Identification and tectonic implications of nano-particle quartz (<Â 50Â nm) by synchrotron X-ray diffraction in the Chelungpu fault gouge, Taiwan

To determine the ultrafine nano-scale grains in a fault gouge; the Chelungpu fault gouge was sampled and analyzed. It was separated into different particle size ranges and was analyzed by synchrotron X-ray diffraction and transmission electron microscopy. The minerals of gouge are predominantly composed of quartz, plagioclase, smectite, illite, chlorite, and kaolinite. The mineral association of < 100 nm particles are quartz, smectite, and illite. However, only smectite and illite are included except quartz in the 1-to-25 nm fractions. We propose that quartz is the index mineral associated with co-seismic fracture and the possible limit grain size is ~ 25 nm on fracturing. The smectite and illite nano-particles may be associated with weathering process of gouge at shallow or surface conditions.