Quantitative analyses of deformation band occurrence and host rock properties in pyroclastic rocks of eastern Taiwan

Abstract

We analyze deformation bands found in a pyroclastics locality at the Shitiping outcrop in eastern Taiwan, allowing close inspection of their features and evolution. To quantify their occurrences and strain distribution, we characterize the architecture of deformation bands based on detailed field investigation, including deformation band frequency, core thickness, cluster width, core displacement, and cluster displacement. We observe that the attitude, deformation style, quantitative characteristics, and microstructure of the deformation bands at the Shitiping outcrop correlate with the porosity, grain size, sorting coefficient, and the derived mean grain crushing pressure which are calculated from grain size and porosity of their host pyroclastic rocks. The frequency of deformation bands is positively correlated to the porosity and inversely proportional to average grain size and sorting coefficient of host pyroclastic layers, indicating that deformation is more localized in coarse-grained pyroclastic rocks. The band frequency is negatively correlated to the deformation band maximum displacement, core thickness, and cluster width; and maximum core thickness is negatively correlated to mean grain crushing pressure. Conversely, maximum core thickness of deformation band is positively correlated to sorting coefficient and average grain size of host rock, suggesting that the maximum core thickness might be affected by maximum grain size of pyroclastic layers. Our results indicate that the host rock properties contribute in affecting the occurrences of deformation bands.