Hostname: page-component-8448b6f56d-mp689 Total loading time: 0 Render date: 2024-04-16T10:54:20.773Z Has data issue: false hasContentIssue false
  • English
  • Français

Differentiation of natrocarbonatite magma at Oldoinyo Lengai volcano, Tanzania

Published online by Cambridge University Press:  05 July 2018

J. Gittins  and
B. C. Jago
J. Gittins
Affiliation:
Department of Geology, University of Toronto, Toronto, Ontario, Canada M5S 3B1
B. C. Jago
Affiliation:
Lakefield Research Ltd., Postal Bag 4300, 185 Concession Street, Lakefield, Ontario, Canada K0L 2H0
Get access Rights & Permissions [Opens in a new window]

Abstract

Natrocarbonatite magma, erupted as lava flows in the Tanzanian volcano Oldoinyo Lengai in June and November of 1988, has evolved chemically since its formation. The June and November flows of 1988 display increasing Cl, F, Ba, K, Mg and Mn, concomitantly with Na, Ca and P depletion. Furthermore, the June magma, at the time of eruption, had higher Cl, F, Ba and K contents and lower Ca than the November magma and evolved to higher levels of Cl, F, Ba and K content and lower Ca, Na and P. The mineralogy of the lavas reflects these trends. Crystallization of fluorite and halite–sylvite solid solution, usually as a symplectic intergrowth, occurs when Cl and F concentrations reach the critical value necessary to stabilize both minerals and explains why neither occurs as a phenocryst phase. Natrocarbonatite magma has undergone considerable and rapid magmatic evolution, probably in small and separate magma chambers. Two minerals, nyerereite and gregoryite, have dominated the crystallization history of natrocarbonatite magma, and many lavas are phenocryst-rich. However, because most of the lavas are composed principally of these two minerals, crystal accumulation has not greatly changed their composition and, consequently, we suggest that the bulk composition of the lavas closely approximates that of the parental magma.

Keywords

natrocarbonatiteOldoinyo Lengaimagmatic evolution
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 6 , December 1998 , pp. 759 - 768
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Church, A. and Jones, A.P. (1995) Silicate-carbonate immiscibility at Oldoinyo Lengai. J. Petrol., 36, 869–89.CrossRefGoogle Scholar
Dawson, J.B. (1962) Sodium carbonate lavas from Oldoinyo Lengai, Tanganyika. Nature, 195, 1075–6.CrossRefGoogle Scholar
Dawson, J.B., Pinkerton, H., Norton, G.E., Pyle, D.M., Browning, P., Jackson, D. and Fallick, A.E. (1995) Petrology and geochemistry of Oldoinyo Lengai lavas extruded in November 1988: magma source, ascent and crystallization. In Carbonatite Volcanism. Oldoinyo Lengai and the Petrogenesis of Natrocarbonatites, (Bell, K. and Keller, J., eds.) IAVCEI Proceedings in Volcanology, 4, 47–69.CrossRefGoogle Scholar
Dawson, J.B., Pyle, D.M. and Pinkerton, H. (1996) Evolution of natrocarbonatite from a wollastonite nephelinite parent: evidence from the June, 1993 eruption of Oldoinyo Lengai. J. Geol., 104, 41–5.CrossRefGoogle Scholar
Dawson, J.B., Smith, J.V. and Steele, I.M. (1992) 1966 ash eruption of the carbonatite volcano Oldoinyo Lengai: mineralogy of lapilli and mixing of silicate and carbonate magmas. Mineral. Mag., 56, 1–16.CrossRefGoogle Scholar
Freestone, I.C. and Hamilton, D.L. (1980) The role of liquid immiscibility in the genesis of carbonatites - an experimental study. Contrib. Mineral. Petrol., 73, 105–17.CrossRefGoogle Scholar
Jago, B.C. (1991) The role of fluorine in the evolution of alkali-bearing carbonatites and the crystallization of carbonatite hosted apatite and pyrochlore deposits. Ph.D dissertation, University of Toronto.CrossRefGoogle Scholar
Jago, B.C. and Gittins, J. (1991) The role of fluorine in carbonatite magma evolution. Nature, 336, 56–8CrossRefGoogle Scholar
Jago, B.C. and Gittins, J. (1999) Mn and F-bearing rasvumite in natrocarbonatite at Oldoinyo Lengai volcano, Tanzania. Mineral. Mag., 63 (in press).CrossRefGoogle Scholar
Keller, J. and Krafft, M. (1990) Effusive natrocarbonatite activity of Oldoinyo Lengai, June 1988. Bull. Volcanol., 52, 629–45.CrossRefGoogle Scholar
Kjarsgaard, B.A. and Hamilton, D.L. (1989) The genesis of carbonatites by immiscibility. In Carbonatites, (Bell, K. ed.), Unwin Hyman, 388–404.Google Scholar
Kjarsgaard, B.A., Hamilton, D.L. and Peterson, T.D. (1995) Peralkaline nephelinite/carbonatite liquid immiscibility: comparison of phase compositions in experiments and natural lavas from Oldoinyo Lengai. In Carbonati te Volcanism. Oldoinyo Lengai and the Petrogenesis of Natrocarbonatites, (Bell, K. and Keller, J., eds.), IAVCEI Proceedings in Volcanology, 4, Springer-Verlag, 163–90.CrossRefGoogle Scholar
Le Bas, M.J. (1977) Carbonatite-nephelinite volcanism. An African case History. John Wiley, 347 pp.Google Scholar
Mitchell, R.H. (1997) Carbonate-carbonate immiscibility, neighborite and potassium iron sulphide from Oldoinyo Lengai natrocarbonatite. Mineral. Mag., 61, 779–89.CrossRefGoogle Scholar
Peterson, T.D. (1990) Petrology of natrocarbonatite. Contrib. Mineral. Petrol., 105, 143–55.CrossRefGoogle Scholar
Pyle, D.M., Pinkerton, G.E., Norton, G.E. and Dawson, J.B. (1995) The dynamics of degassing at Oldoinyo Lengai. In Carbonatite Volcanism. Oldoinyo Lengai and the Petrogenesis of Natrocarbonatites, (Bell, K. and Keller, J., eds. ), IAVCEI Proceedings in Volcanology, 4, Springer-Verlag, 37–46.CrossRefGoogle Scholar