Crustal geometry and anisotropic signature beneath NE Iberia

NE Iberia marks the transition between compressive tectonics in the Pyrenees and the extensional regime along the Gulf of Lion and the Valencia Trough, and includes the Catalan Volcanic Zone, an alkaline volcanic zone field, which represents the southern branch of the European Cenozoic Rift System (ECRIS). While the large-scale geometry of the crust and the general trend of the anisotropy pattern are known from previous studies, new data acquired in the framework of the EPYSIM project allow for a more detailed characterization of these features.

The transition from the central Pyrenees to the Valencia Trough and the Gulf of Lion is defined by an abrupt crustal thinning. New data from two 60 km long profiles, one oriented NE-SW, parallel to the coastline, and the other oriented orthogonally, has been used to construct detailed pseudo-migrated receiver function sections. The coast-orthogonal profile, broadly oriented NW-SE, shows a decrease in crustal thickness from 35 km northwest of the Garrotxa Volcanic Field to 28 km beneath the La Selva Basin, reaching approximately 25 km near the coastline. The coast-parallel profile shows crustal thickness around 30 km in the west, thinning to approximately 25 km to the east, near the Gulf of Roses. Additionally, data acquired by a network of 60 stations covering NE Iberia with interstation distances of about 8 km has been analyzed used using the H-K method, providing independent constrains on crustal geometry.

SKS splitting along these profiles confirms the general E-W orientation of the fast polarization direction (FPD). Projection of results to the piercing point at 200 km depth suggests subtle difference between the Catalan Volcanic Zone, where FPDs are close to the E-W direction, and the south-western area, where they exhibit slightly higher azimuths. This difference may reflect the extension beneath the Valencia Though. Recent estimates of azimuthal anisotropy at the crust and uppermost mantle from surface wave tomography and previous Pn tomography results derived indicate strong variations in FPD orientation at different depths beneath NE Iberia, suggesting that each dataset is sensitive to anisotropy of different origins (e.g., cracks, frozen-in fabrics, asthenospheric flow)

The updated crustal geometry derived from receiver functions analysis and the regional seismic anisotropy pattern will be compared with recent geological models that integrate petrological and geochemical results of volcanic rocks, along with geophysical, structural and geochronological data. These models suggest that volcanism in the Catalan Volcanic Zone is controlled by crustal thinning and development of the NW-SE oriented Transverse Fault System.

This work has been supported by the EPYSIM Project, funded by the Spanish Ministry of Science and Innovation (Ref.: PID2022-136981NB-I00).