Japan Geoscience Union Meeting 2023

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[J] Oral

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG58] New Developments in fluid-rock Interactions: From Surface to Deep Subduction Zone

Sun. May 21, 2023 3:30 PM - 4:45 PM International Conference Room (IC) (International Conference Hall, Makuhari Messe)

convener:Atsushi Okamoto(Graduate School of Environmental Studies), Jun Muto(Department of Earth Sciences, Tohoku University), Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Junichi Nakajima(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Chairperson:Junichi Nakajima(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Atsushi Okamoto(Graduate School of Environmental Studies)

4:30 PM - 4:45 PM

[SCG58-15] High-temperature fluid–rock interactions in the Shimanto mélange unit: Implications for geochemical reactions along major subduction-related faults

*Tetsuro Hirono1, Tsuyoshi Ishikawa2, Ayana Shimamoro3 (1.Department of Geosciences, Graduate School of Science, Osaka Metropolitan University, 2.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth and Technology (JAMSTEC), 3.Department of Earth and Space Science, Graduate School of Science, Osaka University)

Keywords:earthquake, fault, plate-subduction zone

To understand the slip behavior and characteristics of major faults within subduction-related mélange units, we performed microscopic observations and mineralogical and chemical analyses of a primary slip zone and its surrounding host rocks in the Hidakagawa Group of the Shimanto accretionary complex, Kii Peninsula, Japan. The primary slip zone is characterized by the development of composite planar fabrics such as R1 shear planes and abundant sub-micrometer-sized albite particles. Concentrations of fluid-mobile elements such as Sr, Rb, and Cs in the slip zone were anomalous compared to those in the host rocks. Geochemical modeling suggests that fluid–rock interactions in the slip zone occurred at 250–300 °C and were accompanied by albitization. The presence of such high-temperature fluids in slip zones could drastically weaken faults through thermal pressurization, perhaps promoting the occurrence of tsunamigenic earthquakes.