Crystal growth of plagioclase megacrysts through Ostwald Ripening during temperature cycling, suggested by the lineation of sulfide minerals inclusions

Abstract

Ca-rich plagioclase (An > 90 %) larger than 10 mm, which is called anorthite megacryst, occurs commonly from basalt – andesite in Japanese Island arc. We investigated plagioclase megacrysts from Mt. Fubou, Sado island and Fukue island and found sulfide inclusions in all of the specimens. Sulfide inclusions are 30 - 50 µm and droplet shaped. In particular, lineation of sulfide inclusions were observed in bytownite megacrysts from Sado island. Electron microprobe chemical analysis and texture observation of them indicate that these bytownite crystals grew through Ostwald Ripening during temperature cycling.