ALBERT

Description: The strength of the crust and the mantle lithosphere are strongly influenced by the temperature, the thickness and the composition of the crust and mantle lithosphere, and by inherited weaknesses. It consequently strongly depends on the geodynamic setting and is then expected to be different from one orogen to another, which might explain the diversity of deformation styles. Here we use 2D thermomechanical models at lithospheric scale to study the effect of the strength of the upper and middle crust on the geometry of contractional systems. The role of extensional inheritance is included by forward modeling the formation of rift basin or passive margin and using the resulting extensional structure as initial condition for lithospheric scale inversion. Our results demonstrate that: 1) crustal strength strongly controls the width and the elevation of orogenic wedge; 2) relative weak crust facilitates efficient propagating of thick-skinned crustal scale thrusts; 3) contraction of a strong crust leads to the formation of long thrust sheets and an anti-formal stack in the core of the orogen or the accretion of upper crust depending on the depth of the decoupling zone in the mid crust; 4) erosion processes favor the localization of shortening in a narrow crustal orogen; 5) rifting inheritance can explain the presence at shallower depth of lower crustal or mantle material previously upwelled and facilitates the propagation of the deformation in the external part of the chain. The range of predicted behaviors is compared to first order with the Zagros, the Alps and the Pyrenees, three natural examples for which the crustal structure is well constrained by geophysical data.