Abstract
Liquid-liquid immiscibility has been widely observed in iron alloy systems at ambient pressure and is important for the structure and dynamics in iron cores of rocky planets. While such previously known liquid immiscibility has been demonstrated to disappear at relatively low pressures, here we report immiscible S(±Si,O)-rich liquid and H(±C)-rich liquid above ~20 GPa, corresponding to conditions of the Martian core. Mars’ cosmochemically estimated core composition is likely in the miscibility gap, and the separation of two immiscible liquids could have driven core convection and stable stratification, which explains the formation and termination of the Martian planetary magnetic field. In addition, we observed liquid immiscibility in Fe-S-H(±Si,O,C) at least to 118 GPa, suggesting that it can occur in the Earth’s topmost outer core and form a low-velocity layer below the core-mantle boundary.
Highlights
Liquid-liquid immiscibility has been widely observed in iron alloy systems at ambient pressure and is important for the structure and dynamics in iron cores of rocky planets
Previous highpressure and -temperature (P-T) experiments, revealed that a miscibility gap closes below 10–30 GPa in all of these iron alloy systems mentioned above[3–9]
Thermodynamic modeling suggested that the Fe-S-O system exhibits an extensive liquid immiscibility field even under core pressures[10], but it is not supported by high-pressure experiments[5,11]
Summary
Liquid-liquid immiscibility has been widely observed in iron alloy systems at ambient pressure and is important for the structure and dynamics in iron cores of rocky planets. These Fe-S and Fe-H liquids were found to be miscible at relatively high temperatures (>2000 K at ~20 GPa and >~3000 K at higher pressures) (Fig. 1c and Table 1).
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