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Geological Society, London, Special Publications; 1988; v. 38; p. 415-428;
DOI: 10.1144/GSL.SP.1988.038.01.25
© 1988 Geological Society of London

Wenlock to Mid-Devonian Activity in the Caledonian-Appalachian Orogen

Wenlock to mid-Devonian volcanism of the Caledonian-Appalachian orogen

M. F. Thirlwall

Department of Geology, Royal Holloway and Bedford New College, Egham Hill, Egham, Surrey TW20 0EX, UK

Volcanic rocks of Siluro-Devonian age form two distinct petrological provinces in the Caledonian-Appalachian orogen roughly corresponding to regions which last suffered major deformation in the Permo-Carboniferous or the Siluro-Devonian. In France, Germany and SW England the minor volcanism was dominantly marine and mostly produced enriched tholeiites. Abundant volcanism about 410 Ma old in Scotland is calcalkaline and related to subduction on the NW margin of Iapetus, while volcanism in Shetland, E Greenland and Norway is rather younger and more acidic but is calc-alkaline, at least in Shetland. Apart from a metatholeiite in Alabama, Siluro-Devonian volcanism in N America is restricted to New England and the Canadian Appalachians where two major volcanic belts run NE-SW. Chemical data for these rocks are limited but do suggest that at least some rocks in both belts are related to subduction processes. This need not necessarily greatly constrain tectonic models.