The age of the Whin Sill

The Whin Sill and its related dykes are intruded into Carboniferous strata in the North of England. Together they form a distinct petrographical province in which basic magmatism appears to have been closely related to a single phase in the structural history of the area. The relevant stratigraphical, structural and isotopic evidence suggests to the authors that the Whin Sill suite was intruded during the Stephanian, around 295 ± 6 m.y. This conclusion is supported by twenty-one new potassium-argon age determinations accompanied by a petrographical study of the factors which cause discrepancy in isotopic results from Whin Sill rocks.