Analogue modelling of brittle shear zone propagation across upper crustal morpho-rheological heterogeneities

Crustal shearing of pre-tectonic weak bodies (e.g. salt pillows, igneous pockets) associated with basement strike-slip fault systems is common in nature. Yet the structural pattern arising from the interference between a brittle shear zone and such weak rheological heterogeneities is still not fully explained. In the present work, different sand-box analogue modelling experiments were carried out to better understand, not only the shear zone perturbation effect caused by a strictly rheologic (viscous-weak) anomaly, but also the one arising from a combined morphological perturbation (i.e. traverse topographic crest). Obtained results show that the development of different shear zone deformation patterns is in each case essentially determined by the interplay between: (i) ductile wrenching strain accommodation in the (viscous) weak body; and (ii) coincidence vs. mismatch between main brittle-viscous rheological boundaries and (crest-related) topographic steps. Comparison of the experimentally obtained results with complying natural examples is further discussed, and essentially focused on the NE Atlantic tectono-magmatic interference between the Gloria transform fault and the Tore-Madeira submarine ridge.