Projects per year
The North Atlantic V-Shaped Ridges (VSRs) provide a long period (>40 My), spatially extensive and clear record of unsteady mantle convection. VSRs are diachronous ridges of thick crust formed with a periodicity of ∼5 My along the Mid Atlantic Ridge, south of Iceland. We present a new set of dredged basalt samples that, when combined with a legacy dataset, shows chemical variation associated with 2 complete VSR crustal thickness cycles where they intersect the Mid Atlantic Ridge. The new dataset also records the chemical variation associated with a VSR crustal thickness cycle along a plate spreading ﬂowline. Three lines of analysis suggest that VSR melt-ing anomalies were generated by temperature variations within the Iceland Plume head. First, minima in incompatible trace element concentrations and in incompatible/compatible element ratios correlate with maxima in crustal thickness, and there is no signiﬁcant correlated variation in Nd and Sr iso-topes. Secondly, both geochemical and crustal thickness variations can be matched using a time-dependent mid-ocean ridge melting model with a basal boundary condition of sinusoidally varying potential temperature. Thirdly, melt thickness variations estimated by modelling rare earth element concen-trations match crustal thickness variations estimated from legacy wide-angle seismic experiments. The mantle source was depleted by a few percent melt-ing prior to its arrival beneath the VSR study area, probably in the top of the plume conduit beneath SE Iceland, and contains blobs of enriched material on a spatial scale smaller than the VSR wavelength. Our observations and models suggest that VSRs are generated when hotter and cooler blobs are carried up the plume stem beneath SE Iceland and spread radially outward within the asthenosphere. These blobs are then drawn upward into the melt-ing region when passing beneath the Mid Atlantic Ridge. The geometry of the VSRs, the size of the dynamically supported swell and published U-series isotope measurements all suggest that the Iceland Plume is the strongest plume in the Earth at present, with a volume ﬂux of 49 ± 14 km3 yr−1.