10:45 AM - 12:15 PM
[SIT18-P03] 3D distribution of FeS melt in orthopyroxene mantle: Implication to core segregation in planetesimals
Keywords:Core formation, planetesimal, high pressure
Based on the Hf-W chronology, it is reported that rapid core formation occurred in planetesimals within 1-2 Myr after CAI formation (Spitzer et al. 2021). Wetting property of iron-alloy melts in silicate mantle minerals plays an key role for the core formation process in small bodies. In our previous study, we reported that dihedral angles between FeS melt and Opx was below 60° at the pressure below 1.0-1.5 GPa. In this study, to obtain the permeability of FeS melt which is closely related to the melt segregation speed, we carried out 2D and 3D textural observations of the FeS-Opx mixture samples performed at planetesimal interior conditions. We evaluated the effect of pressure on the FeS melt distribution in Opx matrices.
High pressure and temperature experiments were carried out using piston cylinder apparatus. Powder mixtures of FeS and synthetic Opx (Fe#=0.23-0.30) was used as starting material. The sample was enclosed into graphite capsule. The experiments were performed at 0.5-2.5 GPa and 1523 K for 12 hours. 2D and 3D textural observations of the recovered samples were carried out using scanning electron microscope and X-ray computed tomography (CT), respectively. X-ray CT was performed at The University of Edinburgh. Conical X-ray beam setup was used for CT. Projection images were collected at 0-360° with an angle step of 0.18° and voxel sizes were 3.3-3.7 μm.
From X-ray CT images, FeS melts in Opx matrices showed elongated and connected texture at 0.5 GPa whereas FeS melts changed to spherical shape and scattered at 2.5 GPa. These textures and that from SEM indicate that FeS melt forms interconnected networks in Opx grain boundaries at lower pressures while FeS melts were located as isolated pockets at the grain boundaries at higher pressures. Based on the obtained textures, we estimated permeability of FeS melt and discuss the melt segregation speed in planetesimals.
High pressure and temperature experiments were carried out using piston cylinder apparatus. Powder mixtures of FeS and synthetic Opx (Fe#=0.23-0.30) was used as starting material. The sample was enclosed into graphite capsule. The experiments were performed at 0.5-2.5 GPa and 1523 K for 12 hours. 2D and 3D textural observations of the recovered samples were carried out using scanning electron microscope and X-ray computed tomography (CT), respectively. X-ray CT was performed at The University of Edinburgh. Conical X-ray beam setup was used for CT. Projection images were collected at 0-360° with an angle step of 0.18° and voxel sizes were 3.3-3.7 μm.
From X-ray CT images, FeS melts in Opx matrices showed elongated and connected texture at 0.5 GPa whereas FeS melts changed to spherical shape and scattered at 2.5 GPa. These textures and that from SEM indicate that FeS melt forms interconnected networks in Opx grain boundaries at lower pressures while FeS melts were located as isolated pockets at the grain boundaries at higher pressures. Based on the obtained textures, we estimated permeability of FeS melt and discuss the melt segregation speed in planetesimals.