On estimating the strength of calcite rocks under natural conditions
J. H. P. de Bresser, B. Evans, J. Renner, 2002. "On estimating the strength of calcite rocks under natural conditions", Deformation Mechanisms, Rheology and Tectonics: Current Status and Future Perspectives, S. de Meer, M. R. Drury, J. H. P. de Bresser, G. M. Pennock
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Field studies of calcite mylonites often document microstructures produced by dislocation creep. In contrast, flow laws derived from experiments predict that calcite rocks should deform mostly by diffusion creep during tectonic processes. To investigate this apparent discrepancy, we compare stresses estimated by microstructural piezometers to those obtained by extrapolation of experimentally derived flow laws. Considering shear zones from different geological settings, a clear trend is observed of increasing recrystallized grain size with increasing temperature. However, there is a large spread in grain size and associated stress. Because separate flow laws have been defined for various different marbles and limestones, the strengths predicted for a given set of conditions differ significantly. The stress estimates based on the piezometers and strength extrapolated from the various experimentally derived dislocation creep flow laws agree qualitatively, but no single flow law predicts all the palaeostress estimates. Even if experimental data are disregarded, the field observations are not consistent with a hypothetical law for Coble creep; they are consistent with a power law for dislocation creep, but only if the material constants are different from those currently determined in laboratory experiments.
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The motion and deformation of rocks are processes of fundamental importance in shaping the Earth, from outer crustal layers to the deep mantle. Reconstructions of the evolution of the Earth therefore require detailed knowledge of the geometry of deformation structures and their relative timing, of the motions leading to deformation structures and of the mechanisms governing these motions. This volume contains a collection of 22 papers on field, experimental and theoretical studies that add to our knowledge of these processes. They are a mixture of review papers oh selected topics in the field of structural geology and tectonics and papers on current issues and new techniques and are grouped into four themes:
The effect of fluids on deformation
The interpretation of microstructures and textures
Deformation mechanisms and rheology of crust and upper mantle minerals
Crust and lithosphere tectonics
The volume will appeal to researchers in the fields of structural geology and tectonophysics, both in academia and industry.