Publications scientifiques
Gaëlle Sandra Assomo Ngono
Autres affiliations : Institut de Recherches Géologiques et Minières
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Alembert Alexandre Ganwa
Sylvestre Martial Ntomba
Geological Journal
Petrographical, geochemical, and geochronological data obtained from Ngaye high‐grade metasedimentary rocks have contributed to determine the provenance, nature, and evolutionary history of the Adamawa‐Yadé Domain from the Archean to Pan‐African events. The rocks are migmatites formed after TTG and granitic crusts were reworked by partial melting at T = 683–994°C. Geochemical features, for example, low Rb/Sr ratio (0.03–0.53), high Cr/V, and Cr/Th ratios (9.91–100.75; 28.41–686.15), respectively, indicate that these samples were derived predominantly from a mafic crust source. The primordial mantle‐normalized spidergrams are characterized by negative Nb‐Ta anomalies, suggesting melting of crustal rocks. REE fractionation shown (La/Yb) N = 8.48–197.89) indicate melting of crustal source rocks (meta‐TTGs). Low Hf and Zr contents (0.95–5.65 ppm and 23–262.85 ppm, respectively), low Sr/Y ratios (9.17–200.65), and a positive correlation between Th/Sc and Zr/Sc, point to crustal reworking. U–Pb ages on detrital zircon in tonalitic and granodioritic gneisses indicate contribution of Mesoarchean and Paleoproterozoic sources and suggest a maximum deposition age during the Early Paleoproterozoic for their magmatic protoliths. Magmatic zircon grains of granodiorite, with a round shape, Th/U ratio values ranging from 0.02 to 1.23, and an oscillatory zonation yield post emplacement metamorphic ages at 2,077 Ma. The lower intercept ages obtained in this study, match the tectonic reworking of the crust during the Pan‐African event associated with partial melting due probably to regional‐scale shear zone activities and magmatic accretion of juvenile magmas.
