1992 年 87 巻 9 号 p. 351-363
The latest results on the petrology of the upper mantle materials are reviewed. Various mantle processes can be known on two kinds of mantle fragments, xenoliths in mantle-derived magmas and solid intrusive massifs. The Horoman peridotite complex, Hokkaido, is one of the best ones from which we can learn various mantle processes.
Restites, cumulates, metasomatites and frozen melts may constitute the upper mantle. Harzburgites and lherzolites, the commonest mantle materials, are basically restites, which have been modified to various extent by metasomatism. Harzburgites, which are refractory in terms of major elements and mode, are frequently enriched with strongly incompatible trace elements, including light rare earth elements (=REE paradox). The enrichment was possibly performed by percolation of exotic fluids after consolidation of the peridotites. Dunites are not simple restites but are either cumulates from Mg-rich magmas or metasomatites which are produced by selective dissolution of pyroxenes from peridotites due to interaction with exotic melts. Podiform chromitites with dunite envelope can be formed by such mantle-magma interactions.