Papers by Tsuyoshi Toyoshima
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Japan Geoscience Union, 2017
Three pseudotachylyte-producing fault zones develop in Yawatahama-Oshima, Ehime, Japan (Komatsu e... more Three pseudotachylyte-producing fault zones develop in Yawatahama-Oshima, Ehime, Japan (Komatsu et al., 1997, 1998). The Yawatahama-Oshima pseudotachylytes and their related fault rocks were formed under greenschist-facies conditions (upper continental crustal conditions) (Komatsu et al., 1997, 1998; Komatsu, 2001). We illustrate generation of the Yawatahama-Oshima pseudotachylyte accompanied by plastic deformation, as a example of ancient seismogenic fault zones in upper crust. Pressure solution-precipitation structures (pressure solution cleavage accompanied by quartz and feldspar veins) are characteristically abundant in the Yawatahama-Oshima pseudotachylyte-producing fault zones. Modes of occurrence of the Yawatahama-Oshima pseudotachylytes and pressure solution cleavage indicate that seismic slip with pseudotachylyte generation and slow plastic deformation (pressure solution with precipitation) alternated in the same fault zones and along the same fault surfaces. Therefore we c...
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Retrograde metamorphic P-T paths of garnet—pyroxene—bearing mafic gneisses from the Brattnipene n... more Retrograde metamorphic P-T paths of garnet—pyroxene—bearing mafic gneisses from the Brattnipene nunataks in Sør Rondane Mountains, East Antarctica, were examined. The majority of samples preserve irregular—shaped garnet coexisting with clinopyroxene, quartz and plagioclase that developed around magnetite, ilmenite and orthopyroxene. The garnet contains fine—grained worm—like quartz inclusions. The occurrences are common in other mafic gneisses in northern Brattnipene and are interpreted as isobaric cooling textures. In another sample, garnet porphyroblasts have been replaced by symplectites of fine orthopyroxene and plagioclase. The mineral textures indicate near isothermal decompression. Retrograde P-T conditions estimated from rock containing orthopyroxene—plagioclase symplectite are within the range of 6.5 ~ 7.2 kbar, 700 ~ 780℃. Previous reports have revealed that metamorphism around Brattnipene is characterized by counterclockwise P-T path involving near—isobaric cooling. Our n...
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Fault-related Rocks, 1998
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The knowledge of rock composition is significant to understand the dynamics of the lithosphere in... more The knowledge of rock composition is significant to understand the dynamics of the lithosphere in subduction systems. To estimate rock composition of the lithosphere, it is an effective method to compare the elastic wave velocities measured under the high pressure and temperature condition with the seismic velocities obtained by active source experiment and earthquake observation. Until now, various crustal rocks have been determined by means of high P-T measurements [e.g., Christensen and Mooney, 1995]. However, rock composition of the overriding plate is still poorly understood. Due to an arc-arc collision in central Hokkaido, middle to lower crust is exposed along the Hidaka Metamorphic Belt (HMB), providing exceptional opportunities to study crust composition of an island arc. We collected rocks at Hidaka Mountains and have tried to simultaneously measure the travel times of the P and S waves through a rock sample under high P-T conditions using a piston-cylinder apparatus at Yo...
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Earth, Planets and Space, 2008
The Geological Survey of Japan, AIST, has been monitoring groundwater in and around the Kinki and... more The Geological Survey of Japan, AIST, has been monitoring groundwater in and around the Kinki and Tokai districts for earthquake prediction research. The Niigata Prefectural Office has also been observing groundwater for monitoring land subsidence in Niigata Prefecture. The 2004 Niigata-Chuetsu (MJMA6.8) and 2007 Chuetsuoki (MJMA6.8) earthquakes occurred in Niigata Prefecture, Japan, on October 23, 2004 and July 16, 2007, respectively. The two earthquakes have a similar magnitude, epicenter, and mechanism. At many of the observation wells, we detected changes in groundwater level or pressure related to the two earthquakes, but no clear precursory changes. At all of our observation wells in Niigata Prefecture, trend changes were observed after coseismic step-like changes for both of the earthquakes. At some of the stations in and around the Kinki and Tokai districts, coseismic trend changes and/or step-like changes were observed. The pattern of the changes were almost similar for the...
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Polar Science, 2010
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Contributions to Mineralogy and Petrology, 2002
The ultrahigh-temperature (UHT) metamorphism of the Napier Complex is characterized by the presen... more The ultrahigh-temperature (UHT) metamorphism of the Napier Complex is characterized by the presence of dry mineral assemblages, the stability of which requires anhydrous conditions. Typically, the presence of the index mineral orthopyroxene in more than one ...
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Polar Science, 2011
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Annual Meeting of the Geological Society of Japan, 1998
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Annual Meeting of the Geological Society of Japan, 1998
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Annual Meeting of the Geological Society of Japan, 2000
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Annual Meeting of the Geological Society of Japan, 1995
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Annual Meeting of the Geological Society of Japan, 2001
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Annual Meeting of the Geological Society of Japan, 2017
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Annual Meeting of the Geological Society of Japan, 2007
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Annual Meeting of the Geological Society of Japan, 1997
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Annual Meeting of the Geological Society of Japan, 2018
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Papers by Tsuyoshi Toyoshima