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| Titel |
Stable carbon and hydrogen isotopes in CH4 and light alkanes in
magmatic and hydrothermal emissions from Vulcano Island (southern Italy) |
| VerfasserIn |
Andrea Ricci, Jens Fiebig, Franco Tassi, Orlando Vaselli, Christoph Schreiber, Chiara Caponi, Sven Hofmann, Francesco Capecchiacci |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250146750
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| Publikation (Nr.) |
 EGU/EGU2017-10790.pdf |
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| Zusammenfassung |
| Vulcano Island, whose last eruption dates back to 1888-1890, is the southernmost island of
the Aeolian Archipelago (southern Italy), a subduction-related volcanic arc in the
Southern Tyrrhenian Sea. The active volcanic cone, namely La Fossa, displays an
intense fumarolic activity, mostly occurring in its north-western sector. The fumaroles
are characterized by outlet temperatures up to ∼400 ˚ C, and a typical magmatic
composition with relatively high concentrations of HCl, HF and SO2. A second fumarolic
area in the island occurs at Baia di Levante, the bay delimiting the eastern side of
a flat isthmus that connects Vulcano to Vulcanello. In this area, low temperature
(≤ 100˚ C) fumaroles and bubbling gases are discharged, displaying the typical
hydrothermal-type composition, i.e. being characterized by relatively high contents of H2S
and hydrocarbons and by the absence of acid gas constituents. We have investigated
the chemical and isotopic (δ13C and δD) compositions of CH4 and light alkanes
(C2H6, C3H8, C4H10) of the fumaroles venting from both the crater and the bay
area. To the best of our knowledge, the isotopic data of CH4 from La Fossa crater
presented in this work are the first ones on terrestrial high-temperature fumaroles
ever reported. The main aim is to use these geochemical parameters to identify
the fluid source(s) and the processes controlling the isotopic composition of the
hydrocarbons. Our analytical results highlight that the δD–CH4 values of gases from La
Fossa crater are extremely depleted in deuterium (down to -657‰ vs. V-SMOW),
whereas those of the beach fumaroles range from -100‰ to -85‰ vs. V-SMOW. The
13C/12C ratios of CH4 and C2+ n-alkanes in the crater fumaroles also strongly differ
from the isotopic signature measured in the hydrothermal gases, with the carbon
isotopic composition of the low-temperature gases occurring significantly enriched in
13C relative to the magmatic gases. Assuming a deep source for light hydrocarbon
common to both the crater and the beach fumaroles, these preliminary data suggest
the occurrence of not well defined secondary processes able to strongly modify
their primary isotopic signature. Alternatively, two distinct hydrocarbon sources
characterized by dramatically different δ13C and δD values, feeding the magmatic and the
hydrothermal emissions, respectively, are to be invoked to explain the observed data. |
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