Skip to main content
SpringerLink
Log in

Petrology and genesis of natrocarbonatite

  • Published:
Contributions to Mineralogy and Petrology Aims and scope Submit manuscript

Abstract

Microprobe analyses of phenocrysts and groundmass, and crystal-size distributions of phenocrysts of pahoehoe natrocarbonatite lavas of the 1963 eruption of Oldoinyo Lengai have been determined. Nyerereite phenocrysts are homogeneous, with average composition Nc41Kc9Cc50 (neglecting F, Cl, P2O5, and SO3) where Nc=Na2CO3, Kc=K2CO3, and Cc= (Ca,Sr)CO3. Gregoryite phenocrysts have turbid, pale brown, oscillatorily zoned cores (average composition Nc77Kc5Cc18) with 0–30% oriented inclusions of exsolved nyerereite. Overgrowths on gregoryites (30 μm wide) are relatively sodic (Nc81Kc4Cc15) and are free of inclusions. Cores and rims are rich in SO3 (4%) and P2O5 (2%). Blebs of pyrite-alabandite mixtures (≤100 μm) occur in the groundmass. The groundmass has the simplified composition Nc65Kc15Cc20, less calcic than the composition of the 1-kbar nyerereite+gregoryite +liquid cotectic in the ternary system Nc-Kc-Cc. Groundmass quench growth of alkali halides + carbonate was followed by slower growth of coarse-grained and irregular gregoryite +KCl+BaCO3. Crystal size distributions of gregoryite and nyerereite in one sample are linear, implying little loss or gain of phenocrysts by crystal settling. AverageGτ is 0.15 mm, compared toGτ=0.03 mm for combeite phenocrysts from consanguineous nephelinite. Assuming an equal residence time (τ) for both lavas, the apparent crystal growth rate (G) in carbonate melt is 5 times greater than in peralkaline undersaturated silicate melt. Data from experiments with natrocarbonatite and related synthetic systems indicate that Na−K−Ca carbonatite magmas which crystallize calcite cannot fractionate to nyerereite+gregoryite +liquid assemblages. Natrocarbonatites plot in the liquidus field of nyerereite, and minor fractionation of nyerereite to produce the erupted lavas is indicated. The term natrocarbonatite has been inappropriately applied to other eruptive rocks with calcite phenocrysts, and the only known occurrence of gregoryite-bearing natrocarbonatite is Oldoinyo Lengai. Natrocarbonatite probably originates by liquid immiscibility from strongly peralkaline nephelinites, which have also been erupted at Oldoinyo Lengai.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

References

  • Bailey DK (1989) Carbonate melt from the mantle in the volcanoes of south-east Zambia. Nature 338:415–418

    Google Scholar 

  • Barker DS, Nixon PH (1989) High-Ca, low-alkali carbonatite volcanism at Fort Portal, Uganda. Contrib Mineral Petrol 103:166–177

    Google Scholar 

  • Bell K, Dawson JB, Farquahar RM (1973) Strontium isotope studies of alkalic rocks: the active carbonatite volcano Oldoinyo Lengai, Tanzania. Geol Soc Am Bull 84:1019–1030

    Google Scholar 

  • Cashman KC, Marsh BD (1988) Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization II: Makaopuhi lava lake. Contrib Mineral Petrol 99:292–305

    Google Scholar 

  • Clarke MGC, Roberts B (1986) Carbonated melilitites and calcitized alkali carbonatites from Homa Mountain, western Kenya: a reinterpretation. Geol Mag 123:683–692

    Google Scholar 

  • Cooper AF, Gittins J, Tuttle OF (1975) The system Na2CO3−K2CO3−CaCO3 at 1 kilobar and its significance in carbonatite petrogenesis. Am J Sci 275:534–560

    Google Scholar 

  • Dawson JB (1962a) Sodium carbonate lavas from Oldoinyo Lengai, Tanganyika. Nature 195:1075–1076

    Google Scholar 

  • Dawson JB (1962b) The geology of Oldoinyo Lengai. Bull Volcanol 24:349–387

    Google Scholar 

  • Dawson JB (1966) Oldoinyo Lengai — an active volcano with sodium carbonate lava flows. In: Tuttle OF, Gittins J (eds) Carbonatites. Wiley, New York, pp 155–168

    Google Scholar 

  • Dawson JB (1989) Sodium carbonate extrusions from Oldoinyo Lengai, Tanzania: implications for carbonatite complex genesis. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 255–277

    Google Scholar 

  • Dawson JB, Gale NH (1970) Uranium and thorium in alkalic rocks from the active carbonatite volcano Oldoinyo Lengai (Tanzania). Chem Geol 6:221–231

    Google Scholar 

  • Dawson JB, Garson MS, Roberts B (1987) Altered former alkalic carbonatite lava from Oldoinyo Lengai, Tanzania: inferences for calcite carbonatite lavas. Geology 15:765–768

    Google Scholar 

  • Dawson JB, Pinkerton H, Norton C, Pile DM (1988) 1988 activity of the active carbonatite volcano, Oldoinyo Lengai — uniquely low lava temperatures and viscosities. EOS 70:497–498

    Google Scholar 

  • Dawson JB, Smith JV, Steele IM (1989) Combeite (Na2.33-Ca1.74 others0.12)Si3O9 from Oldoinyo Lengai, Tanzania. J Geol 97:365–372

    Google Scholar 

  • Donaldson CH, Dawson JB, Kanaris-Sotiriou R, Batchelor RA, Walsh JN (1987) The silicate lavas of Oldoinyo Lengai, Tanzania. Neues Jahrb Mineral Abh 156:247–279

    Google Scholar 

  • Deans T, Roberts R (1984) Carbonatite tuffs and lava clasts of the Tinderet foothills, western Kenya: a study in calcified natrocarbonatites. J Geol Soc Lond 141:563–580

    Google Scholar 

  • Du Bois CGB, Furst J, Guest NJ, Jennings DJ (1963) Fresh natro carbonatite lava from Oldoinyo Lengai. Nature 197:445–446

    Google Scholar 

  • Eugster HP (1986) Lake Magadi, Kenya: a model for rift valley hydrochemistry and sedimentation? In: Frostick LE, Renaut RW, Reid I, Tiercelin JJ (eds) Sedimentation in the African rifts. Geol Soc Lond Spec Pub 25:177–189

  • Freestone IC, Hamilton DL (1980) The role of liquid immiscibility in the genesis of carbonatites: an experimental study. Contrib Mineral Petrol 73:105–117

    Google Scholar 

  • Gittins J (1989) The origin and evolution of carbonatite magmas. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 580–600

    Google Scholar 

  • Gittins J, McKie D (1980) Alkalic carbonatite magmas: Oldoinyo Lengai and its wider applicability. Lithos 13:213–215

    Google Scholar 

  • Gregory JW (1921) The rift valleys and geology of East Africa. Seeley Service and Company Ltd, London

    Google Scholar 

  • Guest NJ (1956) The volcanic activity of Oldonyo Lengai, 1954. Records Geol Surv Tanganyika IV:56–59

    Google Scholar 

  • 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

    Google Scholar 

  • Hay RL (1983) Natrocarbonatite tephra of Kerimasi volcano, Tanzania. Geology 11:599–602

    Google Scholar 

  • Javoy M, Pineau F, Cheminee JL, Kraft M (1988) The gas-magma relationship in the 1988 eruption of Oldoinyo Lengai (Tanzania). EOS 69:1466

    Google Scholar 

  • Keller J (1981) Carbonatitic volcanism in the Kaiserstuhl alkaline complex: evidence for highly fluid carbonatitic melts at the Earth's surface. J Volcan Geotherm Res 9:423–431

    Google Scholar 

  • Keller J (1989) Extrusive carbonatites and their significance. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 70–88

    Google Scholar 

  • Keller J, Krafft M (1989) Composition of natrocarbonatite lavas, Oldoinyo Lengai 1988. Terra Abs 1:286

    Google Scholar 

  • Kirkpatrick RJ, Robinson GR, Hayes JF (1976) Kinetics of crystal growth from silicate melts: anorthite and diopside. J Geophys Res 81:5715–5720

    Google Scholar 

  • Kjarsgaard BA, Hamilton DL (1988) Liquid immiscibility and the origin of alkali-poor carbonatites. Mineral Mag 52:43–55

    Google Scholar 

  • Kjarsgaard BA, Hamilton DL (1989a) Melting experiments on Shombole nephelinites: silicate/carbonate immiscibility, phase relations and the liquid line of descent. GAC Program with Abstracts 14:A50

  • Kjarsgaard BA, Hamilton DL (1989b) The genesis of carbonatites by immiscibility. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 388–404

    Google Scholar 

  • Le Bas MJ (1977) Carbonatite-nephelinite volcanism. John Wiley and Sons, London

    Google Scholar 

  • LeBas MJ (1981) Carbonatite magmas. Mineral Mag 44:133–140

    Google Scholar 

  • LeBas MJ (1987) Nephelinites and carbonatites. In: Fitton JG, Upton BGJ (eds) Alkaline igneous rocks. Blackwell: pp 53–85

  • Le Bas MJ (1989) Diversification of carbonatite. In: Bell K (ed) Carbonatites: genesis and evolution. Unwin Hyman, London, pp 428–447

    Google Scholar 

  • Maaløe S, Tumyr O, James D (1989) Population density and zoning of olivine phenocrysts in tholeiites from Kauai, Hawaii. Contrib Mineral Petrol 101:176–186

    Google Scholar 

  • Marsh BD (1988a) Crystal size distributions (CSD) in rocks and the kinetics and dynamics of crystallization I. Theory. Contrib Mineral Petrol 99:277–291

    Google Scholar 

  • Marsh BD (1988b) Crystal capture, sorting, and retention in convecting magma. Geol Soc Am Bull 100:1720–1737

    Google Scholar 

  • McKie D, Frankis EJ (1977) Nyerereite: a new volcanic carbonate mineral from Oldoinyo L'engai, Tanzania. Z Kristallogr 145:73–95

    Google Scholar 

  • Milton C (1968) The “natrocarbonatite” of Oldoinyo Lengai, Tanzania. Geol Soc Am Spec Pap 121:202

    Google Scholar 

  • Peterson TD (1989a) Peralkaline nephelinites I. Comparative petrology of Shombole and Oldoinyo L'engai, East Africa. Contrib Mineral Petrol 101:458–478

    Google Scholar 

  • Peterson TD (1989b) Peralkaline nephelinites II. Low pressure fractionation and the hypersodic lavas of Oldoinyo L'engai. Contrib Mineral Petrol 102:336–346

    Google Scholar 

  • Reck H (1914) Oldoinyo L'engai, ein tätiger Vulkan in Gebiete der Deutsch Ostafrikanischen Bruschstufe. Branca Festschrift 7:373–409

    Google Scholar 

  • Turner DC (1988) Volcanic carbonatites of the Kaluwe complex, Zambia. J Geol Soc London 145:95–106

    Google Scholar 

  • Twyman JD, Gittins J (1987) Alkalic carbonatite magmas: parental or derivative? In: Fitton JG, Upton BGJ (eds) Alkaline igneous rocks. Blackwell, London, pp 85–94

    Google Scholar 

  • Wallace ME, Green DH (1988) An experimental determination of primary carbonatite magma composition. Nature 335:343–346

    Google Scholar 

  • 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

    Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Geological Survey of Canada, 588 Booth Street, K1A 0E4, Ottawa, Canada

    Tony D. Peterson

Authors
  1. Tony D. Peterson
    View author publications

    You can also search for this author in PubMed Google Scholar

Rights and permissions

Reprints and permissions

About this article

Cite this article

Peterson, T.D. Petrology and genesis of natrocarbonatite. Contr. Mineral. and Petrol. 105, 143–155 (1990). https://doi.org/10.1007/BF00678981

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1007/BF00678981

Keywords

Search

Navigation