Subaerial volcanism in the western North Atlantic

Abstract Three regions of subaerial volcanism occur near the eastern edge of the North America plate: Iceland, Jan Mayen and the Azores. In Iceland the ridge axis emerges above sea level, most of the volcanic pile was generated subaerially along its trace, and superimposed flank zones are situated off the accretion zone. The Azores lie on both sides of the oceanic ridge axis topping an extensive platform adjoining it. The platform was generated by excess volcanic production on the transecting ridge crest similar to the ridge formation in Iceland. The islands are stratovolcanoes formed off the ridge crest by flank volcanism. The volcanism and tectonic setting of Jan Mayen and the Azores is compared to the flank zones of Iceland, of which they appear to be close analogs. Direct access to an active oceanic spreading axis makes Iceland particularly significant. The crust generated there suffers erosion which exposes the uppermost 1–2 km for three dimensional view. Subaerial volcanism in Iceland’s accretion zone produces a layered igneous sequence due to a wider rift zone and extensive lateral spread of lava flows as opposed to the deep ocean ridge with a much narrower rift and outflow zone of lava. Subaerial spreading may also have been important in early rifting of the North Atlantic margins (Hinz, 1981). As a result, submerged layered extrusives with units thickening downdip towards the spreading axis and offlapping in the direction of spreading may exist near some of the North Atlantic continental margins (Tucholke and Ludwig, 1982).