Temperature and melting of a ridge-centred plume with application to Iceland. Part I: Dynamics and crust production

Abstract

SUMMARY In this study and a companion paper, numerical models of convection and melt generation in a ridge-centred plume system are developed for plumes with different temperature anomalies ΔTP and varying fractions of retained melt ϕex. The produced melt in excess of the retention threshold is used to generate ridge and plume crust respectively, whose thickness is found to be sensitive to changes in ΔTP and ϕex. Comparison of calculated crustal thicknesses with observations from mid-oceanic ridges and from Iceland confirms earlier findings that ΔTP of the Iceland plume in the upper mantle is about 150–200 K and that the Icelandic crust is thick. It also suggests that the retained melt fraction in partially molten mantle is at most 1 per cent. In the preferred model, plume melting occurs between ca. 25 and 110 km depth, at up to ∼250 km from the spreading centre. The temperature and melt fraction fields from the numerical models are used as input for the derivation of seismic velocity anomalies and magnetotelluric response functions in the companion paper. Furthermore, the models reveal that the high temperatures of plumes result in a superlinear increase of crustal thickness with plume excess temperature through the combined effects of enhanced melting, active upwelling and the extent and geometry of the melting zone.