Asthenosphere motion recorded by the ocean floor south of Iceland

Abstract On the sea floor south of Iceland, V-shaped basement features symmetrical about the spreading axis, converge southward, crossing progressively younger isochrons. This relationship between basement ridges and crustal isochrons suggests asthenosphere flow, at least under the spreading axis, away from the Iceland ‘hot spot’ (mantle plume). Two conditions necessary for the hypothesis that such plume flow derives the crustal plates are apparently met here: (1) Flow rate, under the Reykjanes Ridge, is about 20 cm/yr, an order of magnitude greater than spreading rate. (2) There is a rough correlation between basalt discharge rate and spreading rate. Absolute plume discharge is of the order 10 to 100 km3/yr, from which no more than 0.5 km3/yr basaltic crust is produced. Discrimination between limiting models of predominantly pipe flow (under and along the ridge axis) and radial flow may depend on rates of apparent downstream flow deceleration.