The eastern part of the Pyrenean range had a different tectonic evolution since upper Eocene, as compared to the central and western Pyrenees, due to the influence of the European Neogene rifting episode. The passive margins of the Gulf of Lion and Valencia trough, correspond to the western margin of the Algero-Provençal basin which opened due to the Oligo-Aquitanian rifting, but also to the Burdigalian oceanic accretion associated with the south-eastward drifting of the Corsica Sardinia block. This extensional episode is linked to back arc opening in the context of African and European plate convergence (Figure 1). Extensional faulting affects the pre-rift Mesozoic cover, which is detached above the paleozoic basement, the latter one being undeformed during the rifting. Inland, the margin is bounded by several inherited NE-SW major faults (Cevennes, Nîmes, Têt and Vallès-Penedès faults), which limit a system of half graben basins. Offshore, the structure of the Gulf of Lion is segmented by several NW-SE transfer faults and can be divided into a north-east domain, where the grabens trending N030 are narrow, and a south-west domain characterised by two 7 to 8km deep depressions (Mauffret et al., 1995). The transition zone between the Gulf of Lion structures and the Catalan margin structures corresponds to a major NW-SE transfer zone (Catalan transfer zone). A NNE-SSW to N-S trend is observed in the northern part of the steep and narrow Catalan margin, in contrast with the E-W and NE-SW orientations which characterise the Catalan grabens of the southern margin.

Inland, in the eastern part of the Pyrenees, the Oligo-Aquitanian extension episode corresponds to the opening of three deep sedimentary basins along major normal faults: 

a) the Roussillon graben bounded to the north by the NE-SW Têt fault and to the south by the ENE-WSW Alberes fault which limits the Palaeozoic Alberes massif; 
b) the Empordà basin, limited by the Albanyà and the Roses faults, trending NW-SE;
c) the Vallès-Penedès graben, trending ENE-WSW.

The western limit of the region of influence of the rifting is assumed to correspond to the Miocene Cerdanya half graben, which is filled with more than 900m of Neogene sediments.

The stress regime associated with the rifting, and deduced from microtectonic measurements, gives an horizontal minimum stress s₃ trending NW-SE in Languedoc-Roussillon and a slightly different orientation (WNW-ESE) in Empordà and Vallès-Penedès. The central and western part of the Pyrenees were still in a compressive stress regime during the same period.

The south-eastward drifting of the Corsica Sardinia block stopped at the end of Burdigalian time. Since that time, the tectonic regime in the western part of the Mediterranean sea gradually changed from extension to compression due to the effects of the N-S convergence between the African and European plates. This modification of the stress regime is not synchronous at the scale of the Gulf of Lion and the Catalan margin. The first evidences of deformation under compression appear: 

a) in the northern part (Ventoux-Lure area) during the upper Miocene (Serravalian),
b) in Languedoc-Roussillon during the early Pliocene;
c) in Catalonia at the end of the Pliocene (Figure 2) (Philip et al., 1991; Grellet et al, 1993; Fleta et al., 1996).

The NE-SW (Nîmes, Têt faults) Oligo-Aquitanian normal faults seem to have been reactivated with a predominant reverse strike-slip component, while the E-W segments show mostly pure reverse faulting, even though the intensity of deformation remains moderate.

1 .............2

Figure 1 : Oligo-Miocene period. ..............................::::............................Figure 2 : Plio-Quaternary period.