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| Titel |
Fingerprinting the temperature and fluid source of fracture-filling calcite
in geothermal systems using clumped isotopes |
| VerfasserIn |
John M. MacDonald, Amelia Davies, John Faithfull, Chris Holdsworth, Michael Newton, Sam Williamson, Cedric John |
| 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 |
250138867
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| Publikation (Nr.) |
 EGU/EGU2017-2002.pdf |
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| Zusammenfassung |
| Geothermal energy production relies on maintaining open fractures within the rock through
which fluids can flow, but precipitation of minerals in fractures can modify and reduce fluid
flow. Most geothermal fluids are rich in dissolved material, and readily precipitate minerals
such as calcite within fracture systems. Such mineral deposition can be a key limiting
factor in viable geothermal energy production. We need to better understand the
relationship between fluid temperatures, mineral precipitation, and fracture filling in such
systems.
Clumped isotopes offer a new way of characterising the temperature and fluid source of
fracture-filling calcite. This technique is based on the thermodynamic relationship between
carbonate mineral growth temperature and the abundance of chemical bonding (“clumping”)
between 13C and 18O isotopes (expressed as Δ47) within single carbonate ions
(e.g. Eiler, 2007). In the gas phase, isotopic exchange between CO2 molecules
and water is continuous and so CO2 gas will record the ambient fluid temperature.
When the CO2 is trapped in a solid mineral phase, the isotope ratio is fixed. As a
result, clumped isotopes will record the temperature of crystallisation, enabling
the application of clumped isotope palaeothermometry to a range of geological
problems.
Samples from active geothermal fields (the Kawerau geothermal field, New Zealand
(McNamara et al., 2017)) and analogues to basaltic geothermal systems in Western Scotland
have been analysed with clumped isotopes. We present petrography, δ13C and δ18O, and
clumped isotope data from these samples to show how clumped isotopes can fingerprint the
temperature and fluid source of fracture-filling calcite in geothermal systems. Having this
understanding of fracture filling conditions can lead to focused development of remediation
measures.
References
Eiler, J. M., 2007. EPSL 262(3-4), 309-327.
McNamara, D. D., Lister, A., Prior, D. J., 2016. JVGR 323, 38-52. |
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