Abstract

The Thulean Volcanic Line, 3200 km long, is defined here as the series of Paleogene and younger volcanic areas extending approximately along a great circle with pole at close to long. 120°E, lat. 20°N from Britain through the Faeroes, Iceland and Greenland to Baffin Island. The line is unusual in extending from continental crust within one plate across a spreading ridge and onto continental crust on the adjacent plate.

Extensive subaerial flood basalts, basaltic dyke swarms and intrusive centres characterized by granophyres, granites, syenites and gabbros are the typical constituents of each area. Work during the last decade has shown that several of the submarine banks between Britain and the Faeroes, the Iceland-Faeroe Rise and the Davis Strait area also form parts of the volcanic line. Recent geophysical study of both continental and oceanic parts of the line have shown elements of its deeper structure. The intrusive centres continue to considerable crustal depths, or perhaps to the mantle, as plug-like masses of high density basic or ultrabasic material. Iceland appears to be underlain by a large upper mantle thermal anomaly, responsible for the present excess elevation and volcanic activity. Other components of the line may have been formed at earlier times over the same thermal anomaly. The main period of formation of the volcanic areas that occur on continental crust was between 56 and 53 m.y. (GSC). Iceland formed during the last 24 to 27 m.y. The rises flanking Iceland are thought to have formed about an extinct spreading axis now located within the Norwegian Basin, but the available age information is insufficient to test this hypothesis.

The formation of the line may have had a wide range of effects, from providing the driving force for the opening of the North Atlantic-Greenland Sea and Baffin Bay-Labrador Sea areas to giving rise to subsidence and maturation conditions suitable for the formation of potential petroleum-bearing sediments.