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Rhyolites of the Mbépit Massif in the Cameroon Volcanic Line: an early extrusive volcanic episode of Eocene age

Abstract : The Mbépit Massif, one of the oldest volcanoes of the Cameroon Volcanic Line, was built up during the Eocene (40K/40Ar ages of 45.5 and 44.0 Ma). Located in the Eastern part of the Noun Plain, North-East of Foumbot, this massif is made up mainly of rhyolitic domes and thick, viscous lava flows. Such felsic lavas are rather rare in the Cameroon Volcanic Line. Most rhyolites are porphyritic and contain phenocrysts of K-feldspars (Or97–89), Na-feldspars (Ab99–88) and quartz. Scarce Fe–Ti oxides comprise titanohaematite and hemo-ilmenite. Owing to their low CaO contents, rhyolite compositions range from metaluminous to peraluminous (with normative corundum) and less commonly, peralkaline (normative aegirine). Chondrite-normalised REE patterns show LREE enrichment; and LaN/YbN ratios between 12.2 and 17.2, with prominent negative Eu anomalies (0.16 < Eu/Eu* < 0.62). The Th/Ta ratios range between 2.6 and 3. Initial 87Sr/86Sr ratios (0.7047 and 0.7050) and 143Nd/144Nd ratios (0.5125 and 0.5126, εNd of −1.04 to +1.22) suggest mantle sources (HIMU (high µ with μ = 238U/204Pb), EM (Enriched Mantle), FOZO (FOcal ZOne) components) of the rhyolites accompanied by little or no crustal contamination.
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Submitted on : Tuesday, January 20, 2009 - 3:15:15 PM
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Pierre Wandji, Dieudonné Tchokon Seuwui, Jacques-Marie Bardintzeff, Hervé Bellon, Bernard Platevoet. Rhyolites of the Mbépit Massif in the Cameroon Volcanic Line: an early extrusive volcanic episode of Eocene age. Mineralogy and Petrology, Springer Verlag, 2008, 94 (3-4), pp.271-286. ⟨10.1007/s00710-008-0013-6⟩. ⟨insu-00354667⟩

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