Alteration and mass transfer inferred from the Hirabayashi GSJ drill penetrating the Nojima Fault, Japan

Abstract

Mineralogical and geochemical studies on the fault rocks from the Nojima-Hirabayashi borehole, south-west Japan, are performed to clarify the alteration and mass transfer in the Nojima Fault Zone at shallow depths. A complete sequence from the hornblende-biotite granodiorite protolith to the fault core can be observed without serious disorganization by surface weathering. The parts deeper than 426.2 m are in the fault zone where rocks have suffered fault-related deformation and alteration. Characteristic alteration minerals in the fault zone are smectite, zeolites (laumontite, stilbite), and carbonate minerals (calcite and siderite). It is inferred that laumontite veins formed at temperatures higher than approximately 100°C during the fault activity. A reverse component in the movement of the Nojima Fault influences the distribution of zeolites. Zeolite is the main sealing mineral in relatively deep parts, whereas carbonate is the main sealing mineral at shallower depths. Several shear zones are recognized in the fault zone. Intense alteration is localized in the gouge zones. Rock chemistry changes in a different manner between different shear zones in the fault zone. The main shear zone (MSZ), which corresponds to the core of the Nojima Fault, shows increased concentration of most elements except Si, Al, Na, and K. However, a lower shear zone (LSZ-2), which is characterized by intense alteration rather than cataclastic deformation, shows a decreased concentration of most elements including Ti and Zr. A simple volume change analysis based on Ti and Zr immobility, commonly used to examine the changes in fault rock chemistry, cannot account fully for the different behaviors of Ti and Zr among the two gouge zones.

Healing microstructures of experimental and natural fault gouge

“…Pseudotachylytes related to this deformation episode [ Boullier et al , 2001] were dated at 56 ± 4 Ma by fission tracks on zircons [ Murakami and Tagami , 2004]. The deformation was followed by an alteration producing laumontite [ Fujimoto et al , 2001] which indicates temperatures of 150°C–280°C [ Zen and Thompson , 1974, Boullier et al , 2004].…”

Deformation mechanisms and fluid behavior in a shallow, brittle fault zone during coseismic and interseismic periods: Results from drill core penetrating the Nojima Fault, Japan

“…In fact, the underground water level lowered on the mountain side at the hanging wall and waters came up from underground at the area of the footwall side of the Nojima Fault when the Hyogoken‐Nanbu earthquake struck in this area, suggesting that water flowed through the fault zone (Tokunaga 1999). Footwall material was seen to be altered in cores obtained by the Geological Survey of Japan (GSJ; drilled depth of approximately 700 m; Tanaka et al 1999; Fujimoto et al 2001) and by the National Research Institute of Earth Science and Disaster Prevention (NIED; drilled depth of approximately 1140 m; Kobayashi et al 2001; Matsuda et al 2001), suggesting the influence of co‐ or postseismic inflows of water from the hanging wall. The brecciated rocks reacted with fluids and subsequently formed a new fault gouge zone.…”

Fault-Drilling Investigation of Earthquake Slip Behavior and Physicochemical Processes

“…える発熱が推定され (Fukuchi and Imai, 2001) さらに K-Ar 年代測定やフィッショントラック 解析を通して 断層活動による年代の若返りや熱 水変質による再加熱などの影響が明らかにされた (Tagami et al, 2001 (Ohtani et al, 2000;Fujimoto et al, 2001;Tanaka et al, 2001a;Boullier et al, 2004 伊藤ほか, 1996;Ohtani et al, 2001;Ikeda, 2001;小村ほか, 2003;Tanaka et al, 2007b;Mizuno et al, 2008 力配置の変化が認められた (Lin et al, 2007;Wu et al, 2007) Hirono et al (2006) . (Hirono et al, 2007(Hirono et al, , 2008Mishima et al, 2006Mishima et al, , 2009 Hirono et al (2009) .…”