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[PPS21-06] Metal-silicate partitioning of chlorine: Implications for the origin of terrestrial missing chlorine
Keywords:Chlorine, Partitioning of elements, Primordial oceans, Core composition
Metal-silicate partitioning behavior of elements is controlled mainly by temperature, pressure, and oxygen fugacity of magma oceans. In this study, we first investigated the oxygen fugacity dependency for the partitioning coefficient of chlorine. Starting materials were prepared from a mixture of high-purity oxides (SiO2, Al2O3, CaO, MgO) and metal (Fe). The relative abundances of each component in the mixture were assumed to be CI chondrite. Chlorine was added to the mixutre as FeCl2(2wt.%). Oxygen fugacity was controlled by adding metallic Si to the samples. The starting materials were enclosed in graphite capsules. The experiments were performed at 4GPa and 1900K for 15 min using multi-anvil high pressure apparatus at Institute for Solid State Physics, The University of Tokyo. The sample was quenched by turning off the power to the heater. The elemental composition of recovered samples were analyzed by wavelength-dispersive electron microprobe at Atmosphere and Ocean Research Institute, The University of Tokyo.
The metal-silicate partitioning coefficient of chlorine in recovered samples was within the range between 0.001〜0.01, suggesting that chlorine is a highly lithophile element. In addition, oxygen fugacity dependence on the partitioning coefficient was not observed. If such a highly lithophilic behavior of chlorine observed in our study does not depend significantly on pressure, terrestrial missing chlorine might require primordial ocean blow off during the main-accretion phase.
Reference: Sahrp, Z.D. and D.S. Draper, 2013, Earth Planet. Sci. Lett. 369-370, 71-77.