The continuation of the Canadian Appalachians into the Caledonides of Britain and Ireland

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Abstract
Summary: Three zones can be recognised in the Canadian Appalachian-British Caledonian belt. The NW Marginal Zone extends from NW Scotland and Ireland through N Newfoundland to Quebec. It consists of late Precambrian to early Palaeozoic clastic sequences and an extensive Cambro-Ordovician carbonate platform. Orthotectonic deformation and metamorphism occurred in the early Ordovician, and middle Ordovician allochthons and obducted ophiolite characterise this zone in N America. The SE Marginal Zone extends from Wales and the English Midlands through SE Ireland to E Newfoundland, Nova Scotia and S New Brunswick. It is characterised by extensive late Precambrian volcanicity, late Precambrian orthotectonic deformation and metamorphism and the development of lower Palaeozoic basins in Wales and Nova Scotia. Late Precambrian orogenic activity locally involved ophiolite. The Axial Zone can be subdivided into a number of subzones, some of which do not extend for great distances along strike. It contains local ophiolites, trench complexes and calc-alkaline volcanics ranging in age from Cambrian to Silurian. Volcanicity was most pronounced in the Ordovician on both sides of this zone and extended into the marginal zones. Middle Ordovician deformation and metamorphism is locally intense but elsewhere Ordovician and Silurian sequences are apparently conformable. The Axial Zone and adjacent parts of the marginal zones have all suffered Siluro-Devonian, generally paratectonic, deformation and metamorphism. The history of the whole belt indicates that subduction was active on the SE in the late Precambrian, on the NW and in the Axial Zone in the lower and middle Ordovician and extended into the Silurian. Final closure of the Iapetus ocean was delayed until the upper Silurian-Devonian. Plate-tectonic models must involve multiple subduction zones.

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