Metastable growth of corundum adjacent to quartz in a spinel‐bearing quartzite from the Archaean Napier Complex, Antarctica

• Published in: Journal of Metamorphic Geology
• Main Authors: MOTOYOSHI, Y., HENSEN, B. J., MATSUEDA, H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1990
• Subjects: Napier; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1111/j.1525-1314.1990.tb00459.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1525-1314.1990.tb00459.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1525-1314.1990.tb00459.x

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.