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Carboniferous dikes of West Connacht, Ireland

Published online by Cambridge University Press:  03 November 2011

J. G. Mitchell  and
P. Mohr
J. G. Mitchell
Affiliation:
School of Physics, The University, Newcastle-upon-Tyne NE1 7RU, England.
P. Mohr
Affiliation:
Department of Geology, University College Galway, Galway, Republic of Ireland.
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Abstract

Vigorous Carboniferous extensional tectonism and associated igneous activity is a feature of Ireland and the neighbouring areas of Newfoundland and Britain. In West Connacht, Ireland, dolerite dikes of late Carboniferous age are newly recognised and distinguished from Tertiary dolerites. In the N, the 320 Ma-old Logmor dike trends N–S across the Ordovician South Mayo Trough, and has an evolved, mildly alkaline basalt geochemistry. In the S, in Connemara, a diffuse and arcuate swarm of ENE–NE trending, 305 Ma-old dolerite dikes, the Teach Doite swarm, cuts the Galway Granite batholith and its envelope of Dalradian gneisses. These more tholeiitic dolerites reveal the mineralogical and geochemical effects of varying degrees of pervasive hydrothermal alteration, imposed on an original magmatic composition similar to that of mid-ocean ridge basalts. Variscan overprinting on k–Ar ages from West Connacht dolerites clusters at 300, 245 and 205 Ma. Overprinting is also a feature of much of the Galway Granite. Carboniferous diking in West Connacht may have responded to nascent opening of the proximate North Atlantic, its pattern related to domal uplift adjacent to the rifted zone.

Keywords

dike swarmGalway Granitegeochemistrypetrographyradiometric datesrare-earth elementstectonothermal eventsVariscan.
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 78 , Issue 3 , 1987 , pp. 133 - 151
Copyright
Copyright © Royal Society of Edinburgh 1987

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