Geochemical evaluation of the fluid-rock interaction at the Gosukebashi Fault, northeastern area of the Rokko Mountains

Abstract

Understanding of the fluid-rock interaction in fault gouges is important to evaluate the activity of faults and reactivation of the inactive faults. The fluid-rock interaction in Taiwan Chelungpu fault activated at the Chi-Chi earthquake has been discussed by Ishikawa et al. (2008) based on the elemental distribution in hydrothermal experiments with sediments and trace elements concentrations and isotope ratios of the fault gouges. In this study, we tried to evaluate the fluid-rock interaction in the Gosukebashi Fault of Rokko Granite based on geochemical compositions of the fault gouge in the similar approach with the above. The analyses of chemical compositions and Sr isotopes of the Gosukebashi Fault samples indicated that the fluid-rock interaction in the Gosukebashi Fault was different from that at 350 degree C seen in Chelungpu fault and the gouge in this study did not interact with hot fluid during past faulting movements. We will carry more detailed chemical composition and isotope analysis to reveal the changes in chemical composition of the gouge caused by fault movement and understand the fluid-rock interaction of the Gosukebashi Fault gouge.