Prograde and retrograde metamorphism of hematitebearing basic schists in the Sanbagawa belt in central Shikoku |
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| Authors: | M OTSUKI S BANNO |
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| Institution: | Geological Institute, University of Tokyo, Hongo, Tokyo, 113 Japan;Department of Geology and Mineralogy, Kyoto University, Sakyo, Kyoto, 606 Japan |
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| Abstract: | The mineral assemblages of hematite-bearing basic schists in intermediate high-pressure metamorphism are temperature dependent. For assemblages with excess hematite, albite, muscovite and quartz, the paragenetic relations can be dealt with in terms of a four-component system, without omitting or grouping major components.
In the Sanbagawa belt in central Shikoku, the dominant amphibole in the hematite-bearing basic schists changes from winchite, via crossite and barroisite to hornblende. The stability of amphibole is described chemographically within a pseudoternary system with another excess phase, epidote. Many amphiboles are chemically heterogeneous owing to retrograde reactions which produced low- T/P amphibole around the prograde amphibole. The examination of amphibole zoning makes it possible to draw a retrograde P-T trajectory which passes on the lower pressure side of the prograde one. |
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| Keywords: | amphibole stability basic schist hematite-bearing schist Sanbagawa schist |
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