Post-orogenic exhumation in the western Pyrenees: evidence for extension driven by pre-orogenic inheritance

We discuss the drivers of the Pyrenean post-orogenic exhumation, including drainage migration, flexural rebound and tectonic reactivation.We provide new low-temperature thermochronological data and inverse thermal modeling from both the hinterland and foreland of the western Pyrenees. Our new thermochronological ages range from 6.6 to 61.4 Ma and reveal a Late Miocene exhumation phase in several massifs. The contrasting thermal histories define a domain of focused exhumation in the western Pyrenees that coincides with the present-day extensional tectonics in a region to the north of the Axial Zone. Based on the inferred cooling rates and paleogradient estimates, we highlight an exhumation phase of c. 1 mm yr(-1) between 11 and 9 Ma in the Axial Zone, well above rates expected for a post-orogenic evolution. The thermal evolution inferred from three boreholes of the Aquitaine foreland basin reveals that sediments eroded from the hinterland did not accumulate in the Piedmont region but were transported offshore in the Bay of Biscay. We infer that the significant c. 10 Ma post-orogenic exhumation event must be related to the modern normal faulting regime of the western Pyrenees, associated with contrasting crustal thickness and densities, inherited from the Mesozoic rift evolution of the northern Pyrenees.

Automated summary

A Late Miocene exhumation phase was revealed in the western Pyrenees, with contrasting thermal histories and a focused exhumation domain identified. The exhumation event of around 10 million years ago is related to the modern normal faulting regime and inherited crustal characteristics from the Mesozoic rift evolution of the northern Pyrenees. The study also highlights the transportation of eroded sediments offshore in the Bay of Biscay instead of accumulation in the Piedmont region.