The Japan Trench Fast Drilling Project (JFAST) demonstrated that the shallow plate boundary fault was weak during the 2011 M_w 9.0 Tohoku-Oki earthquake. This conclusion is derived from: (1) the high fraction of smectite in the fault, (2) high-velocity friction experiments on fault material showing low shear resistance, (3) the low temperature anomaly on the fault, and (4) the decreased in situ horizontal stress in the frontal prism above the fault.

View full abstract

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is an international project which attempts to directly observe the seismogenic megathrust fault of the Nankai Trough where large earthquakes have repeatedly occurred in the past. In this talk, I will briefly introduce the outline and current state of the NanTroSEIZE project, as well as our interest from the geological view point.

 

View full abstract

It has been generally accepted that hydration due to plate bending-induced normal faults (bend-faults) occurs in the region between trench and outer rise. The northwest Pacific (NW Pacific) region is one of the oldest, thus coldest, and most studied oceanic plates. Geophysical data suggest that hydration has extensively progressed to deeper section of the oceanic plate since the 2011 Tohoku Earthquake. In-situ physical properties and lithofacies will be best obtained by ocean drilling. 

View full abstract

Oman Drilling Project (ODP) aims at drilling fresh core samples that were constituents of the oceanic crust and mantle, with using Oman ophiolite. Scientific objectives of the ODP are to unravel oceanic crust formation at the mid-ocean ridge and interaction occurring within the oceanic crust-mantle at hydrosphere, the atmosphere and the biosphere. The ODP scientific studies are expected to launch next year. I will introduce its scientific impact and fascination, with showing several examples.

View full abstract

Nishinoshima, one of the submarine volcanoes in the Ogasawara Arc, ~1,000 km south of Tokyo, Japan, suddenly erupted in November 2013, after 40 years of dormancy. The Nishinoshima volcano might represent the missing link between the mantle and the continental crust because (1) Nishinoshima, whose underlying crust is only 21 km thick, is one of the world’s closest volcanoes to the mantle, and (2) the lavas have been andesites and were similar in composition to the continental crust.

View full abstract

Ultradeep mantle drilling project “MoHole to Mantle (M2M)” can only be pursued by using the Deep Sea Drilling Vessel Chikyu. M2M proposes to penetrate through the 6 km thick oceanic crust and recover the pristine in-situ mantle material first time in the human history in order to understand the nature of the Moho and the geodynamics of convecting mantle, and to shed lights on the origin of water and deep global circulation of carbon, and to know the ultimate limits of deep biosphere. 

View full abstract

We develop a thermodynamic model to calculate phase equilibrium between the hydrous melt and olivine using machine-learning. Cross-validation, a method to evaluate the model predictability, is used to obtain the optimal set of equation and parameters. 

View full abstract

To constrain the thermal structure of the upper mantle in the NE Japan arc, the conditions of magma generation were estimated for basalts from Akita-Komagatake volcano, using a petrological approach. We estimated that the primary magma was generated by 16% partial melting of the mantle with 0.54 wt.% H₂O at 1298°C and 14.2 kbar. This result suggests that the temperature of the sub-arc mantle at 45 km depth is ~1300°C, which is higher than those estimated by geophysical studies by >100°C. 

View full abstract

The origin of rear-arc magmatism was investigated for basalts from Rishiri volcano. The estimated temperature of the slab surface, from which the fluids were released, was remarkably higher than those predicted by thermal models. This result, along with seismic tomography results, suggest that the magmatism resulted from the production of large amounts of slab fluids, caused by an injection of hot mantle materials into a fracture in the distorted portion of the plate at the arc-arc junction.

View full abstract

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.

View full abstract

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.

View full abstract

High-pressure melting experiments and analyses of zoning profile on olivine phenocrysts were performed to estimate conditions of magma chamber and the time scale from ascent of magma to eruption. Temperature, pressure and H₂O content in melt for magma chamber condition were ~1100°C, ~150MPa, 3.0wt.%, respectively. Magma might ascend to shallower part and remain for a few days to a few dozen days before eruption.

View full abstract

Foam collapse is the necessary process for explaining non-explosive silicic eruptions. However, no direct evidence showed that the foam collapse was actually operating in natural magma. We analysed groundmass glass of Mukaiyama rhyolite lava using an FE-EPMA, and observed spatial heterogeneity in the volatile content. We interpret this heterogeneity as reflecting the history of degassing and compaction of magma.

View full abstract

Hydrothermal experiments (230̊C, P_sat) were carried out in olivine (Ol)–quartz (Qtz)–H₂O system, as analogues of crust-mantle boundary. The mineralogy of the reaction products in the Ol-hosted region changed with increasing distance from the Ol–Qtz boundary, from talc to serpentine + magnetite. On the other hand, in Qtz-hosted region, talc was also formed. Talc zone was formed 1.0 mm from the boundary in Ol-hosted region, whereas it also formed 0.5 mm from the boundary in Qtz-hosted region.

View full abstract

Hydrothermal alteration experiments in sulfuric acid solution with graphite and CO₂ atmosphere were carried out. Sulfuric acid oxidizes Fe^{2 +} in silicate minerals and make Fe-Oxide. Presence of graphite, however, can inhibit the formation of Fe-Oxide with sulfuric acid under CO₂ atmosphere.

View full abstract

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.

View full abstract

Physicochemical properties of water in thin film show different characteristics compared with that of free water. In this study, molecular dynamics simulations were performed to investigate the properties of interfacial water on quartz at high temperature and high pressure. The reduction of self-diffusion coefficient of water were observed near the quartz surface even at high temperature.

View full abstract

Gabbroic core samples from the Atlantis Massif (Hole U1309D, IODP Exp. 304/305) were analyzed the relationship between the mineral mode, chemistry, the degree of alteration and P-wave velocity in detail.

View full abstract

Knowledge of solute diffusivity in intergranular fluid is essential for modeling pressure solution creep in upper crust. In this study, we evaluated the diffusion coefficient of dissolved SiO₂ in intergranular fluid using a molecular dynamics simulations.

View full abstract

In order to investigate the mechanism of fluid expulsion from polycrystalline aggregates, we carried out sintering experiments of quartzite with variable X_CO2 (CO₂/H₂O+CO₂). When X_CO2=0, fluids were expelled through interconnected networks to the upper part of the experimental capsules within 192 h. When X_CO2=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.

View full abstract

Our new target of geothermal resources is in 2000-5000m depth and temperature is over 350 degree celsius. In this region, the mechanical behavior of the rocks is considered to be ductile. In this study, we investigated the granite-porphyry system, located in central Akita Prefecture. As a results, homogenization temperature of these fluid inclusions indicate bimodal pattern and PT conditions of these mineral filling veins were estimated. We show the formation model of deep geothermal resource.

View full abstract

Fractures provide significant influences on transport of energy and heat. We conducted hydrothermal flow through experiments using pure water and silica supersaturated solution to reveal a porosity structure and permeability evolution during the dissolution-precipitation in granite fracture. In dissolution experiments, local dissolution of Qtz Gouges made some flow paths and increase fracture permeability. In precipitation experiments, silica precipitation strongly decreased the permeability.

View full abstract

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.

View full abstract

In the 'Hadeba mélange zone' in the Besshi area, Sanbagawa metamorphic belt, tourmaline(Tur)-rich layer indicative of B-bearing fluid infiltration is observed in reaction zones between host metapelites and serpentinite- and marble-lenses. B-bearing fluid infiltrated after peak metamorphism and Ss schistosity formation. Ds deformation continued after it as indicated by E-W trending boudinage of the Tur. K-feldspar veins replacing Tur implies that alkaline fluid infiltration followed it.

View full abstract

Fluids released from dehydration reactions are thought to rise pore fluid pressure within subduction zone; however, little evidence has not been reported from metamorphic rocks. We report skeletal garnet in metachert, which contains large amount of quartz inclusions. The microstructural observations suggest grain-boundary cracking induced by dehydration. By using a model with distinct element method, the conditions and mechanism of reaction-induced fracturing and fluid flow are discussed.

View full abstract

I have been determining salinity data from fluid inclusions in mantle perdidotite xenoliths of subduction mantle wedges, and in jadeite-rich rocks in exhumed subduction channels together with my colleagues. I will summary the salinity data from our on-going works and from the previous works for last twenty five years.   I will suggest a hypothesis on the saline fluids recycling from the ocean to the volcanoes through the subduction channel and the mantle wedge.

View full abstract

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.

View full abstract

We tried to rapid decompression experiment using granite sample with hydrothermal condition. Experimental sample has a borehole, and rapid decompression is started in borehole. Experimental conditions are 600 ˚C - 45 MPa maximum. After the experiments, porosity of fractured sample was 3.3 %. P-wave velocity was decreased from intact sample. Some fractured sample has a very low P-wave velocity as water's one. These results suggest that rapid decompression can make the rock fracture.

View full abstract

The multivariate analysis of deep groundwater database has been performed to detect a chemical characteristics of deep-origin fluid. Since chemical composition of groundwater was determined in 10 or more dimensions, multivariate analysis such as principal component analysis (PCA) and independent component analysis (ICA) can be effective. In this paper, we provide the results of PCA/ICA and discuss characteristics of two analysis.

View full abstract

2016 Kumamoto earthquake caused numerous landslides in Aso area even on relatively gradual slopes. Flat surface of landslide bottom lays in altered volcanic ash strata. XRD analysis revealed that the main component of the altered volcanic ash is halloysite (10Å). Strong earthquake may fluidize swellable clay minerals in gradual slopes.

View full abstract

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.

View full abstract

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.

View full abstract

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.        

View full abstract

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.

View full abstract

Antigorite serpentinization is an important process for the fluid migration at the wedge mantle. Oxidization coincides with progression of the antigorite serpentinization at Higashi-akaishi peridotite body, indicated by the petrological studies of antigorite, altered chromite and sulfide minerals. Relativity reduce condition recorded in the samples is a legacy of peridotite stage. It is not brought by the serpentinization, as the formation of lizardite and chrysotile at low temperature.

View full abstract

 Antigorite serpentinite affects mantle convection and temperature structure of upper mantle. Then the perpose of this study is understanding the plastic behavior of antigorite serpentinite in subduction zone by observing its microstructure. In this study, we used serpentinites from Erro-Tobbio peridotite body which underwent the deformation in subduction zone and has its history. And we observed the microstructure corresponding to the past deformation event.

View full abstract

In this study we examined 45 synthetic diamonds from a gemological point of view to find difference from natural stones. These diamonds were melee-size grown by HPHT method in the range between colorless to near-colorless. All the samples were round brilliant-cut loose stones weighing between 0.0075 and 0.023 ct which were produced in China. These stone can be identified by PL spectroscopy and UV luminescence image.

View full abstract

Quartz such as amethyst is one of gem materials which have a lot of circulation and there are many amethysts difficult to identify natural or synthetic. In this study, we used LA-ICP-MS for trace element analysis of natural and synthetic amethyst. We found discriminat analysis with  with ⁷Li, ⁹Be, ¹¹B, ²³Na, ²⁷Al, ³⁹K, ⁴⁵Sc, ⁴⁷Ti, ⁶⁶Zn, ⁶⁹Ga, ⁷²Ge, ⁹⁰Zr and ²⁰⁸Pb is a good indicator for the identification of natural and synthetic amethyst.

View full abstract

We confirmed the orientation shown by HKL channel 5  (Flamenco, Oxford Instruments) was just consistent with the SEM image rotated by 180 degree around the sample normal direction. We propose a solution for this problem amd confirm to obtain the consistent orientation relationship between SEM images and the crystal orientations obtained by the standard-EBSD and transmission-EBSD by changing the setting parameters ofsample tilt (degree) = -70 and detector orientation (degree) = 180, 90, 0.

View full abstract

Wurtzite is a main constituent mineral in the chimney forming by hydrothermal solution at seefloor. On the basis of observation for their textures and occurrence, we discuss about precipitation processes of wurtzite in chimney at Okinawa trough. 

View full abstract

Lithiophorite from Nagatare pegmatite consists of fine disk-shape crystals with 1 µm in diameter, 500 nm in thickness. The chemical composition and unit cell parameters are (Li_1.00Al_2.00)_Σ3.00(Mn⁴⁺_2.00Mn³⁺_0.86Fe³⁺_0.03Al_0.11)_Σ3.00O₆(OH)₆, and a = 2.921(5), c = 28.44(5) and V = 210.1(7). Alternative MnO₆ octahedral sheet and (Al,Li)(OH)₆ octahedral sheet were observed in STEM-HAADF image. HRTEM image indicates ordered structure in (Al,Li)(OH)₆ octahedral sheet. 

View full abstract

We report a new mineral, kannanite from Kannan Mountain, Ehime Prefecture, Japan. Kannanite corresponds to Ca-rich analogue of ardennite-(V).

View full abstract

Microprobe analyses were carried out on Mn-rich amphiboles in a quartz schist from the Iimori mine, Wakayama Prefecture, Japan. The amphiboles are chemically heterogeneous within single grains. Their compositions vary from magnesio-riebeckite to suenoite (manganocummingtonite) with Mn at the M4 site = 0.00-1.81 apfu.

View full abstract

The oolitic calcite from Shirahone hot spring is famous from the end of 19th century . It was designated to special natural monument in 1952. However, after a study of Sato (1922), the modern mineralogical study was not done. I observed microstructure of the oolitic calcite using SEM-EDS this time. As for the spherical calcite, a concentric-formed transparent part (long prismatic calcite) and an translucent part (granular calcite) make alternated layers.

View full abstract

I report a characteristic of the petrography of a abyssal peridotite sample  from  Gakkel Ridge in this announcement. In the rare-earth element pattern of the monoclinal pyroxene, the flat pattern that the decrease in light rare earth element was not seen in was recognized. In this announcement, I argue about the variety of these patterns including result of mineral chemical composition in mylonite.

View full abstract

Ce- and Ba-bearing pryochlores
were examined in the Nb-ore specimen from Araxá, Minas Gerais, Brazil. EPMA chemical analyses and single crystal diffraction works revealed that they are identified as a Nb-analogue of hydroxykenomicrolite, ( ,REE,Ba)₂(Nb,Ti)₂O₆(OH,F), and a Ba-bearing hydropyrochlore, (H₂O,Ba)₂Nb⁵⁺₂(O,OH)₆(H₂O).

View full abstract

A B-bearing hingganite related mineral shows an ordering of (Y,Yb)/(Y,Ca) at the 8-coordinated Y-sites to lower the symmetry of monoclinic crystal structure from P2₁/a to P2₁. This mineral, [(Y,Yb)(Y,Ca)]( ,Fe)Si₂₍Be,B)₂O₈(OH)₂, is characterized with a solid solution towards datolite composition [Ca₂ Si₂B₂O₈(OH)₂] in addition to the other end member composition [YCa _⅔Fe³⁺_⅓Si₂Be₂O₈(OH)₂].

View full abstract

In the 2014 General Meeting of Mineralogical Society of Japan, we reported focus size of 14.4keV g-ray of Mössbauer microspectorometer using a multi-capillary X-ray lens (MCX) and proportional counter detector.  In that report, a proportional counter was used as γ-ray detector.  In this report, a Si-PIN semi-conductor, of which energy resolution is better than a proportional counter, is used to fix the spot size of focused g -ray by MCX. 

View full abstract

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.

View full abstract

Gandolfi diffractogram from each particles should be simulated precisely when we utilize the pattern collected from "one or a few" particles. Bragg cones made of one Bragg position could successfully be simulated as a function of the angle between scattering vector K and one of two rotation axes (A" axis) on the camera. We succeeded to simulate Bragg cones for typical Bragg positions, one on the A" axis and others 60° apart from the axis.

View full abstract