Palaeo-elevation and effective elastic thickness evolution at mountain ranges: inferences from flexural modelling in the Eastern Pyrenees and Ebro Basin

Abstract

The results are presented of a two-dimensional flexural modelling study of the lithosphere underlying the southern Pyrenees and the Ebro Basin. The modelling is based on a crustal-scale balanced cross-section along a profile through the north-eastern part of the Iberian plate. Two time slices of the structural evolutions of the mountain chain are modelled: the present day configuration and the configuration at Middle Lutetian time (47 Ma), where important structural and sedimentological changes are observed. The flexure model incorporates lateral variations in the effective elastic thickness (EET) of the lithosphere. The present day deflection in the profile is simulated using boundary forces and a northward decreasing EET that varies from 30 to 11 km. Models for Middle Lutetian times indicate EET values of 26-18 km in the northern part of the profile, assuming that the EET at the distal margin of the Ebro Basin has not significantly changed since Middle Lutetian times. These higher values for the EET at Middle Lutetian times suggest that the effect of the Cretaceous extensional phase on the present day flexural rigidity is small and, therfore, the inferred northward decreasing rigidity is predominantly related to the Pyrenean collision. Flexural modelling provides also constraints for the palaeo-elevation of the inner part of the chain. Including the assumption that the EET at the distal margin of the Ebro Basin has not significantly changed since Middle Lutetian times, the model predicts a maximum palaeo-elevation of ∼2000 m, which is in agreement with geological observations concerning the relation between basin-fill and palaeo-elevation.