Alkaline Rocks and Carbonatites of the World

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Bukavu (South Kivu, Haute Ruzizi) And Kamituga (Mwenga)

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Occurrence number: 
038-00-018
Country: 
Comoros
Location: 
Longitude: 28.7, Latitude: -2.33

The Bukavu volcanic field lies to the south and southwest of Lake Kivu and extends for some 80 km from north to south. The somewhat smaller Kamituga volcanic field lies further to the south-southeast. The Bukavu field comprises three cycles the first of which is tholeiitic and the second alkaline while the rocks of the third cycle are generally silica undersaturated but less alkaline than the second (Kanika et al., 1981; Kampunzu et al., 1983). Lavas are predominant but there are pyroclastic rocks, forming cones, and the most evolved rocks form lava domes. The rock types of the alkaline series are olivine basalt, ankaratrite, basanite, hawaiite, mugearite, benmoreite, trachyte and phonolite. The hawaiites include biotite and the mugearites a brown amphibole. The benmoreites are alkali feldspar rocks with aegirine and opaque phases and may include any combination of fayalite, amphibole and biotite. Both trachytes and phonolites comprise alkali feldspar and aegirine; the former may contain fayalite, biotite and amphibole, while the latter include nepheline, fayalite, katophorite and aenigmatite. Brief petrographic descriptions and a range of rock analyses are given by Kanika et al. (1981) and Kampunzu et al. (1983). A fuller geochemical treatment, with trace element data, including REE, is that of Auchapt et al. (1987). Although the Kamituga field consists principally of tholeiitic basalts, according to Auchapt et al. (1987) the alkaline cycle is also represented here, but petrographic descriptions have not been found.

Age: 
The basalts of the first cycle were erupted from 70 to 7 Ma, the alkaline rocks of the second cycle beween 7.8 and 1.9 Ma, but the third cycle only commenced 14,000 years ago (Kampunzu et al., 1983; Auchapt et al., 1987). A list of all Bukavu dates is given by Kampunzu et al. (1998b).
References: 
AUCHAPT, A., DUPUY, C., DOSTAL, J. and KANIKA, M. 1987. Geochemistry and petrogenesis of rift-related volcanic rocks from South Kivu (Zaire). Journal of Volcanology and Geothermal Research, 31: 33-46.KAMPUNZU, A.B., VELLUTINI, P-J., CARON, J-P.H., LUBALA, R.T., KANIKA, M. and RUMVEGERI, B.T. 1983. Le volcanisme et l’évolution structurale du Sud-Kivu (Zaïre). Un modèle d’interprétation géodynamique du volcanisme distensif intracontinental. Bulletin des Centres de Recherches Exploration-Production Elf-Aquitaine, 7(1): 257-71.KAMPUNZU, A.B., BONHOMME, M.G. and KANIKA, M. 1998b. Geochronology of volcanic rocks and evolution of the Cenozoic western branch of the east African rift system. Journal of African Earth Sciences, 26: 441-61.KANIKA, M., KAMPUNZU, A.B., CARON, J-P.H. and VELLUTINI, P.-J. 1981. Données nouvelles sur le volcanisme de la Haute Ruzizi (Sud Kivu, Zaïre). Comptes Rendus des Séances de l’Académie des Sciences, Paris, Ser 2, 292: 1277-82.
Location: 
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