Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: 35.42, Latitude: -3.18

The Sadiman volcano is younger than Lemagrut the products of which it overlaps. It is made up largely of nephelinitic tuffs and agglomerates. Subsidiary lavas include nephelinite, phonolitic nephelinite, melilite nephelinite, phonolitic trachyte and sodalite phonolite. Analyses of foidite and nepheline, including trace element and Sr, Nd and Pb isotope data, are in Paslick et al. (1995 and 1996). On the Eyasi Plateau north of Lake Eyasi and west of Lemagrut and Oldeani are extensive Pleistocene tuffs which probably erupted from the Sadiman volcano. These tuffs include the Laetoli Beds which preserve an extraordinary array of fossil footprints including those of early hominids. A stunning photograph of these ~3.5 million year old footprints will be found in Hay and Leakey (1982). Hay (1978) and Hay and O’Neil (1983) report that the upper unit of the Laetoli Beds contains approximately 25 carbonatite and 35 melilitite-carbonatite air-fall layers, the chemistry of which they describe.

Three K-Ar age determinations on nephelinite quoted by Foster et al. (1997) ranged from 3.32(0.06 to 4.5(0.4 Ma.
FOSTER, A., EBINGER, C., MBEDE, E. and REX, D. 1997. Tectonic development of the northern Tanzanian sector of the East African rift system. Journal of the Geological Society of London, 154: 689-700.GITTINS, J. 1966. Summaries and bibliographies of carbonatite complexes. In: O.F. Tuttle and J. Gittins (eds), Carbonatites. 417-541. John Wiley, New York. HAY, R.L. 1978. Melilite-carbonate tuffs in the Laetolil Beds of Tanzania. Contributions to Mineralogy and Petrology, 67: 357-67.HAY, R.L. and LEAKEY, M.D. 1982. The fossil footprints of Laetoli. Scientific American, 246: 50-7.HAY, R.L. and O’NEIL, J.R. 1983. Carbonatite tuffs in the Laetolil Beds of Tanzania and the Kaiserstuhl in Germany. Contributions to Mineralogy and Petrology, 82: 403-6.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.PASLICK, C., HALLIDAY, A.N., JAMES, D. and DAWSON, J.B. 1996. Indirect crustal contamination: evidence from isotopic and chemical disequilibrium in minerals from alkali basalts and nephelinites from northern Tanzania. Contributions to Mineralogy and Petrology, 125: 277-92.PICKERING, R. 1964. Endulen. Geological Survey of Tanzania, Quarter Degree Sheet, 52.
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith