Abstract
Two fractionation trends in sodic alkaline ultramafic liquids have been predicted from experiments in subsystems of the join Di-Ak-Ne-Lc-Qz. The products of these trends are equated with contrasting suites of peralkaline nephelinites from two nephelinite-carbonatite volcanos of the south Gregory Rift, Shombole (southern Kenya) and Oldoinyo L'engai (northern Tanzania). In both trends, peralkalinity is interpreted to result from fractional crystallization of aluminous clinopyroxene. The “Shombole trend” has olivine nephelinite as its parental magma, and the differentiation products are mildly peralkaline [(Na+K)/Al≈1.15] nephelinites. It is the most common lineage observed in nephelinite-carbonatite centres. The “Oldoinyo L'engai trend” has melilitite or olivine-melilite nephelinite as its parental magma, and produces extremely peralkaline [(Na+K)/Al=1.4–2.3] wollastonite- and combeite- (Na2 Ca2Si3O9) bearing nephelinites. The presence of a reaction relation between wollastonite and liquid to produce combeite, indicated by corroded wollastonite phenocrysts armoured by combeite in some nephelinites from Oldoinyo L'engai, is confirmed by melting experiments. Combeite nephelinites from Oldoinyo L'engai were erupted simultaneously with natrocarbonatite ash, and are very similar in composition to silicate liquids that have been shown by experiment to be immiscible with natrocarbonatite. Because the L'engai trend is rarely expressed at extrusive centres (combeite has been recorded at only three localities), and combeite nephelinites are highly evolved magmas, it is unlikely that natrocarbonatite is primary to other carbonatite types. It is proposed that carbonatite liquid is exsolved at crustal pressures from a wide range of nephelinitic liquids: Mg-rich carbonatite from primitive, olivine-bearing alkaline ultramafic liquids, Ca-rich carbonatite from olivine-free nephelinites of low peralkalinity, and natrocarbonatite from strongly peralkaline combeite nephelinites.
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References
Alibert C, Michard A, Albaréde F (1983) The transition from alkali basalts to kimberlites: isotope and trace element evidence from melilitites. Contrib Mineral Petrol 82:176–186
Bailey DK (1974) Continental rifting and alkaline magmatism. In: Sørensen H (ed) The Alkaline Rocks. Wiley, London, pp 148–159
Bailey DK (1978) Continental rifting and mantle degassing. In: Neumann ER, Ramberg IB (eds) Petrology and geochemistry of continental rifts. Reidel, Dordrecht Boston, pp 1–13
Bailey DK, Schairer JF (1966) The system Na2O-Al2O3-Fe2O3-SiO2 at 1 atmosphere, and the petrogenesis of alkaline rocks. J Petrol 7:114–170
Baker BH, Mohr PA, Williams LAJ (1972) Geology of the Eastern Rift System of Africa. Geol Soc Am Spec Pap 136
Baker BH, Goles GG, Leeman WP, Lindstrom MM (1977) Geochemistry and petrogenesis of a basalt-benmoreite-trachyte suite from the southern part of the Gregory Rift, Kenya. Contrib Mineral Petrol 64:303–332
Baker MB, Wyllie PJ (1988) High pressure liquid immiscibility in the system nephelinite-CaCO3-Na2CO3. EOS 69:1511
Barth TFW, Ramberg IB (1966) The Fen circular complex. In: Tuttle OF, Gittins J (eds) Carbonatites. Wiley, London, pp 225–260
Bell K, Dawson JB, Farquahar RM (1973) Strontium isotope studies of alkalic rocks: the active carbonatite volcano Oldoinyo L'engai, Tanzania. GSA Bull 83:1019–1030
Brey GP (1978) Origin of olivine melilitite-chemical and experimental constraints. J Vol Geotherm Res 3:61–88
Brey GP, Green DH (1977) Systematic study of liquidus phase relations in olivine melilitite-H2O+CO2 at high pressure and the petrogenesis of an olivine melilitite magma. Contrib Mineral Petrol 61:141–162
Cahen L, Snelling NJ (1984) The geochronology and evolution of Africa. Clarendon Press, Oxford
Clague DA, Frey FA (1982) Petrology and trace element geochemistry of the Honolulu volcanics, Oahu: Implications for the oceanic mantle below Hawaii. J Petrol 23:447–504
Cooper AF, Gittins J, Tuttle OF (1975) The system NaCO-KCO-CaCO at 1 kilobar and its significance in carbonatite petrogenesis. Am J Sci 275:534–560
Crossley R (1979) The Cenozoic stratigraphy and structure of the western part of the rift valley in southern Kenya. J Geol Soc London 136:393–405
Currie KL (1975) Geology and petrology of the Ice River alkaline complex, British Columbia. Geol Surv Canada Bull 245
Currie KL, Eby GN, Gittins J (1986) The petrology of the Mt. Saint Hilair complex, southern Quebec: an alkaline gabbroperalkaline syenite association. Lithos 19:67–83
Dawson JB (1962) The geology of Oldoinyo L'engai. Bull Volcanol 24:349–387
Dawson JB (1966) Oldoinyo L'engai: an active volcano with sodium carbonatite flows. In: Tuttle OF, Gittins J (eds) Carbonatites. Wiley, London, pp 155–168
Deans T, Roberts R (1984) Carbonatite tuffs and lava clasts of the Tinderet foothills, western Kenya: a study in calcified natrocarbonatites. J Geol Soc London 141, 563–580
Donaldson CH, Dawson JB, Kanaris-Sotiriou R, Batchelor RA, Walsh JN (1987) The silicate lavas of Oldoinyo L'engai. Neues Jahrb Mineral Abh 156:247–279
Eggler DH (1978) The effect of CO2 upon partial melting of peridotite in the system Na2O-CaO-Al2O-MgO-SiO2-CO2 to 35 kb, with an analysis of melting in a peridotite-H2O-CO2 system. Am J Sci 278:305–343
Eggler DH (1987) Discussion of recent papers on carbonated peridotite, bearing on mantle metasomatism and magmatism: an alternative. EPSL 82:398–400
Fischer RX, Tillmans E (1983) The Kristallstrukturen von natürlichem Na2Ca2Si3O9 vom Mt Shaheru (Zaire) und aus dem Mayener Feld (Eifel). Neues Jahrb Mineral 2:49–59
Freestone IC, Hamilton DL (1980) The role of liquid immiscibility in the genesis of carbonatites: an experimental study. Contrib Mineral Petrol 73:105–117
Gee LL, Sack RO (1989) Experimental petrology of melilite nephelinites. J Petrol 29:1233–1256
Gerasimovsky VI, Balashov YuA, Karpushina VA (1972) Geochemistry of the rare earth elements in the extrusive rocks of the East African rift zones. Geokhimiya 5:515–530
Gittins J (1988) The origin of carbonatites. Nature 335:295–296
Gittins J, McKie D (1980) Alkalic carbonatite magmas: Oldoinyo L'engai and its wider applicability. Lithos 3:213–215
Gupta AK, Venkateswaran GP, Lidiak EG, Edgar AD (1973) The system diopside-nepheline-akermanite-leucite and its bearing on the genesis of alkali-rich mafic and ultramafic rocks. J Geol 81:209–218
Hay RL (1983) Natrocarbonatite tephra of Kerimasi volcano, Tanzania. Geology 11:599–602
Heinrich EW (1966) The geology of carbonatites. Rand McNally, Chicago
Javoy M, Pineau F, Cheminee JL, Kraft M (1988) The gas-magma relationship in the 1988 eruption of Oldoinyo L'engai (Tanzania). EOS 69:1466
King BC (1965) Petrogenesis of the alkaline igneous rock suites of the volcanic and intrusive centres of eastern Uganda. J Petrol 6:67–100
King BC, Sutherland DS (1966) The carbonatite complexes of Eastern Uganda. In: Tuttle OF, Gittins J (eds) Carbonatites. Wiley, London, pp 73–126
Kjarsgaard BA, Hamilton DL (1988) Liquid immiscibility and the origin of alkali-poor carbonatites. Mineral Mag 52:43–55
Kjarsgaard BA, Hamilton DL (1989) Melting experiments on Shombole nephelinites: silicate/carbonate immiscibility, phase relations and the liquid line of descent. GAC-MAC Progr with Abstr (in press)
LeBas MJ (1977) Carbonatite-nephelinite volcanism. Wiley, London
LeBas MJ (1981) Carbonatite magmas. Mineral Mag 44:133–140
LeBas (1984) Oceanic carbonatites. In: Kornprobst J (ed) Kimberlites. I: Kimberlites and related rocks. Elsevier, New York, pp 169–178
LeBas MJ (1987) Nephelinites and carbonatites. In: Fitton JG, Upton BGJ (eds) Alkaline igneous rocks. Blackwell, Oxford, pp 53–85
MacDonald R (1974) The role of fractional crystallization in the formation of the alkaline rocks. In: Sørensen H (ed) The alkaline rocks. Wiley, London, pp 442–458
McIver JR (1981) Aspects of ultrabasic and basic alkaline intrusive rocks from Bitterfontein, South Africa. Contrib Mineral Petrol 78:1–11
Melcher GC (1966) The carbonatites of Jacupiranga, Sao Paulo, Brazil. In: Tuttle OF, Gittins J (eds) Carbonatites. Wiley, London, pp 169–182
Milton C (1968) The “natrocarbonatite” of Oldoinyo L'engai, Tanzania. Geol Soc Am Spec Pap #121, 202
Mitchell RH (1980) Pyroxenes of the Fen alkaline complex, Norway. Am Mineral 65:45–54
Mitchell RH, Brunfelt AO (1975) Rare earth element geochemistry of the Fen alkaline complex, Norway. Contrib Mineral Petrol 52:247–259
Mitchell RH, Platt RG (1983) Primitive nephelinitic volcanism associated with rifting and uplift in the Canadian Arctic. Nature 303:609–612
Morey GW, Bowen NL (1925) The ternary system sodium metasilicate-calcium metasilicate-silica. J Soc Glass Tech 9:226–263
Nash WP (1972) Mineralogy and petrology of the Iron Hill carbonatite complex, Colorado. Geol Soc Am Bull 83:1361–1382
Nash WP, Carmichael ISE, Johnson RW (1969) The mineralogy and petrology of Mount Suswa, Kenya. J Petrol 10:409–439
Olafsson M, Eggler DH (1983) Phase relations of amphibole, amphibole-carbonate, and phlogopite-carbonate peridotite: petrologic constraints on the asthenosphere. EPSL 64:305–315
Onuma K, Yagi K (1967) The system diopside-akermanite-nepheline. Am Mineral 52:227–243
Onuma K, Yamamoto M (1976) Crystallization in the silica-undersaturated portion of the system diopside-nepheline-akermanitesilica and its bearing on the formation of melilitites and nephelinites. J Fac Sci Hokkaido Univ Ser IV, vol 17, pp 347–355
Peterson TD (1987) The petrogenesis and evolution of nephelinite carbonatite magmas. Ph D thesis, The Johns Hopkins University, Baltimore
Peterson TD (1988) Phonolite production at Shombole volcano, Kenya. GAC Progr Abstr 13: A98
Peterson TD (1989) Peralkaline Nephelinites. I. Comparative petrology of Shombole and Oldoinyo L'engai, East Africa. Contrib Mineral Petrol 101:458–478
Peterson TD, Marsh BD (1986) Sodium metasomatism and mineral stabilities in alkaline ultramafic rocks: implications for the origin of the sodic lavas of Oldoinyo L'engai. EOS 67:389–390
Piotrowski JM, Edgar AD (1970) Melting relations of undersaturated alkaline rocks from south Greenland compared to those of Africa and Canada. Med Grønland 181, #9
Platt RG, Edgar AD (1972) The system nepheline-diopside-sanidine and its significance to the genesis of melilite- and olivine-bearing alkaline rocks. J Geol 80:224–236
Sack RO, Walker D, Carmichael ISE (1987) Experimental petrology of alkalic lavas at 1 atmosphere: constraints on cotectics of multiple saturation in natural basic liquids. Contrib Mineral Petrol 96:1–23
Sahama ThG (1976) Composition of clinopyroxene and melilite in the Nyiragongo rocks. Carnegie Inst Washington Yearb 75:585–590
Sahama ThG, Hytönen K (1957) Götzenite and combeite, two new minerals from the Belgian Congo. Mineral Mag 31:503–510
Schairer JF, Yoder HS (1960) The nature of residual liquids from crystallization, with data on the system nepheline-diopside-silica. Am J Sci 258A:273–283
Schneiderhöhn H (1948) Neue Beobachtungen und Hypothesen im Kaiserstuhl. Mitt bad Geol Landesanst, 330–368
Sood MK, Edgar AD (1970) Melting relations of undersaturated alkaline rocks from the Ilimaussaq intrusion and GrøennedalIka complex, south Greenland, under water vapour and controlled partial oxygen pressure. Med Grønland 181
Spivak J (1944) The system NaAlSiO4-CaSiO4-Na2SiO3. J Geol 52:24–52
Strong DF (1972) Petrology of the island of Moheli, western Indian Ocean. Geol Soc Am Bull 83:389–406
Taylor RP, Strong DF, Kean BF (1980) The Topsails igneous complex: Silurian-Devonian peralkaline magmatism in western Newfoundland. Can J Earth Sci 17:425–439
Turner DC (1988) Volcanic carbonatites of the Kaluwe complex, Zambia. J Geol Soc London 145:95–106
Twyman JD, Gittins J (1987) Alkalic carbonatite magmas: parental or derivative? In: Fitton JG, Upton BGJ (eds) Alkaline igneous rocks. Blackwell, Oxford, pp 85–94
Velde D, Yoder HS (1976) The chemical composition of melilite-bearing eruptive rocks. Carnegie Inst Washington Yearb 75:574–580
Wallace ME, Green DH (1988) An experimental determination of primary carbonatite magma composition. Nature 335:343–346
Wilkinson JFG, Stolz AJ (1983) Low-pressure fractionation of strongly undersaturated alkaline ultrabasic magma: the olivinemelilite-nephelinite at Moiliili, Oahu, Hawaii. Contrib Mineral Petrol 83:363–374
Wimmenauer W (1966) The eruptive rocks and carbonatites of the Kaiserstuhl, Germany. In: Tuttle OF, Gittins J (eds) Carbonatites. Wiley, London, pp 183–204
Woolley AR (1987) Alkaline rocks and carbonatites of the world. Part 1: North and South America. University of Texas Press, Austin
Wyllie PJ (1977) Mantle fluid compositions buffered by carbonates in peridotite-CO2-H2O. J Geol 85:187–207
Wyllie PJ (1978) Mantle fluid compositions buffered in peridotite-H2O-CO2 by carbonates, amphibole, and phlogopite. J Geol 86:687–713
Wyllie PJ (1987) Discussion of recent papers on carbonated peridotite, bearing on mantle metasomatism and magmatism: response. EPSL 82:401–402
Yoder HS (1979) Melilite-bearing rocks and related lamprophyres. In: Yoder HS (ed) The evolution of the igneous rocks. Princeton Univ Press, Princeton, pp 391–412
Yoder HS, Kushiro I (1972) Composition of residual liquids in the nepheline-diopside system. Carnegie Inst Washington Yearb 71:413–416
Yoder HS, Velde D (1976) Importance of alkali content of magma yielding melilite-bearing rocks. Carnegie Inst Washington Yearb 75:580–585
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Peterson, T.D. Peralkaline nephelinites. Contrib Mineral Petrol 102, 336–346 (1989). https://doi.org/10.1007/BF00373727
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DOI: https://doi.org/10.1007/BF00373727