Seismic evidence of Alpine crustal thickening and wedging from the western Pyrenees to the Cantabrian Mountains (north Iberia)

Abstract

The Alpine collision between the Iberian and European plates resulted in a complex crustal structure beneath the northern Iberian Peninsula, as revealed from a new set of seismic refraction/wide‐angle reflection profiles. The study area is characterized by two major E‐W ranges, the Cantabrian Mountains and the Pyrenees, which are relayed to the south by the Iberian Chain. Important variations in crustal thickness and velocity distribution are found in a 560‐km‐long E‐W transect. In contrast to the typical 30‐ to 32‐km‐thick European Variscan crust of the western end of the profile, a continuous Alpine crustal root is evidenced from the Cantabrian Mountains to the central Pyrenees, with a Moho depth of 46–48 km, locally rising to ∼40 km depth in between, beneath the Basque‐Cantabrian Basin. Another outstanding feature is the inferred presence of high velocities of 6.40–6.75 km/s at midcrustal depths, which can be associated with portions of a lower crustal wedge from the northern (European) domain indenting the southern (Iberian) crust during the Alpine stage of compression. This indentation produces the delamination of the Iberian crust, with northward underthrusting of its lower half and the consequent crustal thickening. The indenting wedge has a discontinuous presence along the longitudinal section, as it was controlled and/or affected by N‐S to NE‐SW structures. Further evidence of the northward subduction of the Iberian plate is provided by another profile toward the Aquitaine Basin, while a N‐S profile across the Iberian Chain reveals an Alpine midcrustal thickening beneath this belt with Moho depths of ∼42 km.

Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

“…Accordingly, the Pyrenean root was continued to the west to the Cantabrian region Gallastegui, 2000;Pedreira et al, 2003). The unmigrated vertical-incidence ESCIN-2 seismic profile images a reflective deep crust plunging down to 15 s TWT under the Cantabrian Mountains and margin ( Fig.…”

“…Descriptions and references of the upper crustal structure can be found in Alonso et al (1996), Gallastegui (2000) and Cadenas and Fernández-Viejo (2016). Previous crustal models have been proposed by Pulgar et al (1996), Fernández-Viejo et al (1998, 2000 Gallastegui (2000) and Pedreira et al (2003Pedreira et al ( , 2015, and are synthesized in Fig. 3D.…”

Alpine tectonic wedging and crustal delamination in the Cantabrian Mountains (NW Spain)

“…This thickening of the crust has also been interpreted in magnetotelluric profiles (Pous et al, 2001) and explored using teleseismic receiver function analysis of P to S conversions at main crustal interfaces ). Pedreira et al (2003Pedreira et al ( , 2007 and Díaz et al (2012) proved that this structure extends eastwards beneath the Basque-Cantabrian basin and in fact it is the continuation of the same crustal root interpreted beneath the Pyrenees from other seismic experiments (ECORS Pyrenees Team, 1988;Bois et al, 1990;Muñoz, 1992;Teixell, 1998). From a geological point of view, both areas are parts of the same Alpine belt.…”

Degree of Polarization Filter for Frequency-Dependent Signal Enhancement Through Noise Suppression

“…The source is an explosion on land, and the wave fields are recorded with almost 100 3-c stations separated by about 2.5 km. Our data correspond to shot J of a large field experiment with several profiles that were used by Pedreira et al (2003) to determine the crustal structure in the Cantabrian-Pyrenean area. The preprocessing consisted in bandpassing the data using cutoff and corner frequencies of 1, 2.5, 15, and 18 Hz and resampling about one third of the traces to obtain a record section with a uniform sample interval of 10 msec.…”

“…Although the seismic profile is from the Western Pyrenees with a very complex geology (Pedreira et al, 2003), we determine the travel time curves of reflections/conversions within a simplified 1D crust model. A good signal alignment along the theoretical travel times can not be expected because of the strong lateral heterogeneities.…”