Brittle plus plastic deformation of gypsum aggregates experimentally deformed in torsion to high strains: quantitative microstructural and texture analysis from optical and diffraction data
Published:January 01, 2010
M. Zucali, V. Barberini, D. Chateigner, B. Ouladdiaf, L. Lutterotti, 2010. "Brittle plus plastic deformation of gypsum aggregates experimentally deformed in torsion to high strains: quantitative microstructural and texture analysis from optical and diffraction data", Advances in Interpretation of Geological Processes: Refinement of Multi-scale Data and Integration in Numerical Modelling, M. I. Spalla, A. M. Marotta, G. Gosso
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This contribution presents a quantitative microstructural analysis of a polycrystalline aggregate of gypsum, deformed in torsion (T=70–90 °C) at γ (shear strain) ranging from 0 to 4.82. Quantitative microstructural analysis is used to compare the evolution of microstructures observed by optical microscope with those obtained from analysis of X-ray and neutron diffraction data. This analysis shows that during experimental deformation, gypsum accommodated strain by brittle and plastic deformation mechanisms, developing Riedel-like microfaults with plastic foliations and crystallographic preferred orientation (CPO). The relations of microstructures show that with increasing strain, the Riedel systems start from R planes with an angle of ≈30° to the Imposed Shear Plane. This angle decreases (5°–15°) when strain increases, and Y planes develop. Quantitative texture analysis (QTA) shows that S-foliations start developing at low γ and maintain their orientation up to high γ, and that the most active slip system is the (010) along normal to (100) and the -axis. Shape preferred orientation (SPO) of gypsum does not coincide with the theoretical orientation as it does not decrease with increasing strain. This discrepancy is explained by the role of the brittle shear planes that impose a back rotation to gypsum. No brittle to plastic transition occurs. But both plastic and brittle structures contemporaneously accommodate and localize strain.
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Advances in Interpretation of Geological Processes: Refinement of Multi-scale Data and Integration in Numerical Modelling
Iterative comparison of analytical results and natural observations with predictions of numerical models improves interpretation of geological processes. Further refinements derive from wide-angle comparison of results from various scales of study. In this volume, advances from field, laboratory and modelling approaches to tectonic evolution – from the lithosphere to the rock scale – are compared. Constructive use is made of apparently discrepant or non-consistent results from analytical or methodological approaches in processing field or laboratory data, P–T estimates, absolute or relative age determinations of tectonic events, tectonic unit size in crustal scale deformation, grain-scale deformation processes, various modelling approaches, and numerical techniques. Advances in geodynamic modelling critically depend on new insights into grain- and subgrain-scale deformation processes. Conversely, quantitative models help to identify which rheological laws and parameters exert the strongest control on multi-scale deformation up to lithosphere and upper mantle scale.