Experimental study of partial melting of mantle peridotite - A discussion about the genesis of silica-rich fluids (melts)

Experiments on partial melting of mantle lherzolite have been realized at 0 .6 and 1.0 GPa and the chemical compositional variations of melts during di fferent melting stages have been first discussed. The results show that the trends of variations in SiO2, CaO, Al2O3, Na2O and TiO2 are different at d ifferent melting stages. The melts produced at lower pressure are richer in SiO2 than those at higher pressure. The mantle-derived silica-rich fluids (silicate melts) are polygenetic, but the basic and intermediate-acid silic ate melts in mantle peridotite xenoliths from the same host rocks, which ha ve equivalent contents of volatile and alkali components and different cont ents of other components, should result from in-situ (low-degree) partial m elting of mantle peridotite under different conditions (e.g. at different d epths, with introduction of C-O-H fluids or in the presence of metasomatic minerals). The intermediate-acid melts may be the result of partial melting (at lower pressure) Opx + Sp + K-Na-rich fluid + (Amphi) + (Phlog) = Ol melt. But the intermediate-acid magmas cannot be produced from the partial melting of normal mantle peridotite unless the crustal materials are introd uced to some extent.