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Gas filter-pressing origin for segregation vesicles in dykes

Published online by Cambridge University Press:  01 May 2009

I. S. Sanders
I. S. Sanders
Affiliation:
Department of Geology, Trinity College, Dublin 2, Ireland
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Abstract

Segregation vesicles have been recognized in two plagiophyric dolerite dykes in northwestern Ireland. The vesicles are each outlined by a rim of tangentially arranged plagioclase, and filled to a variable extent by a fine-grained, crescent-shaped lining of fractionated residual melt. They closely resemble segregation vesicles reported from Atlantic ocean-floor basalts.

It is suggested (1) that the vesicles began as CO2-rich bubbles released during decompression; (2) that these bubbles grew very little during crystallization, while H2O became concentrated in the residual melt; and (3) that exsolution and expansion of H2O-rich vapour forced interstitial residual melt through the rigid but permeable framework of crystals and into the existing CO2-rich bubble cavities.

Type
Articles
Information
Geological Magazine , Volume 123 , Issue 1 , January 1986 , pp. 67 - 72
Copyright
Copyright © Cambridge University Press 1986

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