New K-Ar ages, and a provisional chronology, for the offshore part of the British Tertiary Igneous Province

Abstract

Synopsis New K-Ar whole-rock ages are presented from 13 offshore locations to the north and west of Scotland. Ten of these locations have yielded ages which are considered to be geologically significant. Together with previously published ages, these suggest that the earliest sills of the Faeroe-Shetland Intrusive Complex were intruded at c. 80 Ma (Campanian), although the bulk of the complex was probably emplaced at 55–53 Ma (early Eocene). Lavas on the Hebrides Shelf exhibit a range of ages from c. 63–46 Ma (Danian-Lutetian). New K-Ar ages from Rosemary Bank are inconclusive but, combined with calcareous nannofossil analysis and the known magnetic polarity of the bank, suggest that it may have formed during the Late Cretaceous (70–68 Ma or earlier). The new data are incorporated into the chronology of all the major onshore and offshore components of the British Tertiary Igneous Province. Sources for the offshore lavas include the Faeroe Islands, central igneous complexes and large fissures such as those beneath the Wyville–Thomson Ridge and the Hebridean Escarpment.