V-shaped ridges around Iceland: Implications for spatial and temporal patterns of mantle convection

Abstract : V-shaped lineations in the bathymetry and in the free-air gravity field surrounding Iceland result from crustal thickness variations caused by temporal variations in melt production rate at the Mid-Atlantic Ridge. We have studied the record of V-shaped ridges in the basins surrounding Iceland by plotting the short-wavelength component of the gravity field in terms of age versus distance from Iceland. The V-shaped ridge gravity signal is obscured by crustal segmentation and by sediment more than 1-2 km thick. The best V-shaped ridge record is found in the unsegmented part of the Irminger Basin, where Oligocene-Recent V-shaped ridges occur with a primary periodicity of 5-6 Myr and a secondary periodicity of 2-3 Myr. V-shaped ridge records from the Iceland Basin and from east of the Kolbeinsey Ridge to the north of Iceland correlate with the record from the Irminger Basin but are less complete. A record of uplift of the Greenland-Iceland-Faroes Ridge based on paleoceanographic data is correlated with the gravity record of V-shaped ridges. There is less decisive evidence for V-shaped ridges in crust of Eocene age. The observation that V-shaped ridges propagate up to 1000 km from Iceland is compatible with a model in which the Iceland Plume head spreads out from the plume stalk below a depth of ∼100 km, as suggested by geochemical arguments and studies of mantle rheology. Time-dependent flow in the plume head probably results from time-dependent flow up the plume stalk from deep below Iceland. These pulses may have triggered jumps in location of the spreading axis observed in the Icelandic geological record.