Metastable growth of corundum adjacent to quartz in a spinel-bearing quartzite from the Archaean Napier Complex, Antarctica |
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Authors: | Y MOTOYOSHI B J HENSEN H MATSUEDA |
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Institution: | Department of Applied Geology, University of New South Wales, Kensington, NSW 2033, Australia;Department of Geology and Mineralogy, Hokkaido University, Kita-10, Nishi-8, Sapporo 060, Japan |
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Abstract: | In a granulite-facies spinel-bearing quartzite, corundum, orthopyroxene and sapphirine (and rarely cordierite and sillimanite) form partial rims separating spinel from quartz. Textures indicate the reactions: spinel + quartz = orthopyroxene + corundum, and spinel + quartz = orthopyroxene + sapphirine. Thus, corundum and sapphirine are produced by reactions involving quartz. The low Al-content of the orthopyroxene (0.5–2.8 wt %) and low values for Mg–Fe distribution coefficient for spinel–sapphirine and spinel–orthopyroxene reflect low-temperature conditions during formation of the reaction products. Absence of zoning in spinel and a constant Mg–Fe distribution coefficient for spinel–sapphirine and spinel–orthopyroxene, over a compositional range, indicate Mg–Fe equilibration. It is suggested that stable reactions such as spinel + quartz = cordierite or spinel + quartz = garnet + sillimanite were over-stepped and that metastable reactions give rise to the anomalous juxtaposition of corundum + quartz. |
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Keywords: | Key-words: corundum + quartz metastable equilibrium Napier Complex Antarctica overstepping reactions |
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