PALAEO-ELEVATION AND EFFECTIVE ELASTIC THICKNESS EVOLUTION AT MOUNTAIN-RANGES - INFERENCES FROM FLEXURAL MODELING IN THE EASTERN PYRENEES AND EBRO BASIN

The results are presented of a two-dimensional flexural modelling stud y of the lithosphere underlying the southern Pyrenees and the Ebro Bas in. The modelling is based on a crustal-scale balanced cross-section a long a profile through the north-eastern part of the Iberian plate. Tw o time slices of the structural evolutions of the mountain chain are m odelled: the present day configuration and the configuration at Middle Lutetian time (47 Ma), where important structural and sedimentologica l changes are observed. The flexure model incorporates lateral variati ons in the effective elastic thickness (EET) of the lithosphere. The p resent day deflection in the profile is simulated using boundary force s 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 north ern part of the profile, assuming that the EET at the distal margin of the Ebro Basin has not significantly changed since Middle Lutetian ti mes. 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 decr easing rigidity is predominantly related to the Pyrenean collision. Fl exural 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 sin ce Middle Lutetian times, the model predicts a maximum palaeo-elevatio n of similar to 2000 m, which is in agreement with geological observat ions concerning the relation between basin-fill and palaeo-elevation.