三郡帯足立地域の変ハンレイ岩中のホルンブレンド-アクチノ閃石のFおよびCl含有量  [in Japanese] F and Cl contents of hornblende-actinolite from metagabbros in Ashidachi area of the Sangun belt, Southwest Japan  [in Japanese]

Zoned amphiboles, consisting of brownish hornblende core and colorless actinolite rim, occur in metamorphosed gabbros enclosed as a number of small blocks in highly serpentinized ultramafics in the Ashidachi area, in the Sangun metamorphic belt, Southwest Japan. The gabbros are considered to have undergone ocean-floor metamorphism preceding the Sangun metamorphism. Microprobe analyses of amphiboles show that chlorine content is considerably high in the hornblende core (<0.4 wt%) and decreases in the actinolite rim (<0.1 wt%). Fluorine content is low relative to chlorine throughout the zoned amphiboles (<0.2 wt%), and shows no systematic variation from the hornblende core to the actinolite rim. Local equilibrium between hornblende and actinolite was attained in some zoned amphiboles. microprove analyses of the hornblende-actinolite pairs show that hornblende is more preferable for chlorine than actinolite. Chlorine and fluorine contents and the related crystallo-chemical features of the zoned amphiboles from Ashidachi were discussed, comparing with those of previously reported amphiboles formed by hydration during deuteric alteration and ocean-floor alteration.