Lithospheric-scale structures from the perspective of analogue continental collision

Analogue models were employed to investigate continental collision addressing the roles of (1) a suture zone separating different crustal blocks, (2) mid-crustal weak layers and (3) mantle strengths. These models confirmed that low-amplitude lithospheric and crustal buckling is the primary response to shortening with a wavelength mainly controlled by the strong upper crust and/or lithospheric mantle. With increasing shortening, bivergent thrusts formed across the brittle layers (equivalent to upper crust) at inflection points of the buckles while ductile layers (lower crust and mantle) continued being folded. The resulting geometries displayed pop-ups and pop-downs above the boundaries (sutures) between blocks. Further shortening led to wider, thrust-bounded deformation zones (Σ-belts) in front of the stronger blocks identified as “effective indenters”. During shortening upward extrusion into Σ-belts allowed exhumation of deep material. Weak layers enhanced strain localisation. These modelling results have similarity in large-scale structures of modern orogens and are relevant to the understanding of natural collisional processes.