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First occurrence of the rare ‘corundum + quartz’ assemblage in the high-grade zone from the Namaqualand Metamorphic Complex, South Africa: evidence for higher-P, T metamorphism?

Published online by Cambridge University Press:  05 July 2018

H. Mouri ,
M. A. G. Andreoli ,
J. R. Kienast ,
M. Guiraud  and
S. A. De Waal
H. Mouri*
Affiliation:
Department of Geology, University of Pretoria, South Africa
M. A. G. Andreoli
Affiliation:
South African Nuclear Energy Corporation, P.O. Box 582, Pretoria 0001, South Africa
J. R. Kienast
Affiliation:
Laboratoire des Geosciences Marine, Université Paris 7, France
M. Guiraud
Affiliation:
USM 201 Minéralogie, FRE CNRS 2456, Dpt Histoire de la Terre, MNHN Paris, France
S. A. De Waal
Affiliation:
Department of Geology, University of Pretoria, South Africa
*
* E-mail: [email protected]
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Abstract

We report in this paper the first occurrence of the rare assemblage corundum + quartz in the high-grade metamorphic zone in the core of the Namaqualand Metamorphic Complex (NMC) (South Africa). The magnetite-bearing rocks hosting the corundum-quartz assemblage are very rare, and occur discontinuous bands a few cm wide, associated with diorite, tonalite and anorthosite within quartzfeldspar ± sillimanite ± biotite ± spinel supracrustal rocks extensively intruded by a foliated granite gneiss. The magnetite-bearing rocks are characterized by the presence of abundant crystals of magnetite together with ilmenite, spinel and large (∽1 cm in diameter) euhedral crystals of corundum both displaying a sharp contact with magnetite and quartz. However, in some micro-domains, spinel and quartz, as well as corundum and quartz, are separated by a thin corona of sillimanite with or without magnetite. These textural features suggest that the following reactions have taken place: quartz + corundum → sillimanite, and quartz + spinel + O2 → sillimanite + magnetite. These reactions are interpreted as occurring at higher, as yet unknown, P-T conditions than previously estimated for the NMC. Whether corundum and quartz were once in equilibrium is worth investigating, as it could constitute a geothermobarometric assemblage for ultra-high T granulites.

Keywords

corundumquartzNamaqualand Metamorphic ComplexSouth Africa.
Type
Research Article
Information
Mineralogical Magazine , Volume 67 , Issue 5 , October 2003 , pp. 1015 - 1021
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2003

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Footnotes

†

Present address: Schonland Research Centre for Nuclear Science, University of the Witwatersrand, P.O. Box 3, Wits 2050, South Africa

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