研究者詳細 - 道林　克禎

論文 - 道林　克禎

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Physical properties and seismic structure of Izu-Bonin-Mariana fore-arc crust: Results from IODP Expedition 352 and comparison with oceanic crust 査読有り国際共著 Open Access

Christeson G. L., Morgan S., Kodaira S., Yamashita M., Almeev R. R., Michibayashi K., Sakuyama T., Ferre E. C., Kurz W.

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 17 巻 ( 12 ) 頁： 4973 - 4991 2016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：Geochemistry, Geophysics, Geosystems

Most of the well-preserved ophiolite complexes are believed to form in suprasubduction zone (SSZ) settings. We compare physical properties and seismic structure of SSZ crust at the Izu-Bonin-Mariana (IBM) fore arc with oceanic crust drilled at Holes 504B and 1256D to evaluate the similarities of SSZ and oceanic crust. Expedition 352 basement consists of fore-arc basalt (FAB) and boninite lavas and dikes. P-wave sonic log velocities are substantially lower for the IBM fore arc (mean values 3.1–3.4 km/s) compared to Holes 504B and 1256D (mean values 5.0–5.2 km/s) at depths of 0–300 m below the sediment-basement interface. For similar porosities, lower P-wave sonic log velocities are observed at the IBM fore arc than at Holes 504B and 1256D. We use a theoretical asperity compression model to calculate the fractional area of asperity contact Af across cracks. Af values are 0.021–0.025 at the IBM fore arc and 0.074–0.080 at Holes 504B and 1256D for similar depth intervals (0–300 m within basement). The Af values indicate more open (but not necessarily wider) cracks in the IBM fore arc than for the oceanic crust at Holes 504B and 1256D, which is consistent with observations of fracturing and alteration at the Expedition 352 sites. Seismic refraction data constrain a crustal thickness of 10–15 km along the IBM fore arc. Implications and inferences are that crust-composing ophiolites formed at SSZ settings could be thick and modified after accretion, and these processes should be considered when using ophiolites as an analog for oceanic crust.

DOI： 10.1002/2016GC006638

High-flux plasma exposure of ultra-fine grain tungsten 査読有り国際共著 Open Access

Kolasinski, RD; Buchenauer, DA; Doerner, RP; Fang, ZZ; Ren, C; Oya, Y; Michibayashi, K; Friddle, RW; Mills, BE

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS 60 巻頁： 28 - 36 2016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：International Journal of Refractory Metals and Hard Materials

In this work, we examine the response of an ultra-fine grained (UFG) tungsten material to high-flux deuterium plasma exposure. UFG tungsten has received considerable interest as a possible plasma-facing material in magnetic confinement fusion devices, in large part because of its improved resistance to neutron damage. However, optimization of the material in this manner may lead to trade-offs in other properties. We address two aspects of the problem in this work: (a) how high-flux plasmas modify the structure of the exposed surface, and (b) how hydrogen isotopes become trapped within the material. The specific UFG tungsten considered here contains 100 nm-width Ti dispersoids (1 wt%) that limit the growth of the W grains to a median size of 960 nm. Metal impurities (Fe, Cr) as well as O were identified within the dispersoids; these species were absent from the W matrix. To simulate relevant particle bombardment conditions, we exposed specimens of the W-Ti material to low energy (100 eV), high-flux (> 1022 m− 2 s− 1) deuterium plasmas in the PISCES-A facility at the University of California, San Diego. To explore different temperature-dependent trapping mechanisms, we considered a range of exposure temperatures between 200 °C and 500 °C. For comparison, we also exposed reference specimens of conventional powder metallurgy warm-rolled and ITER-grade tungsten at 300 °C. Post-mortem focused ion beam profiling and atomic force microscopy of the UFG tungsten revealed no evidence of near-surface bubbles containing high pressure D2 gas, a common surface degradation mechanism associated with plasma exposure. Thermal desorption spectrometry indicated moderately higher trapping of D in the material compared with the reference specimens, though still within the spread of values for different tungsten grades found in the literature database. For the criteria considered here, these results do not indicate any significant obstacles to the potential use of UFG tungsten as a plasma-facing material, although further experimental work is needed to assess material response to transient events and high plasma fluence.

DOI： 10.1016/j.ijrmhm.2016.05.006

S-wave velocities and anisotropy of typical rocks from Yunkai metamorphic complex and constraints on the composition of the crust beneath Southern China 査読有り国際共著

Ji Shaocheng, Wang Qian, Shao Tongbin, Endo Hiroto, Michibayashi Katsuyoshi, Salisbury Matthew H.

TECTONOPHYSICS 686 巻頁： 27 - 50 2016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：Tectonophysics

In order to constrain the interpretation of seismic data from receiver functions and deep profiles of the crust beneath southern China (Cathaysia and Yangtze blocks), we have measured S-wave velocities (Vs) and splitting as a function of hydrostatic confining pressure up to 650 MPa for 22 representative samples (i.e., granite, diorite, felsic gneiss and mylonite, amphibolite, schist, and marble) from the Yunkai metamorphic complex (China) that represent the crystalline basement beneath the region. The experimental data were combined with electron backscattering diffraction (EBSD) analysis of rock-forming minerals to constrain variations of Vp/Vs ratios and understand the origin of seismic anisotropy. The crusts beneath the Yangtze and Cathaysia blocks have different average thicknesses (H = 35.4 ± 6.3 km and 29.8 ± 1.8 km, respectively) but display almost the same Vp/Vs values (1.73 ± 0.08 and 1.74 ± 0.04, respectively). These ratios correspond to an average of bimodally distributed granitic and gabbroic lithologies which are dominant, respectively, in the upper and lower crusts, instead a homogeneous andesitic composition of the overall crust. Positive and negative correlations between H and Vp/Vs occur in west and east parts of southern China, respectively. The negative correlation indicates basaltic underplating from a partially molten mantle wedge above the subducting Pacific plate into the southern China crust, whereas the positive correlation implies that much larger thinning strain has taken place in the high temperature mafic lower crust (high temperature) than in the low temperature felsic upper crust during Mesozoic-Cenozoic tectonic extension.

DOI： 10.1016/j.tecto.2016.07.017

Melt-rock interactions and fabric development of peridotites from North Pond in the Kane area, Mid-Atlantic Ridge: Implications of microstructural and petrological analyses of peridotite samples from IODP Hole U1382A 査読有り国際共著 Open Access

Harigane, Y; Abe, N; Michibayashi, K; Kimura, JI; Chang, Q

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 17 巻 ( 6 ) 頁： 2298 - 2322 2016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：Geochemistry, Geophysics, Geosystems

North Pond is an isolated sedimentary pond on the western flank of the Kane area along the Mid-Atlantic Ridge. Drill-hole U1382A of IODP Expedition 336 recovered peridotite and gabbro samples from a sedimentary breccia layer in the pond, from which we collected six fresh peridotite samples. The peridotite samples came from the southern slope of the North Pond where an oceanic core complex is currently exposed. The samples were classified as spinel harzburgite, plagioclase-bearing harzburgite, and a vein-bearing peridotite that contains tiny gabbroic veins. No obvious macroscopic shear deformation related to the formation of a detachment fault was observed. The spinel harzburgite with a protogranular texture was classified as refractory peridotite. The degree of partial melting of the spinel harzburgite is estimated to be ∼17%, and melt depletion would have occurred at high temperatures in the uppermost mantle beneath the spreading axis. The progressive melt–rock interactions between the depleted spinel harzburgite and the percolating melts of Normal-Mid Ocean Ridge Basalt (N-MORB) produced the plagioclase-bearing harzburgite and the vein-bearing peridotite at relatively low temperatures. This implies that the subsequent refertilization occurred in an extinct spreading segment of the North Pond after spreading at the axis. Olivine fabrics in the spinel and plagioclase-bearing harzburgites are of types AG, A, and D, suggesting the remnants of a mantle flow regime beneath the spreading axis. The initial olivine fabrics appear to have been preserved despite the later melt–rock interactions. The peridotite samples noted above preserve evidence of mantle flow and melt–rock interactions beneath a spreading ridge that formed at ∼8 Ma.

DOI： 10.1002/2016GC006429

Natural olivine crystal-fabrics in the western Pacific convergence region: A new method to identify fabric type 査読有り国際共著 Open Access

Michibayashi, K; Mainprice, D; Fujii, A; Uehara, S; Shinkai, Y; Kondo, Y; Ohara, Y; Ishii, T; Fryer, P; Bloomer, SH; Ishiwatari, A; Hawkins, JW; Ji, SC

EARTH AND PLANETARY SCIENCE LETTERS 443 巻頁： 70 - 80 2016年6月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth and Planetary Science Letters

Crystallographic preferred orientations (CPOs) of olivine within natural peridotites are commonly depicted by pole figures for the [100], [010], and [001] axes, and they can be categorized into five well-known fabric types: A, B, C, D, and E. These fabric types can be related to olivine slip systems: A with (010)[100], B with (010)[001], C with (001)[001], D with {0kl}[100], and E with (001)[100]. In addition, an AG type is commonly found in nature, but its origin is controversial, and could involve several contributing factors such as complex slip systems, non-coaxial strain types, or the effects of melt during plastic flow. In this paper we present all of our olivine fabric database published previously as well as new data mostly from ocean floor, mainly for the convergent margin of the western Pacific region, and we introduce a new index named Fabric-Index Angle (FIA), which is related to the P-wave property of a single olivine crystal. The FIA can be used as an alternative to classifying the CPOs into the six fabric types, and it allows a set of CPOs to be expressed as a single angle in a range between -90° and 180°. The six olivine fabric types have unique values of FIA: 63° for A type, -28° for B type, 158° for C type, 90° for D type, 106° for E type, and 0° for AG type. We divided our olivine database into five tectonic groups: ophiolites, ridge peridotites, trench peridotites, peridotite xenoliths, and peridotites enclosed in high-pressure metamorphic rocks. Our results show that although our database is not yet large enough (except for trench peridotites) to define the characteristics of the five tectonic groups, the natural olivine fabrics vary in their range of FIA: 0° to 150° for the ophiolites, 40° to 80° for the ridge peridotites, -40° to 100° for the trench peridotites, 0° to 100° for the peridotite xenoliths, and -40° to 10° for the peridotites enclosed in high-pressure metamorphic rocks. The trench peridotites show a statistically unimodal distribution of FIA consisting of the high peak equivalent of the A type, but with some FIAs close to the AG and D types. The variations in the olivine fabrics in the trench peridotites could result from variations in deformation within the supra-subduction uppermost mantle, possibly related to evolution of the mantle since the subduction initiation of the Pacific plate.

DOI： 10.1016/j.epsl.2016.03.019

Effects of olivine fabric, melt-rock reaction, and hydration on the seismic properties of peridotites: Insight from the Luobusha ophiolite in the Tibetan Plateau 査読有り国際共著

Sun, SS; Ji, SC; Michibayashi, K; Salisbury, M

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 121 巻 ( 5 ) 頁： 3300 - 3323 2016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：Journal of Geophysical Research: Solid Earth

In order to constrain the effects of olivine fabric, melt-rock reaction, and hydration on the seismic properties and anisotropy of mantle rocks, we investigated serpentinized peridotites from the Luobusha ophiolite in the Indus-Tsangpo suture of the Tibetan Plateau. A-type and almost random olivine crystal-preferred orientations (CPO) occur in harzburgite and dunite samples, respectively. The dunite resulted from interactions of harzburgite with boninitic melt at ~800–970°C, yielding pyroxene dissolution and olivine precipitation. The olivine neoblasts formed from the melt-rock reaction show no evidence of dislocation creep and developed almost random CPO. Hence, the melt-rock reaction reduced seismic anisotropy. Our results together with those from the literature indicate that A-, B-, C-, D-, and E-type CPOs of olivine generally induce Vp anisotropy patterns with Vp(X) > Vp(Y) > Vp(Z), Vp(Y) > Vp(X) > Vp(Z), Vp(Z) > Vp(X) > Vp(Y), Vp(X) > Vp(Y) ≈ Vp(Z), and Vp(X) > Vp(Z) > Vp(Y), respectively. The effect of serpentinization was calibrated by the comparison of seismic velocities and anisotropy measured up to 600 MPa with the values calculated from the CPO data. Although the low-temperature (LT, <300°C) serpentinization (lizardite and chrysotile) decreases Vp by ~6–10% and Vs by ~12%, it does not change the anisotropy pattern because the mesh-texture characterized by serpentine veins perpendicular to the principal structural directions (X, Y, and Z) reduces the velocities in these orthogonal directions to almost equal extent. Thus, the magnitude of seismic anisotropy alone cannot be used as an indicator of the degree of LT serpentinization in the mantle rocks. Furthermore, Birch's law is found to hold when peridotites undergo serpentinization.

DOI： 10.1002/2015JB012579

Mica-dominated seismic properties of mid-crust beneath west Yunnan (China) and geodynamic implications 査読有り国際共著

Shao, TB; Ji, SC; Oya, S; Michibayashi, K; Wang, Q

TECTONOPHYSICS 677 巻頁： 324 - 338 2016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：Tectonophysics

Measurements of crystallographic preferred orientations (CPO) and calculations of P- and S-wave velocities (Vp and Vs) and anisotropy were conducted on three quartz–mica schists and one felsic mylonite, which are representative of typical metamorphic rocks deformed in the middle crust beneath the southeastern Tibetan plateau. Results show that the schists have Vp anisotropy (AVp) ranging from 16.4% to 25.5% and maximum Vs anisotropy [AVs(max)] between 21.6% and 37.8%. The mylonite has lower AVp and AVs(max) but slightly higher foliation anisotropy, which are 13.2%, 18.5%, and 3.07%, respectively, due to the lower content and CPO strength of mica. With increasing mica content, the deformed rocks tend to form transverse isotropy (TI) with fast velocities in the foliation plane and slow velocities normal to the foliation. However, the presence of prismatic minerals (e.g., amphibole and sillimanite) forces the overall symmetry to deviate from TI. An increase in feldspar content reduces the bulk anisotropy caused by mica or quartz because the fast-axis of feldspar aligns parallel to the slow-axis of mica and/or quartz. The effect of quartz on seismic properties of mica-bearing rocks is complex, depending on its content and prevailing slip system. The greatest shear-wave splitting and fastest Vp both occur for propagation directions within the foliation plane, consistent with the fast Pms (S-wave converted from P-wave at the Moho) polarization directions in the west Yunnan where mica/amphibole-bearing rocks have developed pervasive subvertical foliation and subhorizontal lineation. The fast Pms directions are perpendicular to the approximately E-W orienting fast SKS (S-wave traversing the core as P-wave) directions, indicating a decoupling at the Moho interface between the crust and mantle beneath the region. The seismic data are inconsistent with the model of crustal channel flow as the latter should produce a subhorizontal foliation where vertically incident shear waves suffer little splitting.

DOI： 10.1016/j.tecto.2016.04.024

Temperature dependence of [100](010) and [001](010) dislocation mobility in natural olivine 査読有り国際共著

Wang Lin, Blaha Stephan, Pinter Zsanett, Farla Robert, Kawazoe Takaaki, Miyajima Nobuyoshi, Michibayashi Katsuyoshi, Katsura Tomoo

EARTH AND PLANETARY SCIENCE LETTERS 441 巻頁： 81 - 90 2016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：Earth and Planetary Science Letters

Dislocation recovery experiments were conducted on pre-deformed olivine single crystals at 1450 to 1760 K, room pressure, and oxygen partial pressures near the Ni–NiO buffer to determine the annihilation rates for [100] and [001] dislocations on the (010) plane. Olivine single crystals were first deformed to activate the desired slip systems under simple shear geometry and then annealed at target conditions. The edge and screw dislocations with Burgers vectors, b, of [100] and [001], respectively, both elongated in the [001] direction were produced by the deformation. The dislocation annihilation rate constants of both types of dislocations are identical within 0.3 log unit. The activation energies for both dislocations are also identical, i.e., ∼400 kJ/mol, which is also identical to that of the Si self-diffusion coefficient. This correspondence suggests that olivine dislocation creep controlled by a diffusion-controlled process under low-stress and high-temperature conditions. This study offers a potential insight into the formation of AG-type fabric in olivine.

DOI： 10.1016/j.epsl.2016.02.029

Virtual special issue: Understanding of the largest oceanic core complex on the Earth, Godzilla Megamullion Preface 査読有り国際共著 Open Access

Michibayashi Katsuyoshi, Snow Jonathan E.

ISLAND ARC 25 巻 ( 3 ) 頁： 192 - 192 2016年5月

The effect of a hydrous phase on P-wave velocity anisotropy within a detachment shear zone in the slow-spreading oceanic crust: A case study from the Godzilla Megamullion, Philippine Sea 査読有り

Michibayashi K., Watanabe T., Harigane Y., Ohara Y.

Island Arc 25 巻 ( 3 ) 頁： 209 - 219 2016年5月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Island Arc

We studied the contributions of plagioclase, clinopyroxene, and amphibole to the P-wave velocity properties of gabbroic mylonites of the Godzilla Megamullion (site KH07-02-D18) in the Parece Vela Rift of the central Parece Vela Basin, Philippine Sea, based on their crystal-preferred orientations (CPOs), mineral modes, and elastic constants and densities of single crystals. The gabbroic mylonites have been classified into three types based on their microstructures and temperature conditions: HT1, HT2 and medium-temperature (MT) mylonites. The P-wave velocity properties of the HT1 mylonite are dominantly influenced by plagioclase CPOs. Secondary amphibole occurred after deformation in the HT1 mylonite, so that its effect on P-wave velocity anisotropy is minimal due to weak CPOs. Although the HT2 mylonite developed deformation microstructures in the three minerals, the P-wave velocity properties of the HT2 mylonite are essentially isotropic, resulting from the destructive interference of different P-wave velocity anisotropy patterns produced by the distinct CPOs of the three constituent minerals (i.e., plagioclase, clinopyroxene, and amphibole). The P-wave velocity properties of the MT mylonite are influenced mainly by amphibole CPOs, whereas the effect of plagioclase CPOs on P-wave velocity anisotropy becomes very small with a decrease in the intensity of plagioclase CPOs. As a result, the gabbroic mylonites tend to have weak P-wave velocity anisotropy in seismic velocity, although their constituent minerals show distinct CPOs. Such weakness in the whole-rock P-wave velocity anisotropy could result from the destructive contributions of the different mineral CPOs with respect to the structural framework (foliation and lineation). These results show that amphibole has a high potential for P-wave velocity anisotropy by aligning both crystallographically and dimensionally during deformation in the hydrous oceanic crust. The results also suggest that the effect of a hydrous phase on P-wave velocity anisotropy within the detachment shear zone in a slow-spreading oceanic crust varies depending on the degree of deformation and on the timing of hydrothermal activity.

DOI： 10.1111/iar.12132

Three-dimensional Evolution of Melting, Heat and Melt Transfer in Ascending Mantle beneath a Fast-spreading Ridge Segment Constrained by Trace Elements in Clinopyroxene from Concordant Dunites and Host Harzburgites of the Oman Ophiolite 査読有り Open Access

Akizawa Norikatsu, Ozawa Kazuhito, Tamura Akihiro, Michibayashi Katsuyoshi, Arai Shoji

JOURNAL OF PETROLOGY 57 巻 ( 4 ) 頁： 777 - 814 2016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：Journal of Petrology

Dunite bands and dikes in ophiolitic mantle peridotites are interpreted as fossil melt channels within the suboceanic mantle. Concordant dunite bands (i.e. fossil melt channels transposed by outward transportation from the ridge axis via horizontal mantle flow) are particularly important as they possibly represent the melt channels through which the parental melts of mid-ocean ridge basalt (MORB) were transported to shallower depths beneath the paleo-ridge axis. We conducted field observations and sampling of concordant dunite bands (CDB) and their host harzburgite at selected outcrops covering a wide depth range in the mantle section along an inferred paleo-ridge segment in the northern to central part of the Oman ophiolite. The CDB increase in thickness and decrease in frequency upward. They are thicker and more frequent in the centre of the segment than near the segment ends when compared at the same stratigraphic level. The CDB consist mostly of olivine with minor spinel and very rare amounts of pyroxene. Clinopyroxene has a small grain size and an interstitial position relative to olivine. The constituent minerals in the CDB and their host harzburgite were analyzed by electron microprobe for major elements and by laser ablation inductively coupled plasma mass spectrometry for trace elements. Most of the CDB have refractory major element mineral compositions, such as high Fo [100 ï¿½ Mg/(Mg + Fe)] in olivine (>90ï¿½5), high Cr# [Cr/(Cr + Al)] in chromian spinel (>0ï¿½50), and low Al2O3 (<3ï¿½5 wt %) in clinopyroxene. Chondrite-normalized trace element patterns of clinopyroxene in the host harzburgites consistently show a gentle decrease from heavy REE (HREE) to middle REE (MREE) and a sharp decrease from MREE to light REE (LREE) (= highly depleted), but those in the CDB show weaker LREE depletion, which is more variable depending on the stratigraphic level and position along the paleo-ridge segment. In contrast, the HREE concentrations in clinopyroxene in the CDB are higher than or similar to those of the host harzburgites. Trace element compositions of clinopyroxene in the CDB and their host harzburgites are evaluated with a one-dimensional, steady-state, open-system decompressional melting-reaction model. The modeling results suggest that an LREE-enriched melt generated at high pressure was transported upwards through melt channels to the shallow mantle (up to the Moho transition zone), where it mingled with highly depleted melts accumulated from fractionally melted peridotites to generate normal (N)-MORB-like melts. The mantle started upwelling (= melting) in the garnet stability field in the segment centre, but either in the garnet or in the spinel stability field near the segment ends. This suggests a variation of geothermal gradient along the paleo-ridge segment: higher in the segment centre and lower near the segment ends. This inference is supported by the presence of thicker (up to 250 cm) CDB as well as more frequent occurrence of CDB in the segment centre than near the segment end and by the geochemical evidence for chromatographic N-MORB-like melt percolation into the host peridotite only in the uppermost horizons near the segment ends.

DOI： 10.1093/petrology/egw020

超深海海溝のマントル直接研究～まるで惑星探査みたいなフィールドサイエンス

道林克禎

化学と工業 69 巻頁： 446 - 448 2016年

Magnitude and symmetry of seismic anisotropy in mica- and amphibole-bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast Tibetan Plateau 査読有り国際共著 Open Access

Ji, SC; Shao, TB; Michibayashi, K; Oya, S; Satsukawa, T; Wang, Q; Zhao, WH; Salisbury, MH

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 120 巻 ( 9 ) 頁： 6404 - 6430 2015年9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：Journal of Geophysical Research: Solid Earth

We calibrated the magnitude and symmetry of seismic anisotropy for 132 mica- or amphibole-bearing metamorphic rocks to constrain their departures from transverse isotropy (TI) which is usually assumed in the interpretation of seismic data. The average bulk Vp anisotropy at 600MPa for the chlorite schists, mica schists, phyllites, sillimanite-mica schists, and amphibole schists examined is 12.0%, 12.8%, 12.8%, 17.0%, and 12.9%, respectively. Most of the schists show Vp anisotropy in the foliation plane which averages 2.4% for phyllites, 3.3% for mica schists, 4.1% for chlorite schists, 6.8% for sillimanite-mica schists, and 5.2% for amphibole schists. This departure from TI is due to the presence of amphibole, sillimanite, and quartz. Amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation, forming orthorhombic anisotropy with Vp(X)>Vp(Y)>Vp(Z). Effects of quartz are complicated, depending on its volume fraction and prevailing slip system. Most of the mica- or amphibole-bearing schists and mylonites are approximately transversely isotropic in terms of S wave velocities and splitting although their P wave properties may display orthorhombic symmetry. The results provide insight for the interpretation of seismic data from the southeast Tibetan Plateau. The N-S to NW-SE polarized crustal anisotropy in the Sibumasu and Indochina blocks is caused by subvertically foliated mica- and amphibole-bearing rocks deformed by predominantly compressional folding and subordinate strike-slip shear. These blocks have been rotated clockwise 70-90° around the east Himalayan Syntaxis, without finite eastward or southeastward extrusion, in responding to progressive indentation of India into Asia.

DOI： 10.1002/2015JB012209

A multi-technique analysis of deuterium trapping and near-surface precipitate growth in plasma-exposed tungsten 査読有り国際共著 Open Access

Kolasinski, RD; Shimada, M; Oya, Y; Buchenauer, DA; Chikada, T; Cowgill, DF; Donovan, DC; Friddle, RW; Michibayashi, K; Sato, M

JOURNAL OF APPLIED PHYSICS 118 巻 ( 7 ) 2015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：Journal of Applied Physics

In this work, we examine how deuterium becomes trapped in plasma-exposed tungsten and forms near-surface platelet-shaped precipitates. How these bubbles nucleate and grow, as well as the amount of deuterium trapped within, is crucial for interpreting the experimental database. Here, we use a combined experimental/theoretical approach to provide further insight into the underlying physics. With the Tritium Plasma Experiment, we exposed a series of ITER-grade tungsten samples to high flux D plasmas (up to 1.5 × 1022m-2s-1) at temperatures ranging between 103 and 554 °C. Retention of deuterium trapped in the bulk, assessed through thermal desorption spectrometry, reached a maximum at 230 °C and diminished rapidly thereafter for T > 300 °C. Post-mortem examination of the surfaces revealed non-uniform growth of bubbles ranging in diameter between 1 and 10 μm over the surface with a clear correlation with grain boundaries. Electron back-scattering diffraction maps over a large area of the surface confirmed this dependence; grains containing bubbles were aligned with a preferred slip vector along the <111> directions. Focused ion beam profiles suggest that these bubbles nucleated as platelets at depths of 200 nm-1 μm beneath the surface and grew as a result of expansion of sub-surface cracks. To estimate the amount of deuterium trapped in these defects relative to other sites within the material, we applied a continuum-scale treatment of hydrogen isotope precipitation. In addition, we propose a straightforward model of near-surface platelet expansion that reproduces bubble sizes consistent with our measurements. For the tungsten microstructure considered here, we find that bubbles would only weakly affect migration of D into the material, perhaps explaining why deep trapping was observed in prior studies with plasma-exposed neutron-irradiated specimens. We foresee no insurmountable issues that would prevent the theoretical framework developed here from being extended to a broader range of systems where precipitation of insoluble gases in ion beam or plasma-exposed metals is of interest.

DOI： 10.1063/1.4928184

Izu-Bonin-Mariana fore arc: Testing subduction initiation and ophiolite models by drilling the outer Izu-Bonin-Mariana fore arc 国際共著

Pearce J.A., Reagan M.K., Petronotis K., Morgan S., Almeev R., Avery A.J., Carvallo C., Chapman T., Christeson G.L., Ferré E.C., Godard M., Heaton D.E., Kirchenbaur M., Kurz W., Kutterolf S., Li H., Li Y., Michibayashi K., Nelson W.R., Prytulak J., Python M., Robertson A.H.F., Ryan J.G., Sager W.W., Sakuyama T., Shervais J.W., Shimizu K., Whattam S.A.

International Ocean Discovery Program: Preliminary Reports ( 352 ) 2015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：International Ocean Discovery Program: Preliminary Reports

The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin fore arc to 1. Obtain a high-fidelity record of magmatic evolution during subduction initiation and early arc development, 2. Test the hypothesis that fore-arc basalt lies beneath boninite and understand chemical gradients within these units and across the transition, 3. Use drilling results to understand how mantle melting processes evolve during and after subduction initiation, and 4. Test the hypothesis that the fore-arc lithosphere created during subduction initiation is the birthplace of suprasubduction zone (SSZ) ophiolites. Expedition 352 successfully cored 1.22 km of igneous basement and 0.46 km of over-lying sediment, providing diverse, stratigraphically controlled suites of fore-arc basalts (FAB) and boninite related to seafloor spreading and earliest arc development. FAB were recovered at the two deeper water sites (U1440 and U1441) and boninites at the two sites (U1439 and U1442) drilled upslope to the west. FAB lavas and dikes are depleted in high-field strength trace elements such as Ti and Zr relative to mid-ocean-ridge basalt but have relatively diverse concentrations of trace elements bezcause of variation in degrees of melting and amount of subducted fluids involved in their genesis. All FAB magmas underwent significant crystal fractionation in a persistent magma chamber system. Holes U1439C and U1442A yielded entirely boninitic lavas. We defined three boninite differentiation series based on variations in MgO, SiO2, and TiO2 concentrations of the parental magmas. Lavas in both pairs of holes have compositions that generally become more primitive and have lower TiO2 concentrations upward. The presence of dikes at the base of the sections at Sites U1439 and U1440 provides evidence that boninitic and FAB lavas are both underlain by their own conduit systems and that FAB and boninite group lavas are likely offset more horizontally than vertically. We thus propose that seafloor spreading related to subduction initiation migrated from east to west after subduction initiation and during early arc development. Initial spreading was likely rapid, and an axial magma chamber was present. Melting was largely decompressional during this period, but subducted fluids affected some melting. As subduction continued and spreading migrated to the west, the embryonic mantle wedge became more depleted, and the influence of subducted constituents dramatically increased, causing the oceanic crust to be built of boninitic rather than tholeiitic magma. The general decrease in fractionation upward reflects the eventual disappearance of persistent magma chambers, either because spreading rate was decreasing with distance from the trench or because spreading was succeeded by off-axis magmatism trenchward of the ridge. The extreme depletion of the sources for all boninitic lavas was likely related to the incorporation of mantle residues from FAB generation. This mantle depletion continued during generation of lower silica boninitic magmas, exhausting clinopyroxene from the mantle such that the capping high-Si, low-Ti boninites were generated from harzburgite. Additional results of the cruise include recovery of Eocene to recent deep-sea sediment that records variation in sedimentation rates with time resulting from variations in climate, the position of the carbonate compensation depth, and local structural control. Three phases of highly explosive volcanism (latest Pliocene to Pleistocene, late Miocene to earliest Pliocene, and Oligocene) were identified, represented by 132 graded air fall tephra layers. Structures found in the cores and reflected in seismic profiles show that this area had periods of normal, reverse, and strike-slip faulting. Finally, basement rock P-wave velocities were shown to be slower than those observed during logging of normal ocean crust sites.

DOI： 10.14379/iodp.pr.352.2015

Deformation microstructures of glaucophane and lawsonite in experimentally deformed blueschists: Implications for intermediate-depth intraplate earthquakes 査読有り Open Access

Kim D., Katayama I., Wallis S., Michibayashi K., Miyake A., Seto Y., Azuma S.

Journal of Geophysical Research: Solid Earth 120 巻 ( 2 ) 頁： 1229 - 1242 2015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：Journal of Geophysical Research: Solid Earth

A series of simple-shear experiments on blueschist was performed at 400-500°C and 1-2.5 GPa to understand the deformation of seismically active, subducting oceanic crust. The experiments show that brittle microstructures are mainly found at pressures of 1-2 GPa, whereas ductile microstructures form at 2.5 GPa. J-indices (a measure of fabric intensity) of glaucophane crystal preferred orientations change systematically with changing shear strain and confining pressure, and the angle between the slip plane and the shear direction of samples deformed at >2 GPa is similar to that of a strain ellipsoid. These results, together with the variable orientations of fine grains in a selected area electron diffraction image at 2 GPa, indicate that the brittle-ductile transition for glaucophane occurs at ∼2 GPa. In contrast to this, lawsonite in the experiments show abundant fracturing in most specimens and a poor correlation between the J-index, shear strain, and confining pressure. This demonstrates that lawsonite deformed by brittle failure under all experimental conditions. In the case of a starting material that has a strong fabric and deformed under dry experimental conditions, the brittle-ductile transition zone of glaucophane will be much shallower than 2 GPa. Therefore, our initial experimental results on the deformation behavior of blueschist indirectly support the dehydration embrittlement of subducting oceanic crust (glaucophane) as an important factor in the origin of intraplate earthquakes.

DOI： 10.1002/2014JB011528

最上部マントルかんらん岩の結晶方位ファブリックとP波速度構造査読有り Open Access

道林克禎

地学雑誌 124 巻 ( 3 ) 2015年

Reply to comment by Nozaka (2014) on "Dehydration breakdown of antigorite and the formation of B-type olivine CPO" 査読有り

Nagaya T., Wallis S., Kobayashi H., Michibayashi K., Mizukami T., Seto Y., Miyake A., Matsumoto M.

Earth and Planetary Science Letters 408 巻頁： 406 - 407 2014年12月

Rheological properties of the detachment shear zone of an oceanic core complex inferred by plagioclase flow law: Godzilla Megamullion, Parece Vela back-arc basin, Philippine Sea 査読有り

Michibayashi Katsuyoshi, Harigane Yumiko, Ohara Yasuhiko, Muto Jun, Okamoto Atsushi

EARTH AND PLANETARY SCIENCE LETTERS 408 巻頁： 16 - 23 2014年12月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth and Planetary Science Letters

We tested plagioclase flow laws for rheological properties of the detachment shear zone developed in an oceanic core complex. Gabbroic mylonites occur extensively over the ~125-km length of the Godzilla Megamullion, an enormous oceanic core complex situated in an extinct Philippine Sea back-arc basin. The mylonites were produced in the detachment shear zone at temperatures of 650-850 °C in the lower crust over a period of approximately 4 million years, corresponding to a slow spreading rate of 2.54±0.21 cm/yr (i.e. 8.05×10-10 m/s). Applying the rheological parameters for plagioclase flow laws, combined with the geochronological spreading rate, we calculated deformation mechanism maps of plagioclase as shear strain rates of 10-12 to 10-8 s-1, corresponding to shear zones in thickness of ~0.1 to ~1000 m. Our results show that, assuming a constant stress condition defined by a shear strain rate of 10-12 s-1 for grain size of 1000 μm in a temperature range between 650 and 850 °C, petrofabric parameters such as crystal-preferred orientations and dynamically recrystallized grain sizes along with estimated equilibrium temperatures can be possibly explained by the deformation mechanism maps of plagioclase for shear strain rates mostly of 10-11 to 10-9 s-1. It suggests that even if the entire thickness of the detachment shear zone may lie several hundred meters below the spreading center, the shear zone could be stratified, comprising many anastomosing narrow zones. It implies that, during the development of the detachment fault, strain localization would occur in the lower crust over a broad (~1000 m) zone at high temperatures.

DOI： 10.1016/j.epsl.2014.10.005

Plagioclase preferred orientation and induced seismic anisotropy in mafic igneous rocks 査読有り国際共著 Open Access

Ji Shaocheng, Shao Tongbin, Salisbury Matthew H., Sun Shengsi, Michibayashi Katsuyoshi, Zhao Weihua, Long Changxing, Liang Fenghua, Satsukawa Takako

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 119 巻 ( 11 ) 頁： 8064 - 8088 2014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：Journal of Geophysical Research: Solid Earth

Fractional crystallization and crystal segregation controlled by settling or floating of minerals during the cooling of magma can lead to layered structures in mafic and ultramafic intrusions in continental and oceanic settings in the lower crust. Thus, the seismic properties and fabrics of layered intrusions must be calibrated to gain insight into the origin of seismic reflections and anisotropy in the deep crust. To this end, we have measured P and S wave velocities and anisotropy in 17 plagioclase-rich mafic igneous rocks such as anorthosite and gabbro at hydrostatic pressures up to 650 MPa. Anorthosites and gabbroic anorthosites containing >80 vol% plagioclase and gabbros consisting of nearly equal modal contents of plagioclase and pyroxene display distinctive seismic anisotropy patterns: Vp(Z)/Vp(Y) ≥ 1 and Vp(Z)/Vp(X) ≥ 1 for anorthosites while 0.8 < Vp(Z)/Vp(Y) ≤ 1 and 0.8 < Vp(Z)/Vp(X) ≤ 1 for gabbros. Amphibolites lie in the same domain as gabbros, but show a significantly stronger tendency of Vp(X) > Vp(Y) than the gabbros. Laminated anorthosites with Vp(X) ≈ Vp(Y) Vp(Z) display a strong crystal preferred orientation (CPO) of plagioclase whose (010) planes and [100] and [001] directions parallel to the foliation. For the gabbros and amphibolites characterized by Vp(X) ≈ Vp(Y) > Vp(Z) and Vp(X) > Vp(Y) > Vp(Z), respectively, pyroxene and amphibole play a dominant role over plagioclase in the formation of seismic anisotropy. The Poisson's ratio calculated using the average P and S wave velocities from the three principal propagation-polarization directions (X, Y, and Z) of a highly anisotropic anorthosite cannot represent the value of a true isotropic equivalent. The CPO-induced anisotropy enhances and decreases the foliation-normal incidence reflectivity at gabbro-peridotite and anorthosite-peridotite interfaces, respectively.

DOI： 10.1002/2014JB011352

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