Strain localization during compression of a laterally heterogeneous lithosphere

First order large scale stress fields, associated with active plate tectonic processes, interact with lateral heterogeneities in the lithosphere and generate strain redistribution (Zoback, 1992). Despite the strength of the continental lithosphere is mainly controlled by its depth dependent rheological structure, continents are often the product of the assemblage of domains that suffered different tectonic processes, resulting in lateral changes in composition and thermal structure (Ranalli, 1997; Audet & Burgmann, 2011). Numerous modelling studies investigated the localization of deformation in compressional settings in case of lithospheric weak zones flanked by stronger domains (Cruden et al., 2006; Cerca et al., 2004; Willingshofer et al., 2005). We present a series of lithospheric-scale analogue models designed to investigate strain redistribution resulting from the presence of a stronger rheological heterogeneity embedded in a weak lithosphere. Among the investigated parameters, convergence velocity and thickness of the upper brittle mantle are varied, both playing an important role in the crust-mantle coupling. Furthermore, we examined different orientations of the rheological boundaries with respect to the convergence direction, since reactivated lithosphere heterogeneities are often observed to strike oblique with respect to the main horizontal stress field. Preliminary experimental results indicate that the presence of a strong lithospheric domain induces strong localization of deformation at the rheological boundaries, with associated high relief build-up. Strain rate governs the geometry of the deep lithospheric structure, as well as the dip direction of the main underthrusting plane. The presented results provide valuable insight for strain localization in collisional settings under various rheological and geometrical configurations.