Investigating Earth's Formation History Through Copper and Sulfur Metal-Silicate Partitioning During Core-Mantle Differentiation

Identifying extant materials that act as compositional proxies for Earth is key to understanding its accretion. Copper and sulfur are both moderately volatile elements; however, they display different geochemical behavior (e.g., phase affinities). Thus, individually and together, these elements provide constraints on the source material and conditions of Earth's accretion, as well as on the timing and evolution of volatile delivery to Earth. Here we present laser-heated diamond anvil cell experiments at pressures up to 81 GPa and temperatures up to 4,100 K aimed at characterizing Cu metal-silicate partitioning at conditions relevant to core-mantle differentiation in Earth. Partitioning results have been combined with literature results for S in Earth formation modeling to constrain accretion scenarios that can arrive at present-day mantle Cu and S contents. These modeling results indicate that the distribution of Cu and S in Earth may be the result of accretion largely from material(s) with Cu contents at or above chondritic values and S contents that are strongly depleted, such as that in bulk CH chondrites, and that the majority of Earth's mass (similar to 3/4) accreted incrementally via pebble and/or planetesimal accretion.