High pressure equilibrium of nickel and cobalt between metal and mantle minerals

In order to test the effect of very high pressures on the siderophile behav iour of two elements, Ni and Co, we have carried out diamond anvil cell exp eriments on Ni- and Co-bearing systems, up to 70 GPa. Observation of recove red samples by analytical transmission electron microscopy shows that Ni an d Co remain siderophile at least up to 70 GPa, but that their siderophile c haracter decreases with pressure, as already observed in previous studies a t lower pressures. Our results also suggest that the abundances of Ni and C o observed in the Earth's upper mantle cannot be explained by very high pre ssure equilibrium between silicate perovskite, magnesiowustite, and metal. Copyright (C) 1999 Elsevier Science Ltd.