New igneous zircon Pb/Pb and metamorphic Rb/Sr ages in the Yaounde Group (Cameroon, Central Africa): implications for the Central African fold belt evolution close to the Congo Craton |
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Authors: | Sébastien Owona Marion Tichomirowa Lothar Ratschbacher Joseph Mvondo Ondoa Dieudonné Youmen J?rg Pf?nder Félix M. Tchoua Pascal Affaton Georges Emmanuel Ekodeck |
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Affiliation: | 1. Department of Earth Sciences, Faculty of Science, University of Douala, P.O. Box. 24157, Douala, Cameroon 2. Institute of Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, 09596, Freiberg, Germany 3. Institute of Geology, TU Bergakademie Freiberg, Zeunerstr. 12, 09596, Freiberg, Germany 4. Department of Earth Sciences, Faculty of Science, University of Yaounde, P.O. Box. 812, Yaounde, Cameroon 5. CEREGE, CNRS-Université d’Aix-Marseille III, B.P. 80, 13545, Aix en Provence, France
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Abstract: | Three meta-igneous bodies from the Yaounde Group have been analyzed for their petrography, geochemistry, and 207Pb/206Pb zircon ages. According to their geochemical patterns, they represent meta-diorites. The meta-plutonites yielded identical zircon ages with a mean of 624?±?2?Ma interpreted as their intrusion age. This age is in agreement with previously published zircon ages of meta-diorites from the Yaounde Group. The meta-diorites derived mainly from crustal rocks with minor contribution from mantle material. The 87Rb/86Sr isochron ages of one meta-diorite sample and three meta-sedimentary host rocks are significantly younger than the obtained intrusion age. Therefore, they are not related to igneous processes. 87Rb/86Sr isochron ages differ from sample to sample (599?±?3, 572?±?4, 554?±?5, 540?±?5?Ma) yielding the oldest Neoproterozoic age (~600?Ma) for a paragneiss sample at a more northern location. The youngest Rb/Sr isochron age (~540?Ma) was obtained for a mica schist sample at a more southern location closer to the border of the Congo Craton. The 87Rb/86Sr whole rock-biotite ages are interpreted as cooling ages related to transpressional processes during exhumation. Therefore, several discrete metamorphic events related to the exhumation of the Yaounde Group were dated. It could be shown by Rb/Sr dating for the first time that these late tectonic processes occurred earlier at more distant northern locations of the Yaounde Group and lasted at least until early Cambrian (~540?Ma) more closely to the border of the Congo Craton. |
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