Mode of occurrence of fault rocks in the drilled cores (GSJ and NIED) penetrating the Nojima Earthquake Fault

秀実, 田中; 隆司, 池田; 久男, 伊藤; 崇史, 新井; 具幸, 大谷; 健太朗, 小村; 健太, 小林; 広征, 佐野; 隆, 澤ロ; 倫明, 富田; 直人, 冨田; 孝幸, 樋ロ; 聡, 平野; 光一郎, 藤本; 達生, 松田; 暁子, 山崎

doi:10.5575/geosoc.104.xiii

“…An 1800 m borehole was drilled to penetrate the Nojima Fault by the National Research Institute for Earth Science and Disaster Prevention (NIED) at Nojima Hirabayashi, Awaji Island, Hyogo prefecture, Japan (Ikeda 2001; Ikeda et al 2001). The overview of the drilling cores is shown by Tanaka et al (1998). We observed the characteristic fabrics of deformation and alteration (cataclasite) in cores retrieved from fracture zones at depths of approximately 1140 m, 1300 m and 1800 m (Fig.…”

Section: Introductionmentioning

confidence: 93%

Examination of mineral assemblage and chemical composition in the fracture zone of the Nojima Fault at a depth of 1140 m: Analyses of the Hirabayashi NIED drill cores

Matsuda¹,

Arai²,

Ikeda³

et al. 2001

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A 1800 m deep borehole was drilled at Nojima Hirabayashi, Japan to penetrate through the Nojima Fault, which was activated at the time of the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). Three fracture zones were recognized in cores at approximate depths of 1140 m, 1300 m and 1800 m. The mode of distribution of fault rocks, minerals and chemical elements were analyzed in an interval between depths of 1108 m and 1161 m, focusing on the fracture zone at the depth of 1140 m. Foliated blue-gray fault gouge constituted the central part of the fracture zone. The degree of fracturing appeared to be greater in the hanging wall than in the footwall. The relative amounts of minerals were estimated qualitatively. In the analyzed interval, not only were quartz, orthoclase, plagioclase, biotite and hornblende detected in the parent rock (granodiorite), but also kaolinite, smectite, laumontite, stilbite, calcite, ankerite and siderite, which are related to hydrothermal alteration. In particular, biotite disappeared both in the hanging wall and footwall across the central fault zone; it disappeared over a wider range in the hanging wall than in the footwall. The amounts of major chemical elements were analyzed quantitatively. Concentrations of Al 2 O 3 , Fe 2 O 3 , MnO, TiO 2 , and P 2 O 5 all decreased throughout the interval except at some points. H 2 O + and CO 2 increased throughout the interval. Na 2 O increased in the region outside the central plane, whereas MgO and CaO increased in the hanging wall and decreased in the footwall. SiO 2 and K 2 O decreased in the hanging wall and increased in the footwall. These results elucidate the higher degree of fracturing and chemical changes present in the hanging wall of the 1140 m fracture zone than in the footwall.

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“…Based on the degree of alteration and deformation, we categorized the fault‐related rocks into four types: weakly deformed and altered granodiorite, cataclasite, fault breccia, and fault gouge. The details of the lithology and the mode of distribution are described in Tanaka et al (1998, 1999) and Ohtani et al (2001). Tanaka et al (1999) recognized six shear zones probably associated with subsidiary faults other than the fault core of the Nojima Fault and characterized the seven shear zones in terms of degree of deformation and alteration.…”

Section: Outline Of the Hirabayashi Gsj Boreholementioning

confidence: 99%

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

Fujimoto

¹

,

Tanaka

²

,

Higuchi

³

et al. 2001

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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.

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“…Based on the degree of alteration and deformation, we categorized the fault-related rocks into four types: weakly deformed and altered granodiorite, cataclasite, fault breccia, and fault gouge. The details of the lithology and the mode of distribution are described in Tanaka et al (1998Tanaka et al ( , 1999 and Ohtani et al (2001). Tanaka et al (1999) recognized six lithology; distribution of minerals, which were identified using the X-ray diffraction powder (XRD) method; loss of ignition (LOI) of the whole rock chemistry; and velocity of P-waves (Vp).…”

Section: Outline Of the Hirabayashi Gsj Boreholementioning

confidence: 99%

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

Fujimoto¹,

Tanaka²,

Higuchi³

et al. 2001

Isl Arc

Self Cite

View full text Add to dashboard Cite

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.

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Mode of occurrence of fault rocks in the drilled cores (GSJ and NIED) penetrating the Nojima Earthquake Fault

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Examination of mineral assemblage and chemical composition in the fracture zone of the Nojima Fault at a depth of 1140 m: Analyses of the Hirabayashi NIED drill cores

Examination of mineral assemblage and chemical composition in the fracture zone of the Nojima Fault at a depth of 1140 m: Analyses of the Hirabayashi NIED drill cores

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

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

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