Solubility of K in Fe-S liquid, silicate-K-(Fe-S)^liq equilibria, and their planetary implications

Potassium has been found to have extremely limited absolute solubility in Fe-S liquid in the P-T range of 18-40 kbars, 1050-1150°C, and f{hook}O₂ within the field of metallic iron. It also partitioned to certain silicate phase highly in preference to Fe-S liquid at 30 kbars, 1100°C. The dependence of the partitioning of K between solid silicate and Fe-S liquid on f{hook}O₂ and compositions of mineral solid solutions has been analyzed. These experimental data, along with those of others, limit the amount of K that could fractionate in Fe-S liquid layers or a core in the early history of the moon and, thus, act as localized heat sources in its thermal history models, and also seem to argue against a chondritic abundance of potassium for the earth. The question of fractionation of enough ⁴⁰K in an Fe-S liquid outer core of the earth to provide the necessary thermal energy for the geomagnetic dynamo remains unresolved.