Genesis and development processes of fractures in granite; Petrographic indicators of hydrothermal alteration

Yuguchi, Takashi*; Izumino, Yuya*; Sasao, Eiji   

This study analyzes the relationships among alteration indicators, areal microvoid fractions in chloritized biotite and altered plagioclase, and macroscopic fracture frequencies in the Toki granite, central Japan, to establish the genesis and development processes of fractures in granite. Petrographic alteration indicators as innovative methods are proposed to evaluate the extent of hydrothermal alteration and fracture frequency within granites. Samples with high macroscopic fracture frequencies correspond to a high number of areal microvoid fractions and large alteration indicators. Microvoids are the source of macroscopic fractures and can be evaluated by intrinsic factors, such as alteration indicators.