Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica
High-Mg–Al, silica-undersaturated metapelites from the Oygarden Group of islands, East Antarctica, preserve clear evidence for the stable coexistence of the assemblage orthopyroxene + corundum in natural rocks. The quartz-absent metapelite occurs as pods and isolated layers within a high-strain zone...
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2004
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fthighwire:oai:open-archive.highwire.org:petrology:45/7/1481 2023-05-15T13:34:12+02:00 Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica KELLY, N. M. HARLEY, S. L. 2004-07-01 00:00:00.0 text/html http://petrology.oxfordjournals.org/cgi/content/short/45/7/1481 https://doi.org/10.1093/petrology/egh023 en eng Oxford University Press http://petrology.oxfordjournals.org/cgi/content/short/45/7/1481 http://dx.doi.org/10.1093/petrology/egh023 Copyright (C) 2004, Oxford University Press ARTICLES TEXT 2004 fthighwire https://doi.org/10.1093/petrology/egh023 2013-05-27T23:35:32Z High-Mg–Al, silica-undersaturated metapelites from the Oygarden Group of islands, East Antarctica, preserve clear evidence for the stable coexistence of the assemblage orthopyroxene + corundum in natural rocks. The quartz-absent metapelite occurs as pods and isolated layers within a high-strain zone related to deformation during the c . 0·93 Ga Rayner Structural Episode. Assemblages that include orthopyroxene, corundum, sapphirine, sillimanite, cordierite, garnet and kornerupine are developed across a pre-existing compositional zoning, leading to contrasting mineral Fe–Mg ratios. The assemblage orthopyroxene–corundum is shown to exist in only a very restricted range of bulk compositions and P – T histories. Simplified qualitative FMAS grids have been constructed for kornerupine-absent and -present systems, illustrating MAS terminations and divariant equilibria that help to describe the mineral assemblage and reaction history. Reaction textures that include coronas of sapphirine and sillimanite separating orthopyroxene and corundum, and symplectites of orthopyroxene + sapphirine ± cordierite/plagioclase, orthopyroxene + sillimanite ± cordierite/plagioclase and orthopyroxene + sapphirine + sillimanite embaying garnet, imply a clockwise P – T – t evolution. Conditions of P > 9–10 kbar and T ≈ 800–850°C were attained prior to an initial phase of decompression that was accompanied by heating of up to ≈100°C. Peak temperatures of T ≈ 850–900°C were achieved at P ≈ 9 kbar followed by near-isothermal decompression to pressures of P ≈ 5 kbar. This clockwise isothermal decompression path contrasts markedly with anticlockwise isobaric cooling paths recorded elsewhere in the Rayner Complex, and reflects a second phase of orogenesis within the Rayner Structural Episode. Text Antarc* Antarctica East Antarctica HighWire Press (Stanford University) East Antarctica Oygarden ENVELOPE(57.500,57.500,-66.900,-66.900) Oygarden Group ENVELOPE(57.500,57.500,-66.900,-66.900) Rayner ENVELOPE(-45.166,-45.166,-60.650,-60.650) Journal of Petrology 45 7 1481 1512 |
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Open Polar |
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HighWire Press (Stanford University) |
op_collection_id |
fthighwire |
language |
English |
topic |
ARTICLES |
spellingShingle |
ARTICLES KELLY, N. M. HARLEY, S. L. Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
topic_facet |
ARTICLES |
description |
High-Mg–Al, silica-undersaturated metapelites from the Oygarden Group of islands, East Antarctica, preserve clear evidence for the stable coexistence of the assemblage orthopyroxene + corundum in natural rocks. The quartz-absent metapelite occurs as pods and isolated layers within a high-strain zone related to deformation during the c . 0·93 Ga Rayner Structural Episode. Assemblages that include orthopyroxene, corundum, sapphirine, sillimanite, cordierite, garnet and kornerupine are developed across a pre-existing compositional zoning, leading to contrasting mineral Fe–Mg ratios. The assemblage orthopyroxene–corundum is shown to exist in only a very restricted range of bulk compositions and P – T histories. Simplified qualitative FMAS grids have been constructed for kornerupine-absent and -present systems, illustrating MAS terminations and divariant equilibria that help to describe the mineral assemblage and reaction history. Reaction textures that include coronas of sapphirine and sillimanite separating orthopyroxene and corundum, and symplectites of orthopyroxene + sapphirine ± cordierite/plagioclase, orthopyroxene + sillimanite ± cordierite/plagioclase and orthopyroxene + sapphirine + sillimanite embaying garnet, imply a clockwise P – T – t evolution. Conditions of P > 9–10 kbar and T ≈ 800–850°C were attained prior to an initial phase of decompression that was accompanied by heating of up to ≈100°C. Peak temperatures of T ≈ 850–900°C were achieved at P ≈ 9 kbar followed by near-isothermal decompression to pressures of P ≈ 5 kbar. This clockwise isothermal decompression path contrasts markedly with anticlockwise isobaric cooling paths recorded elsewhere in the Rayner Complex, and reflects a second phase of orogenesis within the Rayner Structural Episode. |
format |
Text |
author |
KELLY, N. M. HARLEY, S. L. |
author_facet |
KELLY, N. M. HARLEY, S. L. |
author_sort |
KELLY, N. M. |
title |
Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
title_short |
Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
title_full |
Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
title_fullStr |
Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
title_full_unstemmed |
Orthopyroxene-Corundum in Mg-Al-rich Granulites from the Oygarden Islands, East Antarctica |
title_sort |
orthopyroxene-corundum in mg-al-rich granulites from the oygarden islands, east antarctica |
publisher |
Oxford University Press |
publishDate |
2004 |
url |
http://petrology.oxfordjournals.org/cgi/content/short/45/7/1481 https://doi.org/10.1093/petrology/egh023 |
long_lat |
ENVELOPE(57.500,57.500,-66.900,-66.900) ENVELOPE(57.500,57.500,-66.900,-66.900) ENVELOPE(-45.166,-45.166,-60.650,-60.650) |
geographic |
East Antarctica Oygarden Oygarden Group Rayner |
geographic_facet |
East Antarctica Oygarden Oygarden Group Rayner |
genre |
Antarc* Antarctica East Antarctica |
genre_facet |
Antarc* Antarctica East Antarctica |
op_relation |
http://petrology.oxfordjournals.org/cgi/content/short/45/7/1481 http://dx.doi.org/10.1093/petrology/egh023 |
op_rights |
Copyright (C) 2004, Oxford University Press |
op_doi |
https://doi.org/10.1093/petrology/egh023 |
container_title |
Journal of Petrology |
container_volume |
45 |
container_issue |
7 |
container_start_page |
1481 |
op_container_end_page |
1512 |
_version_ |
1766050004568375296 |