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Formation of granular-textured layers and laminae within the Rhum crystal pile

Published online by Cambridge University Press:  01 May 2009

I. M. Young  and
C. H. Donaldson
I. M. Young
Affiliation:
Department of Geology, University of St Andrews, Fife, KY16 9ST, U.K.
C. H. Donaldson
Affiliation:
Department of Geology, University of St Andrews, Fife, KY16 9ST, U.K.
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Abstract

In the allivalite of cyclic unit 9 in the Eastern Layered Series of the Rhum intrusion there is an undulatory contact between a relatively dense pyroxene-rich rock and a less dense pyroxene-poor rock. The three-dimensional form of this contact resembles that developed between two fluids deforming under the influence of gravity. Minor layers, laminae and lamination in these rocks in places cut across the contact between the pyroxene-rich and pyroxene-poor rock types. They are, therefore, inferred to post-date the formation of the contact and hence to have formed within a porous crystal pile on the chamber floor. Possible mechanisms of formation are discussed but their origin remains unclear. These observations cast doubt on the common assumption that the combination of granular (cumulus) textures and layering structures is sufficient evidence on which to infer equilibrium of granular crystals with a contemporary magma.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 5 , September 1985 , pp. 519 - 528
Copyright
Copyright © Cambridge University Press 1985

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