Low argon solubility in silicate melts at high pressure

The solubility of rare gases in silicate melts and minerals at high pressure is of importance for understanding the early history of the Earth and its present day degassing. Helium, neon, argon, krypton and xenon were originally incorporated into the Earth during its accretion, and have also been produced by radioactive decay1. These elements have been used as tracers for deciphering mantle structure and constraining the number and size of geochemical reservoirs1,2,3. In particular, it has been proposed that the budget of 40Ar, produced by the radioactive decay of 40K, provides the strongest argument for chemical layering within the mantle1,4. The geochemical models used to arrive at this conclusion are, however, currently under re-examination5, with a large source of uncertainty being the lack of data on argon partitioning during melting. It has previously been assumed, on the basis of low-pressure data, that noble gases are highly soluble in melts at all pressures. But here we present solubility data of argon in olivine melt at very high pressure that indicate that argon solubility is strongly dependent on pressure, especially in the range of 4–5 gigapascals.