Authors: Christian Scheffzük, Alexander Frischbutter, Kurt Walther

Abstract
Selected results of strain-texture measurements on composite and monomineralic rocks will be presented and discussed in brief. Experiments were carried out using neutron-TOF- and synchrotron diffraction at the strain/stress diffractometer EPSILON-MDS and the texture diffractometer SKAT at beam line 7A of the pulsed reactor IBR-2 in Dubna (RUS), at the ROBL beamline (ESRF Grenoble, F), as well as at the ENGIN-diffractometer (ISIS, Chilton, UK). The background is to improve our understanding of strain-texture relations controlling deformation processes in rocks.

A dolomite/anhydrite rock which occasionally responds to mechanical impulses with a break down of its structure has been studied with respect to relations between residual strain and texture of the main rock components. The rock texture, derived from its main components, is of orthorhombic symmetry, with one of its plane of symmetry parallel to the rock’s foliation. Residual strain data for anhydrite and dolomite reflect an opposed state regarding both, compression and dilatation. The combined interpretation of the intracrystalline strain and texture data gives reason to suggest that the direction of the occasional impulse may cause the structural break down. That means, micromechanical conditions are probably more important to the special behaviour of the rock than the effects by the hydration of anhydrite.

A superimposed deformed (16-34 GPa) sample, prepared from quartzite and dunite was studied perpendicular to an artificial established interface. Considerable differences in residual microstrain were determined as the interface was approached: Decreasing tensile and orientation-dependent but uniform residual strain in quartzite is in contrast to weakly increasing and less orientation dependent, tensile residual strain in dunite. Maximum residual tensile strain values were determined for quartz [0001]-orientations, reflecting the non-coaxial, but subordinated component of the texture. Similar results could be derived from experiments using synchrotron radiation. Variations along an investigated scan may be determined at least for quartzite by pre-existing texture. Moreover, tendencies in grain size evolution of scattering crystallites could be evaluated by peak shape analysis. The superimposed deformation produced a new grain structure in dunite, but did not change the older macrostructure of quartzite. Otherwise, grain size of quartzite was reduced about six times more than that of dunite.

A sample of Carrara marble may be characterized by a texture-memory effect: A dominating equigranular microfabric refer to an influence of static recrystallization. Otherwise, the determined type of crystallographic orientation reflects dynamic recrystallization by a well-pronounced fibre-texture. From the geological point of view younger contact metamorphism from Pleistocene granitic intrusions may superimpose dynamic recrystallization fabrics, due to Tertiary alpine tectogenesis.