Lithosphere delamination in continental collisional orogens: A systematic numerical study

Lithosphere delamination is believed to have played a major role in mountain building; however, the mechanism and dynamics of delamination remain poorly understood. Using a 2-D high-resolution thermomechanical model, we systematically investigated the conditions for the initiation of lithosphere delamination during orogenesis of continental collision and explored the key factors that control the various modes of delamination. Our results indicate that the negative buoyancy from lithosphere thickening during orogenesis could cause delamination, when the reference density of the lithospheric mantle is not lower than that of the asthenosphere. In these cases, compositional rejuvenation of depleted continental lithosphere by magmatic/metasomatic plume- and/or subduction-induced processes may play crucial roles for subsequent lithosphere delamination. If the reference density of the lithospheric mantle is less than that of the asthenosphere, additional promoting factors, such as lower crust eclogitization, are required for delamination. Our numerical simulations predict three basic modes of lithosphere delamination: pro-plate delamination, retro-plate delamination, and a transitional double-plates (both the pro-plate and retro-plate) delamination. Pro-plate delamination is favored by low convergence rates, high lithospheric density, and relatively strong retro-plate, whereas retro-plate delamination requires a weak retro-plate. The Northern Apennines and Central Northern Tibetan Plateau are possible geological analogs for the pro-plate and retro-plate delamination modes, respectively. Our model also shows significant impact of delamination on the topographic evolution of orogens. Large-scale lithosphere delamination in continental collision zones would lead to wide and flat plateaus, whereas relatively narrow and steep mountain belts are predicted in orogens without major delamination.