A comparison of numerical and analogue models of subduction initiation at passive margins.

Modelling studies show that subduction initiation requires failure of the load-bearing crustal and mantle layers and critically depends on the buoyancy and strength contrast within the lithosphere. Such findings suggest that the probability of subduction initiation must increases in the vicinity of continental margins. Yet, direct evidence for subduction initiation at passive margin is scarce and the mechanisms of subduction initiation in this particular setting remains a recurrent and long-standing unresolved question. Therefore, our study focuses on the kinematic and rheologic key parameter combinations relevant for the formation of a subduction zone, with the aim of identifying the feasibility of subduction initiation at a passive margin setting. To challenge the existing limits and discriminate processes that fit conditions for subduction nucleation, we compare and combine analogue and numerical modelling techniques. In this work, numerical modelling allows exploring temperature driven feedback mechanisms whereas analogue modelling allows for mapping characteristic length scales of deformation against the mode of subduction initiation. Overall, model results highlight that the convergence rate, the strength contrast at the margin as well as the degree of crust-mantle coupling control the development of a shear zone at the base of the crust, and the propagation of deformation into the mantle lithosphere. In addition, comparison between analogue and numerical modelling results infers that shear heating, weak sediments, magmatic heterogeneities or a serpentinite mantle wedge, are important parameters for the development of a self-sustaining subduction zone. The relevance of the modelling results is demonstrated by comparing length-scales of deformation with observations from inverted continental passive margins and orogenic systems, such as the Alps and Dinarides. Models predict that primary response of the lithosphere to compression is by folding and that tectonic structures and early-stage length-scales of deformation can be used to predict the likeliness of subduction initiation at a passive margin.