DIRECT OBSERVATION OF COMPLETE MISCIBILITY THE ALBITE-H2O SYSTEM

There are essentially two main types of mobile phases in the Earth's c rust and mantle: silicate melts and hydrous fluids. Near the surface o f the Earth, the physical and chemical properties of these phases are fundamentally different, But with increasing pressure, the solubility of water in silicate melts and the solubility of silicate materials in hydrous fluids increase. This has led to the suggestion that, above a certain critical pressure, the compositions of the two phases in mutu al equilibrium become indistinguishable(1-5). Here we report the direc t visual observation of this phenomenon in the albite-H2O system using an externally heated diamond anvil cell, Our results suggest both tha t there should be complete miscibility between silicate melts and hydr ous fluids in the deeper parts of the upper mantle and that, in the pr esence of a hydrous fluid, a melting temperature for this part of the mantle can no longer be defined.