Host: The Japanese Association of Mineralogists, Petrologists and Economic Geologists
The density of a FeO-rich peridotite melt was measured from 6.0 to 15.7 GPa by the buoyancy test. The chemical composition of the peridotite was the same as that of a model Martian mantle (SPB). Sinking and flotation of the diamond were observed at 13.8 and 14.5 GPa, respectively. The experiments using olivine as the buoyancy marker showed that the density crossover between the SPB melt and the equilibrium olivine (Fo89) exists at 9 GPa, which corresponds to a depth of 700 km in Mars's interior.
The melting phase relation of the SPB composition was also determined up to 14.0 GPa. The liquidus phase was olivine up to 10.0 GPa and was substituted to garnet between 10.0 and 14.0 GPa. Since the density of garnet is higher in the Martian mantle condition, the liquidus garnet can be fractionated in the globally molten Martian mantle. On the other hand, olivine can be suspended around a depth of 700 km by its neutral buoyancy.
The present study implies that olivine segregated in the bottom of the magma ocean and formed the olivine-rich layer in the Martian mantle, and that this layer can be a source region of the shergottite parental magma.
