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| Titel |
Geothermal potential of Caledonian granites underlying Upper Palaeozoic sedimentary basins astride the Iapetus Suture Zone in Ireland |
| VerfasserIn |
Tobias Fritschle, J. Stephen Daly, Martin J. Whitehouse, Brian McConnell, Stephan Buhre |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097117
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| Publikation (Nr.) |
 EGU/EGU2014-12665.pdf |
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| Zusammenfassung |
| Upper Palaeozoic sedimentary basins in Ireland overlie crystalline rocks within the
Caledonian Iapetus Suture Zone. Beneath these basins, Lower Palaeozoic rocks, formed and
deformed during the Caledonian orogenic cycle, were intruded by c. 420-390 Ma
late-tectonic granites at various tectonic levels. These include the subsurface Kentstown and
Glenamaddy granites discovered by mineral exploration drilling. While these granites
comprise actual targets for Enhanced Geothermal System (EGS) exploration, several others
likely exist based on geophysical considerations. In order to test the regional geothermal
potential, the buried granites as well as analogue exposed rocks are being investigated
geochemically.
The geothermal potential of the intrusives depends on their heat production rate (HPR),
which is calculated using rock density and concentrations of the heat producing elements
(HPE) uranium, thorium and potassium. In spite of their close spacing and similar ages, the
whole-rock geochemistry of the granites varies significantly, but with no obvious
geographical control (Fritschle et al., 2013; 2014). The granite HPR values range from 1.4
μW/m3 for the Dhoon Granite (Isle of Man) to 4.9 μW/m3 for the Drogheda Granite
(Ireland). This compares with the average HPR for a ‘typical’ granite of 2.7 μW/m3
(Goldstein et al., 2009).
It is demonstrated that an elevated HPR of a granite can be related to enrichment in one of
the HPE alone (e.g., uranium-enrichment in the Foxdale Granite (Isle of Man), or
thorium-enrichment in the Drogheda Granite). Enrichment in HPE in a granite may occur due
to different reasons including hydrothermal (re-) distribution of uranium, or the assimilation
of thorium-rich wall-rocks. Hence, the distribution of the HPE in particular minerals, veins
and source lithologies, along with the petrophysical characteristics of the sedimentary basins
and the granites’ petrogenesis, are currently being investigated as possible mechanisms
controlling their heat production budget.
Fritschle, T., Daly, J.S., Whitehouse, M.J., McConnell, B., Buhre, S., 2013. U-Pb Zircon
Ages from Granites in the Iapetus Suture Zone in Ireland and the Isle of Man. Mineralogical
Magazine, 77(5): 1115.
Fritschle, T., Daly, J.S., Whitehouse, M.J., McConnell, B., Buhre, S., 2014. Zircon
geochronology and Hf-O isotope geochemistry from granites in the Iapetus Suture Zone in
Ireland and the Isle of Man. This issue.
Goldstein, B.A., Hill, A.J., Long, A., Budd, A.R., Ayling, B., Malavazos, M., 2009. Hot
rocks down under – evolution of a new energy industry. Geothermal Resources Council
Transactions, 33: 185–198. |
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