Magmatic zircon in the syenite (bostonite) part of a composite NE–SW-trending cogenetic bostonite–camptonite dyke in Orkney, Scotland, yields a laser ablation inductively coupled plasma mass spectrometry age of 313 ± 4 Ma and εHf(313 Ma) values of +6 to +11. This suggests that the NE–SW-, east–west- and NW–SE-trending Scottish lamprophyre dyke swarms were emplaced during one late Carboniferous magmatic event, contrasting with published K–Ar dates ranging between c. 325 and 250 Ma. This magmatism is interpreted as a response to late Variscan regional extension or an early response to the Skagerrak mantle plume. Lamprophyre magmatism was initiated some 10 Ma earlier in Scotland than in the Oslo Rift.
Thin-section images of the investigated rocks, geochemical data and an REE plot, U–Pb and Hf isotopic data, and a Hf v. time diagram are available at www.geolsoc.org.uk/SUP18501.