Delamination, the foundering of the lower crust and sub-crustal lithosphere, is one of the most important geodynamic processes that is still poorly understood. Geodynamic modeling has constrained conditions and likely outcomes of delamination in orogenically-thickened crust. In this study, I do the same for delamination in extensional settings by using finite element models of young passive margins. Delamination in these models may occur as melt beneath oceanic crust intrudes between the lower continental crust and sub-crustal lithosphere, driven by buoyancy. When sufficient melt is available and the lower crust is weak, the melt wedges between the lower crust and sub-crustal lithosphere, initiating delamination of the sub-crustal lithosphere. The speed of delamination is strongly dependent on weakness of the lower crust followed by the amount of melt present.