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Bulletin de la Societe Geologique de France; September 2007; v. 178; no. 5; p. 331-342; DOI: 10.2113/gssgfbull.178.5.331
© 2007 Societe Geologique de France
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Archaean crustal accretion at the northern border of the Congo Craton (South Cameroon). The charnockite-TTG link

André Pouclet1, Rigobert Tchameni2, Klaus Mezger3, Max Vidal1, Emmanuel Nsifa4, Cosmas Shang4 and Joseph Penaye5

1 Institut des Sciences de la Terre d’Orléans, UMR 6113, Université d’Orléans, B.P. 6759, 45067 Orléans cedex 2, France. e-mail: andre.pouclet{at}tele2.fr
2 Département des Sciences de la Terre, Université de Ngaoundéré, B.P. 454, Ngaoundéré, Cameroun.
3 Institut für Mineralogie, Zentrallabor für Geochronologie, Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany.
4 Département des Sciences de la Terre, Université de Yaoundé I, B.P. 812, Yaoundé, Cameroun.
5 Centre de Recherches Géologiques et Minières, B.P. 333, Garoua, Cameroun.

Magmatic charnockitic rocks and TTG (tonalite-trondhjemite-granodiorite) plutons intruded successively the Archaean greenstone belts of the Ntem Complex, at the northwestern margin of the Congo Craton. Geochemical data, zircon Pb-Pb ages, and Sr-Nd isotope studies, constrain the magmatic features, the genetical timing, and the geodynamic settings of these different suites. Charnockites and TTGs are characterized by high Al2O3 contents, high Na/K ratio, low Th content, LREE enrichment, HREE depletion, negative anomalies in Nb, Ta, and Ti, and positive anomalies in Sr. The Pb-Pb zircon ages indicate that charnockites were emplaced at ca. 2900 Ma and TTGs, which cross-cut the charnockites, at ca. 2830 Ma. TDM Nd mean crustal residence ages of both suites range between 3.10 and 2.93 Ga. The charnockites show slightly positive initial {varepsilon}Nd2.9Ga (+0.3 to +1.3), whereas the TTGs have slightly negative values (+0.1 to –1.5). The charnockitic and TTG magmas may have resulted from different partial melting processes of the primitive Archaean basaltic crust and contaminated mantle, possibly in a hot slab subduction convergent regime. They contribute to a two-stage crustal growth of the Archaean craton.

Key Words: Archaean • Congo Craton • Cameroon • Charnockites • TTG • Pb-Pb zircon age • Nd-Sr isotopes • Crustal accretion






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