A Physico-Chemical Model of Element Separation in the Differentiation of Mantle Material

Available experimental data on the phase equilibria of silicate systems at high pressure under `dry' and `wet' conditions as well as the results obtained by the authors on the separation of elements during zone melting of the silicate phase of chondrites have thrown light on geochemical regularities in the process of differentiation in the Earth's mantle. The basis of the work is the idea of incongruent melting of metasilicates and the concentration of silica and most of the lithophilic elements in the liquid phase. These elements form compounds with SiO$_{2}$ or are dissolved in it, causing a lowering of the liquidus temperature. Regularities in the dynamics of the process of element separation during zone melting of the mantle are established and an explanation is given of the chief physical ideas on which the physico-chemical model of this process is based.