3.2. Feature of fillings in gouge and fractures
The mineralogies of well-preserved fault gouge and fractures distributed
along the fault in the quarry were examined. Fault A in the quarry
is cut by the Fault B, which was presumably formed by recent fault
movement because the zone between Fault B and C is hardly crushed
and Fault B cross-cuts all other structures. Other small Faults D–F are almost
parallel and displace a hydrothermally altered fracture. To investigate
the relationship between the development of the structures and
chemical alteration, detailed mineralogical and geochemical analyses
were focused on the older fault (A) and younger faults (B and C).
First of all, microscopic observations (Figure 6) and XRD analyses revealed
that hydrothermal minerals such as prehnite, quartz and chlorite
occur in the fault gouge of Fault A shown in Fig. 3, whereas calcite and
iron-oxyhydroxides are identified as fillings of the fractures distributed
in the gouge zones of Fault B and C shown in Fig. 3. Microscopically, the
texture of Fault A is characterized as cataclasite (Figure 6a). On the other
hand, clayey gouge materials from along the Faults B and C show that
several tens of micron-sized grains are almost homogenously scattered
through the rock matrices (Figure 6b).