U/pb dating of precambrian rocks from northern cameroon,orogenic evolution and chronology of the pan-african belt of central africa |
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| Institution: | 1. C.R.G.M., B.P. 333, Garoua Cameroon;2. C.R.P.G., B.P. 20, 54501 Vandoeuvre les Nancy Cedex France;3. Université de Nancy I, Laboratoire de Pétrologie, B.P. 239, 54506 Vandoeuvre les Nancy Cedex France;1. Instituto de Geociências, Universidade de São Paulo, São Paulo, Brazil;2. CONICET-Universidad de Buenos Aires, Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires (IGEBA), Argentina;3. Instituto de Ciencias Geológicas, Universidad de la República, Montevideo, Uruguay;4. Université Paris-Saclay, CNRS, GEOPS, 91405 Orsay, France;5. Geoscience Centre, Georg–August–Universität Göttingen, Göttingen, Germany;1. Department of Earth Sciences, University of Yaoundé I, Yaoundé, P.O. Box 812, Cameroon;2. Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK 74078-3031, USA;1. KU Leuven, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, B-3000 Leuven, Belgium;2. Ghent University, Department of Analytical Chemistry, Ghent University, Krijgslaan 281-S12, B-9000 Ghent, Belgium;1. Aix-Marseille Univ., CNRS, IRD, INRA, Coll. France, CEREGE, Aix-en-Provence, France;2. Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Sektion Geochronologie, GeoPlasma Lab, Königsbrücker Landstraße 159, 01109 Dresden, Germany;3. Université officielle du Sud Kivu, Bukavu, Congo |
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| Abstract: | Northern Cameroon has been classically divided into an old ‘basement complex’, a Middle Proterozoic cover (‘séries intermédiaires’) and granites emplaced during the Pan-African orogeny. New U/Pb geochronological data on different rock units from this region are presented. A rhyolite from the Poli schists (‘séries intermédiaires’) gives an age close to 800 Ma. Migmatitic gneisses of the ‘basement complex’ seem to derive from different detrital or magmatic sources. The metadiorites and foliated granites of the ‘basement complex’ give ages around 630 Ma. The 800 Ma age is interpreted as dating volcanic activity, probably related to the initial stage of the Pan-African evolution. Ages around 630 Ma date a syn-tectonic plutonism dominated by a regional-scale basic to intermediate plutonic suite (BIP). Zircons of the BIP suite are almost concordant and show no evidence of inheritance; the suite shows calc-alkaline affinity and relatively low 87Sr/86Sr initial ratios; thus the BIP suite represents material newly added to the crust during the PanAfrican orogeny. These data are at variance with previous interpretations of this part of the mobile belt as old Precambrian crust reactivated during the Pan-African orogeny. The previous distinction between the ‘séries intermédiaires’ and a regional ‘basement complex’ must be reappraised, similar ages being found in both units. A chronological succession of the Pan-African evolution is established and tentatively compared with that of the Trans-Saharan belt in Nigeria and Hoggar. |
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