Azores Hotspot Deep Signature

The Azores archipelago occupies a lateral branch of the Mid-Atlantic ridge near the triple junction of 3 large tectonic plates, the North American, the Eurasian and the African plates. The tectonic setting is even more complex due to the existence of the Azores hotspot and to the hotspot-ridge interaction. But the hotspot origin at depth as a plume and its lateral extent are controversial subjects. High-resolution tomographic models, through the mapping of low velocity and anisotropy anomalies, can provide an important hint to evaluate the depth and lateral extent of mantle plumes. Therefore, we investigate the Azores deep seismic structure as seen on recent global and regional studies. The mapping of S-wave negative velocity anomalies in the different models reveals that the anomaly right beneath the Azores seems to be confined in the upper 200km. Considering the time evolution of a plume, this low velocity anomaly might be the signature of a present-day dying plume, that created the Azores plateau 20Ma ago. In the model from Silveira and Stutzmann (2002), the negative velocity anomaly beneath the Azores archipelago seems to be connected to a deep anomaly further at the South. This deep anomaly ( ∼28^oN/26^oW, 200-400km) is in the middle of the bunch of Azores, Great Meteor, Madeira and Canary hotspots, and might be related to a plume originating either in the transition zone or in the lower mantle. This single deep plume is located too far from the Azores archipelago for being responsible of the Azores plateau formation. But, due to the lithosphere geometry, this single plume might feed at present day Azores, Great Meteor, Madeira, Canaries and Cape Verde hotspots and therefore be at the origin of the present day volcanism. The diverging azimuthal anisotropy around this point below lithosphere is confirming a unique origin of these hotspots.