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The 24th September 2007 ash eruption of the carbonatite volcano Oldoinyo Lengai, Tanzania: mineralogy of the ash and implications for formation of a new hybrid magma type

Published online by Cambridge University Press:  05 July 2018

R. H. Mitchell  and
J. B. Dawson
R. H. Mitchell*
Affiliation:
Department of Geology, Lakehead University, Thunder Bay, ON, Canada P7B 5E1
J. B. Dawson
Affiliation:
School of Geosciences, Grant Institute, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK
*
E-mail: rmitchel@lakeheadu.ca
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Abstract

The September 2007 ash eruption at Oldoinyo Lengai terminated a period of >30 y of relatively quiet extrusion of natrocarbonatite lavas. Ash erupted on the 24th September comprised nuclei of ijolitic phases, surrounded by finer peralkaline, silica-undersaturated material. The mantling material, as well as that forming nucleus-free particles, is dominated by nepheline, Ti-andradite, Na-melilite, combeite and a Na-Ca-phosphate-carbonate with minor amounts of K-Fe-sulphide and Mn-magnetite in a sparse matrix of alkali carbonate. The absence of clinopyroxene precludes this material from being termed either nephelinite or melilitite. We propose that the material represented by the mantles is an extremely undersaturated, peralkaline hybrid magma resulting from interaction between natrocarbonatite and nephelinite.

Keywords

carbonatitevolcanic ashlapillinephelinecombeitemeliliteOldoinyo LengaiTanzania
Type
Research Article
Information
Mineralogical Magazine , Volume 71 , Issue 5 , October 2007 , pp. 483 - 492
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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References

Dawson, J.B. (1962) Sodium carbonate lavas from Oldoinyo Lengai, Tanganyika. Nature, 195, 1075–1076.CrossRefGoogle Scholar
Dawson, J.B. and Hill, P.G. (1998) Mineral chemistry of a peralkaline combeite lamprophyllite nephelinite from Oldoinyo Lengai, Tanzania. Mineralogical Magazine, 62, 179–196.CrossRefGoogle Scholar
Dawson, J.B., Bowden, P. and Clark, G.C. (1968) Activity of the carbonatite volcano Oldoinyo Lengai, 1966. Geologische Rundschau, 57, 865–879.CrossRefGoogle Scholar
Dawson, J.B., Smith, J.V. and Jones, A.P. (1988) A comparative study of bulk rock and mineral chemistry of olivine melilitites and associated rocks from east and south Africa. Neues Jahrbuch für Mineralogie Abhandlungen, 152, 143–175.Google Scholar
Dawson, J.B., Smith, J.V. and Steele, I.M. (1989) Combeite (Na2.33Ca1.74others0.12)Si3O9 from Oldoinyo Lengai, Tanzania. Journal of Geology, 97, 365–372.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. Mineralogical Magazine, 56, 1–16.CrossRefGoogle Scholar
Dawson, J.B., Pinkerton, H., Pyle, D.M. and Nyamweru, C. (1994) June 1993 eruption of Oldoinyo Lengai, Tanzania: exceptionally viscous and large carbonatite lava flows and evidence for coexisting silicate and carbonate magmas. Geology, 22, 799–802.2.3.CO;2>CrossRefGoogle Scholar
Dawson, J.B., Keller, J. and Nyamweru, C. (1995) Historic and recent eruptive activity of Oldoinyo Lengai. Pp. 4–22 in: Carbonatite Volcanism (Bell, K. and Keller, J., editors). Springer Verlag, Berlin.Google Scholar
Dawson, J.B., Pinkerton, H. and Pyle, D.M. (1996) Evolution of natrocarbonatite from a wollastonitenephelinite parent: evidence from the June, 1993 eruption of Oldoinyo Lengai, Tanzania. Journal of Geology, 104, 41–54.CrossRefGoogle Scholar
Donaldson, C.H., Dawson, J.B., Kanaris–Sotiriou, R., Batchelor, R.A. and Walsh, J.N. (1987) The silicate lavas of Oldoinyo Lengai, Tanzania. Neues Jahrbuch für Mineralogie Abhandlungen, 156, 247–279.Google Scholar
Fischer, G.A. (1885) Bericht Über die am Auftrage der Geographischen Gesellschaft in Hamburg unternommene Reise in das Masai–Land 1882–1883. II Begleitwort zur Original Routenkarte. Mitteilungen der Geographischen Gesellschaft in Hamburg, 1885, 189–237.Google Scholar
Hamilton, D.L. (1961) Nephelines as crystallization temperature indicators. Journal of Geology, 69, 321–329.CrossRefGoogle Scholar
Keller, J. and Krafft, M. (1990) Effusive natrocarbonatite activity of Oldoinyo Lengai, June 1988. Bulletin Volcanologique, 52, 629–645.Google Scholar
Keller, J., Zaitsev, A.N. and Wiedenmann, D. (2006) Primary magmas at Oldoinyo Lengai: the role of olivine melilitites. Lithos, 91, 150–172.CrossRefGoogle Scholar
Klaudius, J. and Keller, J. (2006) Peralkaline silicate lavas at Oldoinyo Lengai, Tanzania. Lithos, 91, 173–190.CrossRefGoogle Scholar
Mitchell, R.H. (1997) Carbonate–carbonate immiscibility, neighborite and potassium iron sulphide in Oldoinyo Lengai natrocarbonatite. Mineralogical Magazine, 61, 779–789.CrossRefGoogle Scholar
Mitchell, R.H. (2006) An ephemeral pentasodium phosphate carbonate from natrocarbonatite lapilli, Oldoinyo Lengai, Tanzania. Mineralogical Magazine, 70, 1–8.CrossRefGoogle Scholar
Mitchell, R.H. and Belton, F. (2004) Niocalite–cuspidine solid solution and manganoan monticellite from natrocarbonatite, Oldoinyo Lengai, Tanzania. Mineralogical Magazine, 68, 787–799.CrossRefGoogle Scholar