Abstract

The Hebridean Tertiary igneous province lay 700–900 km south of a presumed plume centre, and >500 km landward of a rifted continental margin prior to opening of the northeast Atlantic. The Province includes a small number of magnesian basalts containing olivine phenocrysts with core compositions equal to, or in excess of, Fo₈₉. Olivine-liquid equilibrium calculations suggest that these phenocrysts formed from liquids with MgO contents of 14–15 wt%, and in rare instances, 18–20 wt%. The liquidus temperatures of these magmas imply mantle potential temperatures of 1350–1460°C at distances up to 900 km from the axis of the Iceland plume. Their emplacement at c. 60 Ma implies either a long-established hotspot, or active channeling of plume material along the base of the plate towards a region undergoing considerable lower crustal extension.