The transfer of tectonic activity from the Pyrenees to the Betics took place at the Oligocene-Miocene transition forcing important geodynamic changes around and inside the Iberian plate (Fig. 13). Major variations along the Pyrenean chain occurred at its eastern termination whereas a slight compression remained to the W.
Since middle Oligocene times the opening of the Valencia Trough created an extensional fault system paralleling most of the eastern coast of NE Spain (e.g., Roca et al., 1999; Roca, 2001), (Fig. 6). However, towards the NE the fault system cut obliquely across the Catalan Coastal Ranges. Concomitant differential crustal-mantle thinning produced the uplift of segments of the Catalan Coastal Ranges as well as of the SE margin of the Ebro Basin (e.g., Morgan and Fernàndez, 1992; Lewis et al., 2000; López-Blanco et al., 2001), recently quantified by apatite fission track studies (Juez-Larré and Andriessen, 2001). This uplift of more than 1.5 km is responsible for the significant dissection of this margin from which the more resistant Eocene, SE-derived conglomeratic fan deltas and alluvial fans of Montserrat and Sant Llorenç del Munt constitute the present-day maximum altitude along this area (Lewis et al., 2000), (Fig. 10 A).
The Pyrenean belt was also affected by extension with the development of Neogene and Quaternary grabens (e.g., Cabrera et al., 1988; Roca, 1996b), (Fig. 14). From middle Miocene to Recent, NW-SE trending faults developed at an almost right angle to the eastern Pyrenean structures (Fig. 6). This extensional system is related to the extrusion of basaltic lavas sourced in the asthenospheric mantle at about 55-60 km of depth (e.g., Martí et al., 1992; Neumann et al., 1999).
Figure 14. Post-collisional history of Eastern Pyrenees and Valencia Trough
Timing of deformation of post-collisional history of Eastern Pyrenees and Valencia Trough from Oligocene to Recent. A system of normal faults cut the eastern end of the Pyrenees forming graben basins (modified from Vergés and Sàbat, 1999).
Increasing topography towards the E along the axis of the Ebro Basin (towards the footwall of the youngest Amer-Brugent normal fault) constitutes the Transverse Range parallel to the fault itself. This eastward increasing of the mean elevation and local relief together with the large-scale tilt of the NE Ebro Basin produced significant uplift related to a combination of lithospheric thinning and crustal faulting since middle Miocene times (Lewis et al., 2000). This younger uplift affected a much broader area than Oligocene-early Miocene uplift and overprinted it (Fig. 15). This uplift has been related to the general westwards migration of normal fault activity and extrusion of volcanics and interpreted as produced by the progressive lithospheric thinning in the same direction (Cabal and Fernàndez, 1995; Lewis et al., 2000).
Figure 15. NE corner of Iberian Peninsula
Map of NE corner of Iberian Peninsula displaying two uplifted areas related to late syn- and post-collisional Cenozoic extension: redish for Oligocene to early Miocene and yellowish for middle Miocene to Recent (modified from Lewis et al., 2000).
The recent history of the Pyrenees is dominated by slight compression as determined from instrumental earthquake focal mechanisms (Goula et al., 1999; Souriau and Pauchet, 1998). An important cluster of seismic activity has been recorded along the western segment of the North Pyrenean Fault Zone suggesting the reactivation of Pyrenean structures.