Ultrahigh-temperature metamorphism from an unusual corundum+orthopyroxene intergrowth bearing Al-Mg granulite from the Southern Marginal Zone, Limpopo Complex, South Africa

G. A. Belyanin, H. M. Rajesh, K. Sajeev, D. D. Van Reenen

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

The Southern Marginal Zone of the Limpopo Complex is composed of granite-greenstone cratonic rocks reworked by a Neoarchean high-grade tectono-metamorphic event. Petrographic and mineral chemical characterization of an Al-Mg granulite from this zone is presented here. The granulite has a gneissic fabric with distinct Al-rich and Si-rich layers, with the former preserving the unusual lamellar (random and regular subparallel) intergrowths of corundum and symplectic intergrowth of spinel with orthopyroxene. The Al-rich layer preserves mineral assemblages such as rutile with orthopyroxene + sillimanite ± quartz, Al-rich orthopyroxene (~11 wt%), spinel + quartz, and corundum in possible equilibrium with quartz, while the Si-rich layer preserves antiperthites and orthopyroxene + sillimanite ± quartz, all considered diagnostic of ultrahigh-temperature metamorphism. Application of Al-in-opx thermometry, ternary feldspar thermometry and construction of suitable pressure-temperature phase diagrams, compositional and model proportion isopleth results indicate P-T conditions as high as ~1,050-1,100 °C, and ~10-12 kbars for the Al-Mg granulite. Our report of ultrahigh-temperature conditions is significant considering that the very high temperature was reached during decompression of an otherwise high-pressure granulite complex (clockwise P-T path), whereas most other ultrahigh-temperature granulites are linked to magma underplating at the base of the crust (counterclockwise P-T path).

Original languageEnglish
Pages (from-to)457-475
Number of pages19
JournalContributions to Mineralogy and Petrology
Volume164
Issue number3
DOIs
Publication statusPublished - Sep 1 2012

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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