A joint geochemical-geophysical record of time-dependent mantle convection south of Iceland

- North Atlantic V-Shaped Ridges (VSRs) record unsteady (pulsing) mantle convection.
- We present compositions of new VSR basalt samples and reinterpret crustal thickness.
- We develop a numerical model to match VSR melt thickness and composition.
- VSRs result from hotter and cooler patches of mantle in the Iceland Plume head.
- The Iceland plume has the strongest flux in Earth's mantle at present.

The North Atlantic V-Shaped Ridges (VSRs) provide a spatially extensive and clear record of unsteady mantle convective circulation over >40 My. VSRs are diachronous ridges of thick crust formed with a periodicity of ∼5 My along the Mid Atlantic Ridge, south of Iceland. We present data from a set of dredged basalt samples that shows chemical variation associated with two complete VSR crustal thickness cycles where they intersect the Mid Atlantic Ridge. The new dataset also records chemical variation associated with a VSR crustal thickness cycle along a plate spreading flow-line. Inverse correlations between crustal thickness and both incompatible trace element concentrations and incompatible element ratios such as Nb/Y and La/Sm are observed. Geochemical and crustal thickness observations can be matched using a time-dependent mid-ocean ridge melting model with a basal boundary condition of sinusoidally varying potential temperature. Our observations and models suggest that VSRs are generated when hot patches are carried up the plume stem beneath SE Iceland and spread radially outward within the asthenosphere. These patches are then drawn upward into the melting region when passing beneath the Mid Atlantic Ridge. The geometry of the VSRs and the size of the dynamically supported swell suggest that the Iceland Plume is the strongest plume in the Earth at present, with a volume flux of 49±14 km3yr−1.