Japan Trench Fast Drilling Project (JFAST) は、2011年3月11日に発生した東北地方太平洋沖地震（Mw9.0）においてなぜプレート境界浅部が大きく滑り巨大津波を引き起こしたのか明らかにするために実施された。掘削地点は、地震時に最も大きく（約50 m）滑った宮城沖の日本海溝近くのプレート境界である。JFASTでは、掘削同時検層を行って掘削地点における物性・応力状態を把握するとともに、プレート境界からコア試料を採取し地震性滑りメカニズムと摩擦特性の検討を行った。更に、掘削孔内に温度計を設置して残留摩擦熱を計測し地震時の摩擦強度を求めた。その結果、ひとたび地震時に断層の摩擦強度が低下すれば、深部からの破壊伝播を促進しプレート境界浅部でも大きな滑りが生じる得ること、このような浅部巨大地震性滑りは日本海溝のようなスメクタイトを大量に含む遠洋性粘土層に沿って起こりやすいことが明らかになった。JFASTにより、巨大津波の引き金となったプレート境界浅部地震性滑りの成因を解明することに成功した。
We examined mineral and melt inclusions in anorthite megacrysts from Ogi Peninsula, Niigata, Japan. The dominant mineral inclusions are Fe-Cu-Ni-sulfides that occur with mafic melt inclusions. In addition, volatile components such as S and Cl were detected in the melt inclusions. These results suggest that the present anorthites have grown in volatile-rich condition owing to the mixing of crustal components into basaltic magma chamber.
We report major element chemistry and dissolved water contents of glassy pillow lava margins from the Troodos Ophiolite. The sampled glasses are basaltic andesites, boninitic basaltic andesites and evolved andesite and dacites. H2 O content of basaltic andesites ranges from 1.5 to 2.5 wt%. Temperature estimates for the primitive boninitic samples are within 1130 to 1190C. Saturation pressures calculated using VolatileCalc at variable CO2 contents are within 300 to 550 bars.
Hydrogen diffusion may play a key role in dehydration processes of hydrous minerals. It has been desired to observe the dynamics of hydrogen cations or their vacancies moving within the structures of dehydrating minerals. Here we apply high-resolution quasielastic neutron scattering for analyzing time and distance scales of hydrogen diffusion in brucite at temperatures to 330 K. A very mobile nature of interstitial-type hydrogen and its potential role in dehydration are revealed and discussed.
In order to investigate the mechanism of fluid expulsion from polycrystalline aggregates, we carried out sintering experiments of quartzite with variable XCO2 (CO2/H2O+CO2). When XCO2=0, fluids were expelled through interconnected networks to the upper part of the experimental capsules within 192 h. When XCO2=0.39-0.79, fluids were retained among the quartzite grains by forming intergranular fluid pockets. These pockets were formed by rearrangement and coagulation of fluid filled pores.
Many quartz veins that filled mode I cracks (extension quartz veins) can be observed in the hanging wall and footwall of the Nobeoka Thrust. In this study, the equilibrium and kinetic model of the formation of the extension quartz veins along the Nobeoka Thrust were estimated to consider the relationship among the distribution of quartz veins, the time scale of crack sealing and the cycle of seismic activities.
To investigate the controlling factors of reaction-induced stress and strain during hydration reactions, the reaction-induced stress and strain were directly measured in CaSO4–H2O system. The results show that reaction-induced stress and strain are primarily controlled by the competitions between reaction rate and deformation rate. This competition determines fracture generations and permeability enhancement, and thus can contribute to the fluid distribution within the wedge mantle and crust.
Hydration is one of the important process involves fluids movement causes changes in the mass balance and redistribution of elements, as well as formation of new minerals. Pyroxenite that are partly hydrated along veins was collected from Mefiell, East Antarctica. By using hornblende-plagioclase thermometer and Al in hornblende geobarometer formatting conditions of hydrated minerals were estimated to be ~ 6 Kbar, 650±50°C, which was equivalent to the metamorphic conditions of the pyroxenite.
Studied peridotites have subject to a series of serpentinization and carbonation. It was estimated that the peridotites were serpentinized mostly through interaction with magmatic and metamorphic fluides and sbjected to carbonation by magamtic and basaltic oceanic crust carbon.
Titanian andradites up to 15.14 wt.% TiO2in chromitite from Nagaland ophiolite, India have been investigated. They are euhedral, complexly zoned and occur typically either as veinlets or in granular aggregates within serpentine-rich veins traversing the chromitites. Major element analysis and elemental mapping across the grains demonstrates several titanium pulses during their growth. Trace element analysis indicates sharp positive europium anomaly and negative strontium anomaly.
The Jandaq ophiolite has suffered different types and phases of metamorphism. In this ophiolite, gabbroic dikes and plugs cross cut the mantle peridotites. Minerals of metagabbros are clinopyroxene, amphibole, plagioclase, titanite, prehnite, epidote, magnetite and calcite. Joints and cracks of gabbroic intrusions are filled by hydrothermal minerals. These hydrothermal veins are consist of clinopyroxene, garnet, epidote, prehnite, chlorite and calcite, and are light in hand specimen.
Electron diffraction is one of the most powerful tool for mineral phase identifications and crystal orientation analyses on nanometer scales, although its application requires a certain degree of crystallographic geometry and diffraction theory. In the present study, an algorithm of semi-automatically indexing for electron diffraction pattern were developed. It enables us to index complex pattern from multiple crystalline phases.