Abstract

A monchquite dyke, in the vicinity of Loch Roag, Lewis, Outer Hebrides has an unusually enriched chemistry, and contains a unique assemblage of megacrysts and xenoliths from the lithosphere of the Hebridean craton. A ⁴⁰Ar/³⁹Ar plateau age of 45.2 ± 0.2 Ma (2σ) of a phlogopite megacryst from the dyke overlaps an earlier reported K–Ar age, and confirms that the British Palaeogene Igneous Province extended into the Eocene. Similar late low-volume melts were erupted in the Eocene and Oligocene in West and East Greenland, suggesting that such late-stage magmatic rejuvenescence is a widespread feature across the North Atlantic Igneous Province.