Comparison of structural features of the fault zone developed at different protoliths: crystalline rocks and mudrocks

We investigated the mesoscopic and microscopic structural features of the Keumwang fault zone, Korea, to determine the effect of different protoliths (crystalline granitic gneiss and mudrock) on fault zone structure including discrete shear surfaces, shear bands, foliation, porphyroclasts and calcite veins. Overall, in crystalline rock, the shear deformation tends to be localized to a fault core or several fault gouge-dominated layers within the fault zone. The cataclastic flow appears to become stronger toward the fault core. Most of the shear deformation appears to be partitioned between slip on discrete shear surfaces and shear bands, and cataclastic flow, including syntectonic alteration in the fine-grained matrix of fault rocks. In contrast, within mudrocks, shear deformation tends to be relatively uniformly distributed within the entire fault zone. Shearing generates continuous S-foliations throughout the whole fault zone. Most of the shearing is accommodated by slip along these foliations and on discrete shear surfaces distributed within the entire fault zone.