Abstract
The geological evolution of the Central African Fold Belt (CAFB) remains debated. The granitoids, orthogneisses and granitic veins from the Goa-Mandja area (Adamawa-Yade domain) are considered to constrain this belt. These rocks are consistent with late-D2 regional emplacement and synchronous with the magmatism at ~600 Ma within the CAFB in Cameroon and its extension into northeastern Brazil, as the zircon UPb dating points to 603–598 Ma crystallization ages. Analytical data reveal slightly elevated δ18Ozrn (6.45–7.17‰) and δ18OWR (8.20–8.61‰), moderate to high SiO2 (59.70–77.23 wt%), low MgO (0.07–2.77 wt%), Cr (0.29–55.12 ppm), Ni (0.45–33.6 ppm), V (1.52–116.62 ppm) and Mg# (0.02–0.36) contents, indicating crustal origin. The low to medium 87Sr/86Sri (0.703328–0.722670) and positive to negative εNd(t) (+5.7 to −9.9), coupled with the diversity of Nd model ages (TDM2) support the heterogeneity of crustal protoliths. The high positive εNd(t) (+5.7) of the granitic vein indicates derivation from juvenile Neoproterozoic (Nd-TDM2 at 854 Ma) crustal protolith. TDM2(Nd) and TDM2(Hf) ages of 1188–2120 Ma and 2173–2480 Ma also suggest the involvement of Mesoproterozoic to Paleoproterozoic crustal protoliths.Samples show metaluminous to weakly peraluminous, high-K calc-alkaline to shoshonitic and I-type granitoid features and are similar with crustal rocks in regard to LILE (Rb, K) and LREE enrichments and HFSE (Nb, Ta, Ti) depletions. These combined features indicate slab subduction related setting for the magma generation. Slab subduction may have generated the heat necessary to provoke partial melting at the lower crustal level. Considering their position close to the Tchollire-Banyo Fault corridor, at the transition between the Adamawa-Yade and northern domains, the subduction derived features shown by the Goa-Mandja I-type granitoids could be related to the subduction of an old plate boundary during amalgamation of Gondwana. Therefore, the Goa-Mandja area records dominant magmatic accretion along the northern margin of the Congo craton (active margin) associated with a possible northwestern subduction.
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