Mantle unrooting in collisional settings

We present a two-dimensional numerical model to study the thermo-mechanical evolution of the lithosphere under a convergence regime in order to define the conditions that lead to lithospheric mantle break-up and consequent unrooting. A Newtonian rheology with a temperature-dependent viscosity is considered. The system is not closed and horizontal flow through lateral boundaries is permitted. A horizontal velocity is imposed at the top of the model to simulate compression, whereas velocity vanishes at the bottom of the model. The initial conditions correspond to a homogeneous lithosphere with a constant heat production in the crust. The analysis of variations of maximum shear stress, strain rate, and total kinetic energy allowed us to define four major stages during the mantle unrooting process: orogenic growth, initiation of gravitational instability until lithospheric failure, sinking of the detached lithosphere, and relaxation of the system. Numerical results also show that the conditions for lithospheric unrooting strongly depend on the convergence velocity, the wideness of the deformation zone, and the imposed rheology.