Melting of albite at high pressures in the presence of water

Abstract

The melting of albite has been investigated in the presence of water in the pressure range up to 30 kb, from the point of view that the effect of water on the melting of silicates is important for the investigation of the state of the earth's interior and the earth's thermal history. The melting relations have been determined under the following conditions: (a) that the water pressure is equal to the total pressure or the albite melt is saturated with water, and (b) that albite melt contains a fixed amount of water (10 wt% and 14 wt%) and is saturated with water up to a certain value of pressure but undersaturated in the higher pressures. As oressure increases, the melting point of albite, in the presence of a fixed amount of water, decreases from 1118°C along the water-saturated melting curve up to a certain value of pressure. In the higher pressure region albite begins to melt incongruently, and the temperatures of the beginning of melting decrease with increase of pressure along the water-saturated melting curve and the temperatures of the end of melting increase approaching asymptotically the curve for the dry condition. In the region between the solidus and the liquids, crystal and liquid co-exist. The value of pressure, where the incongruent melting begins, is in good agreement with the results of the solubility of water in albite melt.