Manengouba

Manengouba is a large strato-volcano rising to 2411 m and with a diameter of 25 km. It has a pair of nested summit calderas: an outer, poorly defined one (Elengoum) which encloses the well preserved Eboga caldera in which there are several small pyroclastic cones, two with crater lakes. An aerial view of the summit area is given by Gèze (1943, Fig. 44). There are numerous pyroclastic cones on the flanks of the volcano. The lavas form a complete suite from hy and ne normative basalts through hawaiites to trachytes and rhyolites. The intermediate rocks commonly contain amphibole and the trachytes phenocrysts of anorthoclase rimmed by oligoclase, pale green pyroxene and in some rocks barkevikitic amphibole (Jérémine, 1943). The rhyolites, amongst which are obsidians, are generally peralkaline and include phenocrysts of alkali feldspar, tiny aegirines, amphibole, possibly sodic, aenigmatite and fayalite (Jérémine, 1941 and 1943). Rock analyses are given by Jérémine (1941), Deruelle et al. (1991) and Fitton (1987), and Rb-Sr, Sm-Nd, U, Pb and O isotopic data on a single hy-normative basalt are in Halliday et al. (1988); Hf, Sr, Nd and Pb isotope data on one sample are given by Ballentine et al. (1997).