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Abiotic methane in the hyperalkaline springs of Genova, Italy.
Language
English
Obiettivo Specifico
7A. Geofisica di esplorazione
Status
Published
JCR Journal
N/A or not JCR
Peer review journal
Yes
Title of the book
Issue/vol(year)
/7 (2013)
Electronic ISSN
1878-5220
Publisher
Elsevier
Pages (printed)
248-251
Issued date
2013
Keywords
Abstract
Serpentinization of ultramafic rocks is considered a major process of production of abiotic methane (CH4) and
hydrogen (H2) on Earth, and it may be responsible for CH4 occurrence on other planets. While serpentinization and
CH4 synthesis have been widely studied and modeled in high temperature hydrothermal conditions, such as on
submarine mid-ocean ridges, the increasing number of discoveries of abiotic CH4 in ophiolites on continents shows
the importance of present-day (meteoric water driven) serpentinization in low temperature (<100 °C) gas synthesis.
As a new case, we report compositional, isotopic, and flux data of gas dissolved in hyperalkaline Ca-OH waters
issuing from serpentinized peridotites at Genova (Italy). CH4 is dominantly abiotic (δ13C: -9 ‰ VPDB; δ2H: -168 to -
225 ‰ VSMOW), similar to that released by ophiolites in Oman, Turkey, the Philippines, and by the submarine Lost
City serpentinization system. While the absence of CO2 was expected in this kind of fluids, the absence of H2 is
unusual. This could be due to hydration of olivine and pyroxene by CO2-rich fluids, eventually associated with high
silica activity, which inhibits H2 formation and produces CH4 directly. Thermodynamic modeling and H2O-CH4
isotope equilibrium confirm the low temperatures (<60°C) of the serpentinization system, and thus the abiotic
methane synthesis.
hydrogen (H2) on Earth, and it may be responsible for CH4 occurrence on other planets. While serpentinization and
CH4 synthesis have been widely studied and modeled in high temperature hydrothermal conditions, such as on
submarine mid-ocean ridges, the increasing number of discoveries of abiotic CH4 in ophiolites on continents shows
the importance of present-day (meteoric water driven) serpentinization in low temperature (<100 °C) gas synthesis.
As a new case, we report compositional, isotopic, and flux data of gas dissolved in hyperalkaline Ca-OH waters
issuing from serpentinized peridotites at Genova (Italy). CH4 is dominantly abiotic (δ13C: -9 ‰ VPDB; δ2H: -168 to -
225 ‰ VSMOW), similar to that released by ophiolites in Oman, Turkey, the Philippines, and by the submarine Lost
City serpentinization system. While the absence of CO2 was expected in this kind of fluids, the absence of H2 is
unusual. This could be due to hydration of olivine and pyroxene by CO2-rich fluids, eventually associated with high
silica activity, which inhibits H2 formation and produces CH4 directly. Thermodynamic modeling and H2O-CH4
isotope equilibrium confirm the low temperatures (<60°C) of the serpentinization system, and thus the abiotic
methane synthesis.
Type
article
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