[S-IT16] Deep Earth Sciences

[SIT16-15] Effects of light elements on the water partitioning between liquid metal and molten silicate under high pressure and temperature

*Taku Tsuchiya¹, Kei Ito¹, Kazushi Kitaguchi¹, Shengxuan Huang¹ (1.Geodynamics Research Center, Ehime University)

Keywords:Ab initio free energy calculations, Metal/silicate water partitioning, Effects of light elements

Metal/silicate water partitioning under high pressure is important to understand the water circulation in Earth's deep interior. Several srudies have therefore been conducted both experimentally and theoretically. However, primarily due to the technical difficulty in quantitative analyses of hydrogen, the reported resuts scatter largely, such as some experiments showed siderophile behaviors of hydrogen under high pressure but some others lithophile behaviors. Recent theoretical studies suggest its siderophile behavior, but an earlier one the opposite. Also, the theoretical studies assumed a simple molecular exchange reaction only and the stability of an experimentally suggested redox reaction has not been investigated. For this confused situation, we have started the ab initio free energy calculations of high-P,T hydrogen partition between liquid iron and molten silicate and reported some preliminary results in my previous talk of the last JpGU meeting that unlike the preconception, the exchange and redox reactions both could occur at high-P,T though hydrogen is basically siderophile. This means that oxygen is also partitioned into iron along with hydrogen. In this preliminary study, we have also examined the effects of oxidation state on the reactions and realized that the stability of exchange reaction strongly depends on the redox condition, indicating that the exchange reaction is more suppressed (hydrogen becomes lithophile under some particular conditions) and the redox reaction becomes more predominat when iron contains more oxygen atoms. These preliminary findings strongly suggest the hydrogen partiotion nature between liquid iron and molten silicate could be sensitive to the light element incorporation into iron, and therefire we have started to investigate the effects of other important light elements (Si and S) comprehensively. In this talk, we will present the currently obtained results and shed light on the nature of complicate hydrogen partition mechanisms between liquid iron and molten silicate under high P,T condition.