Phase boundaries in finite amplitude mantle convection

Summary. Phase boundaries are included in dynamical finite element models of mantle convection. They are represented by point chains which act as additional sources of buoyancy forces when distorted, and as additional source or sink of heat. The influence of the exothermic olivine-spinel transition is studied in both shallow and deep convection models. The flow is only slightly enhanced by the transition. The increase of temperature due to latent heat release is step-like in the deep model, in the case of shallow convection it is more diffuse. Other quantities like ocean-floor topography, gravity anomalies, and stress distribution are no more than moderately affected. In a further investigation the effect of spinel post-spinel transition, whether endothermic or exothermic, on deep convection is examined. The effect on the flow is negligibly small in both cases.