Subduction‐related structures in the North Iberian Margin

Abstract

Abstract. The oblique convergence of Eurasia and Iberia since the Early Cretaceous, caused the formation of the Pyrenean intracontinental collisional orogen in the east, and progressed to continent-ocean collision with subduction of the Bay of Biscay oceanic crust beneath the North Iberian Margin in the west. Two deep multichannel seismic profiles (IAM-12 and ESCIN-4), integrated with gravity modeling and other geological and geophysical data, provide the crustalscale architecture of this margin and its tectonic evolution during the convergence. The North Iberian Margin is modeled with a south or south-southeast dipping oceanic crust beneath the outer part of the continental shelf. Mesozoic basins on the shelf were inverted during the Tertiary, and compressional activity continued until recent times in the ESCIN-4 section, while a shallower, probably Neogene age basin is subjected to active recent erosion in the IAM-12 section. In the oceanic areas, a marginal trough deepens and widens toward the east as a result of the regional east dip of the oceanic basement. The accretionary prism increases in size from west to east (18-56 km), and its internal structure and morphology varies along strike. The prism is buried by postconvergence sediments in both sections and in the iAM-12 section appears to have been active at least during Lutetian to Burdigalian times. The crustal-scale structure of the North Iberian Margin is that of an arrested subduction zone in which a remnant oceanic basin was being consumed near two continental plates that collided obliquely.

Plate kinematics in the Cantabrian domain of the Pyrenean orogen

“…Ambiguous evidence of Iberia subduction exists in the area. In fact, while both gravimetric data (Alvarez-Marrón et al, 1997) and seismic velocity modelling S. Tavani: Plate kinematics in the Cantabrian domain 269 (Fernández-Viejo et al, 1998) Fig. 2) shows a repetition of the lower crust-mantle boundary (Ayarza et al, 1998) matching a north-directed subduction of Iberia.…”

“…Elevation map with main faults of the Iberia-Eurasia collisional margin and orogenic domains marked and crustal-scale cross sections. P1: geological cross section across the Pyrenees (after Muñoz, 1992); P2: geological cross section across the Basque Pyrenees (after Pedreira et al, 2007); P3: geological cross section across the Cantabrian Mountains (modified from Gallastegui, 2000); P4: geological cross section across the western termination of the Cantabrian domain (modified from Alvarez-Marrón et al, 1997). P5: geological cross section along the Cantabrian shelf (modified from Ayarza et al, 1998).…”

“…Both Moho and top of the lower crust of the subducting Iberian Plate, in fact, experience negligible variations across the two domains (e.g. Pedreira et al, 2007), and the subducting Iberian lithosphere can be followed at least until the northwestern corner of the Iberian Peninsula (Gallastegui, 2000), where the amount of convergence was less than 40 km (Alvarez-Marrón et al, 1997). The absence of large-displacement thrusts in the onshore portion of the Cantabrian domain, makes that area one of the few sites in the world where mechanisms operating during initiation of subduction can be easily and directly inferred from the observations of poorly reworked structural and stratigraphic features, although these mechanisms have operated within an atypical subduction zone.…”

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

“…The ESCIN and MARCONI programs and other related projects were planned to study the deep crustal structure and evolution of the Cantabrian Mountains and continental margin from deep seismic reflection and refraction/wideangle data (Pérez-Estaún et al, 1994;Pulgar et al, 1995Álvarez-Marrón et al, 1996Álvarez-Marrón et al, , 1997Gallastegui et al, 1997;Ayarza et al, 1998;Fernández-Viejo et al, 1998, 2000Gallastegui, 2000;Gallastegui et al, 2002;Fernández-Viejo and Gallastegui, 2005;Fernández-Viejo et al, 2011. These studies showed that the deformation of the area due to the Alpine compression affected not only the shallow crustal levels but also the deeper ones.…”

Origin, structure and exposure history of a wave-cut platform more than 1 Ma in age at the coast of northern Spain: A multiple cosmogenic nuclide approach

“…From the Eocene onwards the subduction of oceanic crust in the Bay of Biscay beneath the Iberian continental margin led to the formation of an incipient subduction zone (Figure 9) (Sibuet and Le Pichon, 1971;Boillot et al, 1979;Grimaud et al, 1982;Roest and Srivastava, 1991;Alvarez-Marrón et al, 1997). The subduction continued until the Early Miocene (Boillot et al, 1979;Roest and Srivastava, 1991), and possibly into the Neogene , 1997.…”