To verify whether and how slab-derived fluids may modify the composition of the mantle beneath subduction zones, we determined the noble gas and halogen compositions of olivines in arc lavas from the northern Izu-Ogasawara subduction zone and IODP sediments and basalts recovered from the northwestern margin of the Pacific plate. Across arc variations in Ar isotope ratios and halogen compositions suggest that halogen-poor fluid associated with atmospheric noble gases may be predominantly released from the subducting slab beneath the arc, whilst halogen-rich fluid is released at greater depths and is a significant contributor to the magmas of some rear-arc volcanoes.
Anorthite megacrysts in basaltic andesite from Mt. Fubo, Miyagi Prefecture were examined by EPMA-WDS and SEM-EDS. These observations revealed that anorthite contents of the megacrysts are An92-94 and small Fe-Ni-sulfides (20-50µm) were included in the megacrysts. Our results indicate that these megacrysts have grown in volatile (e.g., H2O and S) rich and low viscosity condition.
Hydrogen concentration of plagioclase xenocrysts in scoriae from the Sannnome-gata volcano, a rear-arc volcano in the northeast Japan arc, was analyzed to understand uptaking process of plagioclase xenocryst (An30) into high-MgO (>8 wt.%) basaltic melt before the eruption. Hydrogen concentration of the outer core of plagioclase is >200 wt. ppm H2O, while that of inner core is 60 wt. ppm H2O. This observation suggests that plagioclase xenocryst was in contact with H2O-rich basaltic melt for a couple of hours before the eruption and that the primary magma of the rear-arc volcano is H2O-rich as well as that of frontal-arc volcano.
Petit-spot volcanism is a phenomenon ubiquitous on Earth occurring where the plate flexes and fractures. To define the geological characteristics of petit-spot volcanoes in the northwestern Pacific, we constructed a comprehensive dataset of geochemistry and 40Ar/39Ar ages of alkaline basaltic rocks and glasses collected from three volcanic fields. This dataset and observed temporal migration of vent fields indicate that the magma originates from isolated melt ponds at the lithosphere–asthenosphere boundary, and that the speed at which the melt ponds are dragged by the plate is only slightly slower than that of the plate motion.
Diffusion experiments of water in SiO2 glass were made to understand the concentration dependence of water diffusion and its mechanism. We propose that water diffusivity in SiO2 glass is controlled by the relative abundance of main diffusion species (molecular water) and numbers of diffusion pathways, which are produced by hydroxyls. Our model is applicable to water diffusion in silicate glasses by considering the effects of concentration of network modifier cations and the water concentration dependence of activation energy.
We construct the model that describes the density of the silicate melt as a function of T, P, H2O content and the melt composition. A set of volumetric parameters for the H2O component in the melt are newly calibrated using the results of previous high pressure experiments. The parameter set will be used for the calculations of density, thermodynamic properties and seismic velocity of various hydrous melts.
The effect of sulfur degassing on fO2 condition of the petit-spot site-B basaltic melt is numerically examined assuming equilibrium batch degassing. The results indicate that the effect of S degassing on fO2 of melt depends on initial fO2 condition of melt. At fO2 ~ QMF+0.7, sulfur degassing does not influence on melt fO2 condition. For melt more/less oxidized than QMF+0.7, melt fO2 increases/decreases as S degasses. By considering < 2000 ppm of sulfur degassing, initial fO2 condition of petit spot melt is estimated to be > QMF+1.4, indicating arc-like fO2 condition of petit-spot mantle.
Halogens are powerful tracers of subducted water. In order to investigate the influence of slab-derived fluids and the phase which control halogens in the mantle wedge, halogens of mantle xenoliths from volcanic fronts (Avacha and Pinatubo) and rear-arc region (Ichinomegata) were determined. Iodine-rich slab-derived halogens strongly extend into the mantle beneath volcanic fronts. Contributions from various components were found in the rear-arc region and they seem to be controlled by halogens in clinopyroxenes.
Peridotite xenoliths from Iraya volcano, the Philippines, are known as metasomatite by SiO2-rich aqueous fluids (and melts). The petrographic features are similar to those of Avacha peridotite xenoliths, containing abundant H2O fluid inclusions, and it is expected that the Iraya xenoliths also contain a large amount of H2O inclusions. We would like to discuss about the relationships between the general features of H2O fluid inclusion and petrographical features (presence or absence of metasomatic minerals and their mode of occurrence) of host peridotite xenoliths.
To understand how partial melting changes the electrical conductivity and viscosity of ascending mantle (ex. beneath mid-ocean ridge), we measured both properties of synthesized lherzolite samples at high temperature under atmospheric pressure. At below solidus, the conductivity and viscosity of samples exhibited a linear distribution in its Arrhenius plot with almost same activation energy (~ 180 kJ/mol and ~ 700 kJ/mol for conductivity and viscosity, respectively). At above solidus, the conductivity and viscosity showed steeper change with temperature increase. The observed increment in conductivity and decrement of viscosity are considered to be related to the increment of melt fraction.
Supercritical geothermal reservoir future geothermal reservoirs are in and around ductile rock bodies. Ductile regime which is estimated beyond brittle zone is target region for future geothermal development due to high enthalpy fluids and relatively weak water-rock interaction. Ductile zone is considered to be developed above 400ºC and below 3 km around active volcanic front in Tohoku District, Japan.
In our previous experimental results, ”Hydrothermally Derived Fracture (HDF)” were progressed under the high temperature and low-pressure condition. The result of detailed observation, it was thought that the thermal stress occurred with rapid cooling of rock/mineral sample surface by low temperature condensed vapor dew contact. similarly, rapid decompression in the high-temperature/pressure state causes the rapid temperature decline by latent/sensible heat effect. And when such situation has happened around the rock/mineral samples, HDF may occur under the hydrothermal condition. When this decompression fracturing mechanism is elucidated, it may be useful for Enhanced Geothermal System or understanding of mineral vain formation.
In this study, the purpose is to establish a geothermal resource evaluation method using the magma temperature and pressure by the analysis of melt inclusions. Crystallization depth estimated by the norm composition of the melt inclusions and the eutectic phase diagram of Qtz-Ab-Or is suggested to be 1.6~10km. The trace element concentration of inclusion in a single crystal shows correlation with the crystallization depth, indicating differentiation during ascent. Major crystallization pressure is 150~250 MPa, and presence of huge magma chamber was suggested at 5~8km. The current magma chamber estimated from seismic exploration is deeper depth, thus it has deepened for 7My.
Water-Rock Interaction has an important role for spatial and temporal change of permeability in the Earth’s crust. In the geothermal field, the permeable-impermeable boundary is at around 3 km depth because of high geothermal gradient. This boundary consists of the local minimum value of quartz solubility in the Kakkonda geothermal field, Japan, due to the phase change of H2O. In this study, quartz solubility is calculated to reveal the relationship between the permeability and dissolution-precipitation of silica minerals in the deep drilling wells in Italy, Iceland, and U.S.A., which recorded overpressure at the bottoms of them.
The Kii peninsula is one of the place where the specific brine is upwelling, in addition to Arima hot spring which is the type locality of Arima-type brine. In this study, we have investigated spring waters in the Kii peninsula in order to constrain the origin and upwelling process, and discuss the relationship between Arima-type brine and geological setting, based on the comparison with volcanic rocks.
Formation of hydrogen and abiotic methane results from serpentinization of ultramafic rocks, though the rate is extremely limited. On the other hand, higher rate of H2 production from oxidation of hydrogen sulfide is reported, so, we investigated the possibility of H2 and CH4 production from sulfur reduction in hydrothermal fluid vent system.We conducted hydrothermal batch-type experiments at the condition hydrothermal fluid vent. Fe3O4 was used for mineral catalyst. After 168 [h] experiment, abiotic CH4 generated 17~102 faster than serpentinization. In this production rate, the concentration of CH4 measured from hydrothermal fluid vent can be generated within fluid circulation period.
Permeability is important for considering the rate and extent of water-rock interaction in the Earth ranging from shallow parts to deep crust. It is an open question what pore structure (e.g., porosity, pore size, pore shape) controls the permeability. In this study, we determined the “characteristic maximum pore-throat size” by measuring the pressure at which gas initially penetrates a water-saturated sample (water-expulsion method). The characteristic maximum pore-throat size is strongly correlated with the permeability for various geologic media, showing that the characteristic pore-throat mainly controls the permeability.
Ca. 1cm-thick Grt-Hbl vein discordantly cuts a gneissose structure of a Grt-Opx-Hbl gneiss in the central Sor Rondane Mountains, East Antarctica. Changes of mineral compositions and mineral assemblages with a distance from the vein suggest that the Grt-Hbl vein was formed by NaCl-KCl brine infiltration in open system under upper amphibolite facies conditions. Moreover, Zn-, Sr-, Ba-, Pb-, and U-contents in Hbl and Li-, Sr-, Ba-, and Pb-contents in Pl decrease with a distance from the vein. Trace elements compositional profiles with a distance from the vein imply the elements diffuse from the vein to the wall rock.
Finero phlogopite peridotite was metazomatized in the mantle wedge in Late Palezoic time.We studied the detail of deformation history of the Finero phlogopite peridotite during the exhumation from the upper mantle through microstructural observation mainly with optical and electron microscopy, SEM/EBSD and TEM. The phlogopite peridotite body was subjected to shear stress, and where samples hold numerous fulid inclusions. In addition, some olivine slip system data shows hydrous condition. In order to reveal the origin of fluid inclusion,we performed noble gases measurement. The results shows the mixture of Air and crust and MORB component.
In the footwall of the MCT at Dhankuta, Nepal, rim composition of tourmaline in ‘normal’ metapelites becomes higher in XMg and Ca/(Ca+Na), and lower in X-site vacancy (X[ ]) as the metamorphic grade increases. Tourmaline in the tourmaline veins shows high X[ ] and constant XMg, and that at several cm away from the vein shows low X[ ] and varied XMg. This probably reflects the difference in water/rock ratio, where tourmaline formed under high water/rock ratio shows high X[ ]. Some of the abnormally tourmaline-rich metapelite show similar tourmaline composition, suggesting its formation through the fluid infiltration.
The role of melt intrusion on the water supply to arc crust has been constrained from hydration reaction of the pargasite–phlogopite peridotite intruded by granitic dyke, Sør Rondane Mountains, East Antarctica. Thermodynamic and mass balance analysis indicates that hydration was rate-limited by the reaction within the host rock. Based on the compositional profile of the reaction zone, the reaction-diffusion model between the melt and crust is established and its effect on the water supply to the arc crust will be discussed.
The conditions of formation of dawsonite-bearing carbonate veins in the northern flank of the Izumi Mountains (southern Osaka prefecture) are investigated on the basis of oxygen acd carbon isotopic compositions of carbonates. The calculated isotopic ratios of calcite largely support the precipitation from CO2-bearing fluid having isotopic characteristics similar to the end-member Arima-type hot brine (Kazahaya et al., 2009).
Seawater-like saline fluid inclusions (FI) were observed in peridotite xenoliths from the mantle wedge beneath the Pinatubo volcano (5.1 wt% NaCl equiv., Kawamoto et al., 2013, PNAS) and the Ichinomegata volcano (3.7 % NaCl, Kumagai et al., 2014, Contrib Mineral Petrol). Saline FI are commonly found in high-pressure metamorphic rocks (Frezzotti and Ferrando, 2015, Am Mineral). Here we report preliminary salinity data of rare aqueous FI in jadeite-rich rocks from serpentinite mélanges of the Rio San Juan Complex (Schertl, et al., 2012, Eur J Mineral).
We report paragenesis and chemical compositions of serpentine and associated minerals in gabbroic rocks recovered during IODP Expedition 345. In contrast to that of peridotites, serpentine of gabbroic rocks shows no evidence for mixing with brucite but suggests local mixing with smectite. The observed variations of compositions such as Si/(Mg+Fe) and Mg/(Mg+Fe) ratios, and the abundance of coexisting magnetite or smectite can be explained as a result of variation in temperature, silica activity, oxygen fugacity and/or water/rock ratio during serpentinization.
Hydrothermal experiments (230̊C, Psat) were carried out in olivine–plagioclase (Pl)–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–Pl boundary, from Al-lizardite to Al-free lizardite + brucite + magnetite. On the other hand, in Pl-hosted region, reaction products were not observed. The estimated element transport distance for Al and Si is 1.5 mm and 3.7 mm from Ol–Pl boundary, respectively. The total H2O content is greater at the contact of Ol and Pl in Ol-hosted region than others.
Water in thin film shows different characteristics compared with that of bulk water. Thin film water can be present at mineral grain boundaries, and its physical properties might be influenced by mineral surface. Molecular dynamics simulations were performed to investigate the self-diffusion coefficients of water confined between quartz surfaces at 298K to 573K. The self-diffusion coefficients of water molecules were reduced near the surface.
Through-diffusion experiment comparing the diffusivity of Si, K, and Cl in sandstone revealed that the diffusion of Si in pore water was slower than predicted from the diffusion coefficients (D0) of Si, K, and Cl in bulk water. Additionally, centrifugal extraction of pore water initially having a Si concentration of 1.7 mM revealed that Si concentration was decreased by precipitation. The results suggested that Si diffusion was retarded by the change of concentration profile in the rock due to precipitation and by the decrease of D0 of Si due to change of dissolved state of Si such as polymerization.
Cleavable olivine shows the distinctive cleavage filled by antigorite. Such olivine has been reported at various serpentinized ultrabasic complexes and in the ultrabasic rocks collected from several serpentinite seamounts in the Izu-Ogasawara-Mariana forearc. However, the formation process of cleavable olivine has not been fully understood, so far. The purpose of this study is to clarify its formation process through microstructural observation. Our study suggests strongly that the subgrain boundary created by dislocation creep and the pipe diffusion of H2O along the subgrain boundary are important to create the cleavable olivine.
Presence of water enhances plastic deformation of minerals. We performed axial compression experiments on very fine grained (~3 μm) anorthite aggregates. We added water of 0.5 wt% and investigated the effects of water on mechanical properties of anorthite in high temperature and pressure conditions. Experiment with 0.5 wt%-added water shows significant strength reduction compared to the strength predicted by lower pressure experiments (Rybacki et al., 2006). This implies that the effect of water in higher pressure condition might be larger than those predicted by lower pressure experiments.
We studied the formation process of cataclasite of crystalline limestone exposed in Hiraodai-Karst, based on field survey, microstructural observation, measurements of homogenization and melting temperatures of fluid inclusions, and measurement of Rb/Sr isotope ratio of fluid inclusion and host calcite grains. The result suggests strongly that the cataclasite was generated by multiple hydrofracturing events related to comparatively high temperature and low salinity geofluid, which was in contact with the crystalline limestone for a long duration of time.
To investigate the effect of grain growth on the fluid distribution in deep-seated rocks, we carried out sintering experiments of fluid-bearing quartzite at 900°C and 1 GPa for 90–382 h. Grain growth and fluid segregation proceeded significantly in 200 h. The volume fraction of the retained fluid in the quartzites with a high initial fluid content (3.7wt%) decreased asymptotically to 0.8 wt% in 200 h. It was observed that the quartzite grains with much initial fluid were more coarsened than those with less. The fluid expulsion was thus coupled with the grain growth in the initial stage of sintering.
We study about serpetinites from Mineoka belt, Boso Peninsula, Chiba Prefecture. Serpentinites mainly onsist of mesh texture and bastite. Ni sulfides are often observed and a few awaruite and native copper are also observed. Values of (Ni+Fe)/S about Ni sulfides changes from 0.78 to 1.82. Perfectly serpentinized mesh texture consist of Fe-rich serpentine or magnetite.
We tested fifteen pieces of type Ib yellow CVD synthetic diamonds which were submitted to the Central Gem laboratory without disclosure. From FTIR analysis, together with optic centers detected by photoluminescence (PL) analysis such as H3, NV or N3 centres, indicate that those stones have undergone post-grown HPHT treatment at about 1900-2200 degree of temperature.
Natural tapered quartz crystals from Goyomatsu mine(Nara) were observed by SEM-CL method. Their images show that the growth history was as follows, facet →, cellular → adhesive-type growth, which were related to that of trapiche quartz.
We report the occurence of α-cristobalite from α-cristobalite from Kodono, Kumakogen-cho, Ehime Prefecture, Japan. The crystal is large (~1mm), and thus it is quite rare occurence. We report the detail.
We discuss about precipitation processes of metastable phases from low temperature solution on the basis of observation for their textures and occurrence. Metastable minerals, which precipitate under metastable condition or out of stable region, are major in mineral species on the earth, and contribute to the diversity of minerals. It is considered that origins of the metastable phase were effects of impurity and interface energy. We will propose a new model for nucleation process of the metastable phase.
We studied about alteration textures of K-feldspar, petalite, Li-tourmaline and montebrasite-amblygonite, and discussed the alteration processes. K-feldspar was altered to cookeite, muscovite and quartz, or tosudite and beidellite-montmorillonite. Petalite was altered to cookeite and montmorillonite-beidellite. Li-tourmaline was altered to cookeite and muscovite. Montebrasite-amblygonite was altered to various phosphates and muscovite. With decreasing temperature, Li-chroritization, sericitization and smectitization had occured. In acidic condition, K-feldspar and petalite had breakdown, and cookeite formed with releasing K+. In acidic to neutral condition, Li-tourmaline had breakdown, and suffered sericitization. It is estimated that Li, B, P and F escape from pegmatite rock with reaction fluids.
X-ray diffraction Rietveld structure-refinement data for synthetic Rb-lepidolite(1M) micas in the Rb-polylithionite (abbreviated here as Rb-pol) – rubidium trilithionite (Rb-tri) – rubidium ephesite (Rb-eph) join, Rb(Li2-xAl1+x)(Si4-2xAl2x)O10(OH/OD,F)2 (x = 0.0–1.0), are reported. As fluoro-rubidium–polylithionite and hydroxyl-rubidium–ephesite end members are stable, up to three micas are in coexistence in this series. Crystal chemical and structural parameters for intermediate rubidium-trilithionites varies continuously, but the F2RbPol- and RbEph-end members crytal-structural parameters are rather of constant.
We have recognized kolbeckite and pretulite-like mineral as the first occurrence in Japan, on the surface of quartz veins including pyrite and sphalerite at Iriki, Satsumasendai City, Kagoshima Prefecture. Kolbeckite was examined by Gandolfi camera and electron probe microanalyzer (EDS).
We performed single-crystal X-ray diffraction study of the type specimen of sakuraiite. In the original description (Kato, 1965), sakuraiite was reported as tetragonal (pseudo-cubic with c = 2a) with an ideal formula of (Cu,Zn,Fe)3(In,Sn)S4. On the other hand, based on X-ray presession images and chemical analyses, Kissin & Owens (1986) concluded that sakuraiite was cubic phase with an ideal formula of (Cu,Zn, Fe,In,Sn)S. In the present study, we obtained a tetragonal P-42m structural model. However, because fine lamellae textures with varying compositions are developed in the type specimen, correspondence of the structure and composition is currently under investigation.
A simple and low-cost pseudo-fixed dead time X-ray counting system is implemented for long-time stable accurate X-ray sampling in electron probe microanalysis (EPMA). The extendable dead time generator is inserted between the single-channel analyzer (pulse-height analyzer) and counter in this study. The dead time of the new design can be considered to be a fixed value when that originated by the proportional counter and single-channel analyzer.
X-ray diffraction Rietveld structure-refinement data for synthetic lepidolite-1M micas in the polylithionite (abbreviated here as Pol) – trilithionite (Tri) – potassium ephesite (K-Eph) join, K(Li2-xAl1+x)(Si4-2xAl2x)O10(OH/OD,F)2 (x = 0.0–1.0), are reported. In the products synthesized with starting materials of the F2Pol100Eph00 (fluoro-Pol) and (OD/OH)Pol0Eph100 (hydroxyl-K-Eph) end members mixtures, up to three coexisting micas are crystallized involving the multisite substitutions, i. e., Li-1Si-1AlAl and F--1(OH/OD)-.
We report Mössbauer spectra of oriented thin sections of natural magnetite to observe crystallographic orientational dependence of sextet of magnetite. Two natural magnetite single crystals from Brazil and Russia were prepared. Among separated 6 peaksdue to internal magnetic field, relative intensities of single crystals were deviated from 2 due to crystal anisotropy. supposing shape magnetic anisotropy of sample, this result can be explained by the <111> easiest magnetization axis. This is consistent with the general easiest magnetization axis of spinel ferrite.
In this study, constituent minerals in the black and red-brown scorias from Kami-Komesuka, Aso, Kumamoto Prefecture, Japan were described in detail, their chemical compositions were determined, and the oxidation state of Fe in olivine were examined using electron microbeam method to evaluate effect of high temperature oxidation on the scoria. The Kami-kometsuka scoria cone consists of black and reddish-brown scorias. The reddish-brown scoria is covered by black scoria. The red-brown scoria is expected to have subjected high temperature oxidation after eruption and deposition. The textures and chemical compositions of the olivine and pyroxene phenocrysts are changed by the effect of high temperature oxidation. In the olivine phenocrysts from reddish-brown scoria, precipitate minerals, less than few μm in size, are occurred and Fo composition are attend to 99 mol%.
Coloration factor of the orange calcite which precipitated in a shellfish fossil were analyzed. Fe was not contained in the fossil and Mn, Mg were detected by ICP analysis. Orange calcite was provided by using solution including a small amount of Mn.
We attempted to find a cause of violet coloration on pyromorphite from Ogoya mine, Japan. Polished section along the c-axis showed violet bands normal to the c-axis. Qualitative EPMA analysis showed presence of Ca and Zr as impurities and further quantitative analysis showed higher (1.5 times) concentration of Zr in violet band. While further investigation is needed, our results strongly suggest Zr as the cause of coloration of the present specimen.