Abstract
The melting of albite has been investigated in the presence of water in the pressure range up to 30 kb. Fixed amounts of water have been contained in the melts so as to satisfy the condition that the melt is saturated with water or P
H2O=P
t up to a certain value of pressure, but at higher pressures the melt is undersaturated or P
H2O<P
t. The results show that the melting relation is largely influenced by the presence of only a very small amount of water and strongly support the partial melting hypothesis for the cause of the low-velocity layer. It is suggested that the temperature in the earth's mantle is quite near the melting curve of the mantle when the melting gradient based on the theory of the lattice defects is adopted.
