GO 326/ES 767
Plate Tectonic Evolution of
The North Atlantic Region

James S. Aber

Tectonic evolution of Greenland/Faeroe region

The North Atlantic region, between the Gibbs and Nansen fracture zones, developed as a result of continental rifting and sea-floor spreading during the Mesozoic and Cenozoic. Several episodes of partial or complete continental rifting took place as North America, Greenland, Svalbard, the British Isles, and Europe were pulled apart. Resulting oceans or seas include the: Labrador Sea and Baffin Bay, North Atlantic, Greenland Sea, Norwegian Sea, and North Sea.

Sea-floor spreading continues today along the Reykjanes, Jan Mayen, Mohns and Kvipovitch Ridges, and across the Icelandic neovolcanic zone--see handout map. A major hot spot is now located below the southeastern corner of Iceland, and Jan Mayen is also the site of an active volcano. Four main phases of tectonic development are now known from the North Atlantic region.

  1. Continental rifting began in the North Sea region during the Jurassic--see handout map. Crustal stretching of about 35% resulted in graben-type faulting and crustal thinning. Volcanic centers developed within several grabens during late Jurassic and early Cretaceous time (Hamar 1982). Thick Jurassic and Cretaceous marine sediments accumulated in the rift zones that are now sites of oil and gas production. Rifting and volcanism ended in early Cretaceous time before the North Sea had developed true oceanic crust.

  2. Continental rifting next developed between North America and Greenland in the late Cretaceous--see handout map. The continental margins of Greenland and North America were first stretched, and then the Labrador Sea began to open up approximately 90 million years ago. Greenland remained joined to Europe.

  3. Early in the Cenozoic, about 55-60 million years ago, sea-floor spreading began between Greenland and Europe. Continued sea-floor spreading between North America and Greenland led to opening of Baffin Bay. Greenland acted as an independent plate during the early Cenozoic, while Svalbard was split off to the east along the Nansen fracture zone.

    Thick basalt plateaus built up in eastern Greenland, western Scotland, northern Ireland and the Faeroes--see handout diagrams. The Faeroes (sheep islands) underwent at least three phases of structural deformation (Geoffroy et al. 1994): (a) NE-SW extension under a strike-slip regime during extrusion of lower and middle basalt series, (b) NE-SW "Faeroe compression" during extrusion of upper basalt series, (c) return to strike-slip deformation postdating extrusions.

    Eroded hill slopes of the northern Faeroe Islands in the vicinity of Tórhavn. Thick lava flows of the Upper Basalt Series form benches on the hill sides. Photo courtesy of P. Jensen.
    Northern Faeroe Islands in the vicinity of Tórhavn. Thick lava flows of the Upper Basalt Series form benches on the hill sides. Traditional buildings with sod roofs are visible in foreground. Photo courtesy of P. Jensen.
    Closeup view of basalt exposed around tunnel entrance. Notice "navy blue" color of the thick lava flow above the tunnel. Northern Faeroe Islands in the vicinity of Tórhavn. Photo courtesy of P. Jensen.

    Meanwhile, volcanic ash beds accumulated in the Fur Formation of northern Denmark. This so-called "mo-clay" formation is quite famous for its fossils, volcanic ash beds, and economic uses. It is considered to be late Paleocene or Eocene in age. The ash has similar geochemistry to plateau basalts of the Faeroes-East Greenland province (Morton and Evans 1988).

    Exposure of the Fur Formation in a clay pit, island of Mors, northwestern Denmark. Thin black and gray layers are beds of volcanic ash of basaltic composition. The ash was presumably derived from a volcanic center in the Skaggerak region, between Denmark and Norway--see handout map. Photo date 6/79, © J.S. Aber.

  4. Labrador sea-floor spreading ceased in the mid-Cenozoic, about 36 million years ago (Eldholm 1990). All plate movement was concentrated along the Reykjanes/Mohns mid-ocean ridge, and Greenland became part of the North American plate. The Faeroe-Iceland-Greenland ridge was built by volcanic eruptions over a large hot spot. Magma migrated northward and southward from the hot spot and built a massive mid-ocean ridge along with Jan Mayen island. Broad thermal and geochemical anomalies are associated with the Iceland hot spot.

Historical volcanism in Iceland

The Reykjanes Peninsula to Langjökull is a direct continuation of the Reykjanes ridge, part of the mid-Atlantic ridge--see handout maps. Much more active is the zone from Surtsey trending northeast and north across Iceland to the Melrakkaslétta Peninsula. This zone is 50-70 km wide; the mid-Atlantic ridge may be shifting eastward in this area. The most active volcanoes include: Katla, Hekla, and Krafla. Eruptions by subglacial volcanoes trigger massive floods of melt water and sediment. An eruption beneath Vatnajökull ice cap generated a jökulhlaup (melt-water flood) in the autumn of 1996.

Geological map of Iceland.

The greatest land eruption in historical times, anywhere in the world, took place at Lakagígar (Laki) in 1783 (Bárdarson 1991). This eruption began on Whit Sunday, June 8, 1783, and lasted until February of the following year. Lava and gas extruded from a fissure 25 km long. Lava covered 565 km² of land with rough, almost impassable flows of "aa" type; the lava volume is estimated at 12 km³.

Several farms, villages, and churches were destroyed by the Laki eruption. Far more disasterous was the "blue haze" of volcanic gas that spread over the island and was even noticed in Europe. It has been estimated that 10 million tons of SO2 were released during the eruption. Gas and ash fall stunted grass growth and led to catastrophic starvation of livestock. During the resulting "haze famine," about one-quarter of the people in Iceland died, the greatest natural disaster to strike the island.

Hekla, one of the most active volcanoes in the world, is located in the eastern tectonic zone of Iceland. This volcano has erupted on average twice per century since it became active 1104. Young lava flows are visible in the foreground. Photo date 8/94, © J.S. Aber.
Scoria and cinders of the Eldgjá volcanic zone, south-central Iceland. Massive fissure eruptions took place in the 10th century. Photo date 8/94, © J.S. Aber.
Conical volcanoes are relatively rare in Iceland. They form when eruptions take place beneath a cover of glacier ice. Mælifell formed in this way during Pleistocene glaciation. It stands more than 200 m (650 feet) above the surrounding terrain, south-central Iceland. Photo date 8/94, © J.S. Aber.
Laki lava flows, southeastern Iceland. The eruption at Lakagígar in 1783-84 was the largest such historical event in the world. The rough lava flows are now covered by soft moss, but the terrain remains largely impassable today. Photo date 8/94, © J.S. Aber.
Tertiary basalt forms the thick ledge over which the water falls at Fagifoss in southeastern Iceland. Photo date 8/94, © J.S. Aber.

References

Return to tectonics syllabus.
GO 326/ES 767 © J.S. Aber (2004).