Japan Geoscience Union Meeting 2022

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-SS Seismology

[S-SS07] Fault Rheology and Earthquake Physics

Mon. May 23, 2022 3:30 PM - 5:00 PM 105 (International Conference Hall, Makuhari Messe)

convener:Makiko Ohtani(Earthquake Research Institute, the University of Tokyo), convener:Keishi Okazaki(Japan Agency for Marine-Earth Science and Technology), Ryo Okuwaki(Mountain Science Center, Faculty of Life and Environmental Sciences, University of Tsukuba), convener:Shunya Kaneki(Disaster Prevention Research Institute, Kyoto University), Chairperson:Shunya Kaneki(Disaster Prevention Research Institute, Kyoto University), Keishi Okazaki(Japan Agency for Marine-Earth Science and Technology)

4:45 PM - 5:00 PM

[SSS07-12] Breccia and Pulverized Rock associated with stibnite mineralization along Median Tectonic Line, Japan

*Geri Agroli1, Masaoki Uno1, Atsushi Okamoto1, Noriyoshi Tsuchiya1 (1.Tohoku University)

Keywords:Breccia, Stibnite, Pulverization, Median Tectonic Line

Rock pulverization is a unique rupture process where fault zone rocks are shattered in situ without significant shear or rotation. Investigations regarding the formation of pulverized fault zone rock (PFZR) suggested that it is a coseismic phenomenon associated with supershear (high-strain rate) or subshear (modest-strain rate). We present the novel field observation of possibly pulverized rock and its evolution toward the fault cataclasite/breccia in the Ichinokawa (stibnite) deposit in Central Shikoku. This deposit also coincides with the Median Tectonic Line (MTL) Based upon the texture of pelitic schist outcrop and particle size distribution (PSD), the breccia is classified into two types. Breccia-1 (bx-1) is characterized by a centimeter-meter (up to 5m) angular breccia-clast with minimum to no shear displacement and rotational block of monomict Sanbagawa pelitic-schist which consider forming under pulverization mechanism. And hydrothermal subsequent activity in this area is responsible to create bx-2 as a result of fluid injection and transporting comminuted-fragment of bx-1 into the damage/fault zone. Bx-2 appears to have chaotic-polymict clast with matrix-supported texture within the fault zone with variable width and cut the bx-1 by recognizable breccia margin. Stibnite deposits mark the latest fluid activity in this area where qtz-stibnite vein truncate both bx-1 and bx-2.