Interaction of two successive Alpine deformation fronts: constraints from low-temperature thermochronology and structural mapping (NW Iberian Peninsula)

The lateral termination of the Alpine-Pyrenean Orogen relief onshore is located in the NW Iberian Peninsula. It overlies a Variscan basement (Iberian Massif), where the sedimentary record of the Alpine tectonic is very scarce. Thus, the characterisation of the tectonic evolution of the lateral termination is difficult and timing and geometries of the main tectonic structures remain unclear. Combining the tectonothermal histories obtained by modelling of the apatite fission-track data (AFT) with structural mapping allows for a comparative study of the different tectonic scenarios and deformation transfer in the lateral termination of an orogen. AFT ages for the studied area vary from 53.5 ± 12.9 and 222 ± 12 Ma (from Late Triassic to Early Eocene). The beginning of the Cenozoic cooling episodes is in agreement with the infilling of the Tertiary basins (Late Eocene or Oligocene). Calculated uplift for the Alpine Orogeny is around 2,400 m. The Cantabrian Mountains were uplifted and emplaced southwards and the main period of exhumation began in the Palaeogene at rates of ~0.02 mm/a and continued during the Neogene at rates of ~0.06 mm/a. However, the Galaico-Leoneses Mountains, located to the south of the studied area, were uplifted and emplaced northwards during the Neogene, showing more rapid uplift rates of ~0.08 mm/a, suggesting that the western termination of the Alpine-Pyrenean Orogen relief is the result of the successive interaction of two Alpine deformation fronts.