Diversity of the Palaeoproterozoic granitoids of the Kédougou inlier (eastern Sénégal): Petrographical and geochemical constraints

Edmond Dioh , Didier Béziat (1) , Pierre Debat (1) , Michel Grégoire (2) , Papa Malick Ngom

1 LMTG - Laboratoire des Mécanismes et Transfert en Géologie
2 DTP - Dynamique terrestre et planétaire

Field, petrographical and geochemical studies of the Palaeoproterozoic granitoids of the Kédougou inlier (Eastern Sénégal) allow to define four compositional types: (i) the Layered Plutonic Complex consisting of sodic calc-alkaline granitoids defining a trend from Opx-, Cpx- and amphibole-bearing layered gabbros to amphibole-bearing tonalite; the latter shows similarities with adakite-like rocks; (ii) amphibole-bearing granitoids with TTG features occurring as composite batholiths and as isolated oval-shaped plutons cross cutting the entire Birimian metavolcanic and metasedimentary formations; (iii) potassic granitoids defining a trend from Opx-, Cpx-bearing gabbros to amphibole-bearing monzodiorite and preferentially emplaced within the calc-alkaline metavolcanites; (iv) peraluminous biotite-bearing granitoids emplaced within the metasediments of the upper part of the Birimian lithostratigraphical pile. The granitoid suites were emplaced within a time interval of about 80 Ma from about 2160 Ma (emplacement of the LPC) to 2080 Ma (emplacement of the youngest plutons such as the amphibole-bearing TTG granitoid or the pyroxene- and K-feldspar-bearing granitoids). The granitoid suites were emplaced in an immature arc environment [Dia, A., Van Schmus, W.R., Kröner, A., 1997. Isotopic constraints on the age and formation of a Palaeoproterozoic volcanic arc complex in the Kedougou inlier, eastern Senegal, West Africa. J. Afr. Earth Sci. 24 (3), 197 213]. Parental magmas were probably derived from the partial melting of a mantle wedge above a subduction zone. Tonalite magmas of distinctive composition were probably produced by partial melting of the subducting slab itself. They could characterize the early stage of the slab-melting, precursor of the TTG magmatism. The close association of calc-alkaline, trondhjemitic and peraluminous granitoids and the successive emplacement of granitoid groups more and more enriched in K2O recognized in the Kédougou inlier is typical of the Paleoproterozoic granitoid series from West Africa.

Domaines: Sciences de la Terre

Edmond Dioh, Didier Béziat, Pierre Debat, Michel Grégoire, Papa Malick Ngom. Diversity of the Palaeoproterozoic granitoids of the Kédougou inlier (eastern Sénégal): Petrographical and geochemical constraints. Journal of African Earth Sciences, 2006, 44, pp.351-371. ⟨10.1016/J.JAFREARSCI.2005.11.024⟩. ⟨hal-00319705⟩