This model of a plume with a dual structure - a voluminous head and far thinner tail - has been generalized by Mark Richards, Bob Duncan, and myself to cover all active hot spots on the globe, or at least those that have not lost their heads under a subduction zone, as Hawaii may have (Fig. 5.4).6 So the hot spot now located under Yellowstone in the USA was born some 16 Ma ago in the form of the great volcanic province of the Columbia River, located only a few hundred kilometers to the west and 30 Ma ago, the Ethiopian Traps marked the arrival at the surface of the hot spot that still remains not far away, in the Afar region, because the African Plate has moved little relative to the mantle. Even longer ago, 57 Ma, the hot spot of Iceland built the enormous volcanic stacks that today form the cliffs of the east coast of Greenland and the entire northwest margin of both the British Isles and the Norwegian continental plateau. In this case the traps were riven shortly afterwards (like the Seychelles and the Deccan) by the propagation of the Mid-Atlantic Ridge, which would give birth to the North Atlantic Ocean. The lesser ridges formed by the hot spot are short and join King Christian IX Land and the F^roe Islands to Iceland. The exceptional emergence of a mid-ocean ridge in Iceland, and also in the Afar region, occurs because here a rather stable hot spot joins forces with normal sea-floor spreading, thus intensifying both lava production and thermal effects.
Well before the Deccan Traps were formed, around 135 Ma ago, the great volcanic expanses of Parana formed in South America, where erosion has since created the superb Iguagu Falls. The Parana Traps can be linked to the hot spot that emerges at the island of Tristan da Cunha in the South Atlantic. Situated right on the mid-ocean ridge, this point also created the Walvis Ridge to the east, on the African Plate. And this latter ridge in turn leads to a small outcropping of
6 See also the work of the Australian National structure for the origin of flood basalts, Earth and University group, for instance I.H. Campbell and Planetary Science Letters, Vol. 99, 79-93, 1990. R.W. Griffiths, Implications of mantle plume
World map of the main traps (or flood basalts). Some have been linked to the currently active hot spot volcanoes, whose birth may be the cause of the traps.
traps on the coast of Namibia (Etendeka), which was separated from the main body of the Parana basalts by the opening of the South Atlantic shortly after both parts were laid down. We can also cite the gigantic submarine Ontong-Java Plateau in the Western Pacific, born perhaps 110 Ma ago with the Louisville hot spot. The Karoo lavas in southern Africa and the Farrar lavas in Antarctica, 184 Ma old, can be linked to the Bouvet hot spot. Other events are thought to have created the Rajmahal Traps in India and the traps along the western margin of the North Atlantic and the Jamaica Plateau. Finally, the immense Siberian Traps may be associated with the hot spot of Jan Mayen, a little north of Iceland. We will come back to these last, because they are of unusual importance in our story.
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