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

Constraining 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 310320 similar to Ma, indicating a primary contribution from Variscan granites of the central Pyrenean Axial Zone. A secondary population at 450600 similar to 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.similar to 241 similar to Ma, corresponding to denudation coeval with the initiation of Atlantic rifting. An Early Cretaceous cooling event at ca.similar to 133 similar to Ma appears consistent with rift-related exhumation and thermal overprint on the Iberian margin. The (U-Th)/He age peaks from ca.similar to 80 similar to Ma to ca.similar to 68 similar to Ma with decreasing depositional ages are interpreted 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 similar to Ma in the Tremp Formation (ca.similar to 65 similar to Ma) to 28 similar to Ma in the Escanilla Formation (ca.similar to 40 similar to Ma), suggests decreasing exhumation rates from 0.4 similar to km similar to Myr1 to 0.2 similar to km similar to Myr1. The apparent inconsistency with convergence rates is used to infer that rocks cooled at 68 similar to Ma may have resided in the crust before final exhumation to the surface. Finally, the cooling event observed at 68 similar to Ma provides support to the inferred acceleration of convergence, shortening and exhumation during Late Cretaceous times.