Deformation of bimineralic materials: the effect on extensional processes at lithospheric scale

In the last few decades, numerous numerical studies demonstrated that the relative strength of frictional plastic and viscous materials in the crust provides a first-order control on the deformation processes in divergent and convergent settings. Most rocks are polymineralic; however, rheologies in a majority of lithospheric scale models approximate the mechanical behavior of the crust and mantle as monomineralic materials composed of wet or dry, plagioclase, quartz or olivine. This approach presumes that the deformation mechanisms of the crust or mantle are either brittle (elastoplatic) or ductile (viscous) and neglects the semi-brittle behavior observe on the field at the scale of the rock or the outcrop. Here, using a numerical modelling approach, we demonstrate that in bimineralic materials the deformation localization is strongly dependent on the mechanical behavior of the two phases, the proportion, and the strength contrast between them. If these parameters vary at the scale of a rock sample, they also vary at lithospheric scale when units with different lithologies are juxtaposed leading to a strongly heterogeneous crust and mantle. In a second part, this contribution discuss therefore the effect of bimineralic composition, assimilated to compositional and structural inheritances on extensional processes at lithospheric scale.