Mineralogy, geochemistry and petrogenesis of the recent magmatic formations from Mbengwi, a continental sector of the Cameroon Volcanic Line (CVL), Central Africa |
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Authors: | Beno?t Joseph Mbassa Emmanuel Njonfang Mathieu Benoit Pierre Kamgang Michel Grégoire Stephanie Duchene Pierre Brunet Bekoa Ateba Félix M. Tchoua |
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Affiliation: | 1. Institut de Recherches Géologiques et Minières, IRGM/ARGV Ekona, B.P. 370, Buéa, Cameroon 4. Département des Sciences de la Terre, Faculté des Sciences, Université de Yaoundé I, B.P. 812, Yaoundé, Cameroon 2. Laboratoire de Géologie, Ecole Normale Supérieure, Université de Yaoundé I, B.P. 47, Yaoundé, Cameroon 3. Géosciences-Environnement-Toulouse Unité Mixte de Recherche 5563, Observatoire Midi Pyrénées, Université Paul Sabatier, 14, avenue édouard-Belin, 31400, Toulouse, France
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Abstract: | The Mbengwi recent magmatic formations consist of volcanics and syenites belonging to the same magmatic episode. Lavas form a bimodal basanite-rhyolite alkaline series with a gap between 50 and 62?wt.% SiO2. Mafic lavas (basanite-hawaiite) are sodic while felsic rocks (trachyte-rhyolite-syenites) are sodi-potassic, slightly metaluminous to peralkaline. The geochemical and isotopic characteristics (0.7031?(87Sr/86Sr)initial?0.7043; 1.03?Ndi?5.17) of these rocks are similar to those of other rocks from the CVL. The main differentiation process is fractional crystallization with two trends of fractionation. Their Rb/Sr isochron age of 28.2?Ma, almost similar to 27.40?±?0.6?Ma?K/Ar age obtained in a trachyte from neighboring Bamenda Mountains system, precludes any local age migration of an hypothetic hotspot. Mafic lavas have OIB features displaying an isotopic signature similar to that of HIMU mantle source different from FOZO known as source of most parental magmas along the CVL. |
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