stripes
Little volcanological information on the Visoke volcano has been traced. On an inset volcanological map (1:150,000) on the Ruhengeri geological map (Antun et al., 1971) the products of the Visoke volcano are combined with those from Sabinyo (No. 137-00-003) and appear to be mostly hidden by flows from Karisimbi (No. 137-00-005). The northern half of the volcano lies in the Democratic Republic of Congo, but within Rwanda the lavas in the immediate vicinity of the summit crater are indicated as being ‘Leucitites diverses’. Marcelot and Rancon (1988) write that the volcano has produced leucitite, olivine nephelinite, basanite and hawaiite lavas and they describe two leucitites in detail; one collected near the summit and the other from the base of the cone. The former rock contains phenocrysts of leucite, diopside-salite and phlogopite and xenocrysts of pyroxene, titaniferous phlogopite and rare olivine in a groundmass of the same minerals, apatite and glass. The rock from the base of the cone contains the same phenocryst assemblage, the leucites being up to 3 mm diameter, in a groundmass of leucite, pyroxene, titanomagnetite and apatite and in which nepheline forms poikilitic patches. Whole rock and numerous mineral analyses are given by Marcelot and Rancon (1988). A further eight whole rock analyses are reproduced in Denaeyer and Schellinck (1965).
DENAEYER, M-E. and SCHELLINCK, F. 1965. Recueil d’analyses des laves du fosse tectonique de l’Afrique Centrale. Annales, Museee Royal de l’Afrique Centrale, Tervuren, Belgique. Serie In 8°, Sciences Géologiques, 49: 1-234.MARCELOT, G. and RANCON, J.P. 1988. Mineral chemistry of leucitites from Visoke volcano (Virunga Range, Rwanda): petrogenetic implications. Mineralogical Magazine, 52: 603-13.MULDER, M. de and PASTEELS, P. 1986. K-Ar geochronology of the Karisimbi volcano (Virunga, Rwanda-Zaire). Journal of African Earth Sciences, 5: 575-9.
