[1] Understanding the three-dimensional (3D) dynamics of subduction-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-trench variations. High resolution thermo-mechanical numerical models, encompassing experimentally-derived flow laws and a pseudo free surface, are employed to unravel lithospheric and topographic evolutions. Firstly, we consider coeval subduction of adjacent continental and oceanic lithospheres (SCO). This configuration yields to two-stage slab detachment during collision, topographic buildup and extrusion, variable along-trench convergence rates and associated trench deformation. The second setting considers a convergent margin, which is laterally limited by a transform boundary (STB). Such collisional system is affected by a single slab detachment, little trench deformation and moderately confined upper plate topography. The effect of initial thermal slab age on SCO and STB models are explored. Similarities with natural analogues along the Arabia-Eurasia collision are discussed.