ミグマタイトと地殻の部分融解

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Study on migmatites is reviewed in the light of recent progress in the research of crustal anatexis and granite magma formation. Migmatite is a heterogeneous rock that characteristically occurs in high-grade parts of many high temperature-type metamorphic terranes in the world. A popular current idea of the migmatite is that it is, if not all, a product of partial melting and partial melt segregation in the continental lower crust, and thus the migmatite is considered to be a key rock for understanding the crustal anatexis phenomena. Despite much descriptive and analytical work on the migmatite in the past, our understanding of the physical processes of its formation is still limited. A difficulty arises from the fact that the migmatite is a heterogeneous and complex rock in its nature and, therefore, accurate description and analysis of the rocks is diffcult. It is also a integrated product of many irreversible physical and chemical processes over a long geologic time, and therefore, ambiguity arises in the interpretation of petrographic observations of the migmatite. It is emphasized that the scheme of description has to be founded on the understanding of physical processes of migmatite formation. The two-phase flow and the compaction theory formulated by McKenzie (1984) had significant influence on the study of melt segregation in the mantle and in the lower crust. The process, however, can be much more complicated in the crust than in the mantle because the former is more heterogeneous in lithological and mechanical aspects. Validity of theoretical modeling of the processes must, therefore, be tested with careful field observations. Two examples of recents study of migmatite that dealt with long-range melt transport, one from French Pyrenees and the other from Japan. are reviewed. Theory of melt segregation is still in progress and field observation of migmatites and its associated rocks in metamorphic terranes will become increasingly important.
特定非営利活動法人日本火山学会の論文
1997-04-25

ミグマタイトと地殻の部分融解

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