* Astronomy

Title: Melting of the Indarch meteorite (EH4 chondrite) at 1 GPa and variable oxygen fugacity: Implications for early planetary differentiation processes
Author: S. Bertheta, b, V. Malavergne, K. Righter

In order to derive constraints on planetary differentiation processes, and ultimately the formation of the Earth, it is required to study a variety of meteoritic materials and to investigate their melting relations and elemental partitioning at variable pressures, temperatures, and oxygen fugacities (fO2). This study reports the first high pressure (HP) and high temperature (HT) investigation of an enstatite chondrite (Indarch). Four series of experiments exploring various fO2 conditions have been carried out at 1 GPa in a piston-cylinder apparatus using the EH4 chondrite Indarch. We show that temperature and redox conditions have important effects on the phase equilibria of the meteorite: the solidus and liquidus temperatures of the silicate portion increase with decreasing fO2, and the stability fields of various phases are modified. Olivine and pyroxene are stable around 1.5 log fO2 unit below the iron-wüstite buffer (IW-1.5), whereas quartz and pyroxene is the stable assemblage under the most reducing conditions, between IW-5.0 and IW-4.0, due to reduction of the silicate. While these changes are occurring in the silicate, the metal gains Si from the silicate, (Fe, Mg, Mn, Ca, Cr)-bearing sulfides are observed at fO2 less than IW-4, and the partitioning of Ni and Mo are both affected by the presence of Si in Fe-S-C liquids. The fO2 has also a significant effect on the liquid metal-liquid silicate partitioning behavior of Si and S, two possible light elements in planetary cores, and of the slightly siderophile elements Cr and Mn. With decreasing fO2, S becomes increasingly lithophile, Si becomes increasingly siderophile, and Cr and Mn both become strongly siderophile and chalcophile. The partitioning behavior of these elements places new constraints on models of core segregation for the Earth and other differentiated bodies.

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