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

Abstract

S U M M A R YIn 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 T P and varying fractions of retained melt ϕ ex . 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 T P and ϕ ex . Comparison of calculated crustal thicknesses with observations from mid-oceanic ridges and from Iceland confirms earlier findings that T P 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.

The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day

“…This result supports those of Reudas et al (2004) whose models included a higher average viscosity than in our models without dehydration and produced better fits to Iceland's crustal thicknesses. We suggest that a viscous, dehydrated lithosphere is present at the Iceland hotspot, but is less viscous than we have simulated.…”

The influence of source heterogeneity on the U–Th–Pa–Ra disequilibria in post-glacial tholeiites from Iceland

“…Extraction of melts from different parts in the 3-D mantle flow regime underneath the Icelandic rift zone, as discussed in Section 5.2, is expected to give rise to variability in melt transport times. Melt transport with a significant horizontal component is thought to be 1-2 orders of magnitude slower compared to buoyancy-driven vertical melt transport (Braun and Sohn, 2003;Ruedas et al, 2004). The time it takes for melts to reach the axis depends on their initial lateral distance from the ridge axis (Katz, 2008).…”

Upper mantle viscosity and lithospheric thickness under Iceland

“…A melt content of 4% is just 125 above the upper limit for estimates for melt that can remain in a peridotite (up to 2-3%; Faul 126 (1997), 1-3%; Ruedas et al (2004)). We have used a higher value of 4% to illustrate that the 127 presence of melt has only a relatively small reducing effect on the overall viscosity within the 128 kilometer is taken to be fully elastic, which is reasonably close to the 10 km elastic thickness 143 of Sigmundsson (1991).…”