Antoine Auzemery and his colleagues tell us about strain localisation for SZI at passive margins:
"It is widely accepted that subduction zone initiation critically depends on the buoyancy and strength of the oceanic lithosphere but it still unclear where and how subduction zones initiate. Therefore, our combined analogue and numerical modelling study provides new insights on the rheologically-controlled mechanisms responsible for the locus of subduction zones. We infer that the locus of subduction is controlled by the rheology of both the crust and the mantle lithosphere at the margin, which is in strong correlation with the thermal age of the oceanic lithosphere. Suitable conditions for subduction zone initiation at passive margins correspond to an intermediate age (ca. 80 Myr) of the margin lithosphere. In all other cases deformation localizes within the oceanic lithosphere or affects the entire continent. We advocate the significance of crust-mantle coupling and weakening mechanisms taking place in the mantle lithosphere such as shear heating and Peierls mechanism."
Auzemery et al. (2020, Global and Planetary Change)