Iceland: The current picture of a ridge-centred mantle plume

Abstract

Currently the North Atlantic ridge is overriding the Iceland plume. Due to several ridge jumps the plume has been virtually ridge-centred since 20-25 Ma giving rise to extensive melting and crust formation. This review gives an overview over the results of the geophysical and, to minor extent, the geochemical research on the general structure of the Icelandic crust and the mantle beneath Iceland. In the first part, results mostly from topography/bathymetry, gravity, seismics/seismology, magnetotellurics, and geodynamical numerical modelling are summarised. They support the main conclusion that the Icelandic crust is up to ca. 40 km thick, whereby the lower crust and the uppermost mantle have an anomalously small density contrast and a gradual transition rather than a well-defined Moho. The interpretation of a good electrical conductor at 10-15 km depth as a molten layer is irreconcilable with a thick crust, so that alternative explanations have to be sought for this still enigmatic feature. In the second part, results from different branches of seismology, geochemistry, and numerical modelling on the Iceland plume arc reviewed and discussed. For the upper mantle, combining seismological models, geodynamical models and crustal thickness data suggests that the plume has a radius of 100-120 km and an excess temperature of 150-200 K, while the structure of the plume head is less well known. The volume flux is likely to be 5-6 km3/a, and numerical modelling indicates that water and its loss upon melting have a substantial impact on melt production and on the dynamics and distribution of segregating melt. Geochemical studies indicate that the plume source is quite heterogeneous and very probably contains material from the lower mantle. An origin of the plume somewhere in the lower mantle is also supported by several seismological findings, but evidence is not unambiguous yet and has still to be improved. © 2007 Springer-Verlag Berlin Heidelberg.