Density of basaltic melt at high pressure and stability of the melt at the base of the lower mantle

We made density measurements of model MORB and picritic melts up to about 15 GPa using the floating diamond method. The compression behavior of the melts is fitted by the Vinet equation of state and extrapolated to higher pressure. A density crossover between the MORB melt and the mantle peridotite is suggested at the base of the lower mantle. Thus, the ultra-low velocity zone in the D″ layer may be explained by the existence of gravitationally stabilized basaltic melt formed by melting of the accumulated slab materials. This region might become unstable due to progressive melting of slab materials and/or supply of volatiles.