Melting relations in the Fe–S–Si system at high pressure and temperature: implications for the planetary core

Abstract

The phase and melting relations in the Fe-S-Si system were determined up to 60 GPa by using a double-sided laser-heated diamond anvil cell combined with X-ray diffraction. On the basis of the X-ray diffraction patterns, we confirmed that hcp/fcc Fe-Si alloys and Fe 3 S are stable phases under subsolidus conditions in the Fe-S-Si system. Both solidus and liquidus temperatures are significantly lower than the melting temperature of pure Fe and both increase with pressure. The slopes of the Fe-S-Si liquidus and solidus curves determined here are smaller than the adiabatic temperature gradients of the liquid cores of Mercury and Mars. Thus, crystallization of their cores started at the core-mantle boundary region.

Fe Alloy Slurry and a Compacting Cumulate Pile Across Earth's Inner‐Core Boundary

“…To better understand the solidification and element partition processes and to build a plausible geodynamic model for the ICB, we investigated the P ‐ T phase diagram of Fe‐Si‐O system from 313 to 329 GPa using literature results, corresponding to the radius of 1,500 to 1,220 km, respectively, in the F layer (Figure ). Pure Fe has a single melting curve at high pressures, while a mixed core composition such as the ternary Fe‐O‐S/Fe‐Si‐S system has both a solidus and liquidus with a temperature gap (Fischer, ; Morard et al, ; Sakairi et al, ; Terasaki et al, ; Figure b). In our model, the core adiabat crosses the liquidus at the top of the F layer, while it is still higher than the solidus, as shown in Figure .…”

“…3); with further cooling, the core grows and by conductive cooling into the overlying mantle. Pure Fe has a single melting curve at high pressures, while a mixed core composition such as Fe-O-S/Fe-Si-S system has both a solidus and liquidus with a temperature gap Morard et al, 2014); (Sakairi et al, 2017;Terasaki et al, 2011) (Fig. 3).…”

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

“…However, the challenge of better constraining the transport properties of the liquid Fe alloy in the core is multifaceted. The uncertainty in evaluation of both thermal conductivity and electrical resistivity of the Fe alloy in the OC is caused by (i) the unresolved compositional makeup and proportions of light elements in the liquid OC (e.g., Litasov & Shatskiy, ) although the consensus tilts toward Si as the major light element in the OC (e.g., Suer et al, ; Zhang, Sekine, et al, ), (ii) the exact effects of light element alloying on the transport properties of the liquid Fe (e.g., Shibazaki & Kono, ; Zhang, Sekine, et al, ), (iii) the amount of heat flow across the CMB (e.g., Ammann et al, ; Nimmo, ), and (iv) a large spread of estimated temperatures at the CMB and ICB (e.g., Andrault et al, ; Anzellini et al, ; Sakairi et al, ; Zhang, Sekine, et al, ). Lastly, from the experimental perspective, reaching and maintaining the core temperatures ( T ) and pressures ( P ) for sufficiently long time, while maintaining liquid sample geometry and purity to collect resistivity data, are still not experimentally achievable (e.g., Williams, ).…”

Evaluation of Recent Measurements of Mercury’s Moments of Inertia and Tides Using a Comprehensive Markov Chain Monte Carlo Method

“…However, we chose not to pursue this for this study, as the temperature profiles in the core would become a strong driver for the size of the inner core. Several studies of the FeSi system indicate relatively large differences in melt temperatures for various weight percentages of Si (Asanuma et al 2010;Fischer et al 2012Fischer et al , 2013Fischer et al , 2014Morard et al 2014;Ozawa et al 2016;Sakairi et al 2017). With the current uncertainties on Mercury's composition, the uncertain influence of impurities in Mercury's core, and the uncertainties of the temperature profile in general, we find it more prudent to decouple the size of the inner core from the local conditions.…”