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Titel |
Quantification and kinetics of H2 generation during hydrothermal serpentinisation experiments |
VerfasserIn |
Teddy Castelain, Colin Fauguerolles, Johan Villeneuve, Michel Pichavant |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250076513
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Zusammenfassung |
H2-rich hydrothermal fluids generated by serpentinisation of mantle rocks at slow-spreading
ridges have been revealed by recent studies [1, 2]. Fluxes and the future of the H2 produced
by this process are poorly constrained [1, 3]. In this study, we aim to quantitatively evaluate
the H2 production fluxes associated with these hydrothermal systems and to document the
kinetics of the hydrogen-producing reaction.
For this matter, hydrothermal serpentinisation experiments are being undertaken on
mixtures composed of a natural peridotite from the Pindus ophiolite and olivine
crystals from San Carlos. The experiments are conducted at a temperature of ~
300Ë C and a pressure of 450-500 bars in large-volume Dickson-Seyfried bombs
for periods of -¥ 1 month. Starting materials are powders between 1 - 100 μm for
the peridotites and individual grains ranging from 1 - 2 mm for the San Carlos
olivine. They are reacted with a homemade artificial seawater in such proportion that
water-rock ratio = 1.8. The reactants are loaded in a modified Ti cell fitted with a
semi-permeable Au-Pd membrane simultaneously allowing direct sampling of the
hydrothermal fluid and in situ monitoring of the pH2 during the advancement of the
reaction. The gas fraction of the fluid sampled is then analyzed by gas chromatography
(GC).
The pH2 readings show traces of H2 to be present from the second day of experiment.
The increase of the pH2 reaches a maximum after ~ 6 days and the pH2 finally stabilizes
after ~ 16 days at ~ 12.5 bars, which corresponds to a local fO2 of about NNO-4. The GC
measurements, performed after 30, 43, 51 and 65 days, yield respectively, H2 concentrations
of 82.4, 89.7, 90.3 and 101 mmol.kg-1 of water, in reasonable agreement with results from
previous studies [4-6]. Further experiments are being undertaken in order to: duplicate
observations, especially the pH2 readings, more closely link the GC measurements
and the in situ pH2 readings, especially during the first 15 days of experiment,
and relate H2 production with the mineralogical composition of products of the
serpentinisation reaction. The possible influence of the oxidation of the Ti cell on the H2
production will be also checked by using a Au bag instead of a Ti cell. However,
from our results, it appears that H2 generation via serpentinisation is surprisingly
rapid.
[1] ] J.-L. Charlou et al., Chem. Geol., 191, 2002. [2] C. Mével, C.R. Geosc., 335,
2003. [3] M. Cannat et al., Geophys. Mono. Series, 188, 2010. [4] D.G. Allen, and
W.E. Jr Seyfried, Geochim. Cosmochim. Acta 67 (8), 2003. [5] M.E. Berndt, et al.,
Geology 24 (4), 1996. [6] W.E. Seyfried,et al., Geochim. Cosmochim. Acta 71, 2007. |
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