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Interactions fluides-roches dans les chondrites carbonées : approche expérimentale et modélisation thermodynamique

Abstract : Iron-rich serpentines are major components of CM carbonaceous chondrites. They formed during early alteration events on their asteroidal parent bodies at an early stage of formation of the Solar System. The study of these minerals aims at better understanding the conditions in which they altered, but it would also help understanding the long term evolution of nuclear waste storage. Indeed, aqueous alteration in chondrites is considered as a good analog for iron-clay-water interactions. During this thesis, we studied the conditions of formation and stability of Fe-rich serpentines, and we paid particular attention to the evolution of the Fe valence state during alteration. Three approaches have been adopted : the synthesis of Fe-rich serpentines, the experimental alteration of chondritic assemblages at low temperature and under anoxygenic conditions, and the refinement of a themodynamic model of serpentines in the Fe2+-Fe3+-Mg-Al-Si-O-H system. This model, mostly refined using data from iron-clay experiments, gave encouraging results, and should allow to better predict equilibrium assemblages in altered chondrites. Out of equilibium processes were also experimentally explored, and our results suggest that there is a kinetic control of the precipitation of Fe-rich serpentines close to the ideal end-member. At the first stages of alteration of primary minerals under anoxic conditions, we observed poorly crystalline phases with a relatively low ferric iron content. Our result suggest that the Fe/Si ratio and the Fe3+ content favor the precipitation of serpentines. They provide interesting insight into the first stages of alteration in chondrites.
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Florent Caste. Interactions fluides-roches dans les chondrites carbonées : approche expérimentale et modélisation thermodynamique. Sciences de la Terre. Université Pierre et Marie Curie - Paris VI, 2016. Français. ⟨NNT : 2016PA066717⟩. ⟨tel-02401865⟩

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