Experimental investigation of Ru isotope fractionation between metal, silicate and sulfide melts

Grützner T, Hopp T, Berndt J, Rohrbach A, Klemme S

Abstract

To improve the understanding of large-scale planetary processes, i.e. differentiation and core formation, of Earthand other planetary bodies, we performed experiments at 1 GPa in a range of temperatures to investigate massdependentisotope fractionation of ruthenium (Ru) between metal, silicate, and sulfide melts. Metal silicatefractionation is 102Ru/99Rusilicate - 102Ru/99Rumetal = 0.02 ± 0.02‰ (95% confidence interval) at 1600 ◦C andtherefore negligible for Earth’s core formation. However, there is resolvable Ru isotope fractionation betweenliquid metal and liquid sulfide: The 102Ru/99Ru ratio of liquid sulfide is 0.11 ± 0.03‰ lighter than that of liquidmetal at 1400 ◦C in sulfur (S)-bearing experiments. The unexpected lighter Ru isotope composition of the sulfidecan be best explained with different Ru–S bonding environments. Our results show furthermore, that addition oftin (Sn) instead of S to experimental charges affects Ru isotope fractionation significantly. The 102Ru/99Ru ratiosin the Sn-bearing phase are 0.18‰ ± 0.01‰ heavier than metal; hence, the presence of Sn not only changes themagnitude of the Ru isotope fractionation but also its direction. The observed Ru isotope fractionations are toosmall to preserve a resolvable isotope fractionation signature during core formation or the Hadean matte scenarioat very high temperatures.