Symposium on Locating Old Mantle Plumes held at the Annual Meeting of the Geological-Society-of-America, Toronto, Canada, 01 October 1998, pp.183-225
My contention-not universally agreed upon-in this paper is that hotspots are related to plumes, which are mantle phenomena and are known by their manifestations at Earth's surface. The most unequivocal of these manifestations is uplift. There is no other process on this planet that creates domes of lithospheric flexure (i.e., falcogenic [large-wavelength] domes) of similar to1000 km diameter and 1 to 2 km amplitude within several million years. Such domes rise rapidly following arrival of a plume under the lithosphere. Uplift probably occurs by detaching pieces of the lithosphere and sinking them into the plume head. Domes do not generate enough extension to form rifts, but they do generate sufficient gravitational potential to lead to rifting. Giant radiating-dike swarms probably form as a result of spatial and temporal proximity of a plume with a pole of extensional rotation. The most active region of plume activity today is in Africa. In the Afar region, a dome of almost 1000 km radius began rising after the early Eocene, and it had probably reached an elevation of more than 1 km by early Oligocene time. Both basalt extrusion and rifting began afterward. A similar sequence of events occurred at the Kenya dome. Rifting and volcanicity at the Kenya dome progressed from north to south, giving the impression of a progressive tearing of Africa from the Afar southward. The uplift argument shows that the widespread late Devonian rifting and volcanism in eastern Europe were not plume-related phenomena, whereas the disruption of Gondwanaland in the Mesozoic was.