Abstract:
We did an experimental study of partition of yttrium, a typical rare earth element, between a coexisting melt and fluid in the model system albite-sodium disilicate-water in the temperature range of 400 to 800°C at a pressure of 1000 bar. A distinguishing feature of phase equilibria in systems of this type is the possibility of a gradual conversion of the albite melt into a low-temperature alkali-aluminosilicate melt-solution system, as a result of fractional crystallization. The properties of the melt-solution system and coexisting fluid phase gradually converge with decreasing temperature, until the difference between these phases disappear in the critical region (320 to 350°C). These experiments explain the geochemical behavior of yttrium (and, by extension, of the entire group of rare earth elements) during emplacement of plutons generated from agpaitic magma (alkalic granite, granites, syenite, etc.).