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A mega-porphyritic dolerite on Long Island, Seychelles Archipelago

Published online by Cambridge University Press:  01 May 2009

J. J. Frankel
J. J. Frankel
Affiliation:
School of Applied Geology, University of New South Wales, Kensington, N.S.W. 2033. Australia.
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Summary

A dolerite intrusion on Long Island, Seychelles contains exceptionally large plagioclase (labradorite) phenocrysts essentially unzoned, set in a doleritic groundmass. Many of the mega-phenocrysts have a dark redbrown interior.

In the groundmass, zoned plagioclase is in a doleritic texture with a slightly titaniferous ferro-augite that has been almost completely replaced by an actinolite uralite.

The mega-phenocrysts are considered to have crystallized slowly at depth and concentrated locally in a chamber of basaltic magma. The portion of magma containing these plagioclase crystals was later injected to higher levels as dykes. Although emplaced in a granitic (continental) environment, the intrusion has oceanic basalt affinities, and in chemical composition resembles high alumina basalts.

Type
Articles
Information
Geological Magazine , Volume 106 , Issue 3 , 04 June 1969 , pp. 260 - 269
Copyright
Copyright © Cambridge University Press 1969

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References

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