Deformation of the Aegean Slab in the Mantle Transition Zone

Consistent with results of earlier tomographic studies, regional non-linear P-wave travel time tomography depicts a slab of previously oceanic lithosphere penetrating into the lower mantle beneath part of the Aegean region. However, our results also suggest that the slab is intensely distorted in the transition zone, with the lower mantle penetration spatially confined to a relatively small area. The deflection of the slab in the transition zone resembles that observed beneath, for instance, the Izu Bonin arc and the Tyrrhenian Sea and can be related to the slab roll-back that has accompanied back-arc extension. In addition, joint P- and S- inversion indicates that the deformed part of the slab is likely to be a bulk sound feature, which is in remarkable agreement with our previous observations pertinent to deflected slabs beneath western Pacific island arcs. The difference between the shear and bulk sound signature of slabs that either deflect in the transition zone or penetrate to larger depths thus seems robust and may contain important information about the interaction of downwellings with the upper mantle discontinuities.