Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.epsl.2021.116955

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

DOI： 10.1111/jace.17429

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jace.17429

Publishing type：Research paper (scientific journal)  

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. The original article can be found online.

DOI： 10.1007/s00410-020-01727-8

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

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Slow-slip events frequently occur, but regular earthquakes are much less active on the H2O fluid-rich subduction interface at depths of ~ 40 km. The characteristic duration for silent earthquakes, which are categorized as the great slow-slip events, is more than five orders of magnitude longer than that for regular earthquakes. Such phenomena are often attributed to the slippage of the softer part of the subduction interface, but the impact of H2O fluid on aseismic slip is still unsolved. Here, we conduct deformation experiments on water-saturated harzburgite at pressures of 1.2 to 3.0 GPa and temperatures of 770 to 1250 K, corresponding to the conditions of the lower part of the overriding plate just above the subduction interface. We observe deformation of the harzburgite followed by silent faulting at a significantly low stress level down to 0.3 GPa under fluid-bearing conditions, even though many acoustic emissions are generated at the onset of faulting in fluid-free harzburgite. We find that the observed silent faulting is caused by the detachment of asperity contacts by high pore pressures and lubrication of the fault plane by a hydration reaction. We therefore propose that H2O fluid may prevent the occurrence of regular intraslab earthquakes, but trigger silent earthquakes.

DOI： 10.1007/s00410-020-01716-x

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Other Link： http://link.springer.com/article/10.1007/s00410-020-01716-x/fulltext.html

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© 2018 Elsevier B.V. Shear and uniaxial deformation experiments on hexagonal close-packed iron (hcp-Fe) was conducted using a deformation-DIA apparatus at a pressure of 13–17 GPa and a temperature of 723 K to determine its deformation-induced crystallographic-preferred orientation (CPO). Development of the CPO in the deforming sample is determined in-situ based on two-dimensional X-ray diffraction using monochromatic synchrotron X-rays. In the shear deformation geometry, the 〈0001〉 and 〈112¯0〉 axes gradually align to be sub-parallel to the shear plane normal and shear direction, respectively, from the initial random texture. In the uniaxial compression and tensile geometry, the 〈0001〉 and 〈112¯0〉 axes, respectively, gradually align along the direction of the uniaxial deformation axis. These results suggest that basal slip (0001)〈112¯0〉 is the dominant slip system in hcp-Fe under the studied deformation conditions. The P-wave anisotropy for a shear deformed sample was calculated using elastic constants at the inner core condition by recent ab-initio calculations. Strength of the calculated anisotropy was comparable to or higher than axisymmetric anisotropy in Earth's inner core.

DOI： 10.1016/j.epsl.2018.03.029

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Language：English   Publisher：Nature Publishing Group  

DOI： 10.1038/d41586-018-02828-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The occurrence of intermediate-depth and deep earthquakes at depths greater than 60 km in subducting slabs has long puzzled geoscientists. These earthquakes require some mechanism to accelerate the fault movement at high pressures above 1.8 GPa. Localized heating would contribute to faulting, but experimental evidence for this mechanism has been limited to pressures of up to 0.5 GPa. Here we conduct deformation experiments on dry dunite samples at pressures of 1.0 to 2.6 GPa and temperatures of 860 to 1,350 K-conditions close to those for relatively shallow intermediate-depth earthquakes. We observe plastic deformation of the dunite, followed by faulting and acoustic emissions at an accelerated strain rate of about 5 x 10(-5) s(-1) or higher. We find that ultrafine-grained gouge layers containing iron-rich melt films, which is indicative of a very high peak temperature of about 2,110 K along the fault planes. We also observe faulting in wet harzburgite-a dehydration product of antigorite-at natural stress levels of 0.3 to 0.4 gigapascals. We therefore suggest that intermediate-depth earthquakes can be induced by localized heating both in dry and wet subducting slabs, if the background strain rate exceeds a threshold value in the range from 10(-16) to 10(-13) s(-1).

DOI： 10.1038/NGEO3011

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

Deformation experiments on olivine aggregates were performed under hydrous conditions using a deformation-DIA apparatus combined with synchrotron in situ X-ray observations at pressures of 1.5-9.8 GPa, temperatures of 1223-1800 K, and strain rates ranging from 0.8 x 10(-5) to 7.5 x 10(-5) s(-1). The pressure and strain rate dependencies of the plasticity of hydrous olivine may be described by an activation volume of 17 +/- 6 cm(3) mol(-1) and a stress exponent of 3.2 +/- 0.6 at temperatures of 1323-1423 K. A comparison between previous data sets and our results at a normalized temperature and a strain rate showed that the creep strength of hydrous olivine deformed at 1323-1423 K is much weaker than that for the dislocation creep of water-saturated olivine and is similar to that for diffusional creep and dislocation-accommodated grain boundary sliding, while dislocation microstructures showing the [001] slip or the [001](100) slip system were developed. At temperatures of 1633-1800 K, a much stronger pressure effect on creep strength was observed for olivine with an activation volume of 27 +/- 7 cm(3) mol(-1) assuming a stress exponent of 3.5, water fugacity exponent of 1.2, and activation energy of 520 kJ mol(-1) (i.e., power-law dislocation creep of hydrous olivine). Because of the weak pressure dependence of the rheology of hydrous olivine at lower temperatures, water weakening of olivine could be effective in the deeper and colder part of Earth's upper mantle.

DOI： 10.1007/s00410-017-1375-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Creep strength of ringwoodite is important for understanding complicated patterns of the mantle convection in and around the mantle transition zone. To determine the creep strength of ringwoodite, we expanded pressure-temperature conditions of in situ stress-strain measurements in a deformation-DIA apparatus combined with synchrotron X-ray to those of the lower part of the mantle transition zone. The expansion of the pressure-temperature conditions was made by shrinking anvil truncation to 2.0 mm and the development of a cell assembly for in situ deformation experiments up to 1700 K. Utilizing the developed technique, creep-strength measurements on polycrystalline ringwoodite were performed at 16.9-18.0 GPa and 1300-1700 K during axial deformation with strain rates of 1.48-3.59 x 10(-5) s(-1) to strains of 13.2-24.9%. Based on mechanical and microstructural observations, we infer that ringwoodite deformed by exponential dislocation creep through the Peierls mechanism at 1300-1400 K and power law dislocation creep at 1500-1700 K. The creep strength of ringwoodite is apparently lower than that of bridgmanite, wadsleyite and olivine. The present result implies the possibility that the lower mantle transition zone is a low-viscosity layer. Further creep-strength data of these minerals are necessary to be determined above 13.5 GPa and high temperatures to determine viscosity structure in and around the lower mantle transition zone at strain rates relevant to the mantle convection. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.08.011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth's upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, similar to 200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 10(19.6) to 10(20.7) Pa.s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size-sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle.

DOI： 10.1126/sciadv.1500360

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Simple-shear deformation experiments on polycrystalline olivine and olivine single-crystal were conducted at pressures of 1.3-3.8 GPa and temperatures of 1223-1573 K to understand the achievement of steady-state fabric strength and the process of dynamic recrystallization. Development of crystallographic preferred orientation (CPO) of olivine was evaluated from two-dimensional X-ray diffraction patterns, and shear strain was measured from X-ray radiographs. The steady-state fabric strength of the A-type fabric was achieved within total shear strain of gamma = 2. At strains higher than gamma = 1, an increase in concentration of the [010] axes mainly contributes to an increase in fabric strength. At strains higher than gamma = 2, the magnitude of V-SH/V-SV (i.e., ratio of horizontally and vertically polarized shear wave velocities) scarcely increased in most of the runs. The V-SH/V-SV of peridotite (70 vol.% olivine + 30 vol.% minor phases) having the steady-state A-type olivine fabric coincides with that of recent global one-dimensional models under the assumption of horizontal flow, suggesting that the seismic anisotropy observed in the shallow upper mantle is mostly explained by the development of A-type olivine fabric. Experimental results on the deformation of single-crystal olivine showed that the CPO of olivine is influenced by the initial orientation of the starting single crystal because strain is concentrated in the recrystallized areas and the relic of the starting single crystal remains. In the upper mantle, the old CPO of olivine developed in the past may affect the olivine CPO developed in the present. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2015.04.004

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Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_530

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Simple-shear deformation experiments on wadsleyite and ringwoodite aggregates were performed at 15-18 GPa and 1473-1873 K to investigate the effect of water on the development of the crystallographic preferred orientation (CPO) of wadsleyite and ringwoodite. The [001] axes of wadsleyite are preferentially sub-parallel to the shear direction and the [010] axes of wadsleyite concentrate in the direction of the shear-plane normal for water content less than 9000 ppm H/Si (i.e., similar to 540 wt. ppm) in wadsleyite. At higher water content in wadsleyite (>= 9000 ppm H/Si), the concentration of the [100] axes of wadsleyite becomes stronger than that of the [010] axes in the direction of the shear-plane normal. The fabric strength of wadsleyite having low water content (<3000 ppm H/Si) was much stronger than that having water content higher than 3000 ppm H/Si. The magnitude of V-SH/V-SV (the ratio of horizontally and vertically polarized shear wave velocities) in the upper transition zone is well explained by the flow of wadsleyite aggregates having water content higher than 3000 ppm H/Si. The back transformation from ringwoodite to wadsleyite may help to suppress the increase in fabric strength of wadsleyite during the deformation. In contrast to wadsleyite, the fabric strength of ringwoodite CPOs was not sufficient to cause robust seismic anisotropy even though the deformation of ringwoodite was controlled by dislocation creep. Thus, the lower transition zone is expected to be largely isotropic. (c) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.03.066

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Simple-shear deformation experiments of olivine were conducted at pressures of 11.1-12.7 GPa and temperatures of 1670-1770K. C-type olivine fabric (developed by the (100) [001) slip system) and similar fabrics were dominantly developed in a wide range of water content (C-OH = 49-19,242 ppm H/Si in olivine). Because the seismic fast a-axes are perpendicular to the shear plane only for C-type fabric, a positive-negative transition of V-SH-V-SV (difference in velocity between horizontally and vertically polarized shear waves) inevitably occurs when C-type fabric is developed by a pressure-induced fabric transition. The positive-negative transition of V-SH-V-SV at similar to 200 km depth reported in global one-dimensional models is known to be well explained by the horizontal flow of olivine with a low water content (<750 ppm H/Si in olivine). Our results demonstrate that the presence of a moderate or high water content in olivine (>= 750 ppm H/Si) results in a drastic increase of the boundary depth for the V-SH-V-SV positive-negative transition (300-370 km depth), namely, "wet" olivine flows cannot account for global one-dimensional models, suggesting that the whole upper mantle is mostly occupied by low-water content regions and the distribution of moderate- or high-water content regions is limited to a small part of the upper mantle. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.11.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

High-pressure and high-temperature deformation experiments on fine-grained synthetic dunite (forsterite aggregate) were conducted to determine the dominant deformation mechanism in the deep upper mantle. The sintered starting material has 90% forsterite, 10% enstatite, and an average grain size of similar to 1 mu m. Deformation experiments were performed using a deformation-DIA apparatus at pressures of 3.03-5.36 GPa, temperatures of 1473-1573 K, and uniaxial strain rates of 0.91x10(-5) to 18.6x10(-5)s(-1) at dry circumstances < 50H/10(6)Si. The steady state flow stress was determined at each deformation condition. Derived stress-strain rate data is analyzed together with that reported from similar but low-pressure deformation experiments using flow law equations for diffusion creep (stress exponent of n=1, grain-size exponent of p=2) and for dislocation-accommodated grain-boundary sliding (GBS-disl, n=3, p=1). The activation volume for diffusion creep (V*(dif)) and for GBS-disl (V*(GBS)) of dunite is determined to be 8.2 +/- 0.9 and 7.5 +/- 1.0 cm(3)/mol, respectively. Calculations based on these results suggest that both diffusion creep and dislocation creep play an important role for material flow at typical deformation conditions in the Earth's asthenospheric upper mantle whereas the contribution of GBS-disl is very limited, and dislocation creep is the dominant deformation mechanism during the deformation of olivine in sheared peridotite xenolith. Though these conclusions are not definitive, these are the first results on potential deformation mechanisms of forsterite aggregate based on extrapolation in the pressure, temperature, stress, and grain-size space.

DOI： 10.1002/2013JB010473

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

Mantle flow in the Earth's mantle transition zone (between 410 and 660km depth) plays a key role to understand the nature of mantle convection, which can be mapped by observed seismic anisotropy combined with crystallographic preferred orientations of mantle minerals. Although wadsleyite is the most important mineral to cause seismic anisotropy observed in the mantle transition zone, there have been limited experimental data on its crystallographic preferred orientation because of experimental limitations. We experimentally evaluated the preferred orientation of wadsleyite developed by shear deformation at pressure-temperature conditions of the mantle transition zone (17.6GPa and 1800-1900K) using a deformation-DIA apparatus. The deformation experiments reveal that the [001] axis and the (010) plane of wadsleyite tend to be subparallel to the shear direction and the shear plane during deformation, respectively. These results demonstrate that polarization seismic anisotropy (velocity contrast between horizontally-polarized and vertically-polarized S-waves, VSH/VSV) observed in the mantle transition zone might be attributed to the preferred orientation of wadsleyite caused by horizontal mantle flow. © 2013 Elsevier B.V.

DOI： 10.1016/j.pepi.2012.12.005

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

Water controls the activity of slip systems in olivine resulting in various types of olivine crystallographic preferred orientation (i.e., fabric) in mantle rocks. The A-type olivine fabric is the most commonly observed olivine fabric in natural peridotites. Development of A-type olivine fabric (developed by the (010)[100] slip system) is known to be limited to the water-poor conditions of the shallow upper mantle (&lt
200km depth). We have performed simple-shear deformation experiments of olivine at 7.2-11.1GPa and 1400-1770 K. Here we show that A-type olivine fabric was developed under water-rich conditions (&gt
2130ppm H/Si in olivine), while B-type fabric (by the (010)[001] slip system) was observed under moderately wet conditions (750-2130ppm H/Si). Developments of C-type (by the (100)[001] slip system) fabric was limited to water-poor conditions (&lt
220ppm H/Si). We found that monotonic decrease in the seismic anisotropy VSH/VSV (the ratio of horizontally and vertically polarized shear waves) with depth in the global one-dimensional models is well explained by the olivine fabrics developed in the horizontal flow of a water-poor mantle. Only A-type olivine fabric can explain the vertical mantle flow which associates the seismic anisotropy of VSH/VSV&lt
1 in the deep upper mantle (&gt
200km depth). A strong anomaly of VSH/VSV&lt
1 observed in the deep upper mantle beneath the East Pacific Rise is well explained by the distribution of water-rich regions (in which A-type olivine fabric is dominantly developed) in the deep upper mantle and upwelling mantle flows. © 2012 Elsevier B.V.

DOI： 10.1016/j.epsl.2012.11.029

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

Dislocation-creep controlled flow of upper mantle materials causes the developments of crystallographic preferred orientation (CPO) of olivine and seismic anisotropy. Olivine CPO pattern controls the relationship between mantle flow geometry and resultant seismic anisotropy in the upper mantle. It has been known that types of olivine CPO are mainly controlled by stress and water fugacity under the upper mantle conditions. Recent experimental studies at high pressures have revealed that pressure is also an important parameter that controls the types of olivine CPO patterns. This review covers experimental studies on the deformation of olivine single crystals and polycrystalline aggregates. The easiest slip system under various conditions can be estimated from the flow laws for oriented single crystals and is consistent with the dominant pattern of olivine CPO. Moreover, experimental techniques for deformation experiments are reviewed. To evaluate the magnitude of seismic anisotropy based on the experimental data, achievements of the steady-state fabric strength in deformation experiments would be important. Deformation of olivine samples with large shear strains under the upper mantle conditions will make a significant contribution to understanding the origin of seismic anisotropy in the upper mantle.<br>

DOI： 10.2465/gkk.120828

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J-GLOBAL

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Deformation experiments on hydrous melt-bearing dunite (olivine+4 vol% orthopyroxene+4 vol% clinopyroxene with less than 2.5 vol% of the melt phase) were conducted at pressures of 1.3-5.7 GPa and temperatures of 1270-1490 K in order to explore the effect of intergranular fluids on the plastic flow of olivine in Earth's upper mantle. The strain rate was proportional to steady-state creep strength to the 2.1 power, and the creep strength markedly increased with increase in grain size. Developments of the crystallographic preferred orientation of olivine and flattening of olivine grains were hardly observed even after 33-55% shortening of the samples. These observations show that grain boundary sliding (GBS) dominated the deformation of olivine (i.e., superplasticity). The creep strength of hydrous melt-bearing dunite was 2-5 times lower than that of melt-free dunite. The dependence of creep rate on melt fraction is known to be expressed empirically as (epsilon) over dot(phi) = (epsilon) over dot(0) exp(alpha phi), where alpha is a constant and phi is the melt fraction. The experimentally obtained value of alpha was in the range of 150-230, corresponding to 5-7 times the reported values for the olivine-basalt system at 0.3 GPa (i.e., creep strength of dunite was efficiently reduced by the hydrous melt). Superplasticity is the dominant creep mechanism of olivine in fluid-bearing fine-grained peridotites under low-temperature and high-stress conditions (i.e., peridotite shear zones in the upper mantle). Superplasticity induced by geological fluids would play an important role in the shear localization (and thus initiation of subduction) in the upper mantle. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.04.032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effects of water on the crystallographic preferred orientation (CPO) of olivine aggregates were investigated through simple-shear deformation experiments under asthenospheric upper mantle conditions (pressure = 2.1-5.2 GPa, temperature = 1490-1830 K) using a deformation-DIA apparatus. Formation of the A-type olivine fabric (developed by the (010)[100] slip system) was observed under water-depleted conditions (C-OH&lt;650 ppm H/Si in olivine), while B-type fabric (by the (010)[001] slip system) or a B-type-like fabric (by the (010)[hOl] slip system) were predominantly formed under water-rich conditions (&gt;1000 ppm H/Si). In comparison with fabrics of anhydrous olivine (&lt;= 111 ppm H/Si), those of olivine having higher water contents (&gt;= 625 ppm H/Si in olivine) showed stronger anisotropic properties (e.g., P-wave anisotropy, S-wave polarization anisotropy, and the ratio of horizontally and vertically polarized shear waves). The water-induced olivine CPO transition from A-type to B-type(-like) fabric accompanies a change in the alignment of the seismic fast a-axes, resulting in flow-parallel and flow-perpendicular shear wave splitting under water-depleted and water-rich conditions, respectively. The rotation of the fast direction of shear-wave splitting across an arc, which is observed in many subduction zones, is well explained by the likely bimodal water distribution along the mantle wedge (i.e., water-rich in fore-arc and water-depleted in back-arc regions) and the developments of two different types of olivine fabrics (i.e., B-type(-like) fabric in fore-arc and A-type fabric in back-arc regions). (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.11.022

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

We report on technical improvements in experiments with a deformation-DIA (D-DIA) apparatus, which enable the study of the rheology of solid materials at P-T conditions of the Earth's mantle transition zone. Dimensions of the anvil truncation, pressure medium, and gasket were optimized to achieve deformation experiments above 1:3 GPa with a relatively low press load (&lt;0.7 MN) to minimize the damage of the X-ray transparent second-stage anvils. The adoption of low X-ray absorbing material (e.g., cubic BN anvils, graphite window in a LaCrO3 heater) along the X-ray path enabled quantitative determination of stress and strain of a sample by means of simultaneous in situ X-ray radial diffraction and radiography using synchrotron radiation at SPring-8. Based on the new technique, a uniaxial deformation experiment with a strain rate of 3.88 x 10(-5) s strains up to 25.5% was carried out on wadsleyite at a pressure of 14.5 GPa and a temperature of 1700 K.

DOI： 10.2138/am.2011.3818

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

Creep strength of oriented orthopyroxene single crystals was investigated via shear deformation experiments under lithospheric conditions [P (pressure) = 1.3 GPa and T (temperature) = 973-1,373 K]. For the A-orientation (shear direction [001] on (100) plane), the samples have transformed completely to clinoenstatite and much of the deformation occurred after transformation. In contrast, for the B-orientation (shear direction [001] on (010) plane), samples remained orthoenstatite and deformation occurred through dislocation motion in orthoenstatite. The strength of orthopyroxene with these orientations is smaller than for olivine aggregates under all experimental conditions. Flow of the B-orientation samples is described by a power-law, and the pre-exponential constant, the apparent activation energy, and the stress exponent are determined to be A = 10(-9.5) s(-1)center dot MPa(-4.2), Q = 114 kJ/mol and n = 4.2. However, for the A-orientation, the results cannot be fit by a single flow law and we obtained the following: A = 10(8.9) s(-1)center dot MPa(-3.0), Q = 459 kJ/mol and n = 3.0 at high temperatures (&gt;= 1,173 K), and A = 10(-27.4) s(-1)center dot MPa(-14.3), Q = 296 kJ/mol and n = 14.3 at low temperatures (&lt; 1,173 K). The stress exponent for the low-temperature regime is high, suggesting that deformation involves some processes where the activation energy decreases with stress such as the Peierls mechanism. Our study shows that orthopyroxene with these orientations is significantly weaker than olivine under the lithospheric conditions suggesting that orthopyroxene may reduce the strength of the lithosphere, although the extent to which orthopyroxene weakens the lithosphere depends on its orientation and connectivity.

DOI： 10.1007/s00410-010-0574-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Verlag  

In the version of the article originally published, Eqs. (6), (7b), and (7c) were shown incorrectly.

DOI： 10.1007/s00410-018-1458-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effects of pressure on crystallographic preferred orientation (CPO) of olivine aggregates were investigated through simple-shear deformation experiments at pressures between 2.1 and 7.6 GPa and temperatures of 1493-1673 K under dry conditions using a deformation-DIA apparatus, and the variations in seismic anisotropy were evaluated under the Earth's upper mantle conditions. We found that the monotonic decrease in seismic anisotropy with depth is caused by the pressure-dependency of the seismic properties of A-type (developed by the (010)[100] slip system) olivine fabric, while the rapid decrease is caused by the fabric transition from A-type to B/C-type (by the (hk0)[001] slip systems) at 7.6 GPa and 1673 K. Moreover, an alternative transition, from A-type fabric to B-type-like fabric (by the (010)[001] slip system), occurs at 7.6 GPa and lower temperature. These two temperature-dependent fabric transitions occurring at 7.6 GPa result in low seismic anisotropy with V-SH/V-SV (the ratio of horizontally and vertically polarized shear waves)&gt; 1 at low temperatures (i.e., old-continental mantle conditions) and V-SH/V-SV &lt; 1 at high temperatures (i.e., oceanic mantle conditions) at greater depths, consistent with seismological observations. Thus, the variations of CPO with pressure and temperature in olivine under dry conditions can explain the seismic anisotropy signatures observed in the upper mantle, without invoking other mechanisms. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.01.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINA UNIV GEOSCIENCES  

A deformation experiment of ringwoodite with a strain of 9% was achieved at 20 GPa and 1 700 K and at a strain rate of 3x10(-5) s(-1) using a deformation-DIA (D-DIA) apparatus and a multi-anvil 6-6 (MA 6-6) assembly. The crystallographic orientations of the deformed sample were successfully analyzed by the electron backscatter diffraction (EBSD) method, although any notable lattice-preferred orientation (LPO) was not observed presumably due to the insufficient strain in the present experiment. In this study, the deformation experiment on ringwoodite succeeded at P-T conditions consistent with the lower part of the mantle transition zone and at a controlled strain rate for the first time. The present study extended the pressure range of deformation experiments in the D-DIA apparatus from 16 GPa in our earlier study to 20 GPa at 1 700 K. The successful extension of the pressure range demonstrates potential importance of the D-DIA apparatus in studying rheological properties of minerals under the P-T conditions of the whole mantle transition zone.

DOI： 10.1007/s12583-010-0120-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINA UNIV GEOSCIENCES  

Technical developments for simple shear deformation experiments at high pressures were made. The newly designed cell assembly can be compressed by deformation-DIA apparatuses with the MA 6-6 system, which consists of six second-stage tungsten carbide anvils (with a truncated edge length of 5 mm) and the anvil guide. Deformation of samples was barely observed during the compression process, showing that the shear strain of the deformed samples can be measured by the rotation of a strain marker. Simple shear deformation experiments on anhydrous and hydrous olivine aggregates were conducted under upper mantle conditions (pressures of 5.2-7.6 GPa and temperatures of 1 473-1 573 K), and sample deformation with a shear strain of gamma=0.8-1.2 was successfully achieved at a shear strain rate of 4.0x10(-5)-7.5x10(-5) s(-1). The present study extended the pressure range of simple shear deformation experiments in the deformation-DIA apparatus from 3 GPa in an early study to 7.6 GPa at high temperatures.

DOI： 10.1007/s12583-010-0110-4

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

The effect of grain growth on the cation exchange between synthesized forsterite aggregates (i.e., dunite) and nickel-rich aqueous fluid was evaluated experimentally at 1.2 GPa and 1,200A degrees C. The grain boundary (GB) migration caused nickel enrichment in the area swept by the GBs in a fashion similar to that reported for stable isotope exchange in the quartz aggregates. The progress of the grain growth resulted in an increase in the average nickel concentration in the dunites of up to similar to 80 times that was calculated for a system having stationary GBs. The overall diffusivity of the nickel along the wet GBs and interconnected fluid networks was found to be 6.5 x 10(-19)-6.7 x 10(-18) m(3)/s, which is 4-5 orders of magnitude higher than the grain boundary diffusivity in the dry dunite. These results show that the grain growth rate is a fundamental factor in the evaluation of the time scale of chemical homogenization in the upper mantle.

DOI： 10.1007/s00410-009-0481-7

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

The isotope exchange between minerals and fluids is enhanced in the area swept by the migrating grain boundaries (GBs; Nakamura et al., 2005; McCaig et al., 2006). This "GB sweeping" mechanism may control the rate processes of chemical transport in the mantle metasomatism and partially molten rocks. To investigate the effect of GB migration on the compatible element exchange between rocks and fluids, we have carried out piston-cylinder experiments in the dunite-Ni system at the uppermost mantle condition. The volume swept by the GBs is at most 50%, and the maximum average concentration of NiO is 4 times as high as that calculated in a static GB diffusion model. In this paper, the experimental results will be presented with their analysis based on the 2-dimensional diffusion model.

DOI： 10.14824/jakoka.2008.0.14.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Grain growth experiments in dunite, clinopyroxenite, and wehrlites having various forsterite/diopside ratios under water-saturated conditions were performed to investigate the effect of water on grain growth kinetics in the Earth's upper mantle. The experiments were conducted at 1200 degrees C and 1.2 GPa for 1.5-763 h using a piston-cylinder apparatus. Both normal grain growth (NGG) and abnormal grain growth (AGG) proceeded in the rocks. The addition of water to the rocks resulted in the inhibition of NGG in dunite and clinopyroxenite, whereas it resulted in the acceleration of NGG of both forsterite and diopside in wehrlites. AGG of the first phase in the rocks tended to be promoted by increasing the amount of water added. The values of the growth exponent n for forsterite and diopside in wehrlites were in the range 1.8-4.8 and 1.8-4.5, respectively. The n-values for the first phase in wehrlites tended to show low values (1.8-2.5), whereas higher n-values (&gt;3) have been reported under dry conditions. This suggests that faster NGG of the first phase with n similar to 2 can proceed in peridotites under water-saturated conditions, whereas much slower NGG of the first phase with n &gt; 3 proceeds under dry conditions. This could have the consequences that the effective viscosity of the water-saturated peridotites can be higher than that under dry conditions in the Earth's upper mantle when the creep mechanism is grain size-sensitive creep. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2007.02.009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Grain growth experiments in dunite, clinopyroxenite, and wehrlites with various forsterite/diopside ratios were performed to investigate the effect of modal composition on grain growth kinetics in the Earth's uppermost mantle. The experiments were conducted using a piston-cylinder apparatus at 1200 degrees C and 1.2 GPa for 2-763 h under dry conditions. Normal grain growth (NGG) occurred in dunite, clinopyroxenite, and relatively forsterite-poor wehrlites (&lt;= 70 vol.% of forsterite). Grain growth rates of forsterite and diopside in relatively forsterite-poor wehrlites were much slower than those in dunite and clinopyroxenite. In the forsterite-rich wehrlites (&gt;= 80 vol. % of forsterite), NGG of diopside and abnormal grain growth (AGG) of forsterite occurred. The growth rate of diopside was significantly slower than that in clinopyroxenite, while the growth rate of forsterite by AGG was found to be similar to that by NGG in dunite. The presence of &lt;= 20 vol.% diopside had the effect of inhibiting the forsterite grain growth during the initial stage, resulting in AGG of forsterite, thus overtaking the growth rate in dunite. Our experimental results suggest that there would be a significant difference in grain growth rate and consequently in effective viscosity between olivine-rich peridotites (depleted mantle) and relatively olivine-poor peridotites (fertile mantle) in the case of grain size-sensitive creep. Variation of mean grain sizes in the upper mantle would result not only from differences in temperature and phase assemblage, but also from the variation of modal compositions. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2006.08.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

A new chemical etching technique has been devised for synthetic Fe-free peridotites composed of forsterite (Fo), enstatite (En), and diopside (Di) Among the etchants were acids, molten carbonates, and borates, but it was found that only molten anhydrous borax (Na2B4O7) dissolved all phases equally. Molten anhydrous borax was found to be a successful etchant in equally enhancing all the grain (i.e., Fo-Fo, En-En, and Di-Di) and interphase (i.e., Fo-En, Fo-Di, and En-Di) boundaries. From the back-scattered electron images of the etched surface, maps of grain- and interphase-boundaries can be obtained semi-automatically for microstructural analysis by using image processing software. An Fe-bearing wehrlite was also etched successfully by molten anhydrous borax, thus showing the usefulness of this technique for enhancing the grain- and interphase-boundaries in many natural peridotites.

DOI： 10.2138/am.2006.1995

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

The microstructure of aqueous fluid-bearing wehrlites was experimentally studied in order to investigate the fluid distribution in polymineralic rocks. Wehrlites of various forsterite/diopside ratios were synthesized with 1.0-1.5 wt% water at 1200°C and 1.2 GPa for 1.5-668 hours. Conspicuous grain growth, drag, and coagulation of pore fluids were observed in the time series experiments. The pore fluids were classified into two types: those surrounded only by a single phase (G-type) and those surrounded by both forsterite and diopside (I-type). In the short, time runs the relative volume fraction of I-type pores in all the pores, FI, agrees well with the value calculated from an ideal pore distribution model in which all the grains are randomly distributed. The FI, of wehrlites with various forsterite/diopside ratios increased with average grain size and reached a steady state value at 80-90% in about 160-163 hours. The increase of FI, is explained by "interphase boundary trapping": G-type pore fluids move faster than I-type, and the number of G-type becoming I-type by being trapped into the interphase boundary per unit time is larger than that of I-type pores transforming to G-type. The experimental results suggest that large fractions of pore fluids might be distributed at the grain junctions surrounded by more than two mineral phases in natural rocks as a result of grain growth. The connectivity of the fluid network in polymineralic rocks may be strongly influenced by modal composition of the rocks as well as by the dihedral angles among the fluid and two mineral phases. Copyright 2006 by the Americn Geophysical Union.

DOI： 10.1029/2004JB003340

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

The microstructure of aqueous fluid-bearing wehrlites was experimentally studied in order to investigate the fluid distribution in polymineralic rocks. Wehrlites of various forsterite/diopside ratios were synthesized with 1.0-1.5 wt % water at 1200 degrees C and 1.2 GPa for 1.5-668 hours. Conspicuous grain growth, drag, and coagulation of pore fluids were observed in the time series experiments. The pore fluids were classified into two types: those surrounded only by a single phase (G-type) and those surrounded by both forsterite and diopside (I-type). In the short time runs the relative volume fraction of I-type pores in all the pores, F-I, agrees well with the value calculated from an ideal pore distribution model in which all the grains are randomly distributed. The F-I of wehrlites with various forsterite/diopside ratios increased with average grain size and reached a steady state value at 80-90% in about 160-163 hours. The increase of F-I is explained by "interphase boundary trapping'': G-type pore fluids move faster than I-type, and the number of G-type becoming I-type by being trapped into the interphase boundary per unit time is larger than that of I-type pores transforming to G-type. The experimental results suggest that large fractions of pore fluids might be distributed at the grain junctions surrounded by more than two mineral phases in natural rocks as a result of grain growth. The connectivity of the fluid network in polymineralic rocks may be strongly influenced by modal composition of the rocks as well as by the dihedral angles among the fluid and two mineral phases.

DOI： 10.1029/2004JB003340

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2006.0_140_2

CiNii Books

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2005.0_117_1

CiNii Books

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2004.abst.0_141_1

CiNii Books

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2003.0_26

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2002.0_15_1

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J-GLOBAL

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_213

J-GLOBAL

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Language：Japanese  

CiNii Books

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J-GLOBAL

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J-GLOBAL

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DOI： 10.14824/jakoka.2011.0.45.0

CiNii Books

J-GLOBAL

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Language：Japanese  

DOI： 10.14824/jakoka.2011.0.47.0

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J-GLOBAL

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J-GLOBAL

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：Shizuoka University  

DOI： 10.14945/00003618

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