Thermo-tectonic evolution of the south-central Pyrenees from rifting to orogeny: insights from detrital zircon U/Pb and (U-Th)/He thermochronometry

International audienceConstraining the thermal and denudational evolution of continental margins from extensional episodes to early orogenic stages is critical in the objective to better understand the sediment routing during the growth of orogenic topography. Here, we report 160 detrital zircon U/Pb ages and 73 (U-Th)/He ages from Albian, Upper Cretaceous and Eocene sandstones from the south-central Pyrenees. All samples show dominant zircon U/Pb age peaks at 310-320 Ma, indicating a primary contribution from Variscan granites of the central Pyrenean Axial Zone. A secondary population at 450-600 Ma documents zircon grains sourced from the eastern Pyrenees. Zircon (U-Th)/He ages recovered from older samples document, a Triassic age peak at ca. 241 Ma, corresponding to denu- dation coeval with the initiation of Atlantic rifting. An Early Cretaceous cooling event at ca. 133 Ma appears consistent with rift-related exhumation and thermal overprint on the Iberian margin. The (U-Th)/He age peaks from ca. 80 Ma to ca. 68 Ma with decreasing depositional ages are inter- preted to reflect the southward-migrating thrust-related exhumation on the pro-wedge side of the Pyrenean orogen. The increase in lag times, from ca. 15 Ma in the Tremp Formation (ca. 65 Ma) to 28 Ma in the Escanilla Formation (ca. 40 Ma), suggests decreasing exhumation rates from 0.4 km Myr-1 to 0.2 km Myr-1. The apparent inconsistency with convergence rates is used to infer that rocks cooled at 68 Ma may have resided in the crust before final exhumation to the surface. Finally, the cooling event observed at 68 Ma provides support to the inferred acceleration of conver- gence, shortening and exhumation during Late Cretaceous times