Resumen de Tectónica colisional alpina y estructura sísmica de la corteza entre el Pirineo y la Cordillera Cantábrica

David Pedreira Rodríguez, Francisco Javier Álvarez Pulgar, Josep Gallart Muset, Diego Córdoba Barba, Jordi Díaz Cusí, Ramon Carbonell Bertran, Juan José Dañobeitia Canales

• The crustal structure of the transition zone between the Pyrenees and the Cantabrian Mountains was investigated from a set of seismic refraction / wide angle reflection profiles acquired in 1997. An E-W profile of 540 km shows important variations in crustal thickness and velocity distribution from the Cantabrian Mountains to the Western Pyrenees. A continuous Alpine crustal root is observed, with Moho depths of 46-48 km, except for the Western part of the Basque Cantabrian Basin, where the Moho is located at about 40 km. Another outstanding feature is the inferred presence of a discontinuous layer of 6.40-6.90 km s~’ at midcrustal depths beneath the Cantabrian Mountains and the Eastern Basque-Cantabrian Basin. Some geological and geophysical constraints suggest that it can represent a wedge of the lower crust of the Cantabrian Margin indenting the Iberian crust during the Alpine compression. This indentation was conditioned and/or affected by some NE-SW structures and this explains its discontinuous presence along the profile. The anomalously low velocity for this lower crustal material could be a consequence of its intense deformation during the collision and crustal indentation