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High-Ti magnetite in some fine-grained carbonatites and the magmatic implications

Published online by Cambridge University Press:  05 July 2018

D. K. Bailey  and
S. Kearns
D. K. Bailey
Affiliation:
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, UK
S. Kearns
Affiliation:
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, UK
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Abstract

Magnetite is present in most carbonatites, and in the most abundant and best-known form of carbonatite, coarse-grained intrusions, it typically falls in a narrow composition range close to Fe3O4. A fine-grained carbonatite from Zambia contains magnetites with an extraordinary array of compositions (from 18–1% TiO2, 10–2% Al2O3, and 16–4% MgO) outranging previously-reported examples. Zoning trends are from high TiO2 to high Al2O3 and MgO. No signs of exsolution are seen. Checks on similar rocks from Germany, Uganda and Tanzania reveal magnetites with comparable compositions, ranges, and zoning. Magnetites from alkaline and alkaline ultramafic silicate volcanic rocks cover only parts of this array. Magnetite analyses from some other fine-grained carbonatites, reported in the literature, fall in the same composition field, suggesting that this form of carbonatite may be distinctive. The chemistry and zoning would be consonant with rapid high-temperature crystallization in the carbonatite melts, with the lack of exsolution pointing to fast quenching: this contrasts with coarse-grained intrusive carbonatites, in which the magnetite compositions are attributed to slow cooling, with final equilibration at low temperature. In some complexes, both forms of carbonatite, with their different magnetite compositions, are represented.

Keywords

high-ti magnetitecarbonatiteZambia
Type
Letter
Information
Mineralogical Magazine , Volume 66 , Issue 3 , June 2002 , pp. 379 - 384
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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References

Bailey, D.K. (1960) Carbonatites of the Rufunsa Valley, Feira District. Geological Survey, Northern Rhodesia, Bulletin, 5, 92 pp., 5 maps, 14 plates.Google Scholar
Bailey, D.K. (1966) Carbonatite volcanoes and shallow intrusions in Zambia. Pp. 127–154 in: Carbonatites.(Tuttle, O.F. and Gittins, J., editors). Wiley & Sons, New York, London and Sydney.Google Scholar
Bailey, D.K. (1989) Carbonate melt from the mantle in the volcanoes of south-east Zambia. Nature, 388, 415–418 (and 374).CrossRefGoogle Scholar
Bailey, D.K. (1993) Carbonate magmas. Journal of the Geological Society, London, 150, 637–651.CrossRefGoogle Scholar
Barker, D.S. & Nixon, P.H. (1989) High-Ca, low-alkali carbonatite volcanism at Fort Portal, Uganda. Contributions to Mineralogy and Petrology, 103, 166–177.CrossRefGoogle Scholar
Church, A.A. (1995) The petrology of the Kerimasi carbonatite volcano and the carbonatites of Oldoinyo Lengai with a review of other occurrences of extrusive carbonatites. PhD thesis, University College, London.Google Scholar
Dawson, J.B. (1994) Quaternary kimberlitic volcanism on the Tanzania craton. Contributions to Mineralogy and Petrology 116, 473–485.CrossRefGoogle Scholar
Dawson, J.B., Steele, I.M., Smith, J.V. and Rivers, M.L. (1996) Minor and trace element chemistry of carbonates, apatites and magnetites in some African carbonatites. Mineralogical Magazine, 60, 415–426.CrossRefGoogle Scholar
Frost, B.R. and Lindsley, D.H. (1991) Occurrence of iron-titanium oxides in igneous rocks. Pp. 433–468 in: Oxide Minerals.(Lindsley, D.H., editor). Reviews in Mineralogy, 25, Mineralogical Society of America, Washington, D.C.CrossRefGoogle Scholar
Gaspar, J. and Wyllie, P.J. (1983) Magnetite in the carbonatites from the Jacupiranga Complex, Brazil. American Mineralogist, 68, 195–213.Google Scholar
Keller, J. (1989) Extrusive carbonatites and their significance. Pp. 70–88 in: Carbonatites.(Bell, K., editor). Unwin Hyman, London.Google Scholar
Keller, J. (2001) Kaiserstuhl Excursion Guide. European Science Foundation Eurocarb Project, IMPG, Freiburg, Germany, 29 pp.Google Scholar
Macdonald, R., Kjarsgaard, B.A., Skilling, I.P., Davies, G.R., Hamilton, D.L. and Black, S. (1993) Liquid immiscibility between trachyte and carbonate in ash flow tuffs from Kenya. Contributions to Mineralogy and Petrology, 114, 276–87.CrossRefGoogle Scholar
McMahon, B.M. and Haggerty, S.E. (1979) The Oka carbonatite complex: magnetite compositions and the related role of titanium in pyrochlore. Pp. 382–392 in: Kimberlites, Diatremes and Diamonds: their Geology, Petrology, and Geochemistry.(Boyd, F.R. and Meyer, H.O., editors). American Geophysical Union, Washington, D.C.CrossRefGoogle Scholar
McMahon, B.M. and Haggerty, S.E. (1984) The Benfontein kimberlite sills: magmatic reactions and high intrusion temperatures. American Journal of Science, 284, 893–941.CrossRefGoogle Scholar
Prins, P. (1972) Composition of magnetite from carbonatites. Lithos, 5, 227–240.CrossRefGoogle Scholar
Riley, T.R., Bailey, D.K. and Lloyd, F.E. (1996) Extrusive carbonatite from the Quaternary Rockeskyll complex, West Eifel, Germany. The Canadian Mineralogist, 34, 389–403.Google Scholar
Stoppa, F. and Cundari, A. (1998) Origin and multiple crystallization of the kamafugite-carbonatite association: the San Venanzo-Pian di Celle occurrence (Umbria, Italy). Mineralogical Magazine, 62, 273–89.CrossRefGoogle Scholar
Stoppa, F. and Lupini, L. (1993) Mineralogy and petrology of the Polino monticellite-calciocarbonatite (Central Italy). Mineralogy and Petrology, 9, 213–231.CrossRefGoogle Scholar
Stoppa, F. and Principe, C. (1997) Eruption styles and petrology of a new carbonatite suite from Mt. Vulture (Southern Italy): The Monticcio Lakes Formation. Journal of Volcanology and Geothermal Research, 80, 137–53.CrossRefGoogle Scholar
Stoppa, F., Woolley, A.R., Lloyd, F.E. and Eby, N. (2000) Carbonatite lapilli-bearing tuff and a dolomite carbonatite bomb from Murumuli crater, Katwe volcanic field, Uganda. Mineralogical Magazine, 64, 641–650.CrossRefGoogle Scholar
Turner, D.C. and Rex, D.C. (1991) Volcaniclastic carbonatite at Kaluwe, Zambia – age and relations to sedimentary rocks in the Zambezi rift-valley. Journal of the Geological Society of London, 148, 13–15.CrossRefGoogle Scholar
Woolley, A.R., Barr, M.W.C., Din, V.K., Jones, G.C., Wall, F. and Williams, C.T. (1991) Extrusive carbonatites from the Uyaynah area, United Arab Emirates. Journal of Petrology, 32, 1143–1167.CrossRefGoogle Scholar