Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences



Occurrence number: 
Longitude: 9.83, Latitude: 5.05

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).

The oldest lava so far dated is a basalt which gave, by K-Ar, an age of 1.55±0.1 Ma (Gouhier et al., 1974). Unpublished work by C.A. Hirst (quoted by Fitton, 1987) showed that the Elengoum caldera probably collapsed between 0.8 and 0.6 Ma ago. The Eboga lavas have ages between 0.56 and 0.26 Ma and the collapse of the Eboga crater probably took place at about 0.25 Ma. However, cinder cones on the floor of the Ebogo caldera are younger.

BALLENTINE, C.J., LEE, D.-C. and HALLIDAY, A.N. 1997. Hafnium isotopic studies of the Cameroon line and new HIMU paradoxes. Chemical Geology, 139: 111-24.DERUELLE, B., MOREAU, C., NKOUMBOU, C., KAMBOU, R., LISSOM, J., NJONFANG, E., GHOGOMU, R.T. and NONO, A. 1991. The Cameroon Line: a review. In A.B. Kampunzu and R.T. Lubala (eds), Magmatism in extensional structural settings. 274-327. Springer-Verlag, Berlin.FITTON, J.G. 1987. The Cameroon line, West Africa: a comparison between oceanic and continental alkaline volcanism. In J.G. Fitton and B.G.J. Upton (eds), Alkaline igneous rocks. 273-91. Geological Society of London Special Publication 30.GÈZE, B. 1943. Géographie physique et géologie du Cameroun occidental. Mémoires du Muséum National d'Histoire Naturelle. Paris, N.S. 17: 1-271.HALLIDAY, A.N., DICKIN, A.P., FALLICK, A.E. and FITTON, J.G. 1988. Mantle dynamics: a Nd, Sr, Pb and O isotopic study of the Cameroon Line volcanic chain. Journal of Petrology, 29: 181-211.Jérémine, 1941 and 1943.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith