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De l'imagerie chimique à la micro-cartographie Pression-Température-Déformation : évolution minéralogique et transport de matière dans des systèmes en déséquilibre thermomécanique.
Applications aux métapélites et aux matériaux de stockage de déchets radioactifs

Abstract : The mineralogical composition of metamorphic rocks or industrial materials evolves when they are submitted to thermomechanical disequilibria, i.e. a spatial or temporal pressure and temperature evolution, or chemical disequilibria as variations in redox conditions, pH... For example, during low temperature metamorphic processes, rocks reequilibrate only partially, and thus record localy thermodynamic equilibria increasing so the spatial chemical heterogeneities. Understanding the P-T evolution of such systems and deciphering modalities of their mineralogical transformation imply to recognize and charaterize the size of these local “paleoequilibria”, and so to have a spatial chemical information at least in 2 dimensions. In order to get this information, microprobe X-ray fluorescence maps have been used. Computer codes have been developped with Matlab to quantify these maps in view of thermobarometric estimations. In this way, P-T maps of mineral crystallisation were produced using the multi-equilibria thermodynamic technique.
Applications on two metapelites from the Sambagawa blue-schist belt (Japan) and from the Caledonian eclogitic zone in Spitsbergen, show that quantitative chemical maps are a powerfull tool to retrieve the metamorphic history of rocks. From these chemical maps have been derived maps of P-T-time-redox-deformation that allow to characterize P-T conditions of minerals formation, and so, the P-T path of the sample, the oxidation state of iron in the chlorite phase. As a result, we underline the relation between deformation and cristallisation, and propose a relative chronology of minerals cristallisation and deformations. The Fe3+ content map in chlorite calculated by thermodynamic has also been validated by a µ-XANES mapping at the iron K-edge measured at the ESRF (ID24) using an innovative method.
Another application relates to an experimental study of clay materials, main components of an analogical model of a nuclear waste storage site. Chemical maps allowed to charaterize the 2D mineralogical evolution of clays toward iron rich end-members. They have also been used as input data in a 2D finit element numerical model aiming to estimate the iron diffusion coefficient in clays at low temperatures, important parameter to modelize the destabilization of nuclear waste storage sites in the course of time.
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Contributor : Vincent de Andrade <>
Submitted on : Tuesday, March 6, 2007 - 11:45:18 PM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
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Vincent de Andrade. De l'imagerie chimique à la micro-cartographie Pression-Température-Déformation : évolution minéralogique et transport de matière dans des systèmes en déséquilibre thermomécanique.
Applications aux métapélites et aux matériaux de stockage de déchets radioactifs. Géologie appliquée. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00135186⟩

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