Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemical Geology  

The carbon isotopic composition of carbon dioxide fluid inclusions trapped within minerals reflects the origin and evolution of the CO2-bearing fluids and melts. Recently, we developed a highly accurate method using Raman spectroscopy to determine the carbon isotopic composition of CO2 fluid inclusions, by simultaneously collecting 13CO2 and hot bands at a controlled temperature, and using the peak height ratio of 13CO2 and one of hot bands near 1410 cm−1 (HR) to determine δ13C value. This microanalytical technique enables precise measurements of the δ13C values of different CO2 fluid inclusions within zoned mineral crystals to reveal the multiple-stages evolution of CO2-bearing fluids and melts. However, when studying fluid inclusions hosted within high laser heating coefficient minerals such as olivine and pyroxene in mantle xenoliths, local temperature near the inclusions will be higher than the temperature controlled by heating-cooling stage. To address this issue, we examined the effects of laser heating on CO2 isotopic standard samples sealed in the silica capillary, and developed a novel procedure to determine the δ13C values of natural fluid inclusions by using two CO2 standard samples with known carbon isotopic compositions. The proposed workflow successfully determines the δ13C values of natural CO2 inclusions, with an average deviation of 0.58 ‰ between the measurements and the model.

DOI： 10.1016/j.chemgeo.2024.122014

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.14943/J.HighEdu.31.65

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Publishing type：Research paper (scientific journal)   Publisher：Applied Optics  

To evaluate the precision of the wavenumber difference between the two main Raman bands of CO2 (designated as ∆, an index of CO2 density), we performed theoretical calculations for the uncertainties of the peak positions of the CO2 Raman bands, and measured Raman spectra of CO2 under the conditions used for the calculations. The ∆ precision improves with increased peak intensity, but the peak intensity–precision relation does not hold beyond an intensity threshold corresponding to the measurement time of 1–2 min. Correction for temporal variation of ∆ by fitting a linear function to the data distribution improved the ∆ precision to ±0.0005 cm−1 at best, corresponding to CO2 density precision as ±0.00015 g/cm3

DOI： 10.1364/AO.507939

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Raman Spectroscopy  

The intensity ratio (αI) and area ratio (αA) obtained using Raman spectroscopy are used widely to characterize the physical properties of gases, fluids, and solids, but the underlying parameters which affect their precision ((Formula presented.) and (Formula presented.)) have not been elucidated. We use simulations, experiments, and theoretical analyses to investigate the effects of instrumental performance, analytical conditions, and sample size on (Formula presented.) and (Formula presented.). We identified the parameters which strongly influence (Formula presented.) : (1) the weaker peak intensity Iw; (2) the ratio of the bandwidth to pixel resolution of the weaker peak Γw/Δxw; (3) the degree of detector saturation; (4) (Formula presented.) with readout noise σR, dark noise σD, and shot noise σS; (5) drift; and (6) sample size. Theoretical and simulation results show that, when Γw/Δxw ≪ (Γs/Δxs)/αI, increasing Iw or Γw/Δxw by n times can improve (Formula presented.) by a factor of (Formula presented.). Results showed that (Formula presented.) is a measure of how much the achievable (Formula presented.) in the experiment differs from that under ideal analytical conditions (i.e., (Formula presented.)). When (Formula presented.) is not the case (i.e., when Iw is low), reducing σD or σR by decreasing the readout speed, setting a lower charge coupled device (CCD) sensitivity, reducing number of readouts, or narrowing vertical binning width can improve (Formula presented.). We demonstrated that evaluations of (Formula presented.) or (Formula presented.) based on small sample sizes can engender physically unattainable precision. When the sample size is n = 5, 10, or 20, the average uncertainties of (Formula presented.) and (Formula presented.) correspond, respectively, to approximately 30%, 20%, and 15%. Giving an accurate and comparable assessment for (Formula presented.) and (Formula presented.) necessitates the reporting of intensity (in units of electrons), bandwidth, Δx, and the sample size.

DOI： 10.1002/jrs.6594

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

We report new noble gas isotopic compositions and abundance ratios (helium, neon, and argon) extracted from six lherzolite xenoliths on Oahu Island, Hawaii, by vacuum crushing. Considering the equilibrium temperature of the xenoliths and the fluid density of their fluid inclusions, they originated from a pressure of 0.98-1.04 GPa, corresponding to 33-34 km depth. The Moho depth beneath Oahu Island is around 15 km, suggesting that the xenoliths are part of the sub-oceanic lithospheric mantle (SOLM), 90 million years old, after generation of mid-oceanic ridge basalts (MORB). The samples have 3He/4He of 3.0-9.5 times atmosphere (Ra). The neon isotope compositions overlap with the data of previous studies for lava flow samples of the Hawaiian Islands, MORB, and air. The 40Ar/36Ar range from atmospheric to 3100. They show very low 4He/40Ar* and 4He/21Ne*, where asterisks denote correction for atmospheric contributions. The low 4He/40Ar* and 4He/21Ne* are characteristic of small fluid inclusions, based on step crushing experiments, indicating that they record kinetic fractionation that occurred in the SOLM most likely due to melt infiltration. Using 4He/40Ar* and 20Ne/22Ne respectively as indices of the kinetic fractionation and atmospheric contribution, we corrected for these effects. The corrected noble gas isotopic compositions are best explained by interaction between plume-derived melts and SOLM. The kinetic fractionation yields a decrease in 3He/238U in SOLM, which should result in a rapid decrease in 3He/4He with time. The slightly elevated 3He/4He (above 8 times atmospheric), as found in the present xenoliths cannot be maintained for more than one million years in the fractionated SOLM with 3He/U molar ratio of similar to 1 x 10-8, which is calculated assuming that the 3He/U has the same degree of kinetic fractionation as 4He/40Ar* and 4He/21Ne*. Therefore, the fractionation event is likely to be recent, and may be related to recent magmatism in the SOLM beneath Oahu Island. Such igneous activity is limited to Honolulu series volcanism (0.35-0.80 Ma). Therefore, the xenoliths contain a record of magmas with plume-derived noble gases, most likely associated with the Honolulu series volcanism.(c) 2022 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2022.117979

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>We measured the Raman spectra of CO₂ fluid at 30 MPa and room temperature (19.1–21.3°C). The spectra showed peaks attributed to the CO₂ combining various isotopes such as ¹²C¹⁶O₂, ¹³C¹⁶O₂, and ¹²C¹⁶O¹⁸O. The relative ratio of ¹²C¹⁶O₂ to ¹²C¹⁶O¹⁸O peaks represents the oxygen isotope ratio of CO₂. To evaluate the precision of the peak ratios, we measured the CO₂ Raman spectra at different exposure times. We examined the standard deviation (1 σ) of the peak intensity ratios and area ones for 20 measurements at each exposure time. The standard deviations of the intensity ratios and area ones were 2.7 and 3.1%, respectively, at a maximum exposure time of 494 s, conversion to peak intensity of ¹²C¹⁶O₂ yields about 2,000,000 counts. The uncertainties are 2.5–3 times greater than expected from the noise of a CCD camera and photon statistics. The oxygen isotope ratios (δ¹⁸O) of natural samples have a range of variation of about 16.6%. Compared to that value, the precision we obtained from this study is very small. Raman spectroscopy can be combined with microscopy to analyze areas as small as approx. 1 μm in diameter. Therefore, oxygen isotope measurement using Raman spectroscopy has potential for application to natural samples as a new method for small CO₂ fluids such as fluid inclusions.</p>

DOI： 10.2343/geochemj.gj23007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

The lithospheric mantle, formed at the mid-ocean ridge as a residue of crustal production, comprises theoretically depleted peridotite, but more fertile components (e.g., lherzolite and pyroxenite) have been reported, creating an enigmatic picture of the lithosphere. The oceanic lithosphere has also been found to be locally modified by intraplate magmatism as proposed from geochemistry of mantle xenolith. Petit-spot xenoliths are particularly notable as direct evidence of old lithospheric mantle and expected to retain essential information about oceanic lithosphere prior to its subduction. In this study, we report on the lithological structure of Pacific lithosphere aged at 160 Ma, just subducting into Mariana Trench, based on petrology and chemistry of ultramafic xenoliths from a petit-spot knoll, and then, we suggest the occurrence of petit-spot melt infiltration resulting in mantle metasomatism and formation of pyroxene-rich vein. Our petit-spot ultramafic xenoliths can be divided into three main types: a depleted peridotite as a residue of crust production, an enriched peridotite, and fertile pyroxenites as the product of melt–rock interactions prior to entrapment. Geothermobarometry also suggests that the depleted peridotite was derived from the uppermost lithospheric mantle, whereas the enriched peridotite and Al-augite pyroxenites were obtained from deeper layers of the lithosphere. Moreover, thermal gradient of the lithosphere estimated from these data is considerably hotter than pristine geotherm estimated on the basis of plate age. Hence, we could illustrate that the oldest portion of the Pacific lithosphere (160 Ma), which was not observed before, was locally fertilized and heated by prior multiple petit-spot magmatic events, and pyroxene-rich metasomatic veins penetrated from the base to the middle/upper lithosphere. Such local lithospheric fertilization is plausible at the plate-bending field, and the nature of Pacific Plate subducting into Mariana Trench may be partly different from what has been assumed so far.

DOI： 10.1186/s40645-022-00518-y

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Other Link： https://link.springer.com/article/10.1186/s40645-022-00518-y/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Spinel is potentially one of the best minerals for elastic geobarometry, but the large uncertainties in the published equation of state (EoS) of spinel prevent the application of elastic geobarometry using spinel. We have determined the EoS of MgAl2O4 from literature data on the volume, elasticity, and isobaric heat capacity by paying particular attention to the consistency of the thermoelastic data within the dataset and the influence of the inversion degree (i; (Mg1-iAli)[MgiAl2-i]O4) on the physical properties. After appropriate data selection, normalization, and correction, the resulting dataset was fitted with various EoS. Thermal pressure EoS that combined the third-order Birch–Murnaghan EoS and the Mie–Grüneisen–Debye EoS explain the data most successfully. The analysis yielded the following six EoS parameters: V0 = 39.78 cm3/mol (fixed), KT0 = 196.43(12) GPa, K′T0 = 4.37(4), θD0 = 898(10) K, γ0 = 1.136(11), and q = 1.94(9). The EoS has the properties at room conditions of αV = 1.6765(10) × 10–5 K–1 and KS0 = 197.55(12) GPa.
Combining our EoS with the published EoS, it was found that MgAl2O4 inclusions trapped in olivine and orthopyroxene derived from the spinel-lherzolite stability field should always have positive residual pressures (Pinc) at room conditions. This implies that elastic geobarometry using these host-inclusion systems can be expected to be new methods for estimating the depth provenance of spinel-bearing peridotites. In contrast olivine, orthopyroxene, and clinopyroxene inclusions in MgAl2O4 are expected to have Pinc > 0 only when trapped (or re-equilibrated) in geological environments with geotherms corresponding to surface heat flows below about 50, 60 and 70 mW/m2, respectively.

DOI： 10.1007/s00410-022-01975-w

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Other Link： https://link.springer.com/article/10.1007/s00410-022-01975-w/fulltext.html

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

We investigated mantle noble gas abundance ratios using a global compilation of data from mid-ocean ridge basalts (MORB) and high 3He/4He ocean island basalts (OIB), coupled with calculated abundances based on closed-system evolution models. Assuming that the mantle sources of MORB and high 3He/4He OIB are derived from the same early Earth parental material, variations in their noble gas abundance ratios are useful to ascertain which source is more depleted or degassed, or if the mantle noble gases might be a hybrid of different parental materials. Therefore, noble gas compositions of mantle sources can be a key to elucidating mantle evolution and structure. We calculated the noble gas abundance patterns using a Monte Carlo approach with validated endmembers, which provides new estimates for the abundance ratios and their uncertainties. The adequacy of the calculated values was confirmed by existing data. We compiled all published noble gas data extracted by total heating of glassy oceanic basalts, which enables estimation of the pristine abundance patterns of noble gases including Kr for both sources of MORB and OIB. The pristine abundance ratios of the mantle sources for oceanic basalts are estimated by correcting measured values for atmospheric influences and elemental fractionation. The corrected abundance ratios resemble mantle values calculated using the proposed end-members for MORB and high 3He/4He OIB. The estimated relative abundance ratios in the high 3He/4He OIB source are similar to those of C1 chondrites in the range of He to Kr, supporting the hypothesis that a less degassed primitive OIB source can exist in the Earth's mantle. By contrast, the MORB source shows depletion of lighter noble gases, but with high relative helium content compared to the OIB source. The contrast in He/Ne abundance ratios between MORB and OIB, is a key constraint on mantle evolution models, andis expected to reflect several stages of diffusive fractionation during Earth history, or different initial mantle sources, which would require heterogeneous Earth accretion.

DOI： 10.1016/j.pepi.2022.106875

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Language：Japanese   Publisher：Institute for the Advancement of Higher Education, Research Division for Higher Education  

Factors Affecting Overall Evaluation of a University Class : Exploring Factors Improving Learning Motivation

DOI： 10.14943/j.highedu.29.15

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>In the Horoman peridotite complex, the peridotite containing olivine-filled channels is known to exist. To examine the distribution pattern of the channel olivine, we performed non-destructive microanalyses of Raman spectra at 51 points of the olivine with 5 mm intervals along the channel. Compared with the Raman spectra of a reference euhedral olivine, for which the crystallographic orientation is known, there is no abrupt change in the crystallographic orientation in the 250 mm line analysis region of the channel. Moreover, Mg/Fe ratios of the channel olivine show gradual change over the entire measured area. If the channel olivine is an aggregate of olivine grains crystallized from magma infiltrating into the channel, then there should be olivine grains with both uneven crystallographic orientation and a homogeneous Mg/Fe ratio. Therefore, the olivine in the channel is regarded as a single crystal with slight growth zoning. The peridotite with the channel had been a part of mantle that was uplifted by the collision of plates. Therefore, the channel is a trace of magma migrating in the mantle. Magma migration in mantle drives the material–thermal circulation system connecting the Earth’s interior and surface. Furthermore, the size of the mineral in mantle reflects its stress field. Therefore, the magma channel involving such a large olivine is a unique specimen that reveals the particular characteristics of magmatism occurring in the Earth’s interior.</p>

DOI： 10.2343/geochemj.gj22003

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DOI： 10.3389/feart.2020.611010

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DOI： 10.2138/am-2021-7332

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DOI： 10.1016/j.chemgeo.2020.119928

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The compositions of volatiles in magmas can be estimated using melt inclusions encapsulated in phenocrysts. Shrinkage bubbles are occasionally observed in natural and rehomogenized melt inclusions. Because of the low solubility of CO2 in melts, CO2 is partitioned in both the melts and shrinkage bubbles in melt inclusions. We developed a method to determine total CO2 in melt inclusions by measuring (1) CO2 concentration in glass with secondary-ion mass spectrometry, (2) CO2 density in bubbles with micro-Raman spectrometry, and (3) bubble/glass volume ratio with micro X-ray computed tomography on rehomogenized melt inclusions. We applied this method to olivine-hosted melt inclusions in high-μ (HIMU)-type ocean island basalts from Raivavae in Austral Islands in French Polynesia. The shape of melt inclusions is predominantly related to their size; larger melt inclusions tend to be more angular than smaller ones. The volume of large melt inclusions may be overestimated by previous approaches in which the dimension of melt inclusions was measured by microscopy and the volume was calculated assuming ellipsoidal shape. CO2 dissolved in glass in rehomogenized melt inclusions ranges up to ~7000 ppm. The glass with a more alkalic composition shows greater CO2 concentration than that with a less alkalic composition in accordance with the composition-dependent CO2 solubility. By contrast, the correlation between the total CO2 content and the chemical composition of the glass is unclear because CO2 in shrinkage bubbles is generally greater than that in the glass. Some melt inclusions demonstrate an extremely high total CO2 content (up to 25,000 ppm). Because these melt inclusions show a large bubble volume proportion in melt inclusions (>12 vol&#37;), they are likely formed by the simultaneous entrapment of melts and fluids during the host olivine growth. Excluding these melt inclusions, the total CO2 content and CO2/Nb ratio in melt inclusions were up to 7000 ppm and 200, respectively. This study offers an accurate determination of CO2 concentration and CO2/Nb of the HIMU basalts from Raivavae.

DOI： 10.1016/j.chemgeo.2020.119855

Language：Others   Publishing type：Research paper (scientific journal)  

© 2020 We report new noble gas isotopic compositions of submarine basaltic glasses sampled from two seamounts discovered offshore of Chile, and inferred to have erupted as petit-spot volcanoes near the Juan Fernández hotspot. The samples have 3He/4He of 1–15 times atmosphere (Ra). Their neon isotope compositions are similar to those of the Hawaiian Islands and Réunion Island. Their 40Ar/36Ar range from atmospheric to 2300. Although the lavas are likely to be influenced by a hotspot-related component, the cause of the 3He/4He variation must be clarified to ascertain the mantle source. Variations in 3He/4He are not attributable to processes occurring at the Earth's surface such as degassing fractionation, mixing with atmosphere dissolved in seawater, or in-situ post-eruptive addition of 4He. A combination of the Ne-Ar isotope ratios corrected for atmospheric influence and He isotope ratios indicates that the noble gas isotopes of the lavas are a mixture of a hotspot magma, MORB-source, and radiogenic components. The lower 3He/4He are attributed to assimilation with the oceanic lithosphere, suggesting that the pristine 3He/4He of the lavas is hotspot-like. These features can be interpreted as indicating that part of the Juan Fernández plume infiltrated the lithosphere–asthenosphere boundary (LAB), and that the ponding magma has erupted as petit-spot volcanoes because of plate bending. The noble gas data indicate that LAB can be a reservoir for exotic melts, which might have lubricated plate tectonics.

DOI： 10.1016/j.epsl.2020.116611

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DOI： 10.1002/jrs.5865

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DOI： 10.1016/j.epsl.2020.116109

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DOI： 10.1002/jrs.5864

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DOI： doi.org/10.2465/jmps.181109b

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DOI： 10.1007/s10853-018-2848-5

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DOI： 10.1016/j.lithos.2018.11.009

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DOI： 10.1016/j.epsl.2018.06.020

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CO2 Raman thermometer improvement: comparing hot band and Stokes and anti-Stokes Raman scattering thermometers

DOI： 10.1002/jrs.5461

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DOI： 10.1080/00206814.2017.1379912

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DOI： 10.2343/geochemj.2.0523

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DOI： 10.1007/s00269-017-0912-3

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Educational program exhibiting formation of dyke: An approach to magma study

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DOI： 10.1002/jrs.5235

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DOI： 10.2343/geochemj.2.0477

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DOI： 10.1016/j.lithos.2016.07.012

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Eruption age of Sakurajima-Satsuma tephra using thermoluminescence dating

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.140782

Language：English   Publishing type：Research paper (scientific journal)  

Young basaltic knolls have been discovered on the old oceanic lithosphere, namely petit-spot volcanoes. Based on their geochemical signatures, they have presumably originated from partial melts in the asthenosphere. However, there is no direct information on the depth provenance of petit-spot formation. Here we report new geothermobarometric data of rare mantle xenoliths discovered from petit-spot lavas exhibiting a geotherm much hotter than expected for the ca. 140 Ma seafloor on which petit-spots were formed. Such an anomalously hot geotherm indicates that melt porosity around the lithosphere-asthenosphere boundary (LAB) must be as high as a few percent. Such high melt porosity would be possible by continuous melt replenishment. Excess pressure induced by the outer-rise topography enables horizontal melt migration along the LAB and sustains a continuous melt supply to petit-spot magmatism. Given the general age-depth relationship of ocean basins, a melt-rich boundary region could also be a global feature.

DOI： 10.1130/G35944.1

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DOI： 10.1007/s00410-014-1056-9

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DOI： 10.2478/s13386-013-0144-3

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We investigated the K-Ar ages and the petrological and geochemical features of lava units from lateral cones and lava distributed around the Aso caldera in central Kyushu, Japan, in order to constrain the spatial range of lateral magma intrusion during the caldera-forming stage. The results of the K-Ar age determination showed that most of the analyzed lava units erupted almost simultaneously with the Aso caldera-forming pyroclastic eruptions (266 to 89. ka). In addition, the petrography, major and trace element compositions, and Sr isotope ratios of these lava units are indistinguishable from the caldera-forming pyroclastic products. The contemporaneous activities of compositionally similar magmas inside and outside of the caldera presumably indicate the occurrence of a lateral intrusion of caldera-forming magma, which had accumulated in a huge magma chamber beneath the caldera system. Our results suggest that a total of 6.3. vol.&#37; of caldera-forming magma in the Aso volcano migrated more than 20. km along the faults from the center of the caldera. © 2013 Elsevier B.V.

DOI： 10.1016/j.chemgeo.2013.06.003

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/jrs.3134

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Based on pressure and temperature (P-T) information of mantle-derived xenoliths, this report describes a geotherm in Far Eastern Russia, which is situated in the backarc of volcanic chains in eastern Asia. The mantle xenoliths have abundant CO2 fluid inclusions. Accurate determination of the internal pressure of the CO2 fluid inclusions enables estimation of the depth provenance of the mantle xenoliths. The depth provenances obtained from five mantle xenoliths are correlated with equilibrium temperatures estimated using a geothermometer. Assuming that the correlation reflects the geotherm in this region, it corresponds to heat flow of around 100 mW/m(2), which is comparable to the surface heat flow in the volcanic arc. Such high heat flow implies a thin lithosphere and high temperature of the shallower upper mantle.
Backarc areas are universally characterized by both high surface heat flow and the occurrence of recent volcanic activities. Furthermore low seismic velocity anomaly is widely observed in the shallower upper mantle in the backarc, especially in eastern Asia. The present xenolith geotherm suggests that the seismic anomaly arises from high temperature of the shallower upper mantle. It would be direct evidence for warming of the lithospheric mantle and subsequent lithospheric thinning, which is likely attributable to asthenospheric upwelling. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2012.06.005

Language：English   Publishing type：Research paper (scientific journal)  

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Study Program to Assess Hinterland Provenance Using Several Separation Methods for Beach Sand

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/jrs.3024

Language：English   Publishing type：Research paper (scientific journal)  

To assess the capacity of fluid inclusions in mantle minerals for CO2 retention, annealing experiments were conducted for two mantle xenoliths with CO2 inclusions for 8 days at 1000 degrees C under atmospheric pressure and fO(2) of 10(-11) MPa. The results show no marked decrease in the CO2 density of the CO2 inclusions for any examined minerals - olivine, orthopyroxene, clinopyroxene, or spinel. The CO2 density of CO2 inclusions in olivine in the present mantle xenoliths is lower than that in pyroxenes or spinel. Results of previous studies indicate that the low CO2 density in olivine is attributable to plastic deformation of olivine around CO2 inclusions during annealing in ascending magma.
Results of this study present fundamental implications for deformation mechanisms that arise from internal pressure of fluid inclusions in silicate minerals. We calculated the stress field in minerals having a CO2 inclusion. Results show a steep stress gradient in the host around the inclusion. Such local stress in the mineral induces a local rise in the density of dislocations around the CO2 inclusions. The orthopyroxene used for this study showed a sparse distribution of dislocations around a CO2 inclusion, whereas olivine showed dense dislocations around CO2 inclusions, implying that the low CO2 density of the CO2 inclusions in olivine results from volume expansion of the CO2 inclusions through plastic deformation of the host mineral during annealing of the xenoliths in ascending magma.
In this respect, constancy of CO2 density during the annealing experiments for all minerals is an interesting finding. Regarding olivines, the reduction of internal pressure of the CO2 inclusions or interaction of the dense dislocations possibly inhibits decrepitation or further volume expansion of the CO2 inclusions during annealing experiments. However, pyroxenes and spinel show higher and similar CO2 density, which reflects the resistance to plastic deformation and which indicates the effectiveness of CO2 inclusions in these minerals as a depth probe for mantle xenoliths.

DOI： 10.1127/0935-1221/2011/0023-2150

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Observation of Magma Formation Using Portable Clay Cooking Stove and Familiar Products

Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 10.2465/jmps.090615

Language：English   Publishing type：Research paper (scientific journal)  

We measured noble gas isotopic compositions of mantle xenoliths and xenocrystic olivines sampled from seamounts-so-called petit-spot volcanoes-on the 135-million-year-old northwestern Pacific Plate. The xenoliths are spinel lherzolites originating from suboceanic lithospheric mantle. The samples' He-3/He-4 ratios are 7.0-8.5 Ra, where Ra signifies atmospheric He-3/He-4. The Ar-40/Ar-36 ratios are as high as 7000. These observations suggest that the noble gas isotopic compositions of suboceanic lithospheric mantle resemble those of mid-ocean ridge basalt (MORB). A mantle source with a He/U ratio as high as an assumed value for MORB source is necessary to maintain the MORB-like He-3/He-4 over 135 million years, implying that melt extraction at mid-ocean ridges only slightly alters the He/U ratio of the oceanic upper mantle.
The He-4/Ar-40* ratios of the samples described herein are much lower than the theoretical radiogenic production ratio, where an asterisk denotes correction for atmospheric contribution. The low He-4/Ar-40* is inferred to result from kinetic fractionation in the mantle. When magma migrates through a mantle source, lighter noble gases in the mantle source diffuse selectively into magma channels. The MORB generation does not cause low He-4/Ar-40*, however. If a mantle source is depleted in lighter noble gases during ancient MORB generation, then noble gas isotopic compositions of the mantle source are affected over time by accumulation of radiogenic nuclides. Thereby, the mantle source adopts a radiogenic or nucleogenic noble gas isotopic composition. Recent kinetic fractionation contributes to the low He-4/Ar-40* in the samples. Based on the diffusive fractionation model, more than 100 years are necessary to produce a residual mantle source with He-4/Ar-40*, as observed in the samples. However, petit-spot volcanoes. found as small knolls, seem to erupt within a short period. The low He-4/Ar-40* of the samples implies prior volcanism in this region. No recent volcanism has occurred near this region aside from petit-spot volcanism, indicating that petit-spot volcanoes are polygenetic with a long active period.
Petit-spot volcanoes are regarded as common magmatism on the subducting oceanic plate. Consequently, the thermal structure and temperature-dependent physical properties of the oceanic plate are, at least partly, affected by remnant heat of the magmatism. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2009.09.009

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.chemgeo.2008.10.020

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Melt extraction and multiple metasomatism beneath French Massif Central: Geochemical and isotopic signatures of ultramafic xenoliths

Language：English   Publishing type：Research paper (scientific journal)  

By crushing olivine and pyroxene phenocrysts in volcanic rocks from Kyushu Island, Japan, we determined (3)He/(4)He of 3-7 Ra and (40)Ar/(36)Ar of up to 1750. These values are lower than those of MORB. (4)He/(40)Ar* (down to 0.1) is much lower than the production ratio of (4)He/(40)Ar* (1-5), where an asterisk denotes correction for the atmospheric contribution. Such values are typical of mantle-derived samples from the island arcs and active continental margins. Although the origin of the low (3)He/(4)He and (40)Ar/(36)Ar of subcontinental mantle has been widely discussed, low (4)He/(40)Ar* has been given little attention. Actually, (3)He/(4) He and (4)He/(40)Ar* of phenocrysts overlap with those of subcontinental mantle xenoliths. Although noble gas compositions of phenocrysts are affected considerably by diffusive fractionation in ascending magma, they have little effect on the noble gases in the mantle xenoliths because it takes 100 years for He/Ar fractionation of ca. 15&#37; for a mantle xenolith with 5 cm diameter. Therefore, the low (4)He/(40)Ar* of the mantle xenoliths is inferred to result from another kinetic fractionation in the mantle.
During generation and migration of magma in the mantle, lighter noble gases diffuse rapidly out into the magma. This diffusive fractionation can explain low (4)He/(40)Ar* and somewhat low (3)He/(4)He in the residual mantle. Furthermore, the combination of the diffusive fractionation and subsequent radiogenic ingrowth explain the fact that data from subcontinental mantle xenoliths have extremely low (3)He/(4)He and various (4)He/(40)Ar*. Consequently, (4)He/(40)Ar* and (3)He/(4) He in mantle-derived materials are proposed as indicators of the degree of noble gas depletion of the source mantle. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2009.01.029

Language：English   Publishing type：Research paper (scientific journal)  

Based on both major and trace element chemistry, the occurrence of the intergranular component in mantle-derived xenoliths from far eastern Russia has been constrained. Whole-rock trace element measurements of one xenolith show apparent negative anomalies in Ce, Th, and high field strength elements on normalized trace element patterns. The trace element pattern of the whole rock differs from those of constituent minerals, indicating that the anomalies in the whole rock are attributable to the presence of an intergranular component. That assumption was confirmed using in situ analysis of trace elements in the intergranular substance and melt inclusion using laser ablation inductively coupled plasma-mass spectrometry. Both the intergranular component and the melt inclusions have identical trace element patterns, which mean that these materials are a cognate metasomatizing agent. The anomalies are regarded as mantle metasomatism related to an aqueous fluid. Hydrous minerals were observed on the wall of the melt inclusions using micro-Raman spectroscopy, indicating that the melt inclusions contained a large amount of water. Thus, this study reveals a trace element composition of a hydrous metasomatizing agent in the mantle.

DOI： 10.1111/j.1440-1738.2008.00642.x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/jrs.2094

Language：English   Publishing type：Research paper (scientific journal)  

Micro-Raman spectroscopy enables precise non-destructive analyses of CO(2) density in a very small volume. By applying this method to CO(2) fluid inclusions in minerals, a contrast is apparent in the CO(2) density specific to mineral species in a mantle-derived spinel lherzolite xenolith entrained by ascending magma. The rock investigated in this study comprises four mineral species: olivine, orthopyroxene (opx), clinopyroxene (cpx), and chromian-spinel (spinel). The CO(2) densities in the fluid inclusions in these minerals are 1.006-1.035, 1.148-1.154, 1.150-1.154 and 1.189-1.194 g/cm(3), respectively. During transport of the rock by magma and subsequent cooling, the CO(2) fluid inclusions change their volume due to both elastic and plastic properties of the host mineral, which are sensitive to differential pressure between internal pressure of the CO(2) fluid inclusion, and stress in surrounding crystal lattice. We tested the possibility that the Volume Of CO(2) fluid inclusion changes by the differential pressure. Existing models dealing with the volume change of fluid inclusion in response to deformation of host mineral do not explain the density gradation, particularly that between pyroxenes and spinel. We propose that combination of precise determination of fluid density in mantle-derived minerals and observation of microstructure in the host mineral provides a deep insight into the deformation mechanism of natural minerals under high differential pressure and temperature.

DOI： 10.1127/0935-1221/2008/0020-1825

Language：English   Publishing type：Research paper (scientific journal)  

Using in situ strength measurements at pressures up to 10 GPa and at room temperature, 400, 600, and 700 degrees C, we examined rheological properties of olivine, orthopyroxene, and chromian-spinel contained in a mantle-derived xenolith. Mineral strengths were estimated using widths of X-ray diffraction peaks as a function of pressure, temperature, and time. Differential stresses of all minerals increase with increasing pressure, but they decrease with increasing temperature because of elastic strain on compression and stress relaxation during heating. During compression at room temperature, all minerals deform plastically at differential stress of 4-6 GPa. During subsequent heating, thermally induced yielding is observed in olivine at 600 degrees C. Neither orthopyroxene nor spinel shows complete stress relaxation, but both retain some stress even at 700 degrees C. The strength of the minerals decreases in the order of chromian-spinel approximate to orthopyroxene > olivine for these conditions. This order of strength is consistent with the residual pressure of fluid inclusions in mantle xenoliths.

DOI： 10.1007/s00269-008-0218-6

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.2008.280

Language：Japanese  

プチスポット総合調査

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1366/000370207781393244

Language：English   Publishing type：Research paper (scientific journal)  

The density, and therefore the pressure, Of CO2 fluid inclusions in minerals can be estimated from the Fermi diad splitting of Raman spectra Of CO2. An accurate determination of the pressure Of CO2 fluid inclusions enables the estimation of the depth origin of rocks from the deep Earth. A micro-Raman densimeter was applied to ultramafic-mafic xenoliths sampled along the Ohku coast of Oki-Dogo Island in the Sea of Japan (East Sea). The density Of CO2 fluid inclusions in the mafic granulite was 1.02-1.05 g/cm(3), while those of Iherzolites were 0.98-1.02 g/cm. In contrast, the density Of CO2 fluid inclusions measured in olivine gabbro, clinopyroxenite, and harzburgite were lower ranging from 0.86- to 0.99 g/cm(3). Taking into account the temperature condition estimated using a pyroxene thermometer, the mafic granulite originated from a depth of 27-30 km and the lherzolites from 2529 km. The overlapping depth of 27-29 km can be interpreted as the depth including the Moho discontinuity under Oki-Dogo Island 3.3 Ma. This estimation is consistent with geophysical observations. (c) 2006 Elsevier B.X. All rights reserved.

DOI： 10.1016/j.epsl.2006.10.038

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1126/science.1128235

Language：English   Publishing type：Research paper (scientific journal)  

Micro-Raman spectroscopy enables nondestructive analyses Of CO2 fluid density in a very small volume. For application of the method to CO2 fluid inclusions in minerals originated from the deep Earth having widely various densities, we extended the relational expression between the density and Raman spectra Of CO2 up to the density corresponding to the boundary between liquid and solid.

DOI： 10.1246/cl.2006.610

Language：English   Publishing type：Research paper (scientific journal)  

Noble gas abundances in basaltic glasses from ocean islands (OIBs) are generally lower than those of mid-oceanic ridge basalts (MORBs), contrary to most geodynamic models which usually require that the source of OIBs is less degassed (resulting in higher primordial noble gas abundances) and more trace element enriched (resulting in higher radiogenic noble gas abundances) than the MORB source. Therefore, noble gas abundances in OIBs are often thought to have been reduced by extensive gas loss from the magma before eruption.
The extent of magmatic degassing can be tested as it will cause characteristic changes in the composition of the volatiles; notably the He-4/Ar-40* ratio (where Ar-40* is Ar-40 corrected for atmospheric contamination) will increase in residual volatiles due to the higher solubility of He relative to Ar. The degree of He-As fractionation for a given fraction of gas loss depends on the ratio of the solubilities, S-He/S-Ar, which is sensitive to (among other things) the CO2 and H2O content of the basalt at the time of degassing.
From a global database of OIB and MORB glasses, we show that He-4/Ar-40* ratios of MORB glasses are broadly consistent with degassing of a magma with an initial Ar-40 of approximate to1.5 x 10(-5) ccSTP/g, i.e., similar to that of the "popping rock." However, OIB glasses generally have lower Ar-40* concentration for a given He-4/Ar-40*. While this would appear to require lower Ar-40* abundances in the undegassed OIB magmas, the higher volatile contents of OIBs will reduce S-He/S-Ar (relative to MORBs) during degassing. By modeling S-He/S-Ar in OIBs, it is possible to show that extensive degassing of OIBs can occur without dramatically increasing the He-4/Ar-40* ratio. We show that undegassed Ar-40 concentrations of OEB magmas were probahl. similar to those of MORBs. Copyright (C) 2005 Elsevier Ltd.

DOI： 10.1016/j.gca.2004.07.014

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jvolgeores.2004.08.003

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DOI： 10.1007/s00410-004-0593-z

Language：English   Publishing type：Research paper (scientific journal)  

By applying both vacuum crushing and stepwise heating methods for the extraction of the noble gases, we have discovered He-3/He-4 ratios much lower than the atmospheric ratio (similar to 0.3 R-A; R-A is the atmospheric He-3/He-4 ratio of 1.4 x 10(-6)) and relatively low Ar-40/Ar-36 ratios (<1 000) in olivine separates from some subcontinental mantle-derived xenoliths from Far Eastern Russia. The low He-3/He-4 ratios cannot be explained by the addition of radiogenic He-4 generated in-situ after the eruption of magma entraining the xenoliths. Furthermore, petrographic evidence suggests that incorporation of crustal fluids is not likely. Hence, it must reflect a feature of the Far Eastern Russian upper mantle.
Spectroscopic and petrographic observations confirm that there are at least two compositionally distinct fluids in these xenoliths; liquid CO2 inclusions and melt inclusions with shrinkage bubbles. Based on the crushing experiments, it is inferred that the inclusions of liquid CO2 have a He-3/He-4 ratio similar to that of MORB, and the component with the low He-3/He-4 ratio is derived from the shrinkage bubbles in the melt inclusions.
For the present samples, the Ar-40/Ar-36 ratios obtained by crushing were less than 1060, suggesting incorporation of atmospheric components in the source materials. Since low Ar-40/Ar-36 ratios were observed irrespective of the occurrence of the liquid CO, inclusions, the atmospheric component exists in the melt inclusions. Ne and Xe isotopes are also consistent with incorporation of atmospheric components.
Since the Far Eastern Russia area was located at a subduction zone in the Jurassic-early Cretaceous Period, it is most likely that the melt inclusions displaying atmospheric noble gas characteristics together with low He-3/He-4 ratios have been derived from the Jurassic-Cretaceous subducted slab. Although we cannot exclude the possibility that low He-3/He-4 ratios are due to the existence of minor U-bearing minerals in the lithospheric continental mantle caused by metasomatism, we have no petrographical evidence for such minerals in this area. On the other hand, He-3/He-4 ratios observed in the liquid CO2 inclusions, which are similar to the MORB-like value, might reflect the general character of the upper mantle. The Far Eastern Russian mantle may therefore be a MORB-like source that has been partly infiltrated by subduction-related fluids. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2004.03.007

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0012-821X(03)00606-X

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/nature02179

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1366/000370203322554473

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Micro-Raman spectroscopic analysis allows us to estimate the internal pressure of small fluid inclusions. We applied this method to CO2-dominated fluid inclusions in mantle-derived xenoliths. The pressures estimated from the equilibration temperature and density of the fluid range from 0.96 to 1.04 GPa corresponding to depths of up to 30 km, which confirms that these rocks and fluids are of uppermost mantle origin. Furthermore, the inclusions show pressures specific to the individual host minerals (spinel greater than or equal to orthopyroxene approximate to clinopyroxene much greater than olivine). In particular. the densities of CO2 in pyroxenes are 10&#37; higher than in olivine. Such an enormous difference cannot be explained by elastic deformation of the minerals during ascent of the xenoliths, although the process may explain the slightly higher density of CO2 in spinel. During the ascent. the strain rate of orthopyroxene calculated using the 'constitutive equation' is several orders of magnitude lower than that of olivine. The difference in densities of CO2 among the host mineral species is therefore attributable to the rheological properties of the minerals. Present internal pressures of fluid inclusions can be a sensitive strength marker of mantle minerals. Conversely, the density of CO2 inclusions in pyroxene (and spinel) may be a useful geobarometer. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0012-821X(02)00528-9

Language：English   Publishing type：Research paper (scientific journal)  

The concentrations of helium and carbon in fluorite associated with Cretaceous to Neogene (90-13 Ma) granitic magmatism in the Japanese are have been measured. Concentrations of Li, U, Th and Gd were measured to correct for secondary generated He-3. The CO2/He-3 of fluorites are almost uniform (1.5 x 10(10)-4 x 10(10)) and in fair agreement with the range of present island are volcanic gases. The calculated mantle C contribution in the Mesozoic subduction zone appear to have been identical to the present one (7-19&#37;) indicating that the C flux from the mantle in supra-subduction zone environments has remained fairly constant during the past 70 million years. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0377-0273(00)00315-2

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DOI： 10.14934/chikyukagaku.41.63

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“環境”という言葉を説明できますか? “環境”を耳にしない日はありませんが、私たちは共通のイメージを持っているのでしょうか。 “環境”を守るとは具体的に何を守ることなのでしょう。 今回は地球を様々な時空間スケールで眺めることで、 “環境”の謎に迫ります!

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Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：Infants,　Schoolchildren,　Junior students,　High school students

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

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