Subcritical Cracking Associated With Subgrain Rotation Recrystallisation in Quartz Inferred From Cathodoluminescence Study

ABSTRACT We employed cathodoluminescence (CL) to study deformed quartz phenocrysts from the Cretaceous granite porphyry in SW Japan and observed fracture‐like planar structures appearing as CL‐dark bands. These CL‐dark bands were aligned with low‐angle grain boundaries formed by subgrain rotation recrystallisation. The low brightness of the CL‐dark bands can be attributed to the precipitation of new quartz with lower dislocation density from fluids that infiltrate into cracks along subgrain boundaries. The cracking along subgrain boundaries may be related to stress corrosion. We propose that stress corrosion occurs along subgrain boundaries, followed by the precipitation of new quartz from crack‐filling fluids. The results of this study indicate that stress corrosion cracking significantly contributes to brittle fracturing and grain‐size reduction in quartz.