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?

H. Mouri, M. A.G. Andreoli, J. R. Kienast, M. Guiraud, S. A. de Waal

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

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 quartz-feldspar ± 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.

Original languageEnglish
Pages (from-to)1015-1021
Number of pages7
JournalMineralogical Magazine
Volume67
Issue number5
DOIs
Publication statusPublished - Oct 2003
Externally publishedYes

Keywords

  • Corundum quartz
  • Namaqualand Metamorphic Complex
  • South Africa

ASJC Scopus subject areas

  • Geochemistry and Petrology

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