Hostname: page-component-586b7cd67f-t8hqh Total loading time: 0 Render date: 2024-11-27T23:20:28.947Z Has data issue: false hasContentIssue false
  • English
  • Français

Significance of compositional zoning in cumulate chromites of the Kabanga chonoliths, Tanzania

Published online by Cambridge University Press:  07 May 2018

David M. Evans
David M. Evans*
Affiliation:
Scientific Associate, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom 21 rue Jean de la Bruyère, 78000 Versailles, France
*
E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Compositional zoning is observed rarely in chrome-spinel grains from slowly-cooled layered intrusions because diffusion of cations continues within the spinel to low temperatures. However, in certain circumstances, such gradational zoning of both divalent and trivalent cations is observed and may be useful in deciphering the thermal history of the host intrusions. The accessory chrome-spinels of the Kabanga mafic-ultramafic chonolith intrusions of the Kibaran igneous event in north western Tanzania are notable because they have preserved gradational compositional zoning. This zoning is demonstrated to predate and be independent of later hydrous alteration of the silicate assemblage. At Kabanga, most chrome-spinel grains within olivine-rich cumulate rocks are gradationally and cryptically zoned from Fe2+-Cr3+ rich cores to more Mg2+-Al3+ rich rims (normal zoning). A few grains are zoned from Mg2+-Al3+ rich cores to more Fe2+-Cr3+ rich rims (reverse zoned). The zoning of divalent cations is proportional to that of trivalent cations with Mg2+ following Al3+ and Fe2+ following Cr3+ from core to rim. The zoning of trivalent and tetravalent cations is interpreted to be caused by either new growth from an evolving melt or peritectic reactions between evolved or contaminated melt and adjacent Al-Cr-bearing ferromagnesian minerals, which is preserved by relatively rapid initial cooling in the small chonolith intrusions. Divalent cation zoning is controlled by sub-solidus exchange of Fe2+ and Mg with adjacent ferromagnesian minerals and continues to lower temperatures, indicated to be 580 to 630°C by the spinel-olivine geothermometer. Preservation of such zoning is more likely in the smaller chonolith intrusions that typically host magmatic nickel-copper sulfide deposits and can be used as an exploration indicator when interpreting chromite compositions in regional heavy indicator mineral surveys.

Keywords

Kibaran igneous eventpicritic intrusionchromitediffusional zoningFe-Mg exchangecooling rate
Type
Article
Information
Mineralogical Magazine , Volume 82 , Special Issue 3: Special Issue dedicated to the work and memory of Professor Hazel M. Prichard (1954–2017) , June 2018 , pp. 675 - 696
Copyright
Copyright © Mineralogical Society of Great Britain and Ireland 2018 

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.)

Footnotes

Associate Editor: Stephen Barnes

This paper is published as part of a thematic set in memory of Professor Hazel M. Prichard

References

Abzalov, M.Z. (1998) Chrome-spinels in gabbro-wehrlite intrusions of the Pechenga area, Kola Peninsula, Russia: emphasis on alteration features. Lithos, 43, 109–134.Google Scholar
Barkov, A.Y., Nixon, G.T., Levson, V.M., Martin, R.F. and Fleet, M.E. (2013) Chromian spinel from PGE-bearing placer deposits, British Columbia, Canada: mineralogical associations and provenance. Canadian Mineralogist, 51, 501–536.Google Scholar
Barnes, S.J. (1998) Chromite in komatiites, I. Magmatic controls on crystallization and composition. Journal of Petrology, 39, 1689–1720.CrossRefGoogle Scholar
Barnes, S.J. (2000) Chromite in komatiites, II. Modification during greenschist to mid-amphibolite facies metamorphism. Journal of Petrology, 41, 387–409.Google Scholar
Barnes, S.J. and Kunilov, V.Y. (2000) Spinels and Mg ilmenites from the Noril'sk 1 and Talnakh intrusions and other mafic rocks of the Siberian flood basalt province. Economic Geology, 95, 1701–1717.Google Scholar
Barnes, S.J. and Tang, X. (1999) Chrome spinels from the Jinchuan Ni-Cu sulfide deposit, Gansu Province, People's Republic of China. Economic Geology, 94, 343–356.Google Scholar
Barnes, S.J., Mole, D.R., Le Vaillant, M., Campbell, M.J., Verrall, M.R., Roberts, M.P. and Evans, N.J. (2016) Poikilitic textures, heteradcumulates and zoned orthopyroxenes in the Ntaka Ultramafic Complex, Tanzania: Implications for crystallization mechanisms of oikocrysts. Journal of Petrology, 57, 1171–1198.Google Scholar
Bouvet de Maisonneuve, C., Costa, F., Huber, C., Vonlanthen, P., Bachmann, O. and Dungan, M.A. (2016) How do olivines record magmatic events? Insights from major and trace element zoning. Contributions to Mineralogy and Petrology, 171.Google Scholar
Cameron, E.N. (1975) Postcumulus and subsolidus equilibration of chromite and coexisting silicates in the Eastern Bushveld Complex. Geochimica Cosmochimica Acta, 39, 1021–1033Google Scholar
Dick, H.J.B. and Bullen, T. (1984) Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas. Contributions to Mineralogy and Petrology, 86, 54–76.CrossRefGoogle Scholar
Evans, D.M. (1999) High magnesium basaltic origin of Kibaran intrusions, Tanzania. Abstract in Komatiites, Norites, Boninites and Basalts Conference Volume (Hall, R.P., editor). University of Portsmouth, https://doi.org/10.13140/RG.2.1.3125.0961Google Scholar
Evans, D.M. (2014) Metamorphic modifications of the Muremera mafic-ultramafic intrusions, eastern Burundi, and their effect on chromite compositions. Journal of African Earth Sciences, 101, 19–34.Google Scholar
Evans, D.M. (2017) Chromite compositions in nickel sulphide mineralized intrusions of the Kabanga-Musongati-Kapalagulu Alignment, East Africa: petrologic and exploration significance. Ore Geology Reviews, 90, 307–321.Google Scholar
Evans, D.M., Byemelwa, L. and Gilligan, J. (1999) Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania. Journal of African Earth Sciences, 29, 329–351.Google Scholar
Evans, D.M., Boadi, I., Byemelwa, L., Gilligan, J.M., Kabete, J. and Marcet, P. (2000) Kabanga magmatic nickel sulphide deposits, Tanzania – morphology and geochemistry of associated intrusions. Journal of African Earth Sciences, 30, 651–674.Google Scholar
Fabriès, J. (1979) Spinel-olivine geothermometry in peridotites from ultramafic complexes. Contributions to Mineralogy and Petrology, 69, 329–336.Google Scholar
Fernandez-Alonso, M., Cutten, H., de Waele, B, Tack, L., Tahon, A., Baudet, D. and Barritt, S.D. (2012) The Mesoproterozoic Karagwe-Ankole Belt (formerly the NE Kibara Belt): the result of prolonged extensional intracratonic basin development punctuated by two short-lived far-field compressional events. Precambrian Research, 216–219, 63–86.CrossRefGoogle Scholar
Henderson, P. (1975) Reaction trends shown by chrome-spinels of the Rhum layered intrusion. Geochimica Cosmochimica Acta, 39, l035–1044.Google Scholar
Irvine, T.N. (1965) Chromian spinel as a petrogenetic indicator. Part 1, Theory. Canadian Journal of Earth Sciences, 2, 648–672.Google Scholar
Irvine, T.N. (1967) Chromian spinel as a petrogenetic indicator. Part 2, Petrologic applications. Canadian Journal of Earth Sciences, 4, 71–102.Google Scholar
Jaeger, J.C. (1968) Cooling and solidification of igneous rocks. Pp. 503–536 in: Basalts (Hess, H.R. and Poldevaart, A., editors). Vol. 2. New York, Interscience Publishers.Google Scholar
Jarosewich, E., Nelen, J.A. and Norberg, J.A. (1980) Reference samples for electron microprobe analysis. Geostandards Newsletter, 4, 43–47.Google Scholar
Kamenetsky, V.S., Crawford, A.J. and Meffre, S. (2001) Factors controlling chemistry of magmatic spinel: an empirical study of associated olivine, Cr-spinel and melt inclusions from primitive rocks. Journal of Petrology, 42, 655–671.Google Scholar
Klerkx, J., Liegeois, J-P., Lavreau, J. and Claessens, W. (1987) Crustal evolution of the northern Kibaran Belt, Eastern and Central Africa. Pp 217–233 in: Proterozoic Lithospheric Evolution (Kroner, A., editor). American Geophysical Union, Washington.CrossRefGoogle Scholar
Koegelenberg, C., Kisters, A.F.M., Kramers, J.D. and Frei, D. (2015) U–Pb detrital zircon and 39Ar–40Ar muscovite ages from the eastern parts of the Karagwe-Ankole Belt: Tracking Paleoproterozoic basin formation and Mesoproterozoic crustal amalgamation along the western margin of the Tanzania Craton. Precambrian Research, 260, 147–161.Google Scholar
MacGregor, I.D. and Smith, C.H. (1963) The use of chrome spinels in petrographic studies of ultramafic intrusions. Canadian Mineralogist, 7, 403–412.Google Scholar
Maier, W.D. and Barnes, S-J. (2010) The Kabanga Ni sulfide deposits, Tanzania: II. Chalcophile and siderophile element geochemistry. Mineralium Deposita, 45, 443–460.Google Scholar
Maier, W.D., Barnes, S.-J., Sarkar, A., Ripley, E, Li, C. and Livesey, T. (2010) The Kabanga Ni sulfide deposit, Tanzania: I. Geology, petrography, silicate rock geochemistry, and sulphur and oxygen isotopes. Mineralium Deposita, 45, 419–441.Google Scholar
O'Neill, H.St.C. and Wall, V.J. (1987) The olivine-orthopyroxene-spinel oxygen geobarometer, the nickel precipitation curve, and the oxygen fugacity of the Earth's upper mantle. Journal of Petrology, 28, 1169–1191.Google Scholar
Peltonen, P. (1995) Crystallization and re-equilibration of zoned chromite in ultramafic cumulates, Vammala Ni-belt, southwestern Finland. Canadian Mineralogist, 33, 521–535.Google Scholar
Posner, E.S., Ganguly, J. and Hervig, R. (2016) Diffusion kinetics of Cr in spinel: Experimental studies and implications for 53Mn–53Cr cosmochronology. Geochimica Cosmochimica Acta, 175, 20–35.Google Scholar
Roeder, P.L. and Campbell, I.H. (1985) The effect of postcumulus reactions on composition of chrome-spinels from the Jimberlana Intrusion. Journal of Petrology, 26, 763–786.Google Scholar
Roeder, P.L., Campbell, I.H. and Jamieson, H.E. (1979) A re-evaluation of the olivine-spinel geothermometer. Contributions to Mineralogy Petrology, 68, 325–334.Google Scholar
Roeder, P.L., Poustovetov, A. and Oskarsson, N. (2001) Growth forms and composition of chromian spinel in MORB magma: diffusion-controlled crystallization of chromian spinel. Canadian Mineralogist, 39, 397–416.Google Scholar
Sack, R.O. and Ghiorso, M.S. (1991) Chromian spinels as petrogenetic indicators: thermodynamics and petrologic applications. American Mineralogist, 76, 827–847.Google Scholar
Scowen, P.A.H., Roeder, P.L. and Helz, R.T. (1991) Reequilibration of chromite within Kilauea-Iki lava lake, Hawai'i. Contributions to Mineralogy and Petrology, 107, 8–20.Google Scholar
Sintubin, M. (1989) Characterization of the Kibaran metamorphism in the Kazingwe Complex, S.W. Burundi. Musée Royale de l'Afrique Centrale, Tervuren (Belgique), Département de Géologie et Minéralogie Rapport Annuel 1987–1988, 123–137.Google Scholar
Suzuki, A.M., Yasuda, A. and Ozawa, K. (2008) Cr and Al diffusion in chromite spinel: experimental determination and its implication for diffusion creep. Physics and Chemistry of Minerals, 35, 433–445.Google Scholar
Tack, L. (1990) Late Kibaran structural evolution in Burundi. I.G.C.P. no. 255 Newsletter/Bulletin 3, 77–79.Google Scholar
Tack, L. and Deblond, A. (1990) Intrusive character of the Late Kibaran magmatism in Burundi. I.G.C.P. no. 255 Newsletter/Bulletin 3, 81–87.Google Scholar
Tack, L., Wingate, M.T.D., de Waele, B., Meert, J., Belousova, E., Griffin, B., Tahon, A. and Fernandez-Alonso, M. (2010) The 1375Ma “Kibaran event” in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime. Precambrian Research, 180, 63–84.CrossRefGoogle Scholar
Van Orman, J.A. and Crispin, K.L. (2010) Diffusion in oxides. pp. 757–825 in: Diffusion in Minerals and Melts (Zhang, Y. and Cherniak, D.J., editors). Reviews in Mineralogy & Geochemistry, 72. The Mineralogical Society of America and the Geochemical Society, Chantilly, Virginia, USA.CrossRefGoogle Scholar
Vogt, K., Dohmen, R. and Chakraborty, S. (2015) Fe-Mg diffusion in spinel: new experimental data and a point defect model. American Mineralogist, 100, 2112–2122.CrossRefGoogle Scholar
Wilson, A.H. (1982) The geology of the Great ‘Dyke’, Zimbabwe: the ultramafic rocks. Journal of Petrology 23, 240–292.Google Scholar
Supplementary material: File

Evans supplementary material

Evans supplementary material 1

Download Evans supplementary material(File)
File 8.6 MB