Fluid-assisted large strains in a crustal-scale décollement (Hercynian Belt of South Brittany, France)
F. Le Hebel, D. Gapais, S. Fourcade, R. Capdevila, 2002. "Fluid-assisted large strains in a crustal-scale décollement (Hercynian Belt of South Brittany, France)", 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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Crustal deformations often occur along gently-dipping shear zones, where the scale of fluid transfers and the coupling between deformations and fluid availability are important questions. We present a structural and geochemical study of felsic rocks deformed at about 350–400°C within a crustal-scale décollement zone from the Hercynian Belt of South Brittany. At regional scale, deformations resulted in large distributed strains accumulated by dissolution-crystallization of quartz and feldspars. Mass transfers produced veins growing parallel to the foliation. Veins were major precipitation zones, while adjacent rocks were the main zones of dissolution. Deformation patterns, vein mineralogy, and oxygen isotope data show that both the amount of fluids and the scale of fluid flow were limited, and that the dominant transfer mechanism was diffusion. Results suggest that the deformation zone has acted as a trap for early fluids rather than as a syn-kinematic fluid channel.
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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.