Cainozoic deformation of Iberia: a model for intraplate mountain building and basin development based on analogue modelling

Abstract

The present study provides new insights into the processes of mountain building that occur in plate interiors like Iberia. Laboratory experiments display the effect of boundary conditions represented by lateral variations of lithosphere strength and pre-existent tectonic structures in Iberia (cross-cutting the entire continental crust) on the mode of lithosphere deformation during N-S convergence. Under such a stress field, strain partitioning appears to influence the orientation of mountain ranges through the reactivation of pre-existent faults. Moreover, these faults also may have influenced the wavelength of folding. However, the observed differences in topography from west to east Iberia can also be related to the rheological stratification of the lithosphere and its thermo-mechanical state; i.e. vertical lithosphere de-coupling. The strength of the lithosphere, governed by variations in temperature and composition changes its mechanical properties and, therefore, controls the wavelength of deformation. These differences influenced the mode of strain transfer from plate boundaries to plate interiors and affect the mechanisms of deformation of the lithosphere (i.e. folding versus thickening). The thermal age of the Iberian lithosphere (between 300 Ma and 150 Ma) has predominantly controlled the present-day configuration of mountain ranges during the Cainozoic episode of continental convergence. As a result, periodic (50km to 250 km wavelength) topographic highs evolved under the control of large-scale folds developed during N-S convergence. These folds may also have controlled the high elevation of the Duero basin (≈900m) and the general tilting of Iberia towards the southwest. The spectral analysis carried out for other intra-plate domains like the Moroccan Atlas or Central Asia with similar lithosphere tectono-thermal ages show close similarities with the topographic wavelengths found in Iberia. Therefore, intra-plate mountain building process in Iberia entails folding of the entire lithosphere supported by analogue, and gravity models