11:30 AM - 11:45 AM
[SIT21-10] Constraint on the condition of core melt segregation in pyroxene mantle of planetary embryo
Keywords:Core formation, planetesimal, asteroid, iron-alloy, liquid
It has recently been reported that planetesimals experienced the core-mantle differentiation within first million years after the formation of the solar system (Kruijer et al. 2014). Since planetesimals and planetary embryos are direct building blocks of the terrestrial planets, interior structures of these small bodies are closely linked to planet interiors. Wetting property of iron-alloy melts in silicate mantle minerals controls core formation process in these small bodies. Major mantle minerals in these bodies are olivine and orthopyroxene (opx). Wetting property between Fe–S melt and olivine has been reported (e.g., Minarik et al. 1996, Gaetani and Grove 1999, Terasaki et al. 2005, 2008), while that between the melt and opx are not well known. In some primitive achondrite, opx is reported to be abundant (more than 53 vol%) (Zeng et al. 2019). In this study, we measured dihedral angle between Fe–S melt and opx at 0.5–2.5 GPa and consider the core formation process in opx mantle of planetesimals and planetary embryos.
Starting material was composed of a powder mixture of Fe–S (S=40,50 at%) and synthesis opx (Fe#=0.23-0.30). The sample powder was enclosed into graphite capsule. High pressure and high temperature experiments were performed at 0.5–2.5 GPa and 1474–1523 K using the piston cylinder and multi-anvil apparatus. Duration time of the experiment was 12 h. Textural observation and chemical analysis of the recovered samples were carried out using SEM-EDS and electron microprobe.
Measured dihedral angle between Fe–S melt and opx ranges 54–102o. Interconnected networks of Fe–S melt were observed in opx grain boundaries up to around 1.0–1.5 GPa, whereas Fe–S melt was isolated above these pressures. This behavior is closely related to the variation of melt composition with pressure. Based on the present results, percolative core formation in the opx mantle could occur in the interior of relatively small bodies (R~800 km).
Starting material was composed of a powder mixture of Fe–S (S=40,50 at%) and synthesis opx (Fe#=0.23-0.30). The sample powder was enclosed into graphite capsule. High pressure and high temperature experiments were performed at 0.5–2.5 GPa and 1474–1523 K using the piston cylinder and multi-anvil apparatus. Duration time of the experiment was 12 h. Textural observation and chemical analysis of the recovered samples were carried out using SEM-EDS and electron microprobe.
Measured dihedral angle between Fe–S melt and opx ranges 54–102o. Interconnected networks of Fe–S melt were observed in opx grain boundaries up to around 1.0–1.5 GPa, whereas Fe–S melt was isolated above these pressures. This behavior is closely related to the variation of melt composition with pressure. Based on the present results, percolative core formation in the opx mantle could occur in the interior of relatively small bodies (R~800 km).