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

Belyanin, GA and Rajesh, HM and Sajeev, K and Van Reenen, DD (2012) Ultrahigh-temperature metamorphism from an unusual corundum plus orthopyroxene intergrowth bearing Al-Mg granulite from the Southern Marginal Zone, Limpopo Complex, South Africa. In: CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 164 (3). pp. 457-475.

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Official URL: http://dx.doi.org/10.1007/s00410-012-0747-3

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 +/- A quartz, Al-rich orthopyroxene (similar to 11 wt%), spinel + quartz, and corundum in possible equilibrium with quartz, while the Si-rich layer preserves antiperthites and orthopyroxene + sillimanite +/- A 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 similar to 1,050-1,100 A degrees C, and similar to 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).

Item Type: Journal Article
Additional Information: Copyright for this article belongs to Springer
Keywords: Orthopyroxene plus sillimanite +/- quartz; High-Al orthopyroxene; Antiperthite; Spinel plus quartz; Ultrahigh-temperature metamorphism; Al-Mg granulite; Clockwise P-T path; Southern Marginal Zone; Limpopo complex
Department/Centre: Division of Earth and Environmental Sciences > Centre for Earth Sciences
Date Deposited: 21 Sep 2012 09:48
Last Modified: 21 Sep 2012 09:48
URI: http://eprints.iisc.ernet.in/id/eprint/45076

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