Paleogene propagation of the southern Pyrenean thrust wedge revealed by finite strain analysis in frontal thrust sheets: Implications for mountain building

To better evaluate the sequence of shortening and estimate shortening rates associated with the propagation of the southern Pyrenean front, we propose an original approach based on the reconstruction of finite displacement and finite vertical-axis rotations. This study is based on the quantitative analysis of published datasets including balanced cross-sections, paleomagnetic and thermochronologic data. We distinguish three main episodes of shortening between 41 and 37 Ma, 37 and 30 Ma and between 30 and 16 Ma. They are associated with a decrease of accretionary rates from ~ 3 km/Ma to 0.39 ± 0.27 km/Ma on the pro-wedge side of the Pyrenean orogenic wedge. Based on the comparison between frontal accretionary flux and outcoming fluxes in the Axial Zone of the Pyrenees, we show that the period ranging from 37 to 30 Ma recorded a remarkable increase in erosion that is not compensated by accretion in the wedge. In the context of the overall decrease in the Iberia/Eurasia plate convergence, we suggest that the main cause of the acceleration of erosion on top of the growing Pyrenean orogen is related to climate changes that occurred at the Eocene–Oligocene boundary.