Analysis of microstructures and crystallographic preferred orientation
2016. "Analysis of microstructures and crystallographic preferred orientation", Rock Deformation from Field, Experiments and Theory: A Volume in Honour of Ernie Rutter, D. R. Faulkner, E. Mariani, J. Mecklenburgh
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Recrystallized grains are potentially useful as indicators of palaeostress in naturally deformed rocks, providing that well-calibrated relationships (palaeopiezometers) exist between the recrystallized grain size and stress. Rocks can exhibit microstructures that are heterogeneous, that is, containing recrystallized as well as deformed grains, and showing subgrains within grains that differ in size and character from the grain core to the mantle. Previous studies on palaeopiezometers only rarely took into account such heterogeneous microstructure. We used electron backscattered diffraction (EBSD) to accurately quantify the heterogeneous microstructures in experimentally deformed Carrara marble (flow stress 15–85 MPa, temperature 700–990 °C and natural strain 0.15–0.90). The sizes of bulges, recrystallized grains and deformed grains have been measured. We found that the overall character of the microstructures varies as a function of deformation conditions. In heterogeneous samples showing core-mantle microstructures, the sizes of the bulges and recrystallized grains are independent of strain and show an inverse dependency on stress. The recrystallized grains have been found to nucleate at grain boundary bulges. Our study illustrates that very different microstructures may develop in relation to the complexity of the recrystallization mechanisms. We therefore suggest that piezometers should be calibrated and applied for a single type of overall microstructure.
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Ernie Rutter has made, and continues to make, a significant impact in the field of rock deformation. He has studied brittle and plastic deformation processes that occur within both the oceanic and continental crust, as well as other key properties such as the permeability and seismic velocities of these rocks. His approach has been one that integrates field observations, laboratory experiments and theoretical analyses. This volume celebrates Ernie’s key contribution to rock deformation and structural geology by bringing together a collection of papers that represent this broad approach. The papers within the volume address key issues that remain within these fields. These range from fundamental studies of brittle and plastic behaviour along with the resultant structures and microstructures from both the field and laboratory, to applied problems where a better understanding of the deformation and properties of the crust is still needed.