Solubility of neutral nickel in silicate melts and implications for the Earth's siderophile element budget

Abstract

EXPERIMENTAL studies have so far suggested that an insignificant amount of neutral nickel (Ni^o) is soluble in silicate melts^1–4. This has led to difficulties in explaining the high concentrations of nickel in the modern Earth's mantle, because virtually all nickel (along with other siderophile elements such as cobalt and the noble metals) would have been removed from the mantle when the Earth's metallic core separated from it at low oxygen fugacity^1,2,5. Several models have been proposed to explain the Earth's siderophile element budget^1,6–8, each based on the belief that the solubility of neutral metal species in silicate melts is negligible. Here, however, I present experimental evidence indicating that the solubility of at least one neutral siderophile element, nickel, is not negligible. Because the presence of Ni° will affect the partitioning of nickel between silicate melt and metal, and between silicate melt and crystalline silicate phases, these results have implications for our understanding of petrogenetic processes that take place in conditions of low oxygen fugacity, where Ni^o is an important part of total nickel. In particular, the Ni^o solubilities found in the present study are large enough to explain the anomalously high concentrations of nickel in the Earth's mantle if the temperature of the early mantle was sufficiently high (≳ 1,800°C).