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Initiation of Iapetus subduction under Irish Avalonia

Published online by Cambridge University Press:  01 March 1997

BRIAN McCONNELL  and
JOHN MORRIS
BRIAN McCONNELL
Affiliation:
Geological Survey of Ireland, Beggar's Bush, Dublin 4, Ireland
JOHN MORRIS
Affiliation:
Geological Survey of Ireland, Beggar's Bush, Dublin 4, Ireland
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Abstract

The Dowery Hill Member of metamorphosed basalt, dolerite and siltstone is here recognized as the oldest exposed volcanic unit of the Lower Ordovician Ribband Group, with a minimum age of early Arenig. Peperites and resedimented hydroclastic breccia demonstrate a volcanic origin for the basalts. The igneous rocks are tholeiitic, with a trace element geochemistry indicative of a subduction-modified fertile mantle source, which we interpret as recording an early stage of volcanic arc evolution. The member is therefore the oldest known component of the volcanic arc generated by subduction of Iapetus oceanic lithosphere under southeastern Ireland. Subduction started earlier than predicted by current plate tectonic models, and these should be re-evaluated.

Type
Research Article
Information
Geological Magazine , Volume 134 , Issue 2 , March 1997 , pp. 213 - 218
Copyright
© 1997 Cambridge University Press

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