Plate Tectonic Evolution of
The North Atlantic Region
James S. Aber
|Age of North Atlantic oceanic crust. NOAA|
image obtained from Wikimedia Commons.
|Basalt plateau constructed of thick lava flows near Scoresby Sound, eastern Greenland. Adapted from H. Grobe; obtained from Wikimedia Commons.|
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 © J.S. Aber.|
|General geology of Iceland. Prominent volcanoes and glaciers (jökull) are noted. Notice the rock age pattern across the island. Image obtained from the Nordic Volcanological Institute, Iceland.|
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.|
|Scoria and cinders of the Eldgjá volcanic zone, south-central Iceland. Massive fissure eruptions took place in the 10th century.|
|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.|
|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.|
|Tertiary basalt forms the thick ledge over which the water falls at Fagifoss in southeastern Iceland. All photographs © J.S. Aber.|
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GO 326/ES 767 © J.S. Aber (2017).