DO THE BRITISH ISLES DYKE SWARMS REFLECT THE PALEOGENE LOCATION OF THE ICELAND HOT SPOT?

Dyke swarms associated with central plutonic complexes of the North Atlantic Large Igneous Province (NAIP) have been recognized and mapped since the 19^thCentury. In the early 20^thCentury Arthur Holmes recognized that they are part of a Brito-Arctic or Thulean large igneous province in the North Atlantic region, embracing rocks in Greenland, Iceland, the Faroe Islands and the northwestern British Isles. Their dominantly northwest-southeast trend is clearly shown in early Memoirs of the Geological Survey of Great Britain. While the northeast-southwest extension implied by this trend has been recognized, its potential geodynamic significance appears to have been overlooked. The dikes belong to the older (~60 Ma) phase of magmatism in the North Atlantic region, the younger phase (~55 Ma) coinciding with the rift-drift transition between Europe and Greenland. There are two models for the position of the Iceland hot spot at 60 Ma, one places it in western Greenland and the other in eastern Greenland at the western end of the Iceland-Greenland Ridge. Reconstruction of the North Atlantic region prior to opening of the ocean basin results in the NW-SE trending dykes of the British Isles striking directly toward the hypothetical western Greenland position of the hotpot. Moreover, the igneous rocks of the Disko Island area of West Greenland are dominantly ca. 60 Ma, as are those of far southeast Greenland that lie along the trend of the British dykes. Conversely the igneous rocks of central East Greenland at the termination of the Iceland-Greenland Ridge are mostly younger, belonging to the ca. 55 Ma phase of activity and lie far from the line connecting the British dykes to the Disko Island area. Hence, while petrological and geochemical data indicate that the dykes of the British Isles were ‘fed’ from the local central plutonic centers, the stress system that controlled the NW-SE trend of the fissures into which they were intruded may have resulted from the impingement on the continental lithosphere of a mantle plume below a hot spot located in West Greenland. It may also be significant that the trend of the dykes in the British Isles is in line with the Proterozoic Nagssugtoquidian orogen of southern Greenland that lies between two older Archean crustal blocks.