TRANSITION-METAL PARTITIONING BETWEEN LOWER MANTLE AND CORE MATERIALS AT 27 GPA

Partitioning of transition metals, V, Cr, Mn, Fe, Co, and Ni between Mg-perovskite, magnesiowustite and metallic iron has been studied at 27 GPa and 1700-1900-degrees-C. V, Cr and Mn are strongly enriched in Mg-perovskite and magnesiowustite, whereas Fe, Co, and Ni are strongly concentrated in metallic iron under the present experimental condition. Using these data on partitioning, we tested models of core-mantle separation in the primordial earth. Abundances of V, Cr, and Fe in the upper mantle are consistent with a model of the upper mantle formed by olivine accumulation and/or majorite fractionation in the primordial earth after the core segregation under the core-mantle equilibrium. However, depletion of Mn, and overabundances of Co and Ni in the mantle remain unexplained by this model. Other processes, such as vaporization of Mn before or during accretion and the equilibrium partitioning of Co and Ni between minerals and iron in the deep lower mantle may account for the observed abundances of these elements in the mantle.