Origin of subcrustal reflectivity in SW Iberia: Evidences from wide-angle seismic experiments

From 2001, the IBERSEIS and ALCUDIA controlled source experiments have sampled the lithosphere of SW Spain. Apart from providing high resolution information of the crust of the Variscan South-Portuguese, Ossa Morena and Central Iberian Zones with two ~300 km long vertical incidence transects, these projects have also imaged the lithospheric mantle. A particularly conspicuous sub-crustal reflector was first identified on the IBERSEIS wide-angle reflection transect at offsets around 180 km. This interface, seemingly featuring a positive seismic impedance contrast, was modelled as a boundary at 62-71 km depth, with a Vp increase from 8.2 km/s to 8.3 km/s. The fact that this reflector was not identified in the coincident vertical incidence dataset led us interpret it as a gradient zone. A correlation with the ‘Hales gradient zone’, i.e. the mantle boundary featuring the phase transition between spinel and garnet peridotites was our preferred interpretation.Research supports: CGL2014-56548-P, 2009-SGR-1595Peer Reviewe