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Déformation, transferts de matière et de fluide dans la croûte continentale: application aux massifs cristallins externes des Alpes

Abstract : In order to better understand the mechanisms responsible for mass transfer in quartz-rich rocks, two approaches have been coupled during this work: investigation the relationships between fluid-rock interactions and deformation in the Mont Blanc massif (western Alps) and an experimental work performed at the GFZ (Potsdam). Our attention was mainly focused on diffusive mass transfer that is so often neglected.
A multidisciplinary study based on field observation, mineralogical and geochemical analyses was performed in the Mont Blanc massif where three kinds of structures resulting of the coupling of both deformation and fluid-rock interactions were evidenced. In the central part of the massif, a metasomatic front evidenced by intense precipitation of Mg-rich phyllosilicates indicates up-flow of deep seated fluids across the whole massif. The formation of a shear zone network together with episyenitisation of the granite (dissolution of magmatic quartz and biotite) appears mostly controlled by deformation instead of reactive fluid flow.
Some experiments were performed in hydrothermal laboratory in order to better constrain the processes that are assumed to be responsible of mass transfer within the Mont Blanc massif. Pressure-solution experiments indicate that this deformation process is efficient in quartz-rich rocks even under isotropic P-T conditions. Such process might be responsible of episyenitisation. A similar study performed with glass spheres instead of natural minerals indicates competition of several deformation mechanisms both ductile and brittle. It also shows that a very small amount of water enhances deformation. Other experiments performed under a thermal gradient allow determination of the crystallisation sequence resulting from the cooling of an upwards flowing fluid, which composition is buffered by granitic rocks. This crystallisation sequence (quartz, K-feldspar, mica and clay) is different from that observed within shear zones, which is in agreement with the hypothesis that mineralogical changes in these shear zones are controlled by deformation rather than by reactive fluid flow. A last set of experiments were performed in order to quantify the diffusivity of dissolved silica under P-T conditions of the middle crust.
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https://tel.archives-ouvertes.fr/tel-00011146
Contributor : Magali Rossi <>
Submitted on : Monday, December 5, 2005 - 10:32:31 AM
Last modification on : Tuesday, September 7, 2021 - 3:54:23 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 4:22:23 PM

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  • HAL Id : tel-00011146, version 1

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Magali Rossi. Déformation, transferts de matière et de fluide dans la croûte continentale: application aux massifs cristallins externes des Alpes. Géologie appliquée. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00011146⟩

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