Abstract
Determination of the trace-elements Ba, Ce, La, Nb, Rb, Sr and Zr have been made on lavas from six trachytic and pantelleritic volcanoes in the Kenyan and Ethiopian Rifts. Consideration of these data shows that Ce, La, Nb and Zr have behaved as truly residual elements. In the peralkaline suites examined, plotting other chemical parameters against a residual-element such as Zr appears to be informative. The individual residual-element ratios are constant at any one volcano suggesting that the salic and basic lavas are geochemieally related and that the trachytes and pantellerites do not have an origin independent of the associated basalts.
Different values of individual residual-element ratios characterize different groups of volcanic centres. In the northern part of the Kenyan Rift, progressive change in these ratios with time can be traced.
In the salic lavas, Ba and Sr show patterns of extreme depletion relative to the alkali basalts and these data suggest that the salic rocks are the result of protracted crystal-fractionation.
The relative volumes of the extruded lava-types are discussed and it is suggested that the trachytic and pantelleritic centres developed above cupolas of salic magma situated on top of a large basaltic reservoir. It is likely that the preponderance of salic rocks and the scarcity of lavas of intermediate composition are not criteria by which one can rule out an origin of differentiation by crystal-fractionation.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Abbott, M. J.: Petrology of the Nandewar volcano, N.S.W., Australia. Contr. Mineral. and Petrol. 20, 115–134 (1969).
Bailey, D. K.: Crustal warping—a possible control of alkaline magmatism. J. Geophys. Res. 69, 1103–1111 (1964).
Baker, B. H., Wohlenberg, J.: Structure and evolution of the Kenya Rift Valley. Nature 229, 538–542 (1971).
Baker, I.: Intermediate oceanic volcanics and the “Daly Gap”. Earth Planet. Sci. Lett. 4, 103–106 (1968).
Cann, J. R.: Bimodal distribution of rocks from volcanic islands. Earth Planet. Sci. Lett. 4, 479–480 (1968).
Chao, E. C. T., Fleischer, M.: Abundance of zirconium in igneous rocks. Rep. 21st int. geol. Congr. Norden 1, 106–131 (1960).
Chayes, F.: Relative abundance of intermediate members of the Oceanic basalt-trachyte association. J. Geophys. Res. 68, 1519–1534 (1963).
Dakin, F. M., Gibson, I. L.: A preliminary account of Alutu, a pantelleritic volcano in the main Ethiopian Rift. Bull. Geophys. Obs. Addis Ababa 13, 110–114 (1971).
Dietrich, R. V.: Behaviour of zirconium in certain artificial magmas under diverse P-T conditions. Lithos 1, 20–29 (1968).
Edwards, A. B.: Differentiation of the dolerites of Tasmania. 2. J. Geol. 50, 579–610 (1942).
Ewart, A., Taylor, S. R., Capp, A. C.: Geochemistry of the pantellerites of Mayor Island, New Zealand. Contr. Mineral. and Petrol. 17, 116–140 (1968).
Gast, P. W.: Trace element fractionation and the origin of tholeiitic and alkaline magma types. Geochim. Cosmochim. Acta 32, 1057–1086 (1968).
Gibson, I. L.: Preliminary account of the volcanic geology of Fantale, Shoa, Ethiopia. Bull. Geophys. Obs. Addis Ababa 10, 59–67 (1967).
Gibson, I. L.: A pantelleritic ash flow tuff from the Ethiopian Rift Valley. Contr. Mineral and Petrol. 28, 89–111 (1970).
Harkin, D. A.: The Rungwe volcanics at the northern end of Lake Nyasa. Geol. Surv. Tanganyika Mem. 2 (1960).
Harris, P. G.: Relative abundance of intermediate members of the Oceanic basalt-trachyte association — A discussion. J. Geophys. Res. 68, 5103–5107 (1963).
Harris, P. G.: Segregation processes in the upper mantle. In: Mantles of the Earth and terrestial planets (ed. S. K. Runcorn). London: Interscience 1967.
Herrmann, A. G.: In: Handbook of geochemistry (ed. K. H. Wedepohl), vol. 2, part 2, sect. 39F2. Berlin-Heidelberg-New York: Springer 1970.
Khan, M. A., Mansfield, J.: Gravity measurements in the Gregory Rift. Nature 229, 72–75 (1971).
King, B. C.: Petrogenesis of the alkaline igneous rock suites of the volcanic and intrusive centres of Eastern Uganda. I. Petrol. 6, 67–100 (1965).
King, B. C.: Vulcanity and Rift tectonics in East Africa. In: African magmatism and tectonics (eds. T. N. Clifford, I. G. Gass). Edinburgh: Oliver and Boyd 1970.
Kuno, H., Yamasaki, K., Iida, C., Nagashima, K.: Differentiation of Hawaiian magmas. Jap. J. Geol. Geogr. 28, 179–218 (1957).
Lacroix, A.: Les roches hyperalcalcines du massif du Fantale et du col de Balla. Mem. Soc. Geol. France 14, 89–102 (1930).
Macdonald, G. A.: Hawaiian petrographic province. Bull. Geol. Soc. Am. 60, 1541–1596 (1949).
Macdonald, G. A.: Relative abundance of intermediate members of the Oceanic basalt-trachyte association —a discussion. J. Geophys. Res. 68, 5100–5102 (1963).
Macdonald, R.: The petrology of alkaline dykes from the Tugtutôq area, South Greenland. Bull. Geol. Soc. Denmark 19, 257–282 (1969).
Macdonald, R., Bailey, D. K., Angell, G. R.: Trace element variation in pantellerite volcanoes of the Gregory Rift. J. Geol. Soc. Proc. 127, 411–412 (1971).
McCall, G. J. H.: The five caldera volcanoes of the central Rift Valley, Kenya. Proc. Geol. Soc. Lond. 1647, 54–58 (1968).
McClenaghan, M. P., Weaver, S. D., Webb, P. K.: Pliocene trachyte volcanoes of the northern Rift Valley, Kenya. J. Geol. Soc. Proc. 127, 294 (1971).
Mukherjee, A.: Role of fractional crystallisation in the descent:basalt-trachyte. Contr. Mineral. and Petrol. 16, 139–148 (1967).
Nash, W. P., Carmichael, I. S. E., Johnson, R. W.: The mineralogy and petrology of Mount Suswa, Kenya. J. Petrol. 10, 409–439 (1969).
Nicholls, J., Carmichael, I. S. E.: Peralkaline acid liquids: a petrological study. Contr. Mineral. and Petrol. 20, 268–294 (1969).
Noble, D. C.: Gold Flat Member of the Thirsty Canyon Tuff — a pantellerite ash-flow sheet in southern Nevada. Prof. Pap. U. S. Geol. Surv. 525-B, 85–90 (1965).
Noble, D. C., Haffty, J., Hedge, C. E.: Strontium and magnesium contents of some natural peralkaline silicic glasses and their petrogenetic significance. Am. J. Sci. 267, 598–608 (1969).
Rhemtulla, S.: The South Turkana expedition: Scientific Papers 3. Geogr. J. 136, 61–73 (1970).
Ridley, W. I.: The abundance of rock types on Tenerife, Canary Islands, and its petrogenetic significance. Bull. Volcanol. 34, 196–204 (1970).
Romano, R.: Sur l'origine de l'excès de sodium dans certaines laves de l'Île de Pantelleria. Bull. Volcanol. 33, 1–7 (1969).
Rosholt, J. N., Prijana, Noble, D. C.: Mobility of uranium and thorium in glassy and crystallised silicic volcanic rocks. Econ. Geol. 66, 1061–1069 (1971).
Sceal, J. S. C., Weaver, S. D.: Trace-element data bearing on the origin of salic rocks from the Quaternary volcano Paka, Gregory Rift, Kenya. Earth Planet. Sci. Lett. 12, 327–331 (1971).
Schilling, J. G., Winchester, J. W.: Rare-earth fractionation and magmatic processes. In: Mantles of the Earth and terrestial planets (ed. S. K. Runcorn). London: Interscience 1967.
Searle, R. C.: Evidence from gravity anomalies for thinning of the lithosphere beneath the Rift Valley in Kenya. Geophys. J. Roy. Astron. Soc. 21, 13–31 (1970).
Smith, R. L., Bailey, R. A.: The Bandelier tuff: a study of ash-flow eruption cycles from zoned magma chambers. Bull. Volcanol. 29, 83–103 (1966).
Sutherland, D. S.: Pantelleritic volcanism in the Naivasha area of Kenya. Proc. Geol. Soc. Lond. 1663, 164–165 (1970).
Sutherland, D. S.: The Eburru volcano, Kenya. J. Geol. Soc. Proc. 127, 417 (1971).
Taylor, S. R.: The application of trace element data to problems in petrology. In: Physics and chemistry of the Earth, vol. 6. Oxford and New York: Pergamon Press 1965.
Taylor, S. R., Ewart, A., Capp, A. C.: Leucogranites and rhyolites: Trace element evidence for fractional crystallization and partial melting. Lithos 1, 179–186 (1968).
Thompson, A. O., Dodson, R. G.: Geology of the Naivasha area. Rep. Geol. Surv. Kenya 76, (1963).
Thornton, C. P., Tuttle, O. F.: Chemistry of igneous rocks. 1. Differentiation index. Am. J. Sci. 258, 664–684 (1960).
Wager, L. R., Deer, W. A.: Geological investigations in East Greenland, Part 3. The petrology of the Skaergaard intrusion, Kangerdlugssuaq, East Greenland. Medd. Groenland 105, No. 4, 1–352 (1939).
Williams, L. A. J.: The volcanics of the Gregory Rift Valley, East Africa. Bull. Volcanol. 34, 439–465 (1971).
Wright, J. B.: Petrographic sub-provinces in the Tertiary to Recent volcanics of Kenya. Geol. Mag. 102, 541–557 (1970).
Wright, J. B.: Distribution of volcanic rocks about mid-ocean ridges and the Kenya Rift Valley. Geol. Mag. 107, 125–131 (1970).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Weaver, S.D., Sceal, J.S.C. & Gibson, I.L. Trace-element data relevant to the origin of trachytic and pantelleritic lavas in the East African Rift system. Contr. Mineral. and Petrol. 36, 181–194 (1972). https://doi.org/10.1007/BF00371430
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00371430