A continuous 55-million-year record of transient mantle plume activity beneath Iceland

In the North Atlantic Ocean, a mid-ocean ridge bisects the Icelandic mantle plume, and provides a window into its temporal evolution(1-3). V-shaped ridges of thick oceanic crust observed south of Iceland are thought to record pulses of upwelling within the plume(4-7). Specifically, excess crust is thought to form during the quasi-periodic generation of hot solitary waves triggered by thermal instabilities in the mantle(8). Here we use seismic reflection data to show that V-shaped ridges have formed over the past 55 million years-providing the longest record of plume periodicity of its kind. We find evidence for minor, but systematic, asymmetric formation of crust, due to migration of the mid-ocean ridge with respect to the underlying plume. We also find changes in periodicity: from 55 to 35 million years ago, the V-shaped ridges form every 3 million years or so and reflect small fluctuations in plume temperature of about 5-10 degrees C. From35 million years ago, the periodicity changes to about 8 million years and reflects changes in mantle temperature of 25-30 degrees C. We suggest that this change in periodicity is probably caused by perturbations in the thermal state at the plume source, either at the mantle-transition zone or core-mantle boundary.