Along with the Alps, the Pyrenees represent the second chain of collision marking the French landscape. The formation of this great mountain range results from a complex and polyphase tectonic history, marked by the collision between the Iberian plate and Eurasia.
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The Pyrenees mark the border with Spain. This large mountain range stretches nearly 1,000 km in length, from Provence in the east to the region of Asturias, in Spain.
The formation of the Pyrenees is closely linked to the formation Alpes. The beginning of this story begins 80 to 70 million years ago, in the Campanien. However, the architecture of the Pyrenees testifies to a much more complex past. It results in fact from the succession of several extensive and compressive tectonic cycles initiated from the Paleozoic, 400 million years ago. The Pyrenees are thus marked by the presence of numerous structures inherited from this tectonic past.
A complex tectonic heritage
400 million years ago, a huge mountain chain was formed: the Hercynian chain, also called Varisque chain. These mountains result from the collision of the Laurussia plates and Gondwana, during the formation of the supercontinent Pangea. If the Hercynian range will end up disappearing in the Permian, 270 million years ago, delaminated by erosion and tectonic processes, it will however leave behind it many traces of its passage, imprinted in the continental crust.
This compressive episode succeeds a rifting phase generalized, marked by an extensive dynamic. The Iberian bloc (now Spain) is not at all in its current position. It is attached to the western European margin, the current French Atlantic coast. The Bay of Biscay did not yet exist. Extensive tectonics, associated with the start of the alpine cycle, will then lead to the formation of several intracontinental basins during the Trias.
The movements tectonic plates and in particular the opening of the central Atlantic will modify this continental arrangement. An arm of ocean ridge spread along the current continental margin in the west of France, towards Aquitaine. Under the effect of this oceanic opening, the Iberian plate then began to drift towards the southwest. The current V-shape of the Bay of Biscay thus testifies to the displacement of the Iberian block towards the south and the joint oceanic opening.
The waltz of the Iberian block
The Iberian plate thus performs an anti-clockwise rotation movement before starting a lateral movement towards the east. During this great shear movement with the south of France, the Iberian block will thus move towards the east of 200 km, approaching its current position. This phase is followed by a compressive tectonic regime which will lead to the actual collision between the Iberian plate and the Eurasian plate, causing the start of the uplift of the massif and the formation of the Pyrenees. Under the effect of compression, the Iberian plate begins to pass under Eurasia. The phase oforogeny Pyrenean begins in the Paleocene, about 60 million years ago. the paroxysm of this collision phase is dated 50 to 40 million years ago.
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