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The structure and petrology of ultrabasic rocks in the southern part of the Cuillin Igneous Complex, Isle of Skye

Published online by Cambridge University Press:  03 November 2011

R. V. Claydon  and
B. R. Bell
R. V. Claydon
Affiliation:
Department of Geology and Applied Geology, University of Glasgow, Lilybank Gardens, Glasgow G12 8QQ, Scotland.
B. R. Bell*
Affiliation:
Department of Geology and Applied Geology, University of Glasgow, Lilybank Gardens, Glasgow G12 8QQ, Scotland.
*
* To whom correspondence should be addressed.
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Abstract

The ultrabasic rocks of the southern portion of the Early Tertiary Cuillin Igneous Complex, Isle of Skye, are recognised as forming a Peridotite Series s.l. and have been separated into six distinct structural–lithological units. These units range from almost pure dunite (Unit 1, at the lowest structural level), through to feldspathic peridotites and allivalites (Units 5 and 6, at the highest structural levels). Detailed field and mineralogical studies indicate that both cumulus and postcumulus processes involving ultrabasic (picritic) magmas may be identified, and that the latter processes have significantly modified many of the primary features of these rocks.

Layering, both modal and phase, is present within all six units, although it is more prominent within the higher units, especially Units 5 and 6. Differing orientations of fabrics defined by cumulus spinel and intercumulus plagioclase layers within Unit 3 indicate the important role of compaction and intercumulus melt migration. Unit 4 is extremely heterogeneous, involving material ranging in composition from peridotite to allivalite, and provides clear evidence for postcumulus melt movement, magma-mixing, disruption and brecciation. Units 5 and 6 developed with a more porous cumulus framework, giving rise to dendritic growths involving cumulus olivine and poikilitic plagioclase.

It is concluded that postcumulus melt movement, injection and magma-mixing, involving ultrabasic magmas, were significant processes in the formation of the ultrabasic rocks of the Cuillin Igneous Complex.

Keywords

peridotiteallivalitelayeringcumulatespostcumulushybridisationbrecciamixing.
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 83 , Issue 4 , 1992 , pp. 635 - 653
Copyright
Copyright © Royal Society of Edinburgh 1992

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