Abstract:

Study of sapphirine and related mineral association in the high-grade re- gion of the Larsemann Hills, East Antarctica,shows that sapphirine of the area is characterized by its magnesio-, iron-and aluminum-rich, but silica-poor feature,and the obvious intra-and intergrain changes in compositions. The change is mainly mani-  fested as the Tschermark substitution (Mg, Fe)+Si=2Al. In the high-grade meta- morphism and anatexis process the multistage crystallization of minerals occurred and resulted in the complexity of the mineral association, such as the differentiation of leuco-and melano-components. Among them, the mafic-rich minerals formed earlier, and the differentiation of magnesio-and iron-components is responsible for the earlier presence of iron-rich minerals and later crystallization of magnesio-rich minerals, thus the successive associations of multistage occurred. The rock composition is an impor- tant but not critical factor to the occurrence of sapphirine. It is the mobilization of components that accounts for the formation of sapphirine. The multistage evolution of mineral association to some degree reflects the changing composition and opening of the setting. It is therefore deduced that the protolith from which sapphirine is derived is not necessarily magnesio-rich polite. The heterogeneity of sappbirinc composition is resulted from the various media,not the PT changes.Sapphirine formed at 840～880℃, not the so-called ultrahigh temperature condition (>1000℃). Its for- mation is related to both the filtration and diffusion processes in high-grade metamor- phism and anatexis.

Key words: sapphirine, component mobilization, formation condition, Larsemann Hills