Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Ar resetting in an ultracataclasite by reactivation of a fossil seismogenic fault along the subducting plate interface in the Mugi M
lange of the Shimanto accretionary complex, southwest JapanTonai, Satoshi*; Ito, Shun*; Hashimoto, Yoshitaka*; Tamura, Hajimu; Tomioka, Naotaka*
Journal of Structural Geology, 89, p.19 - 29, 2016/08
Times Cited Count：16 Percentile：48.89(Geosciences, Multidisciplinary)We used the K-Ar ages of clay-sized mineral grains to investigate the timing of activity on the fossil seismogenic Minami-Awa Fault. The K-Ar ages from matrix shale of the mlange range from 85 to 48 Ma and decrease with decreasing amount of detrital mica. In contrast, the K-Ar ages of an ultracataclasite within the fault core are significantly younger, ranging from 29 to 23 Ma, and are unrelated to grain size. This indicates that Ar diffused completely from the ultracataclasite between 29 and 23 Ma. The diffusion of Ar in the ultracataclasite was probably caused by frictional heating or high-temperature fluid migration that occurred when the fault was reactivated. The results indicate that seismogenic faults that separate tectonic mlange from coherent strata in accretionary complex may slip, not only during accretion, but also long after accretion.
Ishii, Eiichi
Journal of Structural Geology, 89, p.130 - 143, 2016/08
Times Cited Count：9 Percentile：31.14(Geosciences, Multidisciplinary)To investigate the role of bedding in the evolution of meso- and microstructural fabrics in fault zones, detailed microscopic, mineralogical, and geochemical analyses were conducted on bedding-oblique and bedding-parallel faults that cut a folded Neogene siliceous mudstone that contains opal-CT, smectite, and illite. An analysis of asymmetric structures in the fault gouges indicates that the secondary fractures associated with each fault exhibit contrasting characteristics: those of the bedding-oblique fault are R1 shears, whereas those of the bedding-parallel fault are reactivated S foliation. The bedding-oblique fault shows the pervasive development of S foliation, lacks opal-CT, and has low SiO
/TiO ratios only in gouge, whereas the bedding-parallel fault exhibits these characteristics in both gouge and wall rocks. The development of S foliation and the lack of silica can result from local ductile deformation involving the sliding of phyllosilicates, coupled with pressure solution of opal-CT. Although such deformation can occur in gouge, the above results indicate that it may occur preferentially along bedding planes, preceding the formation of a gouge/slip surface. Thus, in sedimentary rocks that contain phyllosilicates and soluble minerals, bedding can influence the rheological evolution of meso- and microstructural fabrics in fault zones.
Ono, Takuya; Yoshida, Hidekazu*; Metcalfe, R.*
Journal of Structural Geology, 87, p.81 - 94, 2016/06
Times Cited Count：4 Percentile：14.04(Geosciences, Multidisciplinary)Fracture filling minerals were formed during the development of an accretionary complex. Each mineral formed under favourable geological conditions and can be used to estimate the conditions of accretion. Geological observations and analyses were made on fracture fillings from boreholes of ca. 140 m depth, in the Shimanto Belt of Kyushu. Results revealed that the minerals were formed in 5 stages distinguished by the textural relationships of the minerals. Filling minerals show that the studied rock formation has been subducted to several km depth and the temperature reached was ca. 200 - 300
C. After the subduction, the rock formation uplifted and surface acidic water penetrated up to 80 m beneath the present ground surface. The acid water dissolved calcite fillings to form the present groundwater flow-paths. The results shown here imply that filling minerals can be an effective tool to evaluate the environmental changes during accretionary complex formation.
Ishii, Eiichi
Journal of Structural Geology, 34, p.20 - 29, 2012/01
Times Cited Count：20 Percentile：48.58(Geosciences, Multidisciplinary)Origin and scaling of faults in a massive siliceous mudstone at the Horonobe Underground Research Laboratory site, Japan, were studied by outcrop observations to estimate approximate sizes of the faults from borehole data and to construct a fracture-flow model in and around the Ventilation Shaft in studies related to radioactive waste disposal. Very thin shear or compacted shear bands with weak internal foliations were observed near and along the faults and at and beyond the fault tips. This suggests that the faults originated as such thin bands nucleated by ductile deformation were immediately overprinted by slip surfaces. Such descriptions of faults in mudstone are comparatively rare. Furthermore, good scaling between fault rock thickness and displacement was observed for fault rock thickness less than 8 cm. Although the scaling for fault rock thickness larger than 8 cm was not observed, the scaling of thicker faults was estimated using the cumulative distribution of displacements calculated from fault rock thickness in drill core. A fracture-flow model in and around the shaft was constructed by interpolation/extrapolation from nearby boreholes based on the developed scaling method in this study. This model includes hydraulic pressure responses observed in nearby boreholes associating with inflow into the shaft.
Ishii, Eiichi; Funaki, Hironori; Tokiwa, Tetsuya; Ota, Kunio
Journal of Structural Geology, 32(11), p.1792 - 1805, 2010/11
Times Cited Count：25 Percentile：55.07(Geosciences, Multidisciplinary)In order to assess influences of a remote mean stress on a principal mode of failure near fault tips due to fault slip in a lithologically homogeneous, fractured rock mass, the growth mechanisms of strike-slip faults on outcrop-scale in the siliceous mudstones of northern Hokkaido, Japan, have been studied. A multifaceted approach combining geological characterizations of fractures, rock mechanical characterizations, and theoretical analyses have been done, which suggested (1) the principal mode of failure depend on not only the rock strengths, but also the remote mean stresses, (2) during and/or after uplift and erosion the faults grew mainly by linking with adjacent faults via many splay cracks which are formed by tensile failure above roughly 400 m depth, while, below the depth, the faults predominantly grew by shear failure. Such growth mechanisms are consistent with the fact that highly permeable sections are restricted to depths of less than 400 m.
