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Crystallization history of sector-zoned microcline megacrysts from the Godani Valley pluton, Nigeria
Published online by Cambridge University Press: 05 July 2018
Summary
Sector-zoning is brought out by mineral inclusions (plagioclase, biotite, hornblende, sphene, and apatite) in 2 to 5 cm microcline megacrysts of the Godani Valley pluton, Nigeria. The inclusions are concentrated in the megacryst rims beneath the faces {110} and {20}; the megacryst cores are not sector-zoned. Comparison with other occurrences (Portugal and Czechoslovakia) shows that this type of sector-zoning is not controlled by growth rate. Chemical sector-zoning does not occur in the Godani megacrysts. Growth from magma is proposed, with preference for inclusions on faces at a high angle to the feldspar a-chain. A superficially similar type of sector-zoning occurs in microcline megacrysts of both pluton and wall rock at Papoose Flat, California, suggesting that this feature can be generated either by growth from magma or by replacement.
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- Research Article
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- Copyright © The Mineralogical Society of Great Britain and Ireland 1978
Footnotes
Present address: Department of Earth and Space Sciences, State University of New York, Stony Brook, New York 11794.
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