Geology of the Pyrenees

The Pyrenees form part of the huge alpine orogenic system. This 430 kilometre long, roughly east-west striking, intracontinental mountain chain divides France, Spain, and Andorra. It has an extended, polycyclic geological evolution dating back to the Precambrian. The chain's present configuration is due to the collision between the microcontinent Iberia and the southwestern promontory of the European Plate (i.e. Southern France). The two continents were approaching each other since the onset of the Upper Cretaceous (Albian/Cenomanian) about 100 million years ago and were consequently colliding during the Paleogene (Eocene/Oligocene) 55 to 25 million years ago. After its uplift, the chain experienced intense erosion and isostatic readjustments. A cross-section through the chain shows an asymmetric flower-like structure with steeper dips on the French side. The Pyrenees are not solely the result of compressional forces, but also show an important sinistral shearing.

The Pyrenees sensu stricto stretch in a westnorthwest-eastsoutheast-direction (N 110) over 430 km from the Bay of Biscay in the west to the Golfe du Lion and the Golf de Roses in the east, their width across strike varying between 65 and 150 km. They are bounded in the north by the North Pyrenean Front (French: Front nord-pyrénéen, also North Pyrenean frontal fault or NPFF), a major thrust fault along which units from the North Pyrenean Zone have been transported over the Subpyrenean Zone, southernmost part of the Aquitaine Basin, their northern foreland. Their southern limit is the South Pyrenean Frontal Fault. Here, thrust slices from the Sierras Marginales and their lateral equivalents are displaced southward over the Ebro Basin.

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