The north Atlantic igneous province

The North Atlantic Igneous Province extends from eastern Canada to the British Isles, a pre-drift distance of almost 2000 km. The igneous rocks are predominantly basaltic, but differentiates and anatectic melts are also represented. Two major phases of igneous activity can be discerned. Phase 1 began about 62 m.y. ago with continent-based magmatism in Baffin Island, W and SE Greenland, the British Isles, and possibly central E Greenland (the Lower Basalts around Kangerlussuaq). Phase 2 began about 56 m.y. ago and is represented by seaward-dipping reflector sequences (SDRS) along the continental margins, the Main Series basalts in central E Greenland, the Greenland-Faeroes Ridge, and Iceland. Contamination by continental crust was prevalent during Phase 1 but also occurred during Phase 2, especially during the formation of the early SDRS. Although it is unnecessary to involve the continental lithosphere mantle in the formation of Phase 1 or Phase 2 magmas, it is not possible to completely exclude it. We argue that the Iceland plume played a pivotal role in the formation of the North Atlantic Igneous Province because (1) the simultaneous and widespread initiation of activity requires a major thermal event in the mantle; (2) some of the magmas associated with Phase 1 were highly magnesian, indicating that the liquids and, by implication, the mantle source regions were unusually hot; (3) the SDRS were emplaced subaerially or into shallow water, indicating buoyant support by the mantle during rifting and breakup; and (4) the isotopic and compositional diversity recorded in present-day Icelandic basalts is observed in many of the Palaeocene sequences, after crustal contamination and pressure of melt segregation are taken into account. The widespread and simultaneous activity of Phase 1 activity requires an abnormally high mantle flux rate. This may be associated with the arrival of a start-up plume, but alternatively it represents the arrival of a pulse of hot mantle, following a period of weak plume activity during the Cretaceous. In either scenario, the igneous activity appears to have been focused along lines of weakness in the lithosphere. Phase 2 activity is closely linked to continental breakup. Forced mantle convection, caused by hot mantle flowing into the developing rift zones during continent breakup, may have led to the very high magma production rates (two to three times those observed in present-day Iceland) that formed the SDRS and associated deep crustal intrusions