Alkaline Rocks and Carbonatites of the World

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Tarosero And Monduli


Occurrence number: 
Longitude: 36.37, Latitude: -3.2

The Tarosero and Monduli volcanoes are built on a plateau of basalt and trachybasalt. The lower slopes are essentially basaltic with rare nephelinite, but on Tarosero the basalts are overlain by soda trachytes, in the summit area by sanidine-phyric soda trachytes while peralkaline rhyolites occur on the lower northwestern slopes (J.B. Dawson, pers. comm., 1990). On the northern slopes of this volcano there are two parasitic cones of trachytic agglomerate and tuff and a trachyte dome occurs within a small caldera. South of Tarosero is the Monduli Juu Caldera which may have been formed when the surrounding trachyte tuffs were erupted. Analyses of two rocks from Tarosero and three from Monduli, including trace element and Sr, Nd and Pb isotope data, are in Paslick et al. (1995).

Six K-Ar determinations on olivine basalt and soda trachyte from Tarosero gave ages from 1.90(0.04 to 2.40(0.62 Ma (MacIntyre et al., 1974) and an olivine basalt from Monduli 2.09(0.06 and 2.15(0.05 Ma (Evans et al., 1971).
DAWSON, J.B. and PICKERING, R. 1964. Monduli. Geological Survey of Tanganyika, Quarter Degree Sheet, 54.EVANS, A.L., FAIRHEAD, J.D. and MITCHELL, J.G. 1971. Potassium-argon ages from the volcanic province of northern Tanzania. Nature, Physical Science, 229: 19-20.MACINTYRE, R.M., MITCHELL, J.G. and DAWSON, J.B. 1974. Age of fault movements in Tanzanian sector of East African rift system. Nature, London, 247: 354-6.PASLICK, C., HALLIDAY, A.N., JAMES, D. and DAWSON, J.B. 1995. Enrichment of the continental lithosphere by OIB melts: isotopic evidence from the volcanic province of northern Tanzania. Earth and Planetary Science Letters, 130: 109-26.
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