Using the results of recent seismic investigations of the upper continental lithosphere within the Caledonian–Variscan fold belt in SW Ireland a geological model is developed for the late Caledonian–early Devonian accretion history of the crust. It is suggested that this geological model can explain a variety of geological phenomena. These include the origin of the ‘Newer Granite’ series in Britain and Ireland, the partial preservation of lower Devonian ‘Lower Old Red Sandstone’ rocks, within the braided Caledonian fault network and the relatively low metamorphic grade of the Caledonian basement rocks, into which many of the granites are intruded. The proposed model involves a process called ‘incipient delamination’, in which the mantle part of the lithosphere did not detach completely from the accreted crust during the late Caledonian to Acadian orogenic events.

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