11:00 〜 11:15
[SIT21-08] The Earth core formation process inferred from phosphorus metal-silicate partitioning
キーワード：リン、高圧、コア形成、メタル-シリケイト分配
Metal–silicate partitioning of phosphorus is key to understanding planetary core formation processes, due to its large valence and its moderately siderophile properties. At present, the mantle abundances of phosphorus vary widely among terrestrial planets, with estimates ranging from 90 ppm on Earth (McDonough, 2014 ToG) to 740 ppm on Mars (Yoshizaki & McDonough, 2020 GCA). The mantle phosphorus concentration is expected to change to a large extent depending on the conditions of core formation such as the oxidation state and the pressure-temperature at which core metals reached chemical equilibrium with silicate.
So far, however, the metal-silicate partitioning of phosphorus has been examined in limited pressure and temperature conditions (e.g., Gu et al., 2019 PEPI). The typical Earth’s core formation conditions have been estimated to be approximately 40 GPa and 3500 K on the basis of the metal-silicate partitioning of other moderately siderophile elements, such as Ni (e.g., Fischer et al., 2015 GCA, Siebert et al., 2012 EPSL), but the partitioning of phosphorus under such high pressure and temperature conditions remains unknown. The results of previous low-pressure experiments suggested the conditions of metal-silicate partitioning of phosphorus to explain its mantle abundance to be around 20 GPa and 1000 K (Siebert et al., 2011 GCA), which is very different from those constrained by other siderophile elements.
In this study, we explored the distribution of phosphorus between coexisting molten iron and silicate melts at high pressures and temperatures, approximately 3500–5000 K and 30–60 GPa, covering the conditions of Earth’s core formation based on a combination of laser-heated diamond-anvil cell experiments and chemical/textural analyses using electron microprobes and secondary ion mass spectrometry (SIMS). Our results demonstrate that phosphorus becomes more siderophile with increasing pressures. Based on these experimental data, we will present possible models of Earth’s accretion and core formation that explain phosphorus concentration in the mantle.
So far, however, the metal-silicate partitioning of phosphorus has been examined in limited pressure and temperature conditions (e.g., Gu et al., 2019 PEPI). The typical Earth’s core formation conditions have been estimated to be approximately 40 GPa and 3500 K on the basis of the metal-silicate partitioning of other moderately siderophile elements, such as Ni (e.g., Fischer et al., 2015 GCA, Siebert et al., 2012 EPSL), but the partitioning of phosphorus under such high pressure and temperature conditions remains unknown. The results of previous low-pressure experiments suggested the conditions of metal-silicate partitioning of phosphorus to explain its mantle abundance to be around 20 GPa and 1000 K (Siebert et al., 2011 GCA), which is very different from those constrained by other siderophile elements.
In this study, we explored the distribution of phosphorus between coexisting molten iron and silicate melts at high pressures and temperatures, approximately 3500–5000 K and 30–60 GPa, covering the conditions of Earth’s core formation based on a combination of laser-heated diamond-anvil cell experiments and chemical/textural analyses using electron microprobes and secondary ion mass spectrometry (SIMS). Our results demonstrate that phosphorus becomes more siderophile with increasing pressures. Based on these experimental data, we will present possible models of Earth’s accretion and core formation that explain phosphorus concentration in the mantle.