Microanalytic characteristics of extremely fractured quartz in fault damage zone and implications

The fault damage zone of the active Milun Fault in eastern Taiwan exhibits fractured and altered fault-rock textures, including spotted schist, serpentinite, and associated gouge. In the vicinity of the upper boundary of the damage zone, the recovered drill core hosts a non-cohesive, pulverized quartz body (~20-30 cm in length) within the fault rocks. The pulverized quartz is sandwiched between fractured schist and millimetre-scale laminae subparallel to the zone boundary. Microanalytical observations show that the quartz is shattered into a fine powder without an evident shear sense or preferred fracture orientation. No shear-induced amorphous phase is detected, whereas Laue diffraction indicates pronounced lattice distortion and elevated residual stress. The pulverized quartz displays a dense tensile fracture network, a feature commonly reported for seismically pulverized rocks along seismogenic faults, suggesting a dilatational, tensile-dominated fragmentation mechanism rather than progressive shear comminution. We propose that the quartz pulverization resulted from high strain rates associated with transient tensile stresses during coseismic rupture, potentially favoured by specific lithologic conditions.