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Size-graded, igneous layering in an Icelandic intrusion

Published online by Cambridge University Press:  01 May 2009

M. J. Roobol
M. J. Roobol
Affiliation:
Geology Department, University of the West Indies, Mona, Kingston, Jamaica
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Summary

The Vesturhorn Intrusion of SE Iceland contains a tilted block consisting largely of size-graded, igneous-layered, eucritic gabbro, which is described in some detail. Size-graded, igneous layering is remarkably uncommon and at present there appear to be only two known occurrences. The physical properties of basalt magma suggest that most igneous layering is likely to form from currents moving by laminar flow. Considerations of flow in such a simple system do not satisfactorily account for the scarcity of this structure. It is suggested that size-graded, igneous layering may reflect the availability of convecting magmas containing crystals with appreciable proportions of different grain sizes of each mineral species. Such a grain size distribution, together with other features considered here, may indicate primocryst growth outside the chamber of deposition.

Type
Articles
Information
Geological Magazine , Volume 109 , Issue 5 , September 1972 , pp. 393 - 404
Copyright
Copyright © Cambridge University Press 1972

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