Do calcite rocks obey the power-law creep equation?
Jörg Renner, Brian Evans, 2002. "Do calcite rocks obey the power-law creep equation?", 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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The power-law creep equation, ε̇ ∞ σn exp(−Q/RT), is commonly used to relate strain rate, ε̇, stress, σ, and temperature, T, for thermally activated dislocation creep in rocks. When triaxial deformation experiments on marble and limestone samples are performed at temperatures of 400–1050°C, to strains <0.2, and with strain rates between 10−3 and 10−7s−1, the variations in strength among different rocks at nominally identical conditions are much larger than the experimental uncertainty. During dislocation creep, the strengths of various limestones and marbles decrease with increasing grain size, similar to the Hall-Petch effect in metals. The stress sensitivity of strain rate, n′ = ∂ln ε̇/∂lnσ, and the temperature sensitivity of strain rate, Q′ = −R∂lnε̇/∂ (1/T), differ greatly for the various calcite aggregates. There is a systematic dependence of n′ and Q′ on stress, grain size, and perhaps, temperature, and there is no interval in stress where n′ is constant. Thus, the steady-state power-law equation is an inadequate description of dislocation creep in calcite rocks. To improve the constitutive law, it may be necessary to include at least one additional state variable that scales with grain size.
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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:
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