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Metastable growth of corundum adjacent to quartz in a spinel‐bearing quartzite from the Archaean Napier Complex, Antarctica
Author(s) -
MOTOYOSHI Y.,
HENSEN B. J.,
MATSUEDA H.
Publication year - 1990
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1990.tb00459.x
Subject(s) - spinel , geology , cordierite , corundum , quartz , granulite , geochemistry , mineralogy , sillimanite , materials science , metallurgy , biotite , geomorphology , facies , paleontology , ceramic , structural basin
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.