Géologie, pétrologie et géochimie des syénites de Ninakri : comparaison avec d'autres massifs syénitiques anorogéniques de Côte d'Ivoire et d'Afrique de l'Ouest

The Ninakri complex (Côte d'Ivoire) is made up of two small blocks which intrude into the Birimian formations of the West African Craton. The rocks range from nepheline monzosyenites, aegirine and/or riebeckite syenites to micromonzonites. Their mineralogical and geochemical composition (major and trace) element) show that they belong to A-type granitoids. The zircon typology data and the rocks' content in incompatible elements indicate that they originate in an hypersolvus alkaline to subalkaline magma coming from a partial melting of an attenuated continental crust. This magma was crystallized under low water pressure and low O₂ fugacity. The comparison with others anorogenic syenitic massifs in the Côte d'Ivoire and West Africa (Nigeria, Cameroon, Niger) suggest that these syenites were intruded along paleosutures at the end of the Eburnean Orogen between 1900 to 1600 Ma.