High-Pressure Iron-Sulfur Compound, Fe ₃ S ₂ , and Melting Relations in the Fe-FeS System

Abstract

An iron-sulfur compound (Fe3S2) was synthesized at pressures greater than 14 gigapascals in the system Fe-FeS. The formation of Fe3S2 changed the melting relations from a simple binary eutectic system to a binary system with an intermediate compound that melted incongruently. The eutectic temperature in the system at 14 gigapascals was about 400°C lower than that extrapolated from Usselman's data, implying that previous thermal models of Fe-rich planetary cores could overestimate core temperature. If it is found in a meteorite, the Fe3S2 phase could also be used to infer the minimum size of a parent body.

Mars core structure—concise review and anticipated insights from InSight

“…I parameterize the liquidus temperature as a function of composition for high iron concentrations using the Fe-FeS eutectic compositions and temperatures investigated as a function of pressure from various sources (Buono and Walker 2015;Chudinovskikh and Boehler 2007;Fei et al 1997, 2000, Morard et al 2008. The pressure and compositionally dependent melting temperature is parameterized as…”

“…Earlier estimates for Mars' core from various sources yield a range of 14-17 wt% (and one as low as 10.5 wt%), yet all suggest much more than is believed to be in Earth's core: 1.7 wt% (Dreibus and Palme 1996). Figure 3 shows the approximate melting relations in the Fe-FeS system derived from various sources (Fe melting curve (Nguyen and Holmes 2004), Fe-FeS melting relations (Fei et al 1997;Fei et al 2000;Morard et al 2008;Buono and Walker 2015)). For the conditions in Mars' core, the first solids to crystallize are likely to be Fe 3−x S 2 if the composition is relatively rich in sulfur and Fe otherwise.…”

High-pressure experimental geosciences: state of the art and prospects

“…Datchi et al (2000); Gregoryanz et al (2003)), H 2 O(données de Lin et al (2005a); Goncharov et al (2009)), et péridotite (Fiquet et al, 2010). Fei et al (1997Fei et al ( , 2000). Morard et al (2007); Usselman (1975); Stewart et al (2007); Chudinovskikh and Boehler (2007) (adaptédeFeietal.…”

Water, Life, and Planetary Geodynamical Evolution

“…The melting temperature of the eutectic composition is in general very low (e.g. Fei et al 1997) and it is very difficult to totally freeze the core of a terrestrial planet. This circumstance suggests that once a chemical dynamo has started-which is presumably late in the evolution-its existence is likely to be longstanding and it is difficult to stop as long as the core is cooling.…”