島根県美都町北東部の三郡変成岩中のアルカリ角閃石の産状と共生関係

抄録・要旨

Outline of geology in the studied area is given and original rocks of greenschists distributed in 8 horizons are estimated to be mainly volcanic sand/mudstones. A metamorphosed sheet showing bostonitic texture under the microscope is found in this area and its chemical compositron is similar to that of mugearite and its differentiation products.
The chemical compositions of greenschists are not necessarily basic. Mineral assemblages in greenschists are listed in this paper.
Two kinds of composite amphibole-grains are recognized in the geenschists. One of them is zoned amphibole, in which Al-poor crossite is usually rimmed by actionolite. The other kind of composite amphibole-grain is composed at least of three parts, i.e., magnesian hastmgsitic hornblende, actionolite, and winchite. Although this amphibole grain is optically homogeneous at a glance, back-scattered electron observation reveals chemical heterogeneity in micron scale. The result of line scanning analysis for some major elements shows that the chemical heterogeneity in the amphibole is more complicated, especially in MgO and total FeO contents. On the basis of stability fields of amphibole proposed by BANNO and OTSUKI (1982), P-T condition of the Sangun Metamorphism in this area is tentatively estimated.
This chemical heterogeneity in amphibole in micron scale may be a new mode as to chemical haterogeneity in amphibole.