Abstract
A RECENT paper by Wright1, arguing for a deep crustal or upper mantle origin for plagioclase megacrysts in a Nigerian basalt from Dadin Kowa, attributes to our unpublished study the opinion that these megacrysts are xenocrysts from the underlying metamorphic basement, and that they are responsible for the notable amounts of excess 40Ar found in the enclosing basalt by us and by Fisher2. Our work3 does not in fact come to any such conclusion but leaves the question of the ultimate origin of the megacrysts open. Not only does Wright's paper1 present no new data, merely reiterating conclusions published in a number of other papers4–7, but it attempts to sustain these conclusions by what we consider to be a fallacious argument.
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References
Wright, J. B., Nature Physical Science, 236, 89 (1972).
Fisher, D. E., Nature Physical Science, 232, 60 (1971).
Grant, N. K., Rex, D., and Freeth, S. J., Contr. Min. Petrol. (in the press).
Wright, J. B., Nature, 218, 262 (1968).
Wright, J. B., Min. Mag., 36, 1024 (1968).
Wright, J. B., Bull. Volc., 34, 833 (1970).
Frisch, T., and Wright, J. B., Neues Jb. Miner. Mh., 7, 289 (1971).
Aoki, K. I., Contr. Min. Petrol., 25, 284 (1970).
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GRANT, N., FREETH, S. & REX, D. K/Ar Data and the Origin of Feldspar Megacrysts in Basalt: Rejoinder to J. B. Wright. Nature Physical Science 238, 42–43 (1972). https://doi.org/10.1038/physci238042a0
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DOI: https://doi.org/10.1038/physci238042a0
