Final stages of the Variscan orogeny at the southern Iberian massif: Lateral extrusion and rotation of continental blocks

Abstract

The southern part of the Iberian Massif contains one of the sutures of the European Variscan belt. Several systems of faults and dikes appear as a result of a period of brittle deformation during the late stages of the Variscan tectonic evolution of this zone. A detailed analysis of these structures has been carried out in this work. Four successive deformation phases have been identified: a first strike-slip normal faulting stage, a transcurrent stage, a second strike-slip normal faulting stage, and, finally, a thrusting stage. The age of these phases vary between around 310 Ma and less than 270 Ma. The computed trajectories of the deformation axes show a progressive anticlockwise rotation of around 90°. These data, together with the results of previous geological and geophysical studies of this zone and of the Variscan belt as a whole, lead us to propose a model of tectonic evolution for the last stages of the Variscan collision. Comparison with modern examples of collisional belts and with the results of analog experiments suggests that a promontory of the continental lithosphere of the downgoing plate indented against the active continental margin of the upper plate. The indenter suffered an intense deformation, in accordance with the predictions of some recent analog models simulating the indentation of a four-layer continental lithosphere. The Variscan and Late Variscan brittle deformation episodes represent the waning stages of the Variscan collision, and not an independent tectonic event.