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Amphibole composition as an indicator of subtle grade variation in epidote-glaucophane schists |
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| Authors: | H HOSOTANI S BANNO |
| Institution: | Department of Earth Sciences, Kanazawa University, Kanazawa 920, Japan; Department of Geology and Mineralogy, Kyoto University, Kyoto 606, Japan |
| Abstract: | Abstract The paragenetic relations of epidote-glaucophane schists are described in terms of the system Al Using a group of epidote-glaucophane schists from the Kotu area of the Sanbagawa metamor-phic belt in Shlkoku, Japan (isophysical compositional),univariant boundary lines were determined for the assemblages that, in addition to the ubiquitous quartz + albite + phengitic mica, contain hematite + chlorite, garnet + chlorite and actinolite + chlorite, respectively. The slopes of the univariant boundary lines obtained from petrographical data are in good agreement with those calculated in a model system. The positions of isophysical univariant boundary lines on the amphibole compositional diagram serve to distinguish the grade of metamorphism among the rocks of the same mineral facies. The hematite-chlorite univariant boundary line can be used to divide the zone of epidote-glaucophane schists of the Sanbagawa metamorphic belt into three, and the garnet-chlorite-paragonite invariant equilibrium can be used to divide the epidote zone of New Caledonia into three. |
| Keywords: | Key-words: alkali-amphibole blueschists epidote-glaucophane schists metamorphic grade Sanbagawa metamorphic belt Japan |