Stress-strain rate history of a midcrustal shear zone and the onset of brittle deformation inferred from quartz recrystallized grain size
Published:January 01, 2005
F. Gueydan, C. Mehl, T. Parra, 2005. "Stress-strain rate history of a midcrustal shear zone and the onset of brittle deformation inferred from quartz recrystallized grain size", Deformation Mechanisms, Rheology and Tectonics: from Minerals to the Lithosphere, D. Gapais, J. P. Brun, P. R. Cobbold
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The quantification of quartz shear stress and strain rate within a midcrustal shear zone provides a mechanical frame to describe the evolution from penetrative ductile deformation to localized deformation and the onset of brittle deformation. The quantification is based on the relationships between the quartz recrystallized grain size, the quartz shear stress (piezometric relation) and the strain rate (dislocation creep flow law). Increasing strain is accompanied by a general decrease of quartz recrystallized grain size and a decrease in grain size scattering. These are interpreted as a result of a complex loading history. The evolution from penetrative ductile deformation toward strain localization, marked by an increase of the strain rate by one order of magnitude, is inferred from grain size memory. Brittle deformation is triggered for quartz shear stress of the order of 70 MPa and strain rate close to 10−12 s−1. This relative low value of the quartz shear stress necessary to trigger faulting implies a less important strength for the midcrust compared with strengths predicted by classical rheological envelopes.
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Deformation Mechanisms, Rheology and Tectonics: from Minerals to the Lithosphere
This book consists of 18 papers on deformation mechanisms, theology and tectonics. The main approaches include experimental rock deformation, microstructural analysis, field structural studies, analogue and numerical modelling. New results on various topics are presented, ranging from brittle to ductile deformation and grain-scale to lithosphere-scale mechanisms.
The volume will be of interest to academic and industrial researchers in the fields of structural geology, interactions between metamorphism, fluids and deformation, and large-scale tectonic processes.