Browsing by Author "Ullemeyer, K."

A representative suite of deformed, metamorphic rocks from the TRANSALP reflection seismic traverse in the Eastern Alps was studied in the laboratory with respect to elastic properties and whole-rock texture. Compressional wave (P-wave) velocities and their anisotropies were measured at various experimental conditions (dry, wet, confining pressure), and compared to the texture-related component of anisotropy. Here 'texture' refers to crystallographic preferred orientations (CPOs), which were deter-mined by neutron texture goniometry. In gneisses and schists P-wave anisotropies are mainly controlled by the microcrack fabric. In marbles and amphibolites CPO contributes very significantly to anisotropy. At 200 MPa confining pressure the degree of anisotropy is between 5% and 15%, depending on rock composition and/or CPO intensity. Special emphasis was also put on discussing possible effects of fluids on seismic velocity and anisotropy. Distributions of water-filled microcracks and pores are distinctly anisotropic, with maximum contribution to bulk rock velocity mostly parallel to the foliation pole. Decreasing P-wave velocity and increasing anisotropy of immersed samples may be explained by crack-induced changes of the elastic moduli of bulk rock. The main conclusion regarding interpretation of TRANSALP data is that strong reflections in the deep Alpine crust are probably due to marble-gneiss and metabasite-gneiss contacts, although P-wave anisotropy and boundaries between zones of 'dry' or 'wet' series may contribute to reflectivity to some extent. (c) 2005 Elsevier B.V. All rights reserved.

The deconvolution of the deformation history of rocks is one of the main goals of texture analysis in geology. The frequent observation that the macroscopic structures are obliquely oriented with respect to the margins of the deformation zone gave rise to the hypotheses that the deformation path might be complex, and that the lattice preferred orientation of the rock-forming minerals should reflect such complicated deformation conditions as well. Hence, texture determinations of polyphase rock samples were carried out and the relationship of the mineral textures to the commonly used sample reference frame foliationlineation, which is assumed to represent the principal axes of the bulk finite strain tensor, was investigated. It was confirmed that particular mineral textures are typical for different stages of the deformation path. Especially the quartz textures exhibit an uncommon but consistent deviation from the sample reference frame, which is consistent with respect to the geographical coordinates, too. Such a characteristic may be used to evaluate the direction of a large-scale horizontal shear component, which is known as the transpressive shear vector in the geological literature.