The South Connemara Group

The South Connemara Group is a middle Ordovician (Dapingian(?) to Darriwilian) subduction-accretion complex that is preserved onshore as a roof pendant in the Devonian Galway granite and crops out on the islands of Lettermullen and Gorumna on the north shores of Galway Bay. It is in structural continuity with similar lithologies of the offshore Skird Rocks, some 16 km west, and is believed to trace the westwards continuation of the Southern Uplands fault in Ireland. It comprises a sequence of MORB volcanics and shallow intrusives of the Gorumna Formation which are overlain by manganiferous deep sea cherts of the Golam Formation that pass gradationally upwards into sandstones and conglomerates of the Lettermullen Formation. Tectonism during accretion produced mélange zones and structural repetition. The succession represents the oldest part of the Longford–Down–Southern Uplands accretionary prism and provides evidence for subduction reversal with very rapid uplift at late stages of the short-lived Grampian arc-continent collision orogeny. This excursion provides an opportunity to study ocean floor lithologies that were overlain by continental detritus as they approached a trench.