Test of a ridge–plume interaction model using oceanic crustal structure around Iceland

Segmentation of oceanic crust by fracture zones is controlled both by asthenosphere temperature and by spreading geometry at the time of crustal formation. South of Iceland, young crust adjacent to the Reykjanes Ridge and old crust adjacent to the continental margins is smooth and unsegmented, while intermediate age crust is segmented. The older part of the boundary between segmented and unsegmented crust is coincident with magnetic chron 17 (end Middle Eocene time) and was principally controlled by a coeval change in spreading obliquity of 30°. The younger part of the boundary has moved outwards from Iceland by 500 km between Late Eocene time and the present. The shape of this diachronous part of the boundary is principally controlled by asthenosphere temperature and probably records the position of a critical asthenosphere isotherm in the head of the Iceland Plume. The planform geometry of the diachronous boundary is well matched by a scaling law which predicts the spread of hot plume material along the ridge (or ‘waist width’) if the Iceland Plume is assumed fixed relative to other Indo-Atlantic hotspots. This match suggests that the apparent increase in the size of the Iceland Plume head since Late Eocene time can be explained by westward migration of the Reykjanes Ridge relative to the centre of a plume of constant flux on timescales over 8 Myr. Comparison of observed and predicted waist widths provides a constraint on plume volume flux and allows a direct first-order comparison between Iceland and Hawaiian Plume fluxes.