Regional crustal inheritance explains lateral variation in the style of mountain building in the Pyrenees

The first order control of crustal rheology on the structural style of mountain building has been widely investigated and can explain the main variations in structural style observed in natural systems. However, many natural systems show significant along strike structural variations which are not well understood. The Pyrenean chain, resulting from the collision between the Iberian and the Eurasian plates, is one of the best examples to investigate this question. Generally described as a narrow asymmetric doubly-vergent wedge, the westward disappearance of the basement involved deformation zone (i.e.: Axial zone) and structural differences observed in the two deep seismic profiles crossing the chain suggest that the response to contractional deformation strongly differ along the Pyrenean strike. Also, if the general deformation process of the Pyrenean chain is well understood the reason explaining the non-cylindricity of the chain still require investigation. Here, using a multi-disciplinary approach combining geological-geophysical observations and advanced 2D numerical thermo-mechanical modeling at lithospheric scale we demonstrate how crustal inheritances can explain this non-cylindricity. This work clearly shows that a variation of crustal strength along-strike owing to Variscan inheritances explains 1) the distribution of the deformation during the Mesozoic rifting event in the Pyrenean domain with a localized basin in the western part and a distributed zone of extension in the eastern part 2) the non-cylindricity of the Pyrenean chain resulting of the inversion of this previously rifted area.