Abstract
Three thin, syn-caldera ash flow tuffs of the Suswa volcano, Kenya, contain pumiceous clasts and globules of trachytic glass, and clasts rich in carbonate globules, in a carbonate ash matrix. Petrographic and textural evidence indicates that the carbonate was magmatic. The trachyte is metaluminous to mildly peralkaline and varies from nepheline- to quartz-normative. The carbonate is calcium-rich, with high REE and F contents. The silicate and carbonate fractions have similar 143Nd/144Nd values, suggesting a common parental magma. Chondrite-normalized REE patterns are consistent with a carbonate liquid being exsolved from a silicate liquid after alkali feldspar fractionation. Sr isotopic and REE data show that the carbonate matrix of even the freshest tuffs interacted to some degree with hydrothermal and/or meteoric water. A liquid immiscibility relationship between the trachyte and carbonate is indicated by the presence of sharp, curved menisci between them, the presence of carbonate globules in silicate glass and of fiamme rich in carbonate globules separated by silicate glass, and by the fact that similar phenocryst phases occur in both melts. It is inferred that the carbonate liquid separated from a carbonated trachyte magma prior to, or during, caldera collapse. Viscosity differences segregated the magma into a fraction comprising silicate magma with scattered carbonate globules, and a fraction comprising carbonate globules in a silicate magmatic host.
Explosive disruption of the magma generated silicate-and carbonate-rich clasts in a carbonate matrix. The silicate liquid was disaggregated by explosive disruption and texturally appears to have been budding-off into the carbonate matrix. After emplacement, the basal parts of the flows welded slightly and flattened. The Suswa rocks represent a rare and clear example of a liquid immiscibility relationship between trachyte and carbonate melts.
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References
Andersen T (1984) Secondary processes in carbonatites: petrology of “rodberg” (hematite-calcite-dolomite carbonatite) in the Fen central complex, Telemark (South Norway). Lithos 17:153–170
Andersen T (1986) Magmatic fluids in the Fen carbonatite complex, S.E. Norway: evidence of mid-crustal fractionation from solid and fluid inclusions in apatite. Contrib Mineral Petrol 93:491–503
Andersen T (1987) Mantle and crustal components in a carbonatite complex, and the evolution of carbonatite magma: REE and isotopic evidence from the Fen complex, S.E. Norway. Chem Geol (Isotope Geosci) 65:147–166
Bailey DK (1978) Continental rifting and mantle degassing. In: Neumann ER and Ramberg IB (eds) Petrology and geochemistry of continental rifts. Reidel, Dordrecht, pp 1–13
Bailey DK (1980) Volcanism, earth degassing and replenished mantle lithosphere. Phil Trans R Soc London A297:309–322
Bailey DK (1982) Mantle metasomatism — continuing chemical change within the Earth. Nature 296:525–530
Bailey DK (1987) Mantle metasomatism — perspective and prospect. In: Fitton JG, Upton BGJ (eds) Alkaline igneous rocks. Geol Soc London Spec Pub 30:1–13
Baker BH (1987) Outline of the petrology of the Kenya rift alkaline province. In: Fitton JG, Upton BGJ (eds) Alkaline igneous rocks. Geol Soc London Spec Pub 30:293–311
Barker DS, Nixon PH (1989) High-Ca, low-alkali carbonatite volcanism at Fort Portal, Uganda. Contrib Mineral Petrol 103:166–177
Clarke LB, LeBas MJ (1990) Magma mixing and metasomatic reaction in silicate-carbonate liquids at the Kruidfontein carbonatitic volcanic complex, Transyaal. Mineral Mag 54:45–56
Davies GR, Macdonald R (1987) Crustal influences in the petrogenesis of the Naivasha basalt-comendite complex: combined trace element and Sr−Nd−Pb isotope constraints. J Petrol 28:1009–1031
Freestone IC, Hamilton DL (1980) The role of liquid immiscibility in the genesis of carbonatites: an experimental study. Contrib Mineral Petrol 73:105–117
Gittins J (1989a) The origin and evolution of carbonatite magmas. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 561–579
Gittins J (1989b) Carbonatite origin and diversity. Nature 338:548
Gittins J, Beckett MF, Jago BC (1990) Composition of the fluid phase accompanying carbonatite magma: a critical examination. Am Mineral 75:1106–1109
Hamilton DL, Bedson P, Esson J (1989) The behaviour of trace elements in the evolution of carbonatites. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 405–427
Hay RL (1978) Melilitite — carbonatite tuffs in the Laetolil beds of Tanzania. Contrib Mineral Petrol 67:357–367
Hay RL, O'Neil JR (1983) Carbonatite tuffs in the Laetolil Beds of Tanzania and the Kaiserstuhl in Germany. Contrib Mineral Petrol 82:403–406
Ivanovich M, Harmon RS (eds) (1982) Uranium series disequilibrium: applications to environmental problems. Clarendon, Oxford
Johnson RW (1969) Volcanic geology of Mount Suswa, Kenya. Phil Trans R Soc London A 265:383–412
Katz K, Keller J (1981) Comb-layering in carbonatite dykes. Nature 294:350–352
Keller J (1981) Carbonatite volcanism in the Kaiserstuhl alkaline complex: evidence for highly fluid carbonatitic melts at the earth's surface. J Volcanol Geotherm Res 9:423–431
Keller J (1989) Extrusive carbonatites and their significance. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 70–88
Kjarsgaard BA (1990) Nephelinite — carbonatite genesis: experiments on liquid immiscibility in alkali silicate — carbonate systems. PhD thesis, University of Manchester
Kjarsgaard BA, Hamilton DL (1988) Liquid immiscibility and the origin of alkali-poor carbonatites. Mineral Mag 52:43–55
Kjarsgaard BA, Hamilton DL (1989) The genesis of carbonatites by immiscibility. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 388–404
Kjarsgaard BA, Hamilton DL (1990) The effect of P-T-X on immiscibility and phase relations in carbonated silicate systems. IAVCEI Program with Abstracts, Mainz, p 55
Kjarsgaard BA, Peterson T (1991) Nephelinite — carbonatite liquid immiscibility at Shombole volcano, East Africa: petrographic and experimental evidence. Mineral Petrol 43:293–314
LeBas MJ (1989) Diversification of carbonatite. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 428–447
Mariano AN, Roeder PL (1983) Kerimasi: a neglected carbonatite volcano. J Geol 91:449–453
Nakamura N (1974) Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary chondrites. Geochim Cosmochim Acta 38:757–775
Nash WP, Carmichael ISE, Johnson RW (1969) The mineralogy and petrology of Mount Suswa, Kenya. J Petrol 10:409–439
Noble DC (1970) Loss of sodium from crystallized comendite welded tuffs of the Miocene Grouse Canyon Member of the Belted Range Tuff, Nevada. Geol Soc Am Bull 81:2677–2687
Noble DC, Smith VC, Peck LC (1967) Loss of halogens from crystallized and glassy silicic volcanic rocks. Geochim Cosmochim Acta 31:215–223
Roeder P, Emslie RF (1970) Olivine — liquid equilibrium. Contrib Mineral Petrol 29:275–289
Scott SC (1982) Evidence from Longonot volcano, Central Kenya, lending further support to the argument for a coexisting CO2-rich vapour in peralkaline magma. Geol Mag 19:215–217
Skilling IP (1988) The geological evolution of Suswa volcano, Kenya. PhD thesis, Lancaster University
Sykes D, Baker MB, Wyllie PJ (1992) Viscous properties of carbonate melts at high pressures. Abstracts, AGU Spring Meeting, Montreal, p 372
Thibault Y, Holloway JR (1992) Carbon dioxide interaction with an olivine leucitite melt: solubility and trace element partitioning. Abstracts, AGU Spring Meeting, Montreal, p 351
Thirlwall MF (1982) A triple filament method for rapid and precise analysis of REE by isotope dilution. Chem Geol 35:155–166
Treiman AH (1989) Carbonatite magma: properties and processes. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 90–104
Treiman AH, Schedl A (1983) Properties of carbonatite magma and processes in carbonatite magma chamber. J Geol 91:437–447
Wendtlandt RF, Harrison WJ (1979) Rare earth partitioning between immiscible carbonate and silicate liquids and CO2 vapor: results and implications for the formation of light rare earthenriched rocks. Contrib Mineral Petrol 69:404–419
Williams RW, Gill JB, Bruland KW (1986) Ra-Th disequilibria systematics: timescale of carbonatite magma formation at Oldoinyo Lengai volcano, Tanzania. Geochim Cosmochim Acta 50:1249–1259
Woolley AR, Kempe DRC (1989) Carbonatites: nomenclature, average chemical compositions, and element distribution. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 1–14
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Macdonald, R., Kjarsgaard, B.A., Skilling, I.P. et al. Liquid immiscibility between trachyte and carbonate in ash flow tuffs from Kenya. Contr. Mineral. and Petrol. 114, 276–287 (1993). https://doi.org/10.1007/BF00307762
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DOI: https://doi.org/10.1007/BF00307762