The nature of upper mantle upwelling during initiation of seafloor spreading in the southern Red Sea

The response of the mantle and specifically melt generation during the progression from continental to oceanic rifting is poorly understood due to an absence of direct observations. Specifically, it is unclear when during the rifting process the segmented nature of magma supply typical of seafloor spreading initiates. We have imaged the mantle beneath the southern Red Sea, Afar and the Main Ethiopian rift using Rayleigh-wave tomography. From this we have generated a high-resolution absolute 3-dimensional shear-wave velocity model of the upper 250 kilometres imaging the mantle response during the progression from continental rifting to seafloor spreading. We interpret segmented partial melt beneath the rifts based on observations of low seismic velocities and rift parallel anisotropy. The low velocities are likely formed by focusing of partial melt along the base of the lithosphere in addition to buoyancy driven active upwelling. The segmented anomalies are consistent in scale from the oceanic southern Red Sea rift to the continental Main Ethiopian, suggesting that mantle segmentation beneath oceanic rifts initiates early during continental rifting. The similarity between the observed mantle segmentation and mantle segmentation observed at oceanic rifts worldwide indicates that these interpretations may apply globally