Nuclear magnetic resonance spectroscopy (NMR) is a widely-used powerful method for the analysis of structure and dynamics of hydrogen-bearing materials. Using a diamond anvil cell, we are trying to apply this spectroscopy to various materials at high pressures those constitute the earth and planetary interiors. Here we show the results of some preliminary measurements for brucite (Mg(OH)2), which indicates the existence of mobile protons at around P = 7 GPa.

View full abstract

The genesis of natural polycrystalline diamond, called carbonado, is thought to be different from that of typical natural diamonds. The origin of carbonado is still enigmatic. In this study, we measured infrared absorption spectra on samples after removing hydrous minerals existed in diamond grain boundaries and confirm the existence of fluid inclusion inside of diamond. Infrared absorption spectra of acid treated samples also exhibited a peak assigned to liquid water and carbonate. Infrared absorption spectra of crushed samples heated in vacuum indicated that liquid water exist in diamond crystals. These results strongly support that fluid which is composed mostly of H2O-CO2 was trapped by diamond crystals. Moreover, nitrogen aggregation states measured with higher spatial resolution will be reported in the presentation.

View full abstract

Carbonado is a natural porycrystalline diamond characterized by light carbon isotopic composition, a lack of mantle-derived mineral inclusions, and high porosity. Because carbonado occurs in alluvial deposit, the origin of carbonado has been in controversity. Although investigations about morphology and dislocation texture of carbonado diamonds were done, there is no study about crystal size distribution and crystallographic orientation distribution of carbonado. In this study, crystal size distribution and crystallographic orientation distribution of carbonado were quantitatively analyzed. Grain size of diamond in carbonado varies from <1 to ca. 40 micrometer. Crystal number density decreases exponentially with increase of grain size. Crystallographic orientations of diamond grains in carbonado were random. It is often observed that several neighboring fine grains show identical orientation. This is simillar to subgrain texture. Irregular shaped grain boundaries accompanied with pores were observed. Based on these textural observations, we will discuss on the origin of cabonado.

View full abstract

We report synchrotron X-ray diffraction (SR-XRD) study on crystal structure of CO2-V.As a result, CO2-V phase was identified at above 1500K and 40-100 GPa. The peak profiles can be fitted in terms of beta-cristobalite structure , rather than tridymite structure (Fig. 1). At 50 GPa, lattice parameters of CO2-V are a = 3.584(2), c = 5.908(7) (in angstrom);. beta-cristobalite CO2-V in the present study has a much smaller volume than those indexed as a tridymite structure, and slightly larger than those reported from a theoretical calculation.

View full abstract

Raman spectra of Fe-Mg olivine grains with Mg# 70-100 were measured under pressures up to 4 GPa using a diamond anvil cell. Pressure and Mg# dependences on Raman spectra of olivine were numerically formulated. Using these formula, the method was applied to an olivine inclusion in Udachnaya diamond.

View full abstract

Partially molten state of rocks plays important roles in the Earth's interior such as melt segregation, material transport, rheology, and textural development (textural equilibrium). In particular, 3-D connection of partial melt is the most important factor influencing above properties. However, 3-D structure has not been observed in 3-D owing to the technical difficulty and 3-D connection of melt has been predicted using the 2-D dihedral angle. In this study, 3-D partially molten structure of diopside (90 wt%) - anorthite (10 wt%) samples was observed by the high spatial resolution X-ray CT system using synchrotron radiation at SPring-8. Using CT images, the 3-D real dihedral angles were measured and compared with the 2-D data.

View full abstract

Incorporation of trivalent anions into CaTiO3 perovskite was investigated. In this study CaTiO3-YGaO3, CaTiO3-YbScO3 and CaTiO3-ScAlO3 were examined. Solubility of YGaO3 and YbScO3 into CaTiO3 increase with temperature and with pressure. However CaTiO3-ScAlO3 system shows only a little solid solution up to 1673K or up to 5GPa.

View full abstract

Silicate perovskite is major mineral in the Earth's lower mantle, it is important to know solubilities of some cations to silicate perovskite in the lower mantle. Especially, it should be interesting whether monovalent cations such as Na⁺ can incorporate into silicate perovskite. In this study, samples with various intermediate compositions between Na⁺La³⁺Ti₂O₆ and CaTiO₃ were synthesized from constituent simple oxides at 1273K and 1523K in air using muffle furnace. These samples were characterized by X-ray diffraction and SEM-EDS. Additionally, lattice parameters were determined by Le-Bail analysis using the RIETAN-2000 program.

View full abstract

Neutron diffraction experiments have been succeeded in determining of hydrogen position in many hydrous minerals. By contrast, little application to nominally anhydrous minerals has been done, despite its importance in the earth's interior. Wadsleyite, a high pressure polymorph of olivine, is a main constituent of shallower part of the mantle transition zone at the depth of 410 - 520 km. Ever since Smyth (1987) predicted that protonation of O1 site of wadsleyite results in significant amount of water content up to 3.3 wt%, hydration of wadsleyite and related change in physical properties has attracted much attention. However, several mechanisms of protonation have been proposed and the position of hydrogen in wadsleyite still remains controversial, because previous studies are based on X-ray diffraction and spectroscopic methods. The aim of this study is the precise determination of hydrogen position in wadsleyite by neutron diffraction experiment.

View full abstract

MgSiO₃-perovskite is the most major constituent mineral in the Earth's lower mantle. Recently we found MnSiO₃-perovskite is stable at the lower mantle conditions. It is interesting to know the solubility of MnSiO₃ component into MgSiO₃-perovskite. In this study we tried to synthesize the perovskite type compounds with some intermediate compositions between MgSiO₃ and MnSiO₃ by using a laser-heated diamond anvil cell at the pressure range of 30-65 GPa. Producted phases were identified by synchrotron X-ray diffraction measurements at PF and SP8. It was confirmed that complete solid solution between MnSiO₃ and MgSiO₃ with the orthorhombic perovskite structure occurs in the present experimental conditions and those perovskites are transformed into amorphous during decompression.

View full abstract

Water decreases the melting temperature of mantle minerals, and enhances the magma generation. The water content in magma should define as hydrous liquidus line in the silicate-H2O system, and the water content generated in a P-T condition must be unique. Therefore we have determined the water content in the hydrous magma generated along the representative mantle geotherm at pressures of 8-20 GPa to discuss the magma migration in the mantle.

View full abstract

Previously, phase transitions in Fe2O3 at high pressure and high temperature have been reported, but have not been clarified sufficiently yet. The reported structures and phase boundaries are different each other. Thus, we conducted the high-pressure experiments using various pressure-transmitting media and heating methods to clarify these issues. In three runs, the starting material, Fe2O3 was compressed up to 24-30GPa using DAC. NaCl or MgO was used as pressure medium. The samples were heated for 10 minutes by CO2 laser (over 1000K) or YAG laser(the temperature can not be measured). After heating, X-ray diffraction patterns were recorded at room temperature at PF-NE-1 beam line. Under these PT conditions, in Ono et al.(2005), hematite still exist, whereas transforms to Rh2O3-II type in Ito et al.(2009). However, in our experiments, the results were different from both reports. Moreover, in some run, the obtained XRD patterns were consistent with the high pressure phase of Fe3O4(Fei et al.1999). These results suggest that the valence of iron should be changed due to the heating conditions and/or pressure medium.

View full abstract

We have investigated the nucleation rates of olivine-wadsleyite transformation by the time-resolved 2D X-ray diffraction method. Preliminary results on this kinetic experiment will be presented.

View full abstract

It is expected that anhydrous phase B (Mg14Si5O24:Anh-B) may exist in the upper mantle. In this study, we determined the stability field of Anh-B by both high-pressure experiments and calorimetry. Phase relations in Mg14Si5O24 were determined by high-pressure experiments in 18-23GPa and 1327-1527K. A phase boundary between Anh-B and Mg2SiO4 (Wads)+MgO(Per) was observed at about 20GPa and 1327K. The drop-solution enthalpy of Anh-B was measured using a Calvet-type calorimeter kept at 978 K and lead borate solvent with bubbling technique. The phase boundaries of Fo + Per= Anh-B and Anh-B = Wads + Per were thermodynamically calcurated using their phase transition enthalpies determined in this study.

View full abstract

We have discovered about 200 micrometeorites from 400 kg surface snow near Dome Fuji Station, Antarctica. The collection contains about 10 micrometeorites that have texture, mineralogy, and chemical composition undistinguishable from those of anhydrous interplanetary dust particles (IDPs), which are regarded as cometary origins. We call them "anhydrous snow MMs". They contain GEMS (Glass with embedded metal and sulfide) and enstatite whiskers or platelets, both of which are characteristic constituents of anhydrous IDPs. They also contain kosmochlor-rich high-Ca pyroxene and eifelite, which have been found among Stardust retrieved samples. We analyzed Raman spectroscopy of carbonaceous materials in anhydrous snow MMs and hydrated snow MMs. The former has lower G band center values (omega G) and larger G band FWHM values (gamma G). The studies of Stardust terminal particles claim that primitive carbonaceous materials have rather lower omega G and larger gamma G values than processed ones. Our data indicate that cometary particles contain more primitive carbonaceous materials than asteroidal particles.

View full abstract

Tensile strengths of small pieces (∼100 μm) of carbonaceous chondrites (Murchison, Murray, Ivuna, Orgueil, and Targish Lake) were successively measured using a micro compression testing machine. The mean strengths are about 1-5 MPa and have a tendency of CM>CI>TL. The tensile strengths of seven scoriaceous micrometeorites (4 to 40 MPa) are larger than those of carbonaceous chondrites. Comparison with the strength of larger samples of Murchison may indicate a small size dependency.

View full abstract

Presolar grain survey was performed with 2-D in-situ isotope microscopy in carbonaceous and ordinary chondrites of various chemical groups, and various alteration, and metamorphic degrees. The sizes, and chemical compositions of presolar grains were studied with FE-SEM-EDS. A total 56 C-anomalous and 125 O-anomalous grains were found as presolar SiC, graphite, oxide, and silicate. Most of silicates were Fe-rich olivine. The various abundances of presolar silicates among carbonaceous chondrites indicate the destruction of presolar silicates by the parent body process. The lower abundances of presolar silicates in the least metamorphosed ordinary chondrites than carbonaceous chondrites suggests the destruction of silicates by nebular process in ordinary chondrite forming rigion.

View full abstract

Carbonaceous chondrite Acfer 094 is beliebed to one of the most primitive meteorites. This meteorite contains highly abundance of presolar grains and cosmic symplectite (COS) in the matrix. The COS has not been discovered in other carbonaceous chondrites. The uniqueness of Acfer 094 may be appeared in chemical characteristics of the matrix. In this report, we observed variations of chemical composition of fine-grained matrices among various carbonaceous chondrite groups to compare with Acfer 094. As a result, Al, S and Ca contents of fine-grained matrix minerals are highly variable among the carbonaceous chondrite groups. Acfer 094 matrix has both higher ratios of S/Al and Ca/Al than most chondrite groups. Such difference may result from micro scale elemental redistribution by aqueous and thermal metamorphism. This approach may be useful to classification of chondrite matrix to identify the pristine nature.

View full abstract

From petrographic study, a large Allende type B inclusion, Golfball has experienced at least two melting events. In the present study, we report preliminary results of oxygen and Al-Mg isotopic measurements of spinel and melilite in Golfball to determine ages of the multiple melting events and the oxygen isotopic composition of each melt. Delta O-18= -50 to -40permil for spinel, and the oxygen isotopic composition of melilite is distinct in each petrographic occurrence, Delta O-18= -20 to -10permil for gehlenitic core melilite and Delta O-18= ∼0permil for melilite in the rim. Two isochrons are defined by the Al-Mg data. The gehlenitic core melilite and rim melilite yield initial ²⁶Al/²⁷Al ratios of 4.9±0.8 and 1.9±1.2 x 10^-5, respectively. The age difference between the two isochrons is calculated to be about 1 My. From the chronological and the previous petrographic studies, we discuss the crystallization history of Golfball.

View full abstract

A compound CAI found in the Allende meteorite was investigated for its formation processes by means of petrology, chemical composition and oxygen isotopic compositions. The inferred formation processes are as follows: 1) condensation of the precursor CAI from ¹⁶O-rich nebula gas, 2) multiple melting of the precursor CAI, 3) mixing of the precursor CAI with a chondrule-like material by melting under slightly ¹⁶O-rich nebula gas, 4) chondrule-like rim formation.

View full abstract

We found the clasts including iron oxides in the three CM chondrites. In this study, we investigated them by using scanning electron microscope in detailed. The clasts that magnetite is abundant are found in the three meteorites. These clasts consist of chondrules and the matrices. The matrices mainly composed of serpentine and magnetite. Troilite and Tochilinite are not found in the matrices of the clasts. Moreover, almost magnetite shows framboidal texture. On the other hand, magnetite is rare in their host meteorites. These results show that the clasts in the three meteorites have experienced aqueous alteration on an oxidized condition. Though, it suggests that CM parent body, which exists both reduced and oxidized environments, may be a homogenous body.

View full abstract

Another lithology C is found in NWA 1232 which is a CO chondrite breccia with two lithologies A and B. Here, we present the results of our mineralogical and petrographic study of these three lithologies. Our goal was to reveal the formation history of NWA 1232 and to provide implications of the processes in the CO parent body. Our results have revealed that these three lithologies have different alteration histories. Although lithologies A and B have been affected by significant thermal metamorphism, lithology B has gone through higher degree of thermal metamorphism. Lithology C has been affected by aqueous alteration. These lithologies had been altered in different locations within a single parent body and then mixed during brecciation processes. Thus, the CO parent body has undergone a heterogeneous distribution of its metamorphic condition, and brecciation processes have subsequently occurred in the parent body.

View full abstract

We present the results of our mineralogical and petrological investigation of chondrules and fine-grained rims in the Mokoia CV3 chondrite. Both the chondrules with and without rims show abundant evidence of extensive aqueous alteration. In contrast, the matrix surrounding them largely remains unaltered. These observations suggest that the chondrules with and without rims have not experienced aqueous alteration in the present setting. We suggest that they are actually clasts transported from a precursor material during brecciation on the meteorite parent body, and the rims are fragmented remnants of an interchondrule matrix of the precursor material.

View full abstract

Our observation reveals that the matrix in Ningqiang consists of an intermixture of two distinct regions, Fe-poor and Fe-rich. The Fe-poor regions consist mainly of smaller grains of Fe-rich olivine and nepheline, whereas the Fe-rich regions consist mainly of relatively coarse grains of Fe-rich olivine, Fe sulfide, magnetite and Fe-Ni metal. These characteristics have not been known from any other carbonaceous chondrite matrices. The matrix in Ningqiang may be a mixture derived from two different reservoirs, Fe-poor (Na-rich) and Fe-rich (Na-poor), in the parent body. We fond matrix-like aggregate mainly consists of fine grains of nepheline and melilite, resembling the CAIs with significant amounts of nepheline. These suggest that nepheline in the Fe-poor regions of matrix derived from altered CAIs.

View full abstract

CH chondrites are unusual carbonaceous chondries, and are characterized by Fe-Ni metal with solar Co/Ni ratio, small chondrule size distribution, and refractory inclusions with kushiroite and grossite. Hre we report our discovery of opaque minerals, such as Si-rich metal, barringerite, perryite, suessite, daubreelite and others. Most of them are newly found from CH chondrites. Some of these minerals are also encountered in ureylite, suggesting the silmilar physical condition for the formation. CH chondrites are mixture of the constituent components, originated under highy reducing to oxidizing conditions.

View full abstract

Chemical characteristic is considered to be dependent on the redox state of martian magma, and to know the redox state of magma is important to study origin of martian magma. The new sample found recently shows the Enriched chemical characteristics, however, it is not known whether it shows the same redox state as the other samples studied already, or not. In this study, we investigate the redox state of the new sample to compare other shergottites. We tried to estimate redox states and equilibration temperature by applying two Oxybarometers using Fe-Ti oxide compositions. We also employed synchrotron radiation micro-Fe XANES analysis to measure Fe3+/sigma Fe ratios of kaersutite, ulvospinel, and maskelynite. Oxybarometer study shows the too wide value to estimate the equilibration temperature and we could not determine the redox state. On the other hand, we found that there is no clear difference in Fe3+/sigma Fe ratio of kaersutite and ulvospinel. In contrast, we could find that the Fe3+/sigma Fe ratio of maskelynite shows difference between geochemically-intermediate and enriched samples.

View full abstract

Fe-Ni metal and magnetite nanoparticles are widely present in martian meteorites. According to our shock experiment, Fe-Ni metal nano-particles were formed under relatively reducing condition and magnetite nano-particles were formed under relatively oxidizing condition. However, it is unlikely to suppose drastic change of Martian atmosphere among Martian meteorites. Then, temperature difference during shock could be another possible factor. To verify, we shocked olivine pre-heated at 400 and 800C. As a result, Fe-Ni metal nanoparticles were formed in preheated sample. Thus, Magnetite nanoparticles would be formed when temperature increased moderately. When temperature increase was significant and fO2 during the shock was below the IW buffer, Fe-Ni nano-particles would be formed.

View full abstract

We performed in-situ nano-second time-resolved single-shot Laue diffraction analysis of olivine by synchronizing synchrotron radiation X-ray pulse and Nd-YAG laser pulse to study the development of shock compression in olivine. We found mixtures of sharp diffraction spots with streaks in the Laue images from 1.2-6.5 GPa shock experiments with 6 ns delay time. This observation corresponds to the developing shock wave in olivine. We found that the Laue image at 1.2 GPa shock showed only diffuse reflection for the 30 ns delay time. This is because partial decompression had already started after shock wave traveled to the other end of the sample. This system can be applied for other important rock-forming minerals to understand their properties under shock-compression conditions.

View full abstract

In order to understand kinetic effect on the amorphization process of plagioclase in shocked meteorites, static compression experiments of plagioclase have been performed using an external heated diamond anvil cell. Based on Raman spectroscopy of recovered samples, the amorphization pressures of Ab99 were estimated at ∼39, ∼38 and 32 GPa at room temperature, 170 and 270 ºC, respectively. Concerning chemical-compositional, temperature and kinetic effects, diaplectic plagioclase glass (maskelynite) in shocked ordinary chondrites could have been produced at higher than ∼25 GPa. The present results are consistent with peak pressures of shocked chondrites estimated based on the stability of ultrahigh-pressure minerals in melt veins.

View full abstract

High-sensitivity ion imager corresponding to real-time readout with 250000 pixels is developed. The output signal fluctuation of the pixel caused by 1 incident ion was 150µV/ion pixel which is 5 times improved by adopting smaller pixel capacitance. In order to reduce the readout noise, multiple signal-sampling mechanism was incorporated. The readout noise was achieved to 250 µV corresponding to 1.7 ions with 16 times signal-sampling. The readout speed was achieved to 12.5 frames/sec with single sampling and 8.3 frames/sec with 16 times signal-sampling. The read noise is independent of read out speed and now optimizing with multiple signal-sampling mechanism. Therefore, real-time single ion detection is expected if all the parameters become optimized.

View full abstract

In the present study, we observed details of fractures in experimentally shocked Murchison CM carbonaceous chondrite. The result suggests that formation process of fractures depends on textures of chondrite and fracturing in matrix can be an indicator of induced shock pressure.

View full abstract

To understand aqueous alteration process that carbonaceous chondrites experienced, we conduct hydrothermal alteration experiments of olivine that are major constituents of chondrites. We encapsulate synthetic powder sample of olivine in Au capsule with 1N-HCl (pH= 0), H₂O (pH=7) or 1N-NaOH solution (pH=14). And we alter sample using hydrothermal synthesizing apparatus under 300 degrees, pressure 500 bar and run duration 1 week. From our experiments, it is revealed that alteration degree of olivine change when aqueous solution is changed and alteration products change in case of changing Fe contents of olivine under alkaline condition. It shows that not only Fe contents of olivine but pH in aqueous solution are important parameter deciding type and volume generated material.

View full abstract

CK chondrites underwent thermal and shock metamorphism, but their relationship is poorly understood. Plagioclase would be susceptible to thermal and shock metamorphism. We here present the feature of plagioclase in strongly shocked EET83311 and strongly heated LEW87009. Our goal is to reveal the formation process of each plagioclase. In EET83311, plagioclase exists as glass, and plagioclase glass includes fine-grained Ca-rich pyroxene. In LEW87009, plagioclase mostly exists as crystal, but partially exists as glass. Plagioclase crystals often include coarse-grained Ca-rich pyroxene. Our result revealed that plagioclase glass in EET83311 formed by shock event after thermal metamorphism, and plagioclase in LEW87009 formed by thermal metamorphism and then partially vitrified by shock event.

View full abstract

NWA 1232 CO3 chondrite has three lithologies(lithology A,B,C).We observed this meteorite in detail,and found the new lithology(lithology D).We compared lithology D with lithology A,B,and C.Our goal was to reveal the formation of NWA 1232 chondrite same as the three lithologies.But there are some differences of olivine composition in chondrules and matrix and of the abundance of nepheline in CAIs.Based on this results,we determined the degree of thermal metamorphism (C,D,A,B).We suggest that these lithologies are thermally metamorphosed at different locations in a single parent body and mixed.

View full abstract

Varieties of magnetite morphology were examined in CI chondrite and hydrothermal synthetic experiments were also carried out. Similar types were found.Formation conditions were discussed.

View full abstract