MELTING TEMPERATURE AND PARTIAL MELT CHEMISTRY OF H2O-SATURATED MANTLE PERIDOTITE TO 11 GIGAPASCALS

The H2O-saturated solidus of a model mantle composition (Kilborne Hole peridotite nodule, KLB-1) was determined to be just above 1000 degree s C from 5 to 11 gigapascals. Given reasonable H2O abundances in Earth 's mantle, an H2O-rich fluid could exist only in a region defined by t he wet solidus and thermal stability limits of hydrous minerals, at de pths between 90 and 330 kilometers. The experimental partial melts mon otonously became more mafic with increasing pressure from andesitic co mposition at 1 gigapascal to more mafic than the starting peridotite a t 10 gigapascals. Because the chemistry of the experimental partial me lts is similar to that of kimberlites, it is suggested that kimberlite s may be derived by low-temperature melting of an H2O-rich mantle at d epths of 150 to 300 kilometers.