On the global geodynamic consequences of different phase boundary morphologies

Abstract. Phase transitions can influence mantle convection patterns, inhibiting or promoting vertical flow. One such transition is the ringwoodite-to-bridgmanite plus periclase transition, which has a negative Clapeyron slope and therefore reduces mantle flow between the upper and lower mantle. Interactions between different transitions and significant Clapeyron slope curvature can potentially result in complexities in mid-mantle geodynamics – affecting the stagnation of slabs and free upward motion of plumes. Here, we consider two examples where non-linear phase boundary morphologies have been invoked to explain mid-mantle dynamics: (1) the intersection of the ringwoodite-to-bridgmanite plus periclase transition with the bridgmanite-to-akimotoite and ringwoodite-to-akimotoite plus periclase transitions, forming a “branching” morphology, and (2) the curvature of the garnet-to-bridgmanite transition. Using simple mantle convection or circulation simulations, we find that the dynamic impact of these example phase transitions is limited by either the uniqueness of thermodynamic state or the low magnitude of the phase buoyancy parameter respectively. Therefore it is unlikely that these phase boundary morphologies will, by themselves, prevent material exchange across the mid-mantle.