[SSS15-P01] Geochemical anomaly for estimating the slip behavior of an ancient megasplay fault in the Hidakagawa Formation, Shimanto accretionary complex, Japan
Keywords:megasplay fault, fluid-rock interaction, frictional melting
The localized slip zone was composed of cataclasite and ultracataclasite, and showed granulation of mineral grains, intense shear foliation and melting grains locally. The results of paleo-temperature estimated by Raman spectra showed the burial depth of 5-9 km and thermal gap of host rock. Geochemical analyses revealed an anomaly of trace-element compositions in the slip zone. Although previous studies assumed single, slip event with fluid-rock interaction, we considered melting flow accompanying with frictional melting and the repetition of slip events. Our numerical calculation of fluid-rock interaction revealed that the ultracataclasite has experienced frictional melting and 271-610 times seismic events accompanying with frictional heat of above 350 °C. In contract, reported geochemical anomaly in the western ancient megasplay fault, developed in the Shikoku Island, Japan, showed 35-79 times seismic events together with high temperature of above 350 °C by same calculation. This inconsistency reflects trench-parallel heterogeneity of slip behavior.