In this paper we apply a material model used for years in the engineering community to simulate deformation and failure of metal components to the problem of deformation of silicate minerals in the earth’s mantle. Known as the Bammann inelastic internal state variable (BIISV) model, this formulation utilizes not only the current state (e.g., temperature, density, stress) of each material parcel to compute the current deformation rate, but it also carries along features (internal state variables) that describe the parcel’s deformational history. This history information allows the model to represent more complex modes of material deformation than models which do not include such information. This study reveals for the first time that a type of solid-state plastic deformation known as dislocation glide may well be the crucial mechanism responsible for buoyancy-driven runaway in the mantle of a planet with a mass and gravity field like that of the earth. To explore the tendency for runaway behavior we applied a 2D Cartesian version of the finite element TERRA mantle dynamics program that includes the BIISV model. We obtain BIISV parameters appropriate for the earth’s mantle from experimental measurements of the material properties of the upper mantle rock lherzolite. We find that buoyancy anomalies of plausible size yield spectacular runaway behavior when the dislocation glide mechanism is enabled.
