Temperature anomalies under the Northeast Atlantic rifted volcanic margins

Subsidence analysis of ODP/DSDP drill sites located on oceanic crust on the Southeast Greenland, Edoras Bank, and Vøring Plateau margins, as well as on the Iceland-Faeroe Ridge, shows that the subsidence of these areas does not follow the agerelationship of normal oceanic crust. By correcting for the effect of thickened oceanic crust in raising the level to which subsidence will occur and analyzing the rate of thermal subsidence, it is possible to provide maximum temperature estimates for the underlying asthenosphere through time by identifying periods of anomalous depth to basement. Isostatic models predict crustal thicknesses of 27 km under the Iceland-Faeoe Ridge, around 20 km at Edoras Bank and Southeast Greenland, and 16–17 km at the Vøring Plateau. Asthenospheric temperatures at the time of continental break-up range from 50°C to 100°C above normal mantle, which are insufficient to account for the crustal thicknesses if melting is purely a passive adiabatic process. Asthenospheric upwelling must thus have been more rapid than spreading following break-up. At Edoras Bank the thermal anomaly dissipated within 5 Myr of rifting, similar to that inferred from the eastern US margin, where no plume is considered to have affected the rifting process. The need to invoke thermal input from the Iceland Plume in generating the thickened crust at Edoras Bank, and possibly elsewhere in the Northeast Atlantic, is called into question. However, a 14–20 Myr anomaly, peaking at 12 Myr post-rift, in Southeast Greenland suggests that, although the plume did provide heat to this margin, its strongest influence post-dated break-up.