Numerical simulation showing the subduction and collision stage of model GC1. The model configuration of REF at 110 Myrs serves as initial configuration for this model. At this stage, we replaced in the uppermost 5.5 km of the dry olivine rheology parameters of the exhumed mantle material with antigorite rheology parameters (mimicking serpentinites). Shortening of the basin-margin system induces a lithospheric scale shear zone that evolves into an asymmetric subduction. The serpentinites are sheared off the subducting slab and form a serpentinite subduction channel. The continental crust of the lower plate is subducted down to ca. 120 km depth. The continental upper crust of the subucting plate buckles at shallow depth and triggers extension in the upper plate. Deeply subducted continental units are exhumed as diapirs along the subduction interface. Colouring as indicated in the article.