14:15 〜 14:30
[SIT16-03] High-Pressure Experiments on Fe3S2 and Fe2S and the Phase Diagram of the Fe-FeS System under Martian Core Conditions
キーワード：火星、惑星核、硫化鉄、X線回折、ダイヤモンドアンビルセル
The observations of “Marsquakes” by NASA’s InSight spacecraft provided valuable information on the Mars’s internal structure, including the core size and composition. The data[1] show a larger radius (=low density) of the Martian core than previous estimates, suggesting the presence of larger amounts of light elements, such as >20 wt% S. Even more recent structural models considering a molten silicate layer above the core require >17 wt% S[2]. Therefore, melting phase relations in the S-rich portion of the Fe-FeS system are of importance to discuss and predict the Martian solid inner core. While Fei et al. (2000)[3] reported the phase diagram over the entire Fe-FeS system at 21 GPa, the liquidus phase relations at ~40 GPa corresponding to the pressure at the Mars’ center have been examined only in the Fe-rich portion between Fe and Fe3S (0–16.1 wt% S)[4].
Here we performed high-pressure experiments on Fe3S2 (subsolidus) and Fe2S (subsolidus and melting) between ~30 and ~70 GPa with laser-heated diamond-anvil cell (DAC) techniques at a synchrotron facility, SPring-8. The Fe3S2 and Fe2S samples were synthesized by a multi-anvil press before the DAC experiments. The X-ray diffraction measurements demonstrated that Fe3S2 decomposes into Fe12S7 and FeS above ~30 GPa. We also found that Fe2S melted incongruently to liquid + Fe12S7. Both suggest that Fe12S7 (Fe + 25.1 wt% S) is an important iron sulfide having a liquidus field in the Martian core pressure range and possibly constitutes the Martian inner core if it exists.
References.
[1] Stähler, S.C. et al. Seismic detection of the martian core. Science 373, 443–448 (2021).
[2] Samuel H. et al. Geophysical evidence for an enriched molten silicate layer above Mars’s core. Nature 622, 712–717 (2023).
[3] Fei, Y. et al. Structure type and bulk modulus of Fe3S, a new iron-sulfur compound. American Mineralogist 85, 1830–1833 (2000).
[4] Stewart, A.J. et al. Mars: a new core-crystallization regime. Science 316, 1323–1325 (2007).
Here we performed high-pressure experiments on Fe3S2 (subsolidus) and Fe2S (subsolidus and melting) between ~30 and ~70 GPa with laser-heated diamond-anvil cell (DAC) techniques at a synchrotron facility, SPring-8. The Fe3S2 and Fe2S samples were synthesized by a multi-anvil press before the DAC experiments. The X-ray diffraction measurements demonstrated that Fe3S2 decomposes into Fe12S7 and FeS above ~30 GPa. We also found that Fe2S melted incongruently to liquid + Fe12S7. Both suggest that Fe12S7 (Fe + 25.1 wt% S) is an important iron sulfide having a liquidus field in the Martian core pressure range and possibly constitutes the Martian inner core if it exists.
References.
[1] Stähler, S.C. et al. Seismic detection of the martian core. Science 373, 443–448 (2021).
[2] Samuel H. et al. Geophysical evidence for an enriched molten silicate layer above Mars’s core. Nature 622, 712–717 (2023).
[3] Fei, Y. et al. Structure type and bulk modulus of Fe3S, a new iron-sulfur compound. American Mineralogist 85, 1830–1833 (2000).
[4] Stewart, A.J. et al. Mars: a new core-crystallization regime. Science 316, 1323–1325 (2007).