MANTLE PLUME INTERACTION WITH AN ENDOTHERMIC PHASE-CHANGE

High spatial resolution numerical simulations of mantle plumes impingi ng from below on the endothermic phase change at 660-km depth are used to investigate the effects of latent heat release on the plume-phase change interaction. Both axisymmetric and planar upflows are considere d, and the strong temperature dependence of mantle viscosity is taken into account. For plume strengths considered, a Clapeyron slope of -4 MPa K-1 prevents plume penetration of the phase change. Plumes readily penetrate the phase change for a Clapeyron slope of -2 MPa K-1 and ar rive in the upper mantle considerably hotter than if they had not trav ersed the phase change. For the same amount of thermal drive, i.e., th e same excess basal temperature, axisymmetric plumes are hotter upon r eaching the upper mantle than are planar upwellings. Heating of plumes by their passage through the spinel-perovskite endothermic phase chan ge can have important consequences for the ability of the plume to the rmally thin the Lithosphere and cause melting and volcanism.