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The Glas Eilean lavas: evidence of a Lower Permian volcano-tectonic basin between Islay and Jura, Inner Hebrides

Published online by Cambridge University Press:  03 November 2011

B. G. J. Upton ,
J. G. Fitton  and
R. M. Macintyre
B. G. J. Upton
Affiliation:
Grant Institute of Geology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, Scotland.
J. G. Fitton
Affiliation:
Grant Institute of Geology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, Scotland.
R. M. Macintyre
Affiliation:
S.U.R.R.C, East Kilbride, Glasgow G75 0QU, Scotland.
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Abstract

Subaerial lavas and intercalated sediments crop out on the islet of Glas Eilean and the Black Rock skerries in the Sound of Islay between Islay and Jura. The visible succession is c. 120 m thick and is traceable c. 2 km along strike (NNW–SSE). The lavas are alkali olivine-basalts containing olivine ± plagioclase and augite phenocrysts. Decreasing Mg, Cr and Ni upwards, coupled with decreasing average flow thickness and increasing amounts of inter-flow sediment, suggest progressively waning volcanic activity marked by decreasing ascent rates and greater degrees of differentiation. K-Ar dating on one sample gave an early Permian age of 285 ± 5 Ma. It is inferred that the lavas erupted from an isolated basalt volcano situated on a NNW–SSE trending fracture, associated with a narrow developing half-graben within the Dalradian metasediments. The tectonism and magmatism is inferred to be related to the ‘Clyde Belt’ of fault-bounded basins extending from Cheshire to the Little Minch.

Keywords

alkali olivine-basalthalf-grabensub-aerial lavas
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 77 , Issue 4 , 1987 , pp. 289 - 293
Copyright
Copyright © Royal Society of Edinburgh 1987

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