Melting of MORB at core-mantle boundary

- Partial melting of natural basalt is investigated in laser heated diamond anvil.
- The melting sequence and melt composition are examined by TEM.
- At CMB, the solidus temperature is found to be 3970(±150)K.
- Calcium Perovskite is the liquidus phase.
- The partial melt enriched in FeO indicates gravitational stability at CMB.

We investigated the melting properties of natural mid-ocean ridge basalt (MORB) up to core-mantle boundary (CMB) pressures using laser-heated diamond anvil cell. Textural and chemical characterizations of quenched samples were performed by analytical transmission electron microscopy. We used in situ X-ray diffraction primarily for phase identification whereas our melting criterion based on laser power versus temperature plateau combined with textural analysis of recovered solidus and subsolidus samples is accurate and unambiguous. At CMB pressure (135 GPa), the MORB solidus temperature is 3970(±150)K. Quenched melt textures observed in recovered samples indicate that CaSiO3 perovskite (CaPv) is the liquidus phase in the entire pressure range up to CMB. The partial melt composition derived from the central melt pool is enriched in FeO, which suggests that such melt pockets may be gravitationally stable at the core mantle boundary.