Role of micropores, mass transfer and reaction rate in hydrothermal alteration process of plagioclase in a granite

Yuguchi, Takashi*; Shobuzawa, Kaho*; Ogita, Yasuhiro*  ; Yagi, Koshi*; Ishibashi, Masayuki; Sasao, Eiji   ; Nishiyama, Tadao*

This study presents the plagioclase alteration process with a focus on the role of micropores, mass transfer and reaction rate in the Toki granitic pluton, central Japan. The plagioclase alteration process involves an albitization, K-feldspathization and the formation of illite, calcite, fluorite and epidote. Such secondary minerals of hydrothermal origin in plagioclase within granitic rocks record the chemical characteristics of the hydrothermal fluid. Our results highlight (1) the nature of micropores such as distribution and volume in plagioclase, (2) the reaction nature of plagioclase alteration inferred by petrography and chemistry, (3) the physical conditions including alteration age and temperature, (4) the sequential variations of the fluid chemistry and (5) the mass transfer rate and reaction rate in the plagioclase alteration.