10:45 〜 12:15
[SIT18-P02] The effect of porosity on FeS melt migration in orthopyroxene mantles in planetesimals
キーワード：core formation、planetesimal、melt migration
To understand material distributions in the interior of terrestrial planets, it is important to have information on interior process of planetesimals which are direct building blocks of terrestrial planets. Core formation in planetesimals likely occurred within 1–2 Myr after CAI condensation in the early solar system (Spitzer et al., 2021), and probably occurred within solid mantles of bodies, based on abundance of short-lived radionuclide 26Al in ordinary chondrites (e.g., Yoshino et al., 2003). The major mantle minerals of planetesimals are reported to be olivine and orthopyroxene (Opx) (Vernazza et al., 2016), and meteorite studies suggest that there is a large range of porosity (5–30 %) in planetesimal-sized bodies (Flynn et al., 1999). The wetting properties of Fe–S melt in these mantle minerals has been studied and it is reported that Fe–S melt could form an interconnected network in mantle minerals at the conditions of planetesimal interiors (Terasaki et al., 2008, Miura et al., 2021). However, temporal melt variation and the effect of sample porosity on the melt percolation remain unknown. In this study, we examined the percolation of FeS melt in polycrystalline Opx under planetesimal interior conditions, and investigated the effects of duration time and initial porosity on the percolation of FeS melt.
The starting Opx with a composition of (Mg0.7Fe0.3)SiO3 was synthesized in a gas-mixing furnace. To study the effect of initial porosity, either Opx powder pellets or sintered Opx was used. In percolation experiments, the FeS sample was sandwiched by Opx layers. High pressure experiments were carried out using a piston-cylinder device. The experiments have been performed at 1250 ℃ and 0.75 GPa for 15–60 minutes duration. Textural observations of recovered samples were carried out using SEM/EDS and X-ray CT.
Based on textural observations using SEM and X-ray CT, FeS melt formed interconnected networks and percolated in Opx grains at 0.75 GPa regardless of initial porosity. Both migration distance and melt fraction tend to increase with increasing duration time. In the sample with larger initial porosity, melt migration distance was larger resulting in smaller melt fractions within Opx matrices. This suggests that melt migration is likely to proceed more effectively in the mantle with larger porosity.
The starting Opx with a composition of (Mg0.7Fe0.3)SiO3 was synthesized in a gas-mixing furnace. To study the effect of initial porosity, either Opx powder pellets or sintered Opx was used. In percolation experiments, the FeS sample was sandwiched by Opx layers. High pressure experiments were carried out using a piston-cylinder device. The experiments have been performed at 1250 ℃ and 0.75 GPa for 15–60 minutes duration. Textural observations of recovered samples were carried out using SEM/EDS and X-ray CT.
Based on textural observations using SEM and X-ray CT, FeS melt formed interconnected networks and percolated in Opx grains at 0.75 GPa regardless of initial porosity. Both migration distance and melt fraction tend to increase with increasing duration time. In the sample with larger initial porosity, melt migration distance was larger resulting in smaller melt fractions within Opx matrices. This suggests that melt migration is likely to proceed more effectively in the mantle with larger porosity.