Scaled analogue modelling of syn-orogenic, extensional fault systems

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Crustal-scale extension is inferred to occur during convergence in several orogens. This type of extension may not lead to a net thinning of the crust and therefore, isostatically-driven uplift of the footwall may not occur. Hence, the geometry of the footwall and its exhumation may differ from those of purely extensional systems. Boundary conditions inferred for the Tertiary Alpine extensional systems are used to simulate syn-contractional faulting in analogue experiments scaled for density and viscosity. During these experiments, a 4-layered orogenic zone will be differentially thickened by indentation of rigid bodies with various shapes. The rheological layering of the orogenic zone will be modified from one experiment one experiment to the other in order to test the effect of a strong vs. weak mantle on the initiation and style of extension. Serial cross sections of the models, made at different increments of deformation, will show the evolution of the 3-D structure of a syn-orogenic extensional system through time.