Zircon U-Pb age for the Orkney lamprophyre dyke swarm, Scotland, and relations to Permo-Carboniferous magmatism in northwestern Europe

摘要

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 quites are the most primitive of the alkaline rocks, whereas the coupled plasma mass spectrometry age of 313 ± 4 Ma and e{open}Hf(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.