Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
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Authors: | KELLY N M; HARLEY S L |
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Institution: | 1 DIVISION OF GEOLOGY AND GEOPHYSICS, SCHOOL OF GEOSCIENCES, F05, UNIVERSITY OF SYDNEY, SYDNEY, N.S.W. 2006, AUSTRALIA
2 SCHOOL OF GEOSCIENCES, UNIVERSITY OF EDINBURGH, GRANT INSTITUTE, KINGS BUILDINGS, EDINBURGH EH9 3JW, UK |
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Abstract: | High-MgAl, silica-undersaturated metapelites from theOygarden Group of islands, East Antarctica, preserve clear evidencefor the stable coexistence of the assemblage orthopyroxene +corundum in natural rocks. The quartz-absent metapelite occursas pods and isolated layers within a high-strain zone relatedto deformation during the c. 0·93 Ga Rayner StructuralEpisode. Assemblages that include orthopyroxene, corundum, sapphirine,sillimanite, cordierite, garnet and kornerupine are developedacross a pre-existing compositional zoning, leading to contrastingmineral FeMg ratios. The assemblage orthopyroxenecorundumis shown to exist in only a very restricted range of bulk compositionsand PT histories. Simplified qualitative FMAS grids havebeen constructed for kornerupine-absent and -present systems,illustrating MAS terminations and divariant equilibria thathelp to describe the mineral assemblage and reaction history.Reaction textures that include coronas of sapphirine and sillimaniteseparating orthopyroxene and corundum, and symplectites of orthopyroxene+ sapphirine ± cordierite/plagioclase, orthopyroxene+ sillimanite ± cordierite/plagioclase and orthopyroxene+ sapphirine + sillimanite embaying garnet, imply a clockwisePTt evolution. Conditions of P > 910kbar and T |
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Keywords: | : decompression kornerupine orthopyroxene corundum reaction textures sapphirine symplectite |
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