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Complex relationships among coexisting pyroxenes: the Palaeogene Eskdalemuir dyke, Scotland

Published online by Cambridge University Press:  05 July 2018

B. Bagiński ,
P. Dzierżanowski ,
R. Macdonald  and
B. G. J. Upton
B. Bagiński
Affiliation:
IGMP Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland
P. Dzierżanowski
Affiliation:
IGMP Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland
R. Macdonald
Affiliation:
IGMP Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland
B. G. J. Upton
Affiliation:
IGMP Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland
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Abstract

The composite Eskdalemuir dyke was formed by the intrusion of rhyolitic magma into partly crystallized basaltic magma, the proportion of the silicic component increasing towards the dyke centre. The less silicic parts were effectively supercooled and crystallization was halted when the residual melt quenched to rhyolitic glass which constitutes up to 50% of the dyke's centre. Pyroxene compositions in the mixed magma rocks include augite, pigeonite and orthopyroxene of very variable composition. Individual crystals in the matrix as small as 200 μm can contain compositions occupying a considerable part of the Di-Hd-En-Fs quadrilateral. Pyroxene crystallization took place under extreme disequilibrium conditions, as shown by highly variable zonation patterns; apparently opposite zoning trends can occur in adjacent grains. Small-scale variations in melt composition were probably the dominant control over the compositional and textural complexity in the pyroxenes.

Keywords

composite dykepyroxenesdisequilibrium crystallizationsupercooling
Type
Research Article
Information
Mineralogical Magazine , Volume 73 , Issue 6 , December 2009 , pp. 929 - 942
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2009

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