Abstract
The compositions of amphiboles of four samples which were collected from the Mt. Poroshiri area of the Western Meta-ophiolite zone of the Hidaka metamorphic belt were studied. The four samples (A, B, C & D) show different degrees of recrystallization, i. e. from olivine gabbro to massive amphibolite. The compositions of metamorphic amphiboles are all calciferous but sometimes range from tremolitic to pargasitic amphibole even in the same thin section. Tremolitic amphibole replaces primary clinopyroxene, whereas pargasitic amphibole occurs along the boundary between clinopyroxene and plagioclase or inside plagioclase. Moreover, amphibole with intermediate composition appears between the tremolitic and pargasitic amphiboles. The range of the amphibole composition narrows with the progress of recrystallization, i. e. from A to D. The variation of the amphibole compositions appears to be controlled by different local bulk compositions and by differences in the diffusional process.
