Résumé
The gold-rich Ketté formations belong to the Adamawa-Yadé block of the Neoproterozoic Central Africa Orogenic Belt. They consist of a complex association of tonalite, granodiorite, and heterogeneous granite including rafts of metapyroxenite, amphibolite, paragneiss and migmatite. Metapyroxenite and amphibolite are metaluminous (A/CNK: 0.65-0.95), calc-alkaline, enriched in LILE and LREE, with εNd610 < 0 and TDM ages of 1.7 Ga, highlighting their enriched mantle source. Paragneiss are rich in LREE, Cr, V, Sc and Ni and display A/CNK (1.06-1.08) and A/NK (1.5-3.49) ratios consistent with a sedimentary protolith made of poorly sorted greywackes and litharenites with a contribution from mafic rocks of the juvenile crust. Granitoids display a variety of signatures, ranging from metaluminous to peraluminous (A/CNK: 0.94-1.04), calc-alkaline to alkaline. The heterogeneous granite in diffuse contact with migmatite have εNd654 values of –9.61 and –8.11, and are interpreted to reflect local magma collection within the zone of dominant partial melting of the paragneiss. The tonalite and granodiorite, characterized by magmatic textures, display Mg# of 39.9–48.8, low HFSE contents, and enrichment in LILE and LREE. They were likely formed by the fractional crystallisation of a dioritic magma derived from the partial melting of amphibolite. The main structure of the migmatite is a shallow- to moderately dipping NE–SW trending syn-migmatitic foliation Smgm, marked by alternating leucosome and mesosome layers, with relics of an S0/S1 foliation locally preserved within the mesosome. Granulite-facies relics with a peak at 8-10 kbar/≥800 °C are preserved in metapyroxenite. Networks of texturally continuous leucosome veins concordant to discordant to the syn-migmatitic foliation, localization of granitic veins in shear zones and fold axial planes, attest for deformation in the presence of melt. Granitoids form kilometre-scale plutons with gently dipping magmatic fabrics (Sm-Sm/C2) concordant to the syn-migmatitic foliation. These fabrics are transposed into a steeply dipping (47°-74°) E–W to NW–SE trending mylonitic fabric (Smyl-S3/C3), bearing a moderately plunging (15°-49°) stretching lineation L3, marking the folded Mama Shear Zone (MaSZ). These data indicate that the Ketté region has recorded magmatic accretion of a mafic crust originating from an enriched mantle source. This crust and its associated sediments were subsequently tectonically thickened during the Pan-African orogeny and affected by partial melting. Migration of dioritic to granitic magmas from the partially molten orogenic root led to syntectonic crustal differentiation.