研究者詳細 - 芳野　極

論文 - 芳野　極

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No interconnection of ferro-periclase in post-spinel phase inferred from conductivity measurement 査読

Takashi Yoshino, Daisuke Yamazaki, Eiji Ito, Tomoo Katsura

GEOPHYSICAL RESEARCH LETTERS 35 ( 22 ) L22303 2008年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Electrical conductivities of post-spinel, which are thought to be a dominant assembly in the lower mantle, were investigated at the conditions of the uppermost lower mantle (25 GPa and temperatures ranging from 300 to 2000K) in a Kawai-type multi-anvil apparatus. Post-spinel phases with a bulk composition of ((Mg,Fe)(2)SiO4: X-Fe = 0.09) were measured to constrain the bulk conductivity of the lower mantle. To investigate interconnectivity of ferro-periclase in silicate perovskite matrix, a single phase composed of magnesium silicate perovskite ((Mg, Fe)SiO3: X-Fe = 0.1) and ferro-periclase ((Mg, Fe)O: X-Fe = 0.13) were also measured. The conductivity values of the silicate perovskite are distinctly lower than those for the coexisting ferro-pericalse. Both absolute values and change in activation enthalpy for the conductivity of the post-spinel phases are similar to those for the silicate perovskite. These observations suggest that ferro-periclase in post-spinel are isolated in silicate perovskite matrix. Citation: Yoshino, T., D. Yamazaki, E. Ito, and T. Katsura (2008), No interconnection of ferro-periclase in post-spinel phase inferred from conductivity measurement, Geophys. Res. Lett., 35, L22303, doi:10.1029/2008GL035932.

DOI： 10.1029/2008GL035932

その他リンク： http://orcid.org/0000-0002-5422-7396

Dry mantle transition zone inferred from the conductivity of wadsleyite and ringwoodite 査読

Takashi Yoshino, Geeth Manthilake, Takuya Matsuzaki, Tomoo Katsura

NATURE 451 ( 7176 ) 326 - 329 2008年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

The Earth's mantle transition zone could potentially store a large amount of water, as the minerals wadsleyite and ringwoodite incorporate a significant amount of water in their crystal structure(1,2). The water content in the transition zone can be estimated from the electrical conductivities of hydrous wadsleyite and ringwoodite, although such estimates depend on accurate knowledge of the two conduction mechanisms in these minerals ( small polaron and proton conductions), which early studies have failed to distinguish between(3,4). Here we report the electrical conductivity of these two minerals obtained by high- pressure multi- anvil experiments. We found that the small polaron conductions of these minerals are substantially lower than previously estimated. The contributions of proton conduction are small at temperatures corresponding to the mantle transition zone and the conductivity of wadsleyite is considerably lower than that of ringwoodite for both mechanisms. The dry model mantle shows considerable conductivity jumps associated with the olivine- wadsleyite, wadsleyite- ringwoodite and post- spinel transitions. Such a dry model explains well the currently available conductivity- depth profiles(5) obtained from geoelectromagnetic studies. We therefore conclude that there is no need to introduce a significant amount of water in the mantle transition to satisfy electrical conductivity constraints.

DOI： 10.1038/nature06427

その他リンク： http://orcid.org/0000-0002-5422-7396

Phase boundary between ilmenite and perovskite structures in MnGeO3 determined by in situ X-ray diffraction measurements 査読

Daisuke Yamazaki, Eiji Ito, Yoshinori Tange, Takashi Yoshino, Shuangmeng Zhai, Hiroshi Fukui, Anton Shatskiy, Tomoo Katsura, Ken-ichi Funakoshi

PHYSICS AND CHEMISTRY OF MINERALS 34 ( 4 ) 269 - 273 2007年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

In situ X-ray observations of the phase transition from ilmenite to perovskite structure in MnGeO3 were carried out in a Kawai-type high-pressure apparatus interfaced with synchrotron radiation. The phase boundary between the ilmenite and perovskite structures in the temperature range of 700-1,400 degrees C was determined to be P (GPa) = 16.5(+/- 0.6) -0.0034(+/- 0.0006)T (degrees C) based on Anderson's gold pressure scale. The Clapeyron slope, dP/dT, determined in this study is consistent with that for the transition boundary between the ilmenite and the perovskite structure in MgSiO3.

DOI： 10.1007/s00269-007-0145-y

その他リンク： http://orcid.org/0000-0002-5422-7396

Complete wetting of olivine grain boundaries by a hydrous melt near the mantle transition zone 査読

Takashi Yoshino, Yu Nishihara, Shun-ichiro Karato

EARTH AND PLANETARY SCIENCE LETTERS 256 ( 3-4 ) 466 - 472 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Many physical properties of liquid-bearing rocks in the deep Earth's interior are strongly controlled by its wetting behavior. We report experimental results on the variation of dihedral angle and micro structures in the forsterite-H2O system at 1200 degrees C and pressures ranging from I to 13 GPa. The dihedral angle of the system decreases systematically with pressure and above the mantle transition zone (similar to 400 km depth) it becomes approximately 0 degrees, corresponding to completely wetted grain boundaries. This condition is probably reached because of a decrease in the solid-liquid interfacial energy with pressure due to the dramatically increased solubility of silicates in the liquid. These results suggest that the presence of partial melt would have drastic influences on physical properties of upper mantle around the transition zone even if the melt fraction is very low. Low velocity regions just above the mantle transition zone may result from the presence of hydrous melt. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.02.002

その他リンク： http://orcid.org/0000-0002-5422-7396

Grain growth kinetics of CaIrO<inf>3</inf>perovskite and post-perovskite, with implications for rheology of D″ layer 査読

Takashi Yoshino, Daisuke Yamazaki

Earth and Planetary Science Letters 255 ( 3-4 ) 485 - 493 2007年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Grain growth kinetics of CaIrO3perovskite and post-perovskite aggregates was investigated by time-series experiments at pressures of 2 and 3 GPa and temperatures ranging from 1373 to 1773 K in a piston cylinder apparatus. The experiments were conducted in the stability field of both perovskite and post-perovskite. The increase of grain size (G) with time (t) follows a growth law: Gn-G0n= k · t (k = k0exp(- H*/RT)). The growth exponents (n) for perovskite and post-perovskite are 2.6 ± 0.5 and 4.5 ± 0.9, respectively. The activation enthalpy (H*) of post-perovskite grain growth is 251 ± 35 kJ/mol. Grain growth of post-perovskite is distinctly slower than that of perovskite. Sluggish grain growth of the post-perovskite is caused by its strong anisotropic shape. The phase transition from the perovskite to the post-perovskite at the D" discontinuity would lead to maintenance of small grain size in the D" layer. If diffusion creep is the dominant deformation mechanism of post-perovskite, the phase transformation would induce the significant softening of the D" layer due to slow growth rate of post-perovskite compared with a situation without the phase transition. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.01.010

その他リンク： http://orcid.org/0000-0002-5422-7396

Origin of seismic anisotropy in the D '' layer inferred from shear deformation experiments on post-perovskite phase 査読

Daisuke Yamazaki, Takashi Yoshino, Hiroaki Ohfuji, Jun-ichi Ando, Akira Yoneda

EARTH AND PLANETARY SCIENCE LETTERS 252 ( 3-4 ) 372 - 378 2006年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Seismic anisotropy is one of the significant features in the D" layer of the Earth and is thought to be derived from the lattice preferred orientation (LPO) of constituent materials or shape preferred orientation (SPO) of heterogeneous materials such as melt and inclusions. Recent experimental and theoretical studies strongly suggest that the D" layer consists mainly of a MgSiO3 Postperovskite phase together with ferro-periclase. To understand the anisotropy in the D" layer, we have conducted a series of simple shear deformation experiments at high temperature and pressure on polycrystalline CaIrO3 as an analogue of MgSiO3 and measured the LPO of the post-perovskite phase. Crystallographic orientation analysis of the deformed post-perovskite phase showed strong LPOs with the dominant slip system being [100](010). Calculation of the elastic wave velocities considering the effect of LPOs of post-perovskite and ferro-periclase showed as azimuthal and polarization anisotropies in the horizontal shear plane where the velocity of horizontally polarized S-wave is considerably faster than that of vertically polarized S-wave. Thus, the seismic anisotropy observed in the D" layer can be reasonably explained by the LPO of the mixture of post-perovskite and ferro-periclase, where the LPO may result from the horizontal shear flow generated by the mantle convection. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2006.10.004

その他リンク： http://orcid.org/0000-0002-5422-7396

Hydrous olivine unable to account for conductivity anomaly at the top of the asthenosphere 査読

Takashi Yoshino, Takuya Matsuzaki, Shigeru Yamashita, Tomoo Katsura

NATURE 443 ( 7114 ) 973 - 976 2006年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations(1,2). In the directions parallel and normal to the plate motion, the conductivity is of the order of 10(-1) and 10(-2) Sm(-1), respectively, which cannot be explained by the conductivity of anhydrous olivine(2). But because hydrogen can be incorporated in olivine at mantle pressures(3-5), this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration(1,2,6,7). To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500 - 1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10(-2) Sm(-1). Our data indicate that the hydration of olivine cannot account for the geophysical observations(2), which instead may be explained by the presence of partial melt elongated in the direction of plate motion.

DOI： 10.1038/nature05223

その他リンク： http://orcid.org/0000-0002-5422-7396

Effect of faceting on pore geometry in texturally equilibrated rocks: implications for low permeability at low porosity 査読

Takashi Yoshino, Jonathan D. Price, David A. Wark, E. Bruce Watson

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY 152 ( 2 ) 169 - 186 2006年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SPRINGER

The pore geometry of texturally equilibrated rocks is controlled by the interfacial energy ratio between grain boundaries and solid-liquid boundaries. Faceting at pore walls, which is a common feature of pore networks in rocks, strongly affects the liquid distribution. We investigated the effects of faceting on the equilibrium pore geometries based on image analysis of several systems with various degrees of faceting and dihedral angles. The degree of faceting was assessed by the F value, which is the ratio of the flat interface length at the pore wall to the length of total interfacial boundary between solid and liquid. The F values tend to increase with increasing liquid volume fraction. Little-faceted systems show relatively homogeneous liquid distribution. Moderately-faceted systems with a higher dihedral angle (similar to 55 degrees) are characterized by development of large pores surrounded by faceted walls and complementary shrinkage of triple junction tubes, whereas strongly faceted systems with a low dihedral angle show no evidence of shrinking triple junction tubes, although most pores are surrounded by faceted pore walls. The faceted systems tend to produce more facet boundaries at the pore walls due to the difference of interfacial energies between the flat and curved surfaces. In the systems with the same degree of faceting, heterogeneity of liquid distribution tends to decrease with dihedral angle. For faceting systems, the permeability of texturally equilibrated rocks with low liquid fraction would be significantly decreased by the relative reduction of triple junction volumes or by closure of channels along grain edge due to the truncation of facet walls.

DOI： 10.1007/s00410-006-0099-y

その他リンク： http://orcid.org/0000-0002-5422-7396

Grain boundary wetness of texturally equilibrated rocks, with implications for seismic properties of the upper mantle 査読

T Yoshino, Y Takei, DA Wark, EB Watson

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 110 ( B8 ) 1 - 16 2005年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

Melt- or fluid- filled pore geometry in texturally equilibrated aggregates characterized by various dihedral angles and degrees of faceting was investigated quantitatively by measuring the grain boundary wetness, which is defined as the ratio of solid- liquid boundary area over the total area of interphase boundaries. The wetness ( psi) increases monotonically with increasing liquid volume fraction ( phi). For systems showing no faceting and low dihedral angle, the relation between phi and psi agrees well with the theoretical prediction for an ideal isotropic model assuming tetrakaidecahedral packing. This is true for the olivine- basalt system, whereas partially molten lherzolite shows systematically lower wetness. For systems showing strong faceting, the wetness is systematically lower than the theoretical prediction. For all systems, the obtained psi-phi relationship can be fitted well to the formulae psi = A phi(1/ 2) with fitting parameter A, indicating that the three- dimensional pore shape is a tubular one. Seismic wave velocities are calculated for the model systems in terms of the equivalent aspect ratio ( EAR) of the oblate spheroid model based on the above psi-phi relation. Calculated EARs can be used to predict f in texturally equilibrated rocks using V-P or V-S data and also to interpret the seismologically observed variation of dlnV(S)/ dlnV(P) in terms of the variation of pore geometry. Our results show that seismic wave velocities of partially molten peridotites are not significantly affected by faceting and that values of dlnV(S)/ dlnV(P) larger than 1.5 cannot be explained by texturally equilibrated partially molten rocks.

DOI： 10.1029/2004JB003544

その他リンク： http://orcid.org/0000-0002-5422-7396

Growth kinetics of FeS melt in partially molten peridotite: An analog for core-forrning processes 査読

T Yoshino, EB Watson

EARTH AND PLANETARY SCIENCE LETTERS 235 ( 1-2 ) 453 - 468 2005年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The growth kinetics of molten FeS pools in partially molten peridotite were investigated by time-series experiments in a piston-cylinder apparatus. The starting materials were mixed powders of peridotite +FeS, with FeS=6%, 12% and 18% by volume in order to characterize the effect of volume fraction on the growth laws of Fes. The initial particle size of Fes was about 3.5 mu m. The samples were annealed at temperatures between 1573 and 1723 K at 1.5 GPa for durations ranging from a few seconds to 100 h. The size of Fes pools was determined by analysis of backscattered electron images. The increase of pool size (G) of FeS with time (t) follows a growth law: G(n) - G(0) = k (.) t (k=k(0) exp(- Q/RT)). Samples with higher Fes volume fraction have larger pool size at the same conditions. The growth exponent (n) at 1573 K strongly depends on initial volume fraction of Fes and varies between similar to 2.6 and similar to 6.4, whereas those at 1723 K are almost constant (similar to 2.3) irrespective of the initial volume fraction. The growth exponent (n) tends to decrease with increasing temperature and volume fraction of silicate melt for each run series of different initial volume fraction of Fes. Low volume fractions of Fes and silicate melt leads to sluggish growth of the pools due to pinning of the silicate mineral phases. The activation enthalpy for pool growth is 331 +/- 40 kJ/mol based on the results from samples with 18 vol.% FeS, which show the smallest variation of growth exponent over a range of temperature. These Fes coarsening experiments may serve as tentative analogs for the behavior of a liquid metal phase in hot proto-planetary objects. Assuming exponential heating of such bodies in the early solar system-and allowing for a significant Zener pinning effect of Fe pools-the time spent above the silicate solidus may be insufficient to grow the pools beyond the size where diffusive equilibration with the silicate surroundings can be maintained: in other words, diffusive equilibration may assured because of slow coarsening kinetics. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2005.04.021

その他リンク： http://orcid.org/0000-0002-5422-7396

Crustal growth by magmatic accretion constrained by metamorphic P-T paths and thermal models of the Kohistan arc, NW Himalayas 査読

T Yoshino, T Okudaira

JOURNAL OF PETROLOGY 45 ( 11 ) 2287 - 2302 2004年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：OXFORD UNIV PRESS

Magmatic accretion is potentially an important mechanism in the growth of the continental crust and the formation of granulites. In this study, the thermal evolution of a magmatic arc in response to magmatic accretion is modeled using numerical solutions of the one-dimensional heat conduction equation. The initial and boundary conditions used in the model are constrained by geological observations made in the Kohistan area, NW Himalayas. Taking consideration of the preferred intrusion locations for basaltic magmas, we consider two plausible modes of magmatic accretion: the first involves the repeated intrusion of basalt at mid-crustal depths ('intraplate model'), and the second evaluates the simultaneous intrusion of basalt and picrite at mid-crustal depths and the base of the crust respectively ('double-plate model'). The results of the double-plate model account for both the inferred metamorphic P-T paths of the Kohistan mafic granulites and the continental geotherm determined from peak P-T conditions observed for granulite terranes. The double-plate model may be applicable as a key growth process for the production of thick mafic lower crust in magmatic arcs.

DOI： 10.1093/petrology/egh056

その他リンク： http://orcid.org/0000-0002-5422-7396

Phase relations and equation-of-state of aluminous Mg-silicate perovskite and implications for Earth’s lower mantle. 査読

M. J. Walter, A. Kubo, T. Yoshino, J. Brodholt, K. Koga, Y. Ohishi

Earth and Planetary Science Letters 222 ( 2 ) 501 - 516 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have investigated the effect of Al3+ on the room-temperature compressibility of perovskite for stoichiometric compositions along the MgSiO3-AlO1.5 join with up to 25 mol% AlO1.5. Aluminous Mg-perovskite was synthesized from glass starting materials, and was observed to remain a stable phase in the range of ∼30-100 GPa at temperatures of ∼2000 to 2600 K. Lattice parameters for orthorhombic ( Pbnm ) perovskite were determined using in situ X-ray diffraction at SPring8, Japan. Addition of Al3+ into the perovskite structure increases orthorhombic distortion and unit cell volume at ambient conditions ( V0). Compression causes anisotropic decreases in axial length, with the a axis more compressive than the b and c axes by about 25% and 3%, respectively. The magnitude of orthorhombic distortion increases with pressure, but aluminous perovskite remains stable to pressures of at least 100 GPa. Our results show that substitution of Al3+ causes a mild increase in compressibility, with the bulk modulus ( K0) decreasing at a rate of -67±35 GPa/XAl. This decrease in K0 is consistent with recent theoretical calculations if essentially all Al3+ substitutes equally into the six- and eight-fold sites by charge-coupled substitution with Mg2+ and Si4+. In contrast, the large increase in compressibility reported in some studies with addition of even minor amounts of Al is consistent with substitution of Al3+ into six-fold sites via an oxygen-vacancy forming substitution reaction. Schematic phase relations within the ternary MgSiO3-AlO1.5-SiO2 indicate that a stability field of ternary defect Mg-perovskite should be stable at uppermost lower mantle conditions. Extension of phase relations into the quaternary MgSiO3-AlO1.5-FeO1.5-SiO2 based on recent experimental results indicates the existence of a complex polyhedral volume of Mg-perovskite solid solutions comprised of a mixture of charge-coupled and oxygen-vacancy Al3+ and Fe3+ substitutions. Primitive mantle with about 5 mol% AlO1.5 and an Fe3+/(Fe3++Fe2+) ratio of ∼0.5 is expected to be comprised of ferropericlase coexisiting with Mg-perovskite that has a considerable component of Al3+ and Fe3+ defect substitutions at conditions of the uppermost lower mantle. Increased pressure may favor charge-coupled substitution reactions over vacancy forming reactions, such that a region could exist in the lower mantle with a gradient in substitution mechanisms. In this case, we expect the physical and transport properties of Mg-perovskite to change with depth, with a softer, probably more hydrated, defect dominated Mg-perovskite at the top of the lower mantle, grading into a stiffer, dehydrated, charge-coupled substitution dominated Mg-perovskite at greater depth. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2004.03.014

その他リンク： http://orcid.org/0000-0002-5422-7396

Connectivity of molten Fe alloy in peridotite based on in situ electrical conductivity measurements: implications for core formation in terrestrial planets 査読

T Yoshino, MJ Walter, T Katsura

EARTH AND PLANETARY SCIENCE LETTERS 222 ( 2 ) 625 - 643 2004年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The connectivity of molten Fe-S in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 GPa. Starting materials were powdered mixtures of peridotite KLB-1 with various amounts (0, 3, 6, 13, 19, 24 vol.%) of the 1 GPa eutectic composition in the Fe-FeS binary system. At temperatures above the eutectic point in the Fe-FeS system ( similar to 980 degreesC) and below the solidus of KLB1 ( similar to 1200 degreesC), molten Fe-S in a solid silicate matrix interconnects when the volume fraction is over similar to 5%. Conductivity-temperature paths indicate that in the presence of partial silicate melting the connectivity of molten Fe-S in a peridotite matrix is inhibited. Based on observations of retrieved samples, the percolation threshold of Fe-S melts in the presence of low to moderate degrees of silicate melt is estimated at 13 +/- 2 vol.%. These results indicate that if the volume fraction of Fe-alloy in a planetesimal was initially greater than 5%, and if early heating by decay of radionuclides raised the temperature of the interior above the Fe-alloy melting point, initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix. These conditions were likely met by many terrestrial objects in the early solar nebula. Efficient removal of residual Fe-alloy (5 vol.%) from silicate requires high-degree melting of silicate so that metal can segregate as droplets. Giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high-degrees of melting. Alternatively, if initial metal segregation were delayed until a planetary object grew to large size ( similar to 1000 km in diameter), release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean. (C) 2004 Elsevier B.V All rights reserved.

DOI： 10.1016/j.epsl.2004.03.010

その他リンク： http://orcid.org/0000-0002-5422-7396

Olivine-wadsleyite transition in the system (Mg,Fe)(2)SiO4 査読

T Katsura, H Yamada, O Nishikawa, MS Song, A Kubo, T Shinmei, S Yokoshi, Y Aizawa, T Yoshino, MJ Walter, E Ito, K Funakoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 109 ( B2 ) 2004年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

[1] Phase relations of the olivine-wadsleyite transition in the system (Mg, Fe)(2)SiO4 have been determined at 1600 and 1900 K using the quench method in a Kawai-type high-pressure apparatus. Pressure was determined at a precision better than 0.2 GPa using in situ X-ray diffraction with MgO as a pressure standard. The transition pressures of the end-member Mg2SiO4 are estimated to be 14.2 and 15.4 GPa at 1600 and 1900 K, respectively. Partition coefficients for Fe and Mg between olivine and wadsleyite are 0.51 at 1600 K and 0.61 at 1900 K. By comparing the depth of the discontinuity with the transition pressure, the temperature at 410 km depth is estimated to be 1760 +/- 45 K for a pyrolitic upper mantle. The mantle potential temperature is estimated to be in the range 1550-1650 K. The temperature at the bottom of the upper mantle is estimated to be 1880 +/- 50 K. The thickness of the olivine-wadsleyite transition in a pyrolitic mantle is determined to be between 7 and 13 km for a pyrolitic mantle, depending on the efficiency of vertical heat transfer. Regions of rapid vertical flow ( e. g., convection limbs), in which thermal diffusion is negligible, should have a larger transition interval than stagnant regions, where thermal diffusion is effective. This is in apparent contradiction to short-period seismic wave observations that indicate a maximum thickness of <5 km. An upper mantle in the region of the 410 km discontinuity with about 40% olivine and an Mg# of at least 89 can possibly explain both the transition thickness and velocity perturbation at the 410 km discontinuity.

DOI： 10.1029/2003JB002438

その他リンク： http://orcid.org/0000-0002-5422-7396

Connectivity of aqueous fluid in eclogite and its implications for fluid migration in the Earth's interior 査読

K Mibe, T Yoshino, S Ono, A Yasuda, T Fujii

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 108 ( B6 ) 2003年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

[1] The geometrical distribution of the aqueous fluid in textural equilibrium with eclogite was investigated by measurements of the dihedral angles at aqueous fluid-clinopyroxene-clinopyroxene (thetacc), at aqueous fluid-garnet-garnet (thetagg) and at aqueous fluid- clinopyroxene-garnet (thetacg) triple junctions at 3-5 GPa and 700-800degreesC with a Kawai-type multianvil high-pressure apparatus. The dihedral angles, qcc, qgg, and qcg range from 62degrees to 68degrees and appear constant within the experimental uncertainties at the pressures and temperatures investigated. The constant dihedral angle values could be explained by the counterbalance of the effects of pressure, temperature, and the difference in Mg/(Mg + Fe) in the minerals and the aqueous fluid. The present results lead to the suggestion that the aqueous fluid in eclogite at pressures from 3 to 5 GPa (corresponding to depths of similar to90-150 km) exists as isolated pores, provided circumstances of chemical and textural equilibrium prevail. It is suggested that up to about 1-2 vol% aqueous fluid could be trapped as an interstitial fluid in eclogite and be transported to the Earth's interior at depths of at least 150 km by the subduction of the oceanic crust and by the delamination of the crustal roots.

DOI： 10.1029/2002JB001960

その他リンク： http://orcid.org/0000-0002-5422-7396

Core formation in planetesimals triggered by permeable flow 査読

T Yoshino, MJ Walter, T Katsura

NATURE 422 ( 6928 ) 154 - 157 2003年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation(1,2). But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten(3-5). Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (similar to1,000degreesC) to trigger segregation of iron alloy by permeable flow within the short time-frame indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of preformed cores.

DOI： 10.1038/nature01459

その他リンク： http://orcid.org/0000-0002-5422-7396

Aqueous fluid connectivity in pyrope aggregates: water transport into the deep mantle by a subducted oceanic crust without any hydrous minerals 査読

S Ono, K Mibe, T Yoshino

EARTH AND PLANETARY SCIENCE LETTERS 203 ( 3-4 ) 895 - 903 2002年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The effect of pressure and temperature on the dihedral angles of aqueous fluid in a pyrope matrix was investigated. Experiments were performed on an H2O-pyrope system in a multianvil apparatus over the pressure and temperature ranges of 4-13 GPa and 900-1200degreesC, respectively. The dihedral angle of the fluid in contact with the pyrope exhibited a significant change at pressures around 8-9 GPa. The dihedral angles increased with increasing pressure up to 9 GPa. At pressures above 9 GPa, the dihedral angles were greater than 60degrees at temperatures below 1000degreesC. Therefore, the efficient percolation of aqueous fluid in a pyrope matrix is not feasible in the upper mantle and the transition zone. The fluid released from the breakdown reactions of the hydrous minerals lawsonite and phengite exists in the oceanic crust, which mainly consists of garnet in the upper mantle and transition zone. We conclude that a part of the aqueous fluid released from the hydrous minerals may be retained in the subducted oceanic crust, and transferred into the deep mantle by the subduction process. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0012-821X(02)00920-2

その他リンク： http://orcid.org/0000-0002-5422-7396

Wetting properties of anorthite aggregates: Implications for fluid connectivity in continental lower crust 査読

T Yoshino, K Mibe, A Yasuda, T Fujii

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 107 ( B1 ) 2002年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER GEOPHYSICAL UNION

[1] The connectivity of C-H-O fluids in anorthite aggregate was assessed by measurements of the dihedral angle, theta, at conditions of 800-1000 degreesC and 0.8-1.2 GPa for duration of 1-21 days. The longer-duration experiments show reduction of the effect of crystal anisotropy on pore geometry. Especially, fluid-filled small pores (< 5 mu m) in anorthite aggregate quickly approach to textural equilibrium controlled by minimization of surface energies in <3 days. Anorthite aggregates with CO2 fluid show large dihedral angle over 120degrees. In the anorthite aggregates with aqueous fluid the dihedral angles are over 60degrees at pressure of 1.0 GPa and decrease across critical angle of 60degrees with increasing pressure. Over the range of experimental conditions, isopleths of dihedral angle show nearly zero to negative dP/dT slope with increasing temperature. The observed reduction in dihedral angle with increasing pressure and temperature may be attributed to increase in plagioclase solubility in aqueous fluid. Natural anorthite (with small amounts of albite component) shows smaller dihedral angle than pure anorthite. At higher temperature conditions the anorthite content of the run products deviates progressively from that of starting material. This suggests that preferential solubility of albite component relative to anorthite affects the equilibrium fluid distributions of plagioclase by aqueous fluid. Experimental results point to the likelihood that plagioclase-rich lower continental crust will not allow intergranular fluid flow of C-H-O fluids even in the presence of high geothermal gradient.

DOI： 10.1029/2001JB000440

その他リンク： http://orcid.org/0000-0002-5422-7396

Origin of scapolite in deep-seated metagabbros of the Kohistan Arc, NW Himalayas 査読

T. Yoshino, Madhusoodhan Satish-Kumar

Contributions to Mineralogy and Petrology 140 ( 5 ) 511 - 531 2001年

記述言語：英語掲載種別：研究論文（学術雑誌）

Scapolites developed variably in the deep-seated metagabbros of the Kohistan Arc, north Pakistan, were investigated to evaluate the distribution and migration of C-O-H-S fluid and origin of carbon in the lower crust. Scapolites can be classified, based on their distinct difference in occurrence and chemical composition, into carbonate type and sulfate-rich type. Carbonate-type scapolites occur around carbonate pods in the layered gabbros at the mid-crustal levels and were formed by an increase in the CaO activity in the country rocks and simultaneous decarbonation of calcite. Predicted equilibrium CO2 mole fraction in fluid (Xco2) is sufficiently low to be consistent with removal of CO2. Sulfate-rich scapolites occur in the garnet-bearing granulites at the lower crustal level and were formed by breakdown reactions of garnet and plagioclase under relatively higher CO2 activity (aco2) and oxygen fugacity. The carbon isotopic composition (δ13C) in carbonate scapolite is equivalent to the juvenile mantle (-5 to -6‰), whereas sulfate-rich scapolite has heavy carbon stable isotope values close to 0‰. These results reveal that carbonate scapolite was formed by decarbonation and metasomatism of igneous carbonate pods with the host metagabbros under granulite facies conditions, and sulfate-rich scapolites were formed by infiltration of CO2-rich fluid derived from decarbonation of carbonate-bearing sediments in the subducting slab.

DOI： 10.1007/s004100000207

その他リンク： http://orcid.org/0000-0002-5422-7396

Role of water in conductive anomalies and seismic reflections in the lower crust.

T. Yoshino

Bulletin of the Earthquake Research Institute 76 ( 4 ) 497 - 500 2001年

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