Abstract

The east coast of Ireland is one of the few places where Lower Palaeozoic rocks are exposed adjacent to the supposed surface trace of the Iapetus Suture. North of the Tinure Fault (the local surface expression of the suture), Llandovery and Wenlock strata correlated with the Central and Southern Belts of the Southern Uplands were deformed by post-Wenlock deformation (D1), characterized by southward-verging, northerly-inclined, upright F1 folding and NNE-trending faulting with a component of sinistral transpression. South of the Tinure Fault, D1 structures are northward-verging, southerly-inclined, upright folds also associated with sinistral transpression. Structures on both sides of the Tinure Fault were modified by northwest-directed thrusting and north-verging folding with a component of dextral transpression. This second event affected lamprophyres intruding D1-deformed rocks of Wenlock age, but pre-dates the emplacement of uncleaved, probably Lower Devonian lamprophyre dykes and the unconformable deposition of Lower Carboniferous clastics and limestones. Other southerly-dipping thrusts with a dextral component of motion which occur in Lower Palaeozoic rocks in Ireland and Britain may be of Caledonian rather than Variscan age as is commonly assumed. The northward thrusting accounts for the mismatch between the inferred surface trace of the Iapetus Suture, and that projected from seismic reflectors at 10 km depth.

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