Geochemical character of Silurian volcanism in SW Ireland

Abstract

The Dunquin Group (mid-Silurian) of Dingle, southwest Ireland is a sequence of basaltic to rhyolitic lavas and pyroclastic rocks interbedded with shallow- to non-marine sediments that records one of only four known outbreaks of Silurian volcanicity south of the Iapetus Suture in the British Isles. New geochemical, petrographic and field evidence indicate that the volcanic sequences exposed in the Dunquin inlier, and the islands of Beginish and Inishvickillane could have formed by fractionational crystallization in a layered, repeatedly replenished basaltic magma chamber, the site of which is probably coincident with an intense aeromagnetic anomaly to the southwest of Inishvickillane. The volcanic suite is subalkaline, transitional between calc-alkaline and tholeiitic and is non-bimodal. High LILE/HFSE ratios and high LREE concentrations suggest that the parent basaltic magmas were generated at a destructive continental margin, although subduction may have ceased before eruption.