3.4. In Front of the Africa-Europe Collision Zone: the Iberian Microcontinent

The Iberian microcontinent is rimmed to the North by the Pyrenean-Cantabrian and to the South by the Betic-Balearic orogen, both of which form an integral part of the Alpine-Mediterranean orogenic system (Cavazza et al., 2004). During their Cenozoic evolution, the cratonic part of Iberia was subjected to intense intraplate compression, as well as to extensional forces controlling opening of the oceanic Algero-Provençal Basin. Under the present NW to N-directed stress field the Pyrenees and Betic Cordillera, the Central System and the Mediterranean and Atlantic seaboards of Iberia are seismically active (Fig. 53; Jiménez et al., 1999; Andeweg, 2002; Cloetingh et al., 2005b).

Fig. 53. Map showing topography of Iberia and adjacent areas and bathymetry of the Atlantic and Western Mediterranean together with the distribution and magnitude of earthquakes during 1980-1996 and main stress directions. Seismic activity is mainly concentrated on active and former plate boundaries (after Jiménez et al., 1999; Andeweg, 2002; Cloetingh et al., 2005b).

Fig. 53. Map showing topography of Iberia and adjacent areas and bathymetry of the Atlantic and Western Mediterranean together with the distribution and magnitude of earthquakes during 1980-1996 and main stress directions. Seismic activity is mainly concentrated on active and former plate boundaries (after Jiménez et al., 1999; Andeweg, 2002; Cloetingh et al., 2005b).

Fig. 54. Orientation of principal stresses and principal stress difference ratio in Iberia and surrounding areas, determined by inversion of focal mechanisms of earthquakes. With a predominantly NW-SE oriented Shmax, strike-slip and extensional stresses prevail in most of the Iberian Peninsula, whereas in the south uniaxial compressional stresses dominate (De Vicente et al., 2006).

Fig. 54. Orientation of principal stresses and principal stress difference ratio in Iberia and surrounding areas, determined by inversion of focal mechanisms of earthquakes. With a predominantly NW-SE oriented Shmax, strike-slip and extensional stresses prevail in most of the Iberian Peninsula, whereas in the south uniaxial compressional stresses dominate (De Vicente et al., 2006).

Presently, Iberia is located in an area of low velocity (2 to 4 mm/y) NW-SE directed convergence of the African and Eurasian plates (Argus et al., 1989) with the Azores-Gibraltar fracture zone forming the boundary between them since the Early Miocene when Iberia had joined the Eurasian plate (Fig. 53) (Srivastava et al., 1990). The Cenozoic paleogeographic and tectonic evolution of Iberia is related to closing of the Alpine-Tethys and the Pyrenean rift during the Alpine Orogeny, involving relative movements between the Iberian microcontinent and the Eurasian and African plates and their mechanical coupling (Vegas, 1985; Savostin et al., 1986; Ziegler, 1988; Dewey et al., 1989; Andeweg, 2002; Jabaloy et al., 2002). The neotectonic deformation of Iberia is governed by a combination of collision-related and Atlantic ridge-push forces (Fig. 54) and can be elucidated by taking its Late Cretaceous to Paleogene (Srivastava et al., 1990; Roest and Srivastava, 1991) and Neogene (Mazzoli and Helman, 1994) tectonic history into consideration.

Iberia is a natural laboratory for analyzing the response of continental lithosphere to plate-boundary forces and thermal loads. Combined structural, thermo-geochronological and modelling studies on lithospheric and surface processes have revealed that regional deformation of the lithosphere and the decoupled crust controlled the development of Iberia’s topography, drainage pattern and sedimentary basins (Cloetingh et al., 2002).

TOPO-EUROPE, and specifically TOPO-IBERIA research will focus on the crustal and lithospheric configuration of Iberia and the structure of its sub-lithospheric mantle in order to discriminate between deformations induced by various types of plate boundary forces and by deep-seated thermal anomalies related to mantle plumes and the detachment of the Alpine-Tethys subduction slab. The objective is to assess processes controlling the neotectonic deformation of Iberia, the resulting development of topography and the effects of erosion, sedimentation and climate on the latter. To this end a new generation of predictive dynamic models will be developed for Iberia’s neotectonic deformation and topographic evolution.