Antigorite is a key mineral controlling subduction process. Its single crystal elasticity is important to interpret seismic anisotropy around subduction region. We try to measure single crystal elasticity of antigorite by means of inelastic X ray scattering method.
First-principles calculations were used to study the structural and energetic properties of cristobalite-He I and II at high pressures. Both structures are known to have molar volumes 25%–30% greater than that of cristobalite at high pressures, based on previous high-pressure powder X-ray diffraction experiments using a helium pressure-medium at room temperature. Both cristobalite-He I and II structures were assumed to incorporate helium into large voids in the cristobalite II structure without changing the crystal symmetry of space group P21/c. Of the several structural models tested for both cristobalite structures, two enthalpy-minimized structural models were found to reproduce the observed lattice parameters, energetic properties, and phase transitions at high pressures. They also accurately modeled the X-ray diffraction patterns. Cristobalite-He I and II were found both to include one helium atom per SiO2 with the formula SiO2He, and were predicted to have molar volumes 21% larger at 10 GPa and 23% larger at 4 GPa than cristobalite II due to the penetration of helium atoms into the large voids.
Recent advances of synchrotron radiation technique combined with high P-T generation using a diamond-anvil cell have allowed us to determine physical properties and phase relation of a geological material even to the center of the Earth. On the other hand, chemical evolution in deep Earth remains poorly constrained, although there are increasing geochemical evidences for highly heterogeneous mantle and early earth differentiation. We have investigated the melting phase relations of peridotite and MORB and major/trace element partitioning based on the chemical analysis using FE-EPMA and LA-ICP-MS.
We conducted deformation experiments to directly decide the strength contrast between plagioclase (lower crust) and olivine (upper mantle) utilizing modified Griggs-type solid-medium apparatus. Experimental condition is P = 2GPa and T= 600–1000ºC under dry conditions. The numerical calculation also was performed to investigate the effect of the strength contrast between the crust and mantle on the tectonics of Venus. Rheological structure and tectonics of Venus are discussed based on these results.
Enthalpies of high-pressure phases in the system FeO-SiO2 were measured by oxdative drop-solution calorimetry with the air-bubbling technique. Combining the data with standard entropies of the high-pressure phases, high-pressure transition boundaries were calculated, and compared with those by high-pressure high-tempearture experiments.
It is thought that the 660-km seismic discontinuity in the Earth's mantle is caused by the post-spinel phase transition. The Clapeyron slope of the post-spinel boundary is an important parameter which affects mantle convection style. In this study, the phase transition enthalpy for the post-spinel transition was determined by measuring drop-solution enthalpies of Mg2SiO4 ringwoodite, MgSiO3 perovskite and MgO. Using the newly re-determined enthalpy, the post-spinel phase boundary was re-examined by thermodynamic calculation. The Clapeyron slope was obtained to be -1.2±0.3 MPa/K at 1873 K. It is suggested that the post-spinel phase transition is a less effective barrier to the mantle convection.
Mantle peridotite xenoliths from kimberlite pipes at continental craton sometimes have unusual chemical, modal, and textual compositions (e.g., Boyd, 1989). The cratonic mantle, which consist mainly of olivine, orthopyroxene, garnet and clinopyroxene, are characterized the high amount of orthopyroxene (= high-Si) with high Mg# (= Mg/(Mg + Fe) atomic ratio). Here, based on melting experiments of hydrous pyrolitic lherzolite at upper mantle conditions, we suggest possibilities of the Si- and Mg-rich cratonic peridotites as residues by partial melting of pyrolite at hydrous condition at depth of more than ~100.
Subducting slabs are supplying water into the deep mantle, and some hydrous minerals may be present in the mantle transition zone and even in the uppermost lower mantle. The water storage capacities of mantle minerals are supposed to be significantly coupled with Al by a substitution with Mg2+, Si4+ or Mg2+ + Si4+, because Al3+ is the trivalent cation, and H+ is the monovalent cation. We have examined the effect of Al for the water content and the stability of some hydrous phases in the system MgO - Al2O3 - SiO2 - H2O in the uppermost lower mantle condition.
High pressure melting experiments on Fe-Ni-S system were performed at 10 – 20 GPa, and partitioning behaviors of trace elements between Fe-Ni alloy and sulfide melt were measured. Trace element concentrations in the recovered specimens were determined by LA-ICP-MS. Partition coefficient of Co, Ni, Pd, Os, Ir, Pt, Au show no apparent pressure dependence, while that of Ge was gradually increased with pressure. Observed partition coefficients of Mo, Ru, Rh, W, Re were apparently smaller than those of observed at normal pressure condition.
Carbon is the fourth most abundant element in the solar system. It has an important role in the melting phase relations of mantle rocks and metallic core. However, our understanding of carbon isotopic composition of deep Earth is very limited. Here we review the recent results of experimental determination of partitioning of carbon isotopes at high-pressure high-temperature conditions.
Kimberlite is an igneous rock originated from deep mantle. Compared to ordinary ultramafic rocks, kimberlite is rich in volatile components such as water and carbon dioxide. The halogen elements (chlorine, bromine, iodine) have high aqueous fluid-silicate melt partition coefficients (Bureau et al., 2000). Thus, they (especially iodine) are enriched in pore fluid and have distinct elemental ratios in seawater, pore fluid, sediment, oceanic crust and mantle. In this study, we analyzed concentrations of Cl, Br, and I in kimberlites and mantle-derived xenoliths from six localities to investigate the halogen characteristics and their origins in the kimberlite source regions.
High pressure and temperature experiments using LHDAC was performed to clarify effect of H2 fluid on phase stability and phase relation of enstatite. After heating at 3.1 to 13.8 GPa and 1500 to 2000 K, XRD and Raman measurements indicated that enstatite was decomposed to form forsterite, periclase and coesite/stishovite. SEM and TEM observation of the recovered samples suggested that formation of forsterite and periclase from enstatite under high temperature while, dissolution of SiO2 components.
Petrography and mineral chemistry of serpentinite samples from Iwanai-dake ultramafic body (Kamuikotan, Hokkaido) revealed that serpentinization proceeded via two-stage reactions, in which silica supply from serpentinization of orthopyroxene triggered the formation of magnetite during the second stage.
We present evidence for the nucleation of chromite within hydrothermal solutions. We have found minute euhedal chromite grains enclosed by uvarovite in a diopsidite, metasomatically replacing the layered gabbro of the Oman ophiolite. The uvarovite shows oscillatory concentric zoning in terms of Cr# (= Cr/(Cr + Al)), and the chromite is embedded only in the high-Cr# zones of the uvarovite. The metasomatic agent involved was a Cl-, CO2- and SO2-bearing hydrothermal solution containing appreciable silicate components that could carry Cr, possibly as a complex. The results from this study suggest that a hydrothermal origin is possible for chromites.
Iron hydrite is formed in the serpentinization reaction at around 1.5 GPa and high temperature. This reaction consumes hydrogen and thus hinders formation of methane in the deep crustal and upper most mantle conditions. Thus, iron hydrite is a key for hindering formation of hydrogen, abiotic methane and thus deep life in the deep earth.
Aqueous arsenite distribution experiments to calcite and siderite were conducted under anoxic condition. It was found that siderite sorbed arsenite via outer-sphere surface complexation, while calcite incorporated arsenate within the crystal even in the arsenite system. Although siderite could immobilize more arsenic than calcite, calcite immobilizes arsenic with lower risk of leaching of arsenic into natural water.
Matsushiro earthquake swarm is considered to be a natural analogue of dynamic response associated with CO2 geological storage; the dynamic resoinse includes deformation, rupture and eventual leakage. Geochemical characteristics of source fluid are investigated so as to be an input parameter of fluid flow-rock mechanics coupled simulation analyzing the Matsushiro earthquake swarm. The source fluid is estimated to be higher in salinity than the groundwater recovered from deep well near the Matsushiro Fault.
Geochemical studies of modern and past-tsunami sediments were performed to detect a tsunami invasion proxy. In this study, the modern tsunami sediments from the Pacific coast of Tohoku area, Japan (March.11th, 2011), have been analyzed by EDXRF and ICP-MS. In addition, past-tsunami sediments were also taken from the coastal area of Japan (Jogan, ca. 1100 BP; Yayoi, ca. 2000 BP; Sizuoka, ca. 3000 BP) in order to establish a novel method for the geochemical discrimination of invisible tsunami layers, such as mud and thin sand layers.
Stabilities of metal complexes with hydroxide and oxyanions (carbonate, carboxylate, and phosphate) showed that smaller ions favor hydroxide whereas larger ions oxyanions. The variation can be explained by the different entropy change during the formation of these hydroxides.
Redox potential is an important factor controlling chemical processes in hydrosphere on the earth. In this study, we propose a new redox indicator using the oxidation states of redox sensitive element in the mineral, such as selenium(Se) in barite. Coprecipitation experiments of Se with barite were conducted to investigate the influence of the Se oxidation state on its immobilization into barite. It was found that Se incorporated into barite can reflect the Se(VI)/Se(VI) ratio in water, suggesting that oxidation state of Se in barite can be used as a redox indicator in depositional environment.
Through-diffusion experiments were conducted using three rocks and effective diffusion coefficients (De) of dissolved Si, K and Cl were determined. The De values of Si, determined after correction of the effect of dissolution of Si from the rocks, were approximately 2–3 times smaller than those of K and Cl. This may be attributed to the difference of the diffusion coefficients in bulk water and the precipitation of Si. The difference of De of Si between pH 6 and 11 was small and the effects of the difference of charge state and the presence of multimeric species were not detected.
The dissolution rate of silica glass and temperature and pressure dependency was estimated in supercritical water. The range of dissolution rate of silica glass was from 0.5 to 9.9 x 10-10m/s with temperature and pressure. And the thickness of hydration layer was about 100 microns and thicker at lower pressure. Diffusion coefficient of hydration about 10-14m2/s and the activation energy was about 60KJ/mol. Iron plate activated the dissolution of silica glass due to precipitate Fe2SiO4 on plate.
Structure and physical properties of supercritical H2O-NaCl binary fluid was studied by classical molecular dynamics simulations. The density, bulk modulus, dielectric constant, and electrical conductivity were predicted over the range that was experimentally observed. The fundamental physics behind the change of the physical properties were discussed by the atomic-scale structure.
The present study addresses the thermodynamic properties of aqueous solutions of magnesium chloride and calcium chloride at temperatures up to 523.15 K, pressures to 50 MPa, and concentrations to 4 mol/kg. This study obtains the partial molar volumes and heat capacities of those electrolytes at the standard state from the literature data. Those partial molar quantities are expressed as a function of temperature and pressure. Six and nine parameters are used for the partial molar volume and the partial molar heat capacity, respectively.
Geofluid is considered to provide important effect on earthquake generation related to the subducting slab. We found recently cataclastic rocks in Hiraodai-Karst, which was probably formed by hydrofracturing. In this study, we tried to clarify the formation mechanism of the cataclastic rocks and origin of the fluid. We succeeded in identifying the area of distribution of the cataclastic rocks, which suggests that it was not created by fault activity. And the present data reveals that (1) fluid-induced differential stress produceed cataclasite zone in the marble body, (2) this cataclasite-producing fluid was possibly cogenetic to the magma of adjacent the granodiorite.
Pseudomorphic textures of serpentinites are important to estimation of original rocks, consideration of serpentinization process and so on. We researched microtexture of serpentinites in Oshima peninsula by XRD, SEM-EDS and TEM. Mesh texture and vein texture are observed in these serpentinites. Vein texture contain polygonal serpentine, magnetite and hydrotalcite. Mesh rim near vein texture consist of three layers; outer rim, inner/outer rim boundary and inner rim. Awaruite grains are observed along inner/outer rim boundary and core/rim boundary. Serpentines contain few Al, Ni and a few Fe. By these results, it is expected that formation of these serpentinites has complicated process.
Salar de Atacama is one of the largest salt lakes in the world. This salar contains a high concentration of lithium in the brine covered with salt crust. According to the model of Salar, precipitation and snowmelt from the hinterland is mainly supplied to the salar. In order to understand the component of water supplied to the salar, geological and petrographical studies were carried out on volcanic rocks that appear in the vicinity of the salar. Petrochemical study revealed that lithium contents of these rocks are variable. We will discuss about origin of lithium in the brine.
A 3.77-m-long sediment core (PY608E-PC) was obtained from Lake Pumoyum Co in August 2006 in order to reconstruct climatic and environmental changes in the south Tibetan Plateau. In this study, we performed geochemical, clay mineralogical, and grain size analyses as well as 14C age dating for the sediment core.
Replacement of cordierite by plagioclase in the presence of fluids containing 0.01 and 0.001mol/l NaCl and CaCl2 has been experimentally investigated at 600ºC and 100MPa.Plagioclase were precipitated from solution which starting composition had Ca/(Na+Ca)>0.5 and 0.01mol/l.
K-Ar ages have been determined for 14 volcanic rocks from the late Miocene to Pliocene periods in the north of Kanto Mountains. These volcanic rocks have been collected from volcanoes located behind the TTT triple junction with two subducting slabs of the Pacific and the Philippine Sea plates which are thought to have influenced the magmatism in the region. Based on the stratigraphy and K-Ar ages, three welded tuffs and the associated volcanic products are classified, which suggests that the volcanism in the studied area had continued during the late Miocene to the Pliocene and ceased before the Pleistocene.
Differentiation condition of island arc low-K tholeiite magma was reviewed by comparing data of chemical composition of volcanic rocks from Izu-Oshima volcano during past 40,000 years and data of hydrous melting experiments to simulate crystallization differentiation of arc basalts. Chemical variation of volcanic rocks from Izu-Oshima volcano can be explained by internal mixing of H2O-rich magma crystallizing at higher pressure and H2O-poor magma crystallizing at lower pressure, suggesting low-K island arc tholeiite magma is H2O-saturated and undergoing polybaric degassing.
In this study, Fe-K edge XANES analyses were done for quenched basaltic glasses in six scoria samples dredged from the petit-spot, site B, located on the Pacific Plate ca. 800km from the Sanriku, Japan, to estimate fO2 conditions of the magma. The analyzed glasses revealed similar Fe3+/Fetotal ratios of ca. 0.37. The ratios are consisted with that estimated from the apparent Fe-Mg partition coefficient between olivine and melt. From the ratios, the fO2 condition of the magma was estimated to be QMF+2.3, which is more oxidized than MORB and similar to arc magmas.
We present a new thermodynamic calculation for multi pressure melting phase relation of spinel lherzolite. The thermodynamic model for the calculation, which has been developed based on Ueki and Iwamori (2013), well reproduces the experimentally determined melting phase relation and its pressure dependence.
Knowledge of the dissolution mechanisms of CO2 in silicate melts/glasses is indispensible for understanding how it affects physical and thermodynamic properties. CO2 is generally known to dissolve in silicate melts/glasses as molecular CO2 and CO32- species, but how the latter groups are incorporated in the melt and its effect on the silicate structure have been less certain. Here we report ab initio calculation (vibrational frequencies, 13C chemical shift tensors) and multinuclear NMR study on 13CO2-bearing glasses of diverse silicate compositions. Our calculation suggests that both vibrational frequencies and 13C chemical shift tensor are sensitive to the local environments of carbonates. The experimental data indicate that carbonates are present dominantly as free carbonates (not bonded to tetrahedral Si/Al) in depolymerized melts, and as network carbonates (bonded to two tetrahedral Si/Al via two oxygens) in polymerized glasses. The formation of free carbonates would lead to polymerization of the silicate structure.
We present detailed petrography of nanometer scale crystals (nanolites) in the quenched products of the sub-plinian and vulcanian eruptions from the Shinmoedake, Kirishma volcanic group in 2011. The nanolites were distinguished from microlites by a steeper slope of the CSD plots. The vulcanian eruption products (pumice and juvenile lithic fragments) contain both plagioclase and pyroxene nanolites, while sub-plinian pumices contain only pyroxene nanolites. The nanolite crystallization condition may reflect magma dehydration and residence time in a very shallow conduit, which are not recorded by microlites.
We investigate crystal microstructure in crystal-rich pumice and lava samples (six eruptions in the Central Andes) using X-ray CT. Slopes in the CSDs, which are obtained for phenocrysts, are independent of crystallinity. Phenocryst fragmentation in lavas is limited; this is inconsistent with experimental and theoretical predictions that interaction between crystals in shear flow should result in extensive crystal breakage in crystal-rich magma. This disconnection between natural samples and theoretical studies can be explained by considering that the crystal framework may be collapsed by gas bubbles, resulting in the shear-reduction of crystal-rich magma.
We have developed a new analytical method for H2O and CO2 in silicate glasses by using micro-Raman spectrometry. We analysed H2O- and CO2-bearing basaltic glasses using a Raman spectrometer and an FT-IR, and confirmed linear relationships between peak heights of H2O and CO32- in IR spectra and those in Raman spectra. Therefore, the Raman spectrometry has a potential for quantitative analysis of both H2O and CO2 in glass samples.
The present study addresses the thermodynamic properties of aqueous solutions of magnesium chloride and calcium chloride at temperatures up to 523.15 K, pressures to 50 MPa, and concentrations to 4 mol/kg. Pitzer equation is used to describe osmotic coefficient, mean ionic activity coefficients, apparent molar relative enthalpy, apparent molar volume, and apparent molar heat capacity. This study shows 28 parameters for the temperature and pressure dependence of the Pitzer parameters.
Spectroscopic measurements in the range from 400 nm to 890 nm for pure H2O, CO2, C2H5OH and NaCl aqueous solution under high temperatures and pressures were carried out to observe critical phenomena by using visible-type autoclave. Intensity of transmitted light through the fluid became low drastically around the critical point in each fluid. The minimum intensity of transmitted light was corresponded to critical temperature and pressure of each fluid. Experimentally determined critical temperatures and pressures well coincided to reference data and it is possible to evaluate critical temperature and pressure of multicomponent geofluids by using spectroscopic measurement under hydrothermal conditions.
Molecular structure of water in thin film shows different characteristics compared with that of free water. Thin film water was observed at mineral grain boundaries, and its structure might be influence by mineral surface. High temperature-pressure cell for micro-Raman and FT-IR spectroscopy have been developed to investigate molecular structure of thin film water under subcritical and supercritical conditions. In this study, it was measured the IR absorption spectrum of the thin film water and the Raman spectrum of the free water at PT conditions. The OH-stretching vibration changes with PT and solid surface conditions of water was confirmed.
We conducted pulverization experiments of some clay minerals (kaolinite, sericite, saponite) using planetary ball mill. XRD peaks are disappeared after several hours. We conducted XRD analysis, SEM observation, FT-IR and TG-DTA analysis. We consider the mechanochemiccal behavior of clay minerals and its implications for faulting.
Fractures are dominant fluid pathways in the upper crusts. Ubiquitous occurrences of mineral veins suggest that precipitation of quartz provides significant effects on hydrological and mechanical properties of upper crusts. We conducted hydrothermal flow-through experiments for quartz precipitation and observed internal structures of synthetic veins by X-ray computer tomography. We also discuss the difference of mineralogy and distribution of silica minerals in vapor and supercritical region.
In pelitic gneisses from the eastern Sor Rondane Mountains (SRM), the Cl-rich fluid infiltration took place under ca. 800 oC, 0.8 GPa at 600 Ma, near the metamorphic-peak condition. The mineral assemblage in this sample implies that Cl-rich fluid carried LREE and Th away and brought HREE, Zr and Y in. On the other hand, mafic gneisses from the central region preserve the evidence of retrograde Cl-rich fluid activity, where cm-scale veinlet with Cl-rich amphibole cut the penetrative gneissosity discordantly. The Cl-rich fluid activity is distributed linearly for 200km regardless of lithology, and occurred at several stages in the SRM.
Ophiolite belts widely distribute in Philippines. Ultramafic rocks of the ophiolite appear at the southern part of the Palawan island. The ore deposits at the Rio Tuba mine are lateritic Ni deposits. Results of XRD, IR-spectrometry, chemical analysis will be shown in this study. Behavior of elements during weathering and chemical state of nickel will be clarified.
In order to examine aqueous fluid distribution in the lower continental crust and uppermost mantle, we carried out X-ray CT observations of xenoliths from 9 localities in the world. Intergranular pores were present in almost all the samples, and exhibit characteristic geometries controlled by interfacial-energy minimization. This shows that the pores represent aqueous fluids in the deep Earth. The pore fluids lack grain-scale interconnection, but their volume fraction and connectivity increase when foliated or localized in bands. This suggests that fluid interconnection might be established in a mesoscale structure such as shear-zoned.
Gabbroic xenoliths from the Ichinomegata crater, the NE-Japan arc contain a large amount of pargasite. Some of the pargasite grains are obviously secondary origin, replacing primary clinopyroxene in hornblende-pyroxene gabbros and pyroxene gabbros. The metasomatic formation of hydrous minerals was accompanied with addition of, at least, Ti, Na and K. Clinopyroxenes contain very low amounts of. The secondary pargasite is enriched in Rb, Ba and Nb relative to clinopyroxenes, which contain very low amounts of these elemants. The hydration is characterized by enrichment of incompatible elements, especially LILEs. This was caused by infiltration of fluids related to hydrous arc magmas.
Carbon-dioxides are globally and locally maintained by global circulation among the atmosphere, ocean-water, crustal rocks (except the asteroid destruction). Low temperature-type carbon-dioxides show material changes of three states among atmosphere, ocean-water and crustal rocks (and life) system. As complicated examples of this type reactions, European fields of Gerolstein (Germany) and Borsec (Romania) with carbonates bedrock (carbon origin) reveal continuous formation of low temperature-type carbonated waters and re-crystallized calcites. High temperature-type carbon-dioxides caused for global warming released in the atmosphere which are generated artificially from carbon-bearing resources (coal etc.) isolatedly stored so long, are expected by applying artificial quasi-circulatory system processing.
Chalcedony and agate are aggregates of cryptocrystalline crystals, and composed of quartz and moganite. Numerous optical and transmission electron microscopies observations were carried out, and these results have revealed the characteristic features, e.g., development of Brazil twin lamellae, intergrowth with moganite, optically length-fast form. However, textural data from 1µm to 10 nm sized are not enough to clarify the relation between TEM and optical microscopy observations. We carried out to observation the fine textures of chalcedony and agate by using a field emission type scanning electron microscopy. The results suggest that the textures are grouped mainly to three types and that the optical textures are related with the secondary particle composed of aggregate of nanometer-sized crystals.