2:15 PM - 2:30 PM
[SIT16-03] High-Pressure Experiments on Fe3S2 and Fe2S and the Phase Diagram of the Fe-FeS System under Martian Core Conditions
Keywords:Mars, Core, Iron Sulfide, X-ray diffraction, Diamond anvil cell
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).