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| Titel |
Petrophysical properties of granite from the Melechov Massif, Czech Republic |
| VerfasserIn |
Martin Staněk, Stanislav Ulrich, Yves Geraud |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043370
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| Zusammenfassung |
| The Melechov Massif is a granitic massif constituting the northernmost part of the Central
Moldanubian Pluton, which belongs to the Moldanubian zone of the variscan belt in the
Bohemian Massif. On an area of cca 100 km2 it is formed by 4 types of granite which are
disposed in a concentric manner and are distinguished mainly by their grain size. All the
granites are two-mica S-granites considered to be product of polyphase intrusion of magma
issued from partial melting of the surrounding variscan metasediments. Relative to the
variscan orogeny, the granites are considered to be post-orogenic and are related to isothermic
decompression of upper- to middle-crust during collapse of the orogeny-thickened
lithosphere. Ages of cooling derived from radiometric dating on monazites give values
for all of the types 315 ±Â 10 Ma. The granite massif suffered brittle deformation
related to cooling and induced volume contraction creating systems of joints and, in
a lesser measure, faults. The Melechov massif was intensely studied during the
last two decades, mainly because it has been established as a testing locality by
the radioactive waste repository authority (RAWRA) of the Czech Republic. We
have the intention to complement the studies done so far by detailed petrophysical
and microstructural analysis of samples taken with respect to macroscopic brittle
structures. Several methods are employed to reveal important differences in rock
samples collected from distinct geological setting from surface outcrops, quarries and
a borehole. The concerned petrophysical properties and/or related experimental
methods are namely: thermal conductivity, permeability, porosity, P-wave velocity
measurements; in most cases the anisotropy of these quantities is crucial. Preliminary
analyses of permeability and porosity show low porosity ranging from 3,8 % for
coarse-grained variety to 1,3 % for fine-grained variety and very low permeability
ranging from X.10-18 m2 for fine-grained variety to X.10-20 m2 for coarse-grained
variety. Preliminary analyses of P-wave velocity at low confining pressures (< 100
MPa) show values of more than 10 % of anisotropy for coarse-grained samples and
4-10 % of anisotropy for medium- to fine-grained samples. Analyses of thermal
conductivity (TC) using high resolution optical scanning show several distinct phenomena
affecting this quantity. Joint- or fissure-related oxide alteration in samples from
outcrops and at shallow levels of borehole gives relative rise to TC values by cca 10 %,
closed fissures reduce the TC by up to 20 %, mineralogy inhomogeneities result into
increase of about 10 %. To specify and to increase the confidence of our results
on borehole samples, which are suspect to be critically too small relative to the
prerequisities of the used TC method, we will investigate the influence of volumetric
dimensions of sample on the TC values as well as the possible error induced by
measurement on a cylindrical surface as compared to measurement on an „infinite“ sample. |
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