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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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|
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