[J08-1] Imaging and interpreting lithospheric structures using seismic and geodetic approaches I

[J08-1-06] Seismic Imagings of Sub-Crustal Reflectors Beneath the Iberia Microplate

Imma Palomeras¹, Puy Ayarza¹, Jordi Diaz², Juan Carlos Afondo³, ^○Ramon Carbonell² (1.Universidad de Salamanca, Salamanca, Spain,, 2.CSIC-ICTJA: Inst. Earth Sciences Jaume Almera, Barcelona, Spain, 3.Macquarie University, Sydney, Australia)

Deep upper mantle seismic scattering features have been imaged beneath the Iberia microplate. Normal incidence and wide-angle seismic reflection experiments in the area: ILIHA, IBERSEIS, and ALCUDIA, provide seismic constraints on these sub-crustal structures. Mantle reflectors were identified on the IBERSEIS wide angle shot records at offsets of 180 km. These correspond to an interpreted boundary located at 61-72 km depth with a Vp increase from 8.2 km/s to 8.3 km/s. This layer was interpreted to be characterized by a Vp gradient because the reflector was not identified in the coincident vertical incidence dataset. The ‘Hales gradient zone', i.e. the boundary between spinel and garnet peridotites, was the preferred interpretation. The ALCUDIA experiment also imaged prominent sub-crustal arrivals with similar characteristics. However, these reflections also appear, locally and at 19 s TWT, in the vertical incidence stack. In addition, the ALCUDIA wide-angle dataset show deeper reflectors that maybe, preliminarily, associated to mantle anisotropy fabrics or even with the lithosphere-asthenosphere boundary. Both upper mantle reflectors are modeled at 65 km and 100 km depth, respectively, shallowing to the north to 55 km and 90 km depth. Integration of the information provided by the IBERSEIS and ALCUDIA datasets with older and lower resolution data from the ILIHA project, where three sub-crustal phases were identified in SW Iberia, indicates that, in this area, mantle reflectivity is outstanding. Also, modeling of all the datasets contributes to map, at a regional scale, the Hales discontinuity or gradient zone in southwest Iberia. (Research supports: CGL2014-56548-P, 2009-SGR-1595, CGL2013-47412-C2-1-P).