Contributions to Mineralogy and Petrology

, Volume 82, Issue 4, pp 403–406 | Cite as

Carbonatite tuffs in the Laetolil Beds of Tanzania and the Kaiserstuhl in Germany

  • R. L. Hay
  • J. R. O'Neil


Carbonatite lava and tephra are now well known. The only modern eruptive carbonatites, from Oldoinyo Lengai, Tanzania, are of alkali carbonatite, whereas all of the pre-modern examples are of calcite or dolomite. Chemical and stable isotope analyses were made of separate phases of Pliocene carbonatite tuffs of the Laetolil Beds in Tanzania and of Miocene carbonatite tuffs of the Kaiserstuhl in Germany in order to understand the reasons for this major difference.

The Laetolil Beds contain numerous carbonatite and melilitite-carbonatite tuffs. It is proposed that the carbonatite ash was originally of alkali carbonate composition and that the alkali component was dissolved, leaving a residuum of calcium carbonate. The least recrystallized melilitite-carbonatite tuff contains early-deposited calcite cement and calcite pseudomorphs after nyerereite (?) that have contents of strontium and barium and δ18O and δ13C values suggestive of incomplete chemical and isotopic exchange during alteration and replacement of alkali carbonatite ash.

Carbonatite tuffs of the Kaiserstuhl contain globules composed of calcite phenocrysts and microphenocrysts in a groundmass of calcite with a small amount of clay, apatite, and magnetite. The SrO contents of phenocrysts, microphenocrysts, and groundmass calcite average 0.90, 1.42, and 0.59 percent, respectively. The average δ18O and δ13C values of globules (+14.3 and −9.0, respectively) fall between those of coarse-grained intrusive Kaiserstuhl carbonatite (avg. +6.6, −5.8) and those of low-temperature calcite cement in the carbonatite tuffs (+21.8, −14.9). The phenocrysts and microphenocrysts are primary magmatic calcite, but several features indicate that the groundmass has been recrystallized and altered in contact with meteoric water, resulting in weathering of silicate to clay, leaching of strontium, and isotopic exchange. The weight of evidence favors an original high content of alkali carbonatite in the groundmass, with recrystallization following leaching of the alkalies.


Calcite Magnetite Apatite Miocene Strontium 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Cooper AS, Gittins J, Tuttle OF (1965) The system Na2CO3-K2CO3-CaCO3 at 1 kilobar and its significance in carbonatite petrogenesis. Am J Sci 275:534–560Google Scholar
  2. Dawson JB (1962a) The geology of Oldoinyo Lengai. Bull Volcanol 24:349–387 (1962a)Google Scholar
  3. Dawson JB (1962b) Sodium carbonate lavas from Oldoinyo Lengai, Tanganyika. Nature 195:1075–1076Google Scholar
  4. Dawson JB (1964a) Carbonatite volcanic ashes in northern Tanganyika. Bull Volcanol 27:1–11 (1964a)Google Scholar
  5. Dawson JB (1964b) Carbonatite tuff cones in northern Tanganyika. Geol Mag 101:129–137Google Scholar
  6. Dawson JB, Bowden P, Clark GC (1968) Activity of the carbonatite volcano Oldoinyo Lengai, 1966. Geol Rundsch 57:865–879Google Scholar
  7. Deines P, Gold DP (1973) The isotopic composition of carbonatite and kimberlite carbonates and their bearing on the isotopic composition of deep-seated carbon. Geochim Cosmochim Acta 37:1709–1733Google Scholar
  8. Hay RL (1978) Melilitite-carbonatite tuffs in the Laetolil Beds of Tanzania. Contrib Mineral Petrol 67:357–367Google Scholar
  9. Hay RL, Leakey MD (1982) The fossil footprints of Laetoli. Sci Am 246:50–57Google Scholar
  10. Keller J (1981) Carbonatitic volcanism in the Kaiserstuhl alkaline complex: evidence for highly fluid carbonatitic melts at the earth's surface. J Volcanol Geotherm Res 9:423–431Google Scholar
  11. Knorring O von, Dubois CGB (1961) Carbonatite lava from the Fort Portal area in western Uganda. Nature 192:1064Google Scholar
  12. LeBas MJ (ed) (1977) Carbonatite-Nephelinite Volcanism. p 347. New York: John Wiley and SonsGoogle Scholar
  13. Mkie D, Frankis EJ (1977) Nyerereite: a new volcanic carbonatite from Oldoinyo Lengai, Tanzania Z Krist 145:73–95Google Scholar
  14. Nixon PH, Hornung G (1973) The carbonatite lavas and tuffs near Fort Portal, western Uganda. Overseas Geol Miner Resour 41:168–179Google Scholar
  15. O'Neil JR, Hay RL (1973) O18/O16 ratios in cherts associated with the saline lake deposits of East Africa. Earth Planet Sci Lett. 19:257–266 (1973)Google Scholar
  16. Pyatenko IK, Saprykina LG (1976) Carbonatite lavas and pyroclastics in the Paleozoic sedimentary volcanic sequence of the Kontozero District, Kola Peninsula. Dokl Akad Nauk SSSR:185–187Google Scholar
  17. Silva LC, LeBas MJ, Robertson AHF (1981) An oceanic carbonatite volcano on Santiago, Cape Verde Islands. Nature 294:644–645Google Scholar
  18. Taylor HP Jr, Frechen J, Degens ET (1967) Oxygen and carbon isotope studies of carbonatites from the Laacher See district, West Germany and the Alno district, Sweden. Geochim Cosmochim Acta 31:407–430Google Scholar
  19. Vinogradov AP, Dontsova EI, Geracumovski VI, Kuznetsova LD (1971) Isotopic composition of oxygen in carbonatites from the continental rift zone of East Africa. Geokhimiya 5:507–514Google Scholar
  20. Wyllie PJ, Tuttle OF (1960) The system CaO-CO2-H2O and the origin of carbonatites. J Petrol 1:46Google Scholar

Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • R. L. Hay
    • 1
  • J. R. O'Neil
    • 2
  1. 1.Department of Geology and GeophysicsUniversity of CaliforniaBerkeleyUSA
  2. 2.U.S. Geological SurveyMenlo ParkUSA

Personalised recommendations