Minéralisations uranifères de la ceinture orogénique Pan-africaine du Damara (Namibie) : implication de la fusion partielle, de la migration et de la mise en place des magmas sur le remaniement de la croûte continentale

Abstract : The chronology of continental crust formation is debated but most models converge on the fact that much of the continental crust on the surface of the Earth is present since the Proterozoic (2.5 - 0, 54 Ga) and has essentially undergoes reworking during orogenesises. Uranium which is an incompatible element is a tracer of this crustal evolution, since its initial fractionation by partial melting of the mantle to its reworking in higher crustal levels. Neoproterozoic Pan-African (0.5 ± 0.1 Ga) orogenic belt of the Damara in Namibia is a good geological target to test the relationship between crustal growth and evolution and metallogeny of uranium. It was formed after the collision of the Archean cratons of Congo and Kalahari (subducting plate). This thesis shows that the evolution of the continental crust during the Neoproterozoic Damara Orogen is by reworking of Archaean to Neoproterozoic crustal domains and partial melting of rocks is the predominant mechanism for primary uranium mineralization associated with crystallization of intrusive granites derived from anatexis of paleo- to mesoproterozoic basement fragments. The intrusive granites issued from partial melting of sediments in the upper crustal levels are low or not favorable to high concentrations of uranium because of 1) the low preconcentration of their protoliths and 2) their relatively limited migration. The mineralized intrusive granites correspond to late- to post-collision injections (ca. 520-480 Ma in the central area) and are related to thermal relaxation phases and gravitational collapse subsequent to thickening in crustal orogen in a context of plates convergence
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Wilfried Antoine Bassou Toé. Minéralisations uranifères de la ceinture orogénique Pan-africaine du Damara (Namibie) : implication de la fusion partielle, de la migration et de la mise en place des magmas sur le remaniement de la croûte continentale. Sciences de la Terre. Université de Lorraine, 2012. Français. ⟨NNT : 2012LORR0274⟩. ⟨tel-01749645⟩

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