Alkaline Rocks and Carbonatites of the World

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Badda And Sagatu (Gara Badda)

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Occurrence number: 
054-00-043
Country: 
Ethiopia
Region: 
Main Ethiopian Rift
Location: 
Longitude: 39.45, Latitude: 7.83

Badda is a large volcano lying immediately east of, and overlapping, Chilallo (No. 42). Like Chilallo it appears to be formed predominantly of alkaline trachyte lava flows. Extending southwards from Badda for some 70 km is the Sagatu Ridge which is the dissected remant of a 7 km wide fissure system (Mohr, 1980), the central 2 km of which is the locus of a dyke swarm. In the Badda sector of the swarm, in particular, the dykes are markedly bimodal comprising hawaiite and comendite. The comendites contain anorthoclase phenocrysts up to 1 cm long in a matrix of minute laths of alkali feldspar and accessory aegirine-augite and aegirine, which sometimes form microphenocrysts, riebeckite, aenigmatite, quartz and magnetite. Analyses of 25 rocks, including some trace element data, are given by Mohr (1980), and Sr isotope data are in Kennan et al. (1990).

Age: 
K-Ar determinations on two trachyte and one basaltic dyke ranged from 2.1 to 3.6 Ma (Mohr and Potter, 1976). Later K-Ar work on 10 samples yielded an isochron age of 1.97(0.02 Ma (Kennan et al., 1990).
References: 
DI PAOLA, G.M. 1973. The Ethiopian rift valley (between 7°00' and 8°40' lat. north). Bulletin Volcanologique, 36: 517-60.KENNAN, P.S., MITCHELL. J.G. and MOHR, P. 1990. The Sagatu Ridge dyke swarm, Ethiopian rift margin: revised age and new Sr-isotopic data. Journal of African Earth Sciences, 11: 39-42.KENNAN, P.S., MITCHELL. J.G. and MOHR, P. 1990. The Sagatu Ridge dyke swarm, Ethiopian rift margin: revised age and new Sr-isotopic data. Journal of African Earth Sciences, 11: 39-42.MOHR, P. 1980. Geochemical aspects of the Sagatu Ridge dike swarm, Ethiopian rift margin. Accademia Nazionale dei Lincei. Atti dei Convegni Lincei. 47: 387-406.MOHR, P.A. and POTTER, E.C. 1976. The Sagatu Ridge dyke swarms, Ethiopian rift margin. Journal of Volcanology and Geothermal Research, 1: 55-71.
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