S-Wave velocity, basalt chemistry and bathymetry along the Mid-Atlantic Ridge

Abstract

Major element chemistry of mid-ocean ridge basalt, S-wave velocity and bathymetry along the Mid-Atlantic Ridge are correlated on an intermediate length scale, and the large anomalies in these observations are associated with hotspot locations. The best correlations are for at depths of 100–200 km, and there is no correlation for depths of 300 km or deeper. S-Wave velocities are low directly under the Mid-Atlantic Ridge above 100 km, but the low-velocity regions shift away from the ridge at greater depth, and a sinuous strip of asthenospheric low velocity extends along the Atlantic hotspots from the Azores to Tristan da Cunha. These features suggest that common physical processes in the upper mantle produce these anomalies. An inspection of the history of the Atlantic Ocean suggests that the asthenospheric low-velocity strip may record earlier ridge position or possible upwelling in the mantle. Possible interaction between hotspots and the ridge blurs the distinction between passive and active upwellings