Abstract (eng)
This thesis presents results of an investigation of the microstructural and textural evolution of calcite deformed to high shear strains at confining pressures in the GPa range and temperatures between room temperature and 450 °C with high-pressure torsion. The microstructure analysis by means of synchrotron based X-ray line profile analysis and SEM based electron backscatter diffraction revealed a significant influence of high confining pressures on the deformation behavior. Through the suppression of crack nucleation and propagation, high confining pressures facilitate microstructural characteristics that are typically associated with higher deformation temperatures. Mechanical twins in samples deformed at room temperature show evidence for significant twin broadening and boundary migration, which are expected for deformation temperatures exceeding 150 and 250 °C, respectively, according to calcite twin morphology geothermometers. However, the high confining pressure also inhibits the mobility of point defects and thus impedes dislocation climb and recovery. Thus, microstructural parameters such as grain size, dislocation density or coherently scattering domain size are affected by an increase in the confining pressure in a similar way as by a decrease in the temperature. Furthermore, the stability field of a high pressure polymorph affects the recrystallization process in samples deformed at 450 °C. Deformation in the calcite stability field leads to a dynamic equilibrium of the dislocation density and a core-mantle microstructure after shear strains of about 10 independent of the strain rate. By contrast, deformation in the stability field of the high pressure polymorph delays the dynamic equilibrium of the dislocation density to significantly higher strains and leads to a strain rate dependent recrystallization process, where higher strain rates generate core-mantle microstuctures and lower strain rates result in a more homogeneous break-up of porphyroclasts.