Nature 315, 210 - 212 (16 May 1985); doi:10.1038/315210a0

An Ordovician ophiolite in County Tyrone, Ireland

D. H. W. Hutton^*, M. Aftalion^† & A. N. Halliday^†

^*Department of Geological Sciences, University of Durham, Durham DH1 3LE, UK
^†Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, UK

Ophiolites are regarded widely by geologists as remnants of old oceanic crust that has been obducted onto the continental margins during ocean or marginal basin closure and orogeny. Therefore, they provide evidence for the existence of old oceans and oceanic basins and are a key to the extension of plate tectonic modelling into pre-Mesozoic rock assemblages. In the Caledonide−Appalachian orogen, ophiolites are known although very few of these are dated well enough to provide accurate constraints on plate-tectonic kinematics. We report here the discovery of an ophiolitic sequence within the rocks of the Tyrone Igneous Complex in Northern Ireland. U/Pb dating combined with field evidence indicates that the Tyrone ophiolite was formed and then obducted onto the northern margins of the Iapetus Ocean close to 470 Myr BP (Arenig).

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