INTRACONTINENTAL RIFLING INFERRED FROM THE MAJOR LATE CARBONIFEROUS QUARTZ-DOLERITE DYKE SWARM OF NW EUROPE

The late Carboniferous (Stephanian) quartz-dolerite dyke swarm of nort hern Britain extends eastwards from the Outer Hebrides on an arcuate t rend for up to 200 km from the eastern UK coast, as far as the western margin of the Central Graben. The average trend of the swarm changes by about 45 degrees between its western and eastern extremities. Indiv idual dykes, which are generally up to 30 m wide onshore, attain width s of well over 1 km offshore. Magmatically and spatially, the swarm is closely related to the coeval Oslo Graben volcanic rocks and dykes of southern Norway, which lie on the extrapolation of the arcuate trend. The dyke trends point to a focus of relative tensile stress centred o n the West Shetland Shelf region. Finite element modelling of the NW E uropean area corroborates the stress-focusing hypothesis, which we int erpret in the context of the major period of intra-continental rifting along the line of the proto North Atlantic (the Rockall Trough, Faero e-Shetland Trough and eastern Norwegian Sea) at about 300 Ma. The regi onal distribution of Archaean and Caledonian lithosphere within Pangae a may account for the fact that both the dyke swarm and the Oslo Grabe n were located in northern Britain and southern Norway, rather than in the Faeroe-Shetland region.