocompounds. These processes and their possible thermodynamic controls have been a matter of debate over the past decade. The three main classes of hydrocarbons (alkanes, alkenes and aromatics) in these discharges display recurring distributions among different volcanic and geothermal systems. This finding suggests a similar compositional evolution of light hydrocarbons through common genetic processes. Additionally, the possible role of partial equilibrium in the system can be investigated by the direct comparison of predicted versus experimental data. If we consider the chemical reactions involving C1-C4 alkanes via a free-radical mechanism, even partial chemical equilibrium seems to be only rarely attained. This may be due to the high activation energies required for the breaking of C-C bonds. In contrast, interactions between alkenes and their saturated equivalents (e.g., ethene-ethane, propene-propane and isobutene-isobutane pairs) through dehydrogenation processes seem to be at least partially thermodynamically controlled. The improved understanding of the processes controlling the generation, modification and fate of hydrocarbons in these systems leads to the recognition of certain types of systems and possible predictive applications for volcanic monitoring. For example, temporal monitoring of hydrocarbon species carried out off-shore at Panarea Island after a gas blast occurred in November 2002, as well as monitoring at the Phlegrean Fields (southern Italy) have contributed to the identification of a shift in the feeding systems towards more reducing conditions, possibly due to declining inputs of deep magmatic fluids. For heterocompounds, data have indicated that thiophenes and dimethylsulphide are widely produced and at similar levels, whereas furans have only been recognized in high temperature volcanic gases in agreement with their relative thermodynamic stabilities. Lastly, significant amounts of halocarbons and hydrogenated halocarbons have been measured in volcanic gases, and their relative distribution at Vulcano Island (southern Italy) seems to suggest a non-atmospheric origin. Estimation of total CFC emission rates were provided based on measurements of the whole-gas flux from the active crater of Vulcano Island. The processes controlling the formation of C1-C6 hydrocarbons and heterocompounds and their possible thermodynamic controls, as well as potential applications, will be discussed and reviewed in detail.
DE: 0330 Geochemical cycles (1030)
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 1055 Organic and biogenic geochemistry
DE: 8419 Volcano monitoring (7280)
DE: 8430 Volcanic gases
SC: Biogeosciences [B]
MN: Fall Meeting 2005