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Materialien/Werkstoffe Vortrag: Fr., 10:20–10:40 F-V51
Neutron Texture Analyses of Rocks – Recent Applications and Perspectives
Bernd Leiss 1 , Klaus Ullemeyer 2 , Jens Walter 3
1 Geowissenschaftliches Zentrum der Universität Göttingen (GZG), Abteilung Strukturgeologie
und Geodynamik, Goldschmidtstr. 3, 37077 Göttingen – 2 Geologisches
Institut, Universität Freiburg, Albertstr. 23B, 79104 Freiburg – 3 Mineralogisch-
Petrologisches Institut der Universität Bonn, Aussenstelle am Forschungszentrum
Jülich, MIN/ZFR, D-52425 Jülich
Analyses of the crystallographic preferred orientations (CPO, textures) of mineral
phases contribute significantly to the quantitative characterisation of the anisotropic
physical rock properties, as well as to the understanding of the mechanisms of fabric
development. Most rocks in the Earths crust and mantle are relatively coarse-grained
and are composites of several mineral phases, usually of low crystal symmetry. In addition,
geological structures are often heterogenous and show complicated structures
due to polyphase deformation. Thus, volume-related texture analyses of rocks require
(a) the measurement of large sample volumes, (b) high d-resolution in the diffraction
patterns, and (c) the measurement of large sample series. Due to low absorption in
matter, neutrons are especially suitable for diffraction experiments of large sample volumes.
Both the SKAT time-of-flight diffractometer at the IBR-2 reactor in Dubna and
the SV-7 instrument at the FRJ-2 reactor in Jülich enabled the measurement of large
sample volumes up to 50x50x50 mm 3 . While the SKAT instrument offers a high resolution
of ∆d/d = 0.5 % to the best, the long measuring periods of the SV-7 instrument
allowed the measurement of large sample series. Many innovating projects could be
realized, e.g: (1) The systematic structure-related analysis of carbonate rocks revealed
new texture types and allowed a differentiated interpretation of the deformation history
and the deformation mechanisms of rocks, as well as the understanding of weathering
processes. (2) First quantitative textures analysis of granites showed CPOs for the
quartz and plagioclase phase. In addition to new ideas on the fabric development in
granites, the results are important for predicting anisotropic crack. development, for
the safety of repositories, and for the initiation of fluid pathways for geothermal power
plants. (3) The texture analysis of rock salt from salt dome structures showed unexpected
results, which will strongly contribute to the understanding of the mechanisms
of salt diapirism and, therefore, for the development of concepts of radioactive waste
repositories in Germany. (4) The quantitative correlation of experimentally determined
and texture-derived anisotropic elastic rock properties is helpful for the understanding
of seismic cross sections. (5) Correlation of shape preferred orientations and CPOs of
lava flows in dependence on viscosity, temperature, chemical composition and degree
of crystallization may contribute to the understanding of emplacement mechanisms
of lava flows. – The above examples demonstrate the importance of neutron texture
analyses for the geoscience community. Due to increasing requests for beam time, it
is essential to provide measuring capabilities in the future, and to refine and further
develop neutron diffraction instruments for rock texture analyses.