Résumé
Mantle plumes are traditionally proposed to play an important role in lithosphere erosion. Seismic images beneath Hawaii and Cape Verde show a lithosphere-asthenosphere-boundary (LAB) up to 50 km shallower than the surroundings. However, numerical models show that unless the plate is almost motionless in a hotspot reference frame the thermo-mechanical erosion of the lithosphere does not exceed 30 km. We propose to further investigate this process, focusing on the role of partial melting on the plume-lithosphere interaction, by using a 2D petrological-thermo-mechanical numerical model based on a finite-difference method on a staggered grid and marker in cell method. A homogeneous peridotite composition is used to represent the plate and the underlying mantle. The lithosphere-asthenosphere boundary initially follows the half-space cooling model and we impose a constant velocity at top of the plate. We modeled plumes as a thermal anomaly on the base of the model (700 km) in a mantle deforming by diffusion creep. Partial melting is estimated using batch melting curves for anhydrous melting as a function of pressure. The effect of progressive depletion of the residue on melt production is accounted for by considering the difference between the instantaneous melt fraction and the cumulated one. The effect of partial melting on the viscosity of the sub-lithospheric mantle is modeled using an experimentally-determined flow law for partially molten peridotite, in which the viscosity depends exponentially on melt fraction, pressure, and temperature. The impact of a plume beneath the lithosphere leads to thermal rejuvenation of the lithosphere by favoring small-scale convection in the plume-fed low-viscosity layer at the base of the lithosphere. In absence of melt extraction, partial melting leads to an additional viscosity decrease and more effective erosion, but upwelling of the 1200 degrees C isotherm does not exceeds 35 km. In models with full melt extraction, instantaneous melt fractions are too low (< 1%) to significantly reduce the viscosity at the LAB and the lithosphere erosion is similar to results obtained without considering the influence of melting. Ongoing developments of the models to better represent the effect of melting on the lithosphere erosion atop a plume are: considering the effect of latent heat of melting/crystallization and the changes in density of both the solid residue and the partial molten peridotites.