| dc.description.abstracteng | Texture analysis, i.e. the analysis of the crystallographic preferred orientations of minerals in rocks, contributes to the understanding of the deformation history and physical properties of rocks. Methods generally applied in geosciences, like optical methods, X-ray, neutron, or electron backscatter diffraction are often not suitable for multiphase, polycrystalline rocks rich in phyllosilicates as preparation or measurement procedures are inapplicable. Applying synchrotron radiation for quantitative texture analysis, i.e. high energy X-rays, with its high penetration depth, allows to measure a sample volume, is unaffected by water and overcomes preparation effects on the sample surface. A relative small beam size of 0.5-1 mm in diameter, however, makes it usually inapplicable to materials with larger grain sizes. An advanced workflow from sample preparation, to measuring and data processing was developed to make the method applicable to such specific rocks. Whole “slices” of cylindrical samples are measured and - if necessary - several slices per sample are finally added to represent a bulk rock texture. The applicability of the work flow using synchrotron diffraction was tested by three case studies regarding phyllosilicate-rich rocks. 1) Quantitative texture analysis of Devonian black shales from the Appalachian Plateau in Pennsylvania (USA) was applied to calculate the anisotropy of the magnetic susceptibility. The modeling results are compared to experimental AMS measurements, which show a good agreement and quantitatively prove that the magnetic anisotropy in these samples is carried by the phyllosilicates. Texture and magnetic fabric dominantly reflect compaction, but also far field tectonic imprint from the Alleghenian orogeny. 2) Water-rich muds and mud rocks from the subduction zone offshore Costa Rica were analyzed regarding their composition and texture. The results give insight into the texture development processes as the compaction of these “freshly” sedimented clay-rich rocks and the tectonic overprint at the continental slope. 3) Fresh oceanic serpentinites consisting from chrysotile and lizardite from the Atlantis Massif oceanic core complex show textures which are interpreted by microstructural analyses to be originating from two different processes. In one case, texture was created by the pseudomorphic serpentinization of pyroxenes leading to the formation of bastites, which generates a local texture. In the other case, texture developed due to a preferred orientation of the serpentinizing microfractures which are supposed to be linked to deformation, either prior to serpentinization or due to the volume increase during metamorphosis. Serpentine minerals adopt a growth direction linked to the orientation of the fractures and thereby generate a textured microfabric. Both processes can lead to seismic anisotropy in these rocks. In all three case studies synchrotron texture analysis in combination with Rietveld refinement lead to the successful determination of textures of the extremely complicated rock material and allowed new insights in processes of texture formation and the contribution to the physical anisotropies. This thesis extends the common comprehension and
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applicability of texture analysis usually applied to intra-crystalline plastically deformed rocks to delicate samples affected by sedimentary or metamorphic processes. | de |