Imaging the meso-scale structure of the upper mantle beneath the southern and central Atlantic ocean

Although seismic tomography has provided important constraints on the long-wavelength structure of the mantle and its planform of convection, much is yet not well understood about the dynamic interaction of tectonic plates and deep mantle circulation at intermediate wavelengths (i.e., below plate-scale). In particular, a better understanding of the seismic structure of the oceanic upper mantle could potentially help unraveling the relationships between different scales of mantle convection, hotspot volcanism, and surface observables (e.g., MORB geochemistry, gravity gradients and bathymetry). We here present a new tomographic model of the shear-wave velocity and radial anisotropy structure beneath the central and southern Atlantic ocean constructed from the inversion of surface and body waves waveforms down to 30s period. Preliminary results confirm the existence of quasi-periodically distributed low-velocity regions in the upper mantle (200–350 km depth) organized in horizontally elongated bands some of which are parallel to the direction of absolute plate motion, as previously found in a lower resolution global tomographic models SEMum2 (French et al., 2013) and SEMUCB_WM1 (French and Romanowicz, 2014). Many of these elongated structures overlie vertically elongated plumelike conduits that appear to be rooted in the lower mantle, located, when projected vertically to the surface, in the vicinity of major hotspots.  However, there is no direct vertical correspondence between the imaged plumelike conduits and hotspots locations suggesting a complex interaction between the upwelling flow and the lithosphere/asthenosphere system. We discuss possible relations of this structure with trace element geochemistry of the corresponding hotspots.