Exhumation of the southern Pyrenean fold-thrust belt (Spain) from orogenic growth to decay

The deformation and exhumation history of an orogen reflects the interactions between tectonic and surface processes. We investigate orogenic wedge deformation, erosion, and sedimentation in the Pyrenees by (a) quantifying the spatiotemporal patterns of exhumation across the southern fold-thrust belt (FTB) with bedrock apatite fission track (AFT) thermochronology and (b) comparing the results with existing deformation, exhumation, and sedimentation chronologies. Eighteen new samples record exhumation during and after orogenesis between 90 and 10 Ma. Rocks from the range core (Axial Zone) record rapid exhumation that progresses east to west and north to south, consistent with patterns of tectonically driven uplift. Synorogenic sediments shed into piggyback basins on the southern fold-thrust belt during mountain building retain a detrital exhumation signal from the Axial Zone. In contrast, samples from other structural positions record exhumation of the thin-skinned Pyrenean thrust sheets, suggesting sediment burial and heating of sufficient magnitudes to reset the AFT system (>~3 km). In some locations, exhumation of these fold-thrust structures is likely an erosional response to thrust-driven rock uplift. We identify an exhumation phase ~25–20 Ma that occurs along the central and eastern Spanish Pyrenees at the boundary between thick- and thin-skinned portions of the wedge. We suggest that this distributed exhumation event records (a) a taper response in the southern orogenic wedge to sediment loading and/or (b) a shift to wetter, stormier climate conditions following convergence-driven uplift and full topographic development. A final exhumation phase between ~20 and 10 Ma may record the excavation of the southern fold-thrust system following base level lowering in the Ebro Basin