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

DOI： 10.1016/j.tecto.2021.228978

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

Mafic and ultramafic clasts (mostly ~1–5 cm in size) were recovered from three different serpentinite mud volcanos in the Mariana forearc during Integrated Ocean Drilling Program (IODP) Expedition 366. Mafic clasts from drill sites distant from the trench bear lawsonite, Al-rich riebeckite, jadeitic pyroxene (~80 mol% jadeite), and aragonite as metamorphic minerals. In contrast, mafic clasts from drill sites closer to the trench are characterized by prehnite–pumpellyite-facies mineral associations and/or the presence of analcime and natrolite. An occurrence of antigorite-bearing ultramafic clasts becomes progressively more frequent with distance from the trench. One amphibolite clast from a mud volcano near the trench also has prehnite filling veins, and it also occurs as pseudomorphs after plagioclase. Amphibolite clasts at other mud volcanoes distant from the trench are partially overprinted by blueschist-facies minerals. The apparent metamorphic grades increase with distance from the trench; these metamorphic conditions represent the increasing depth from zeolite- to lawsonite–blueschist-facies conditions in a subduction zone. Considering the consistency of the low-temperature metamorphic grade of mafic and ultramafic clast mineralogy in each mud volcano, they likely reflect the thermal structure of the slab-mantle interface before the ascent. As a result, these clasts were brought up to the seafloor en masse by the serpentinite mudflow. The polymetamorphosed amphibolite clasts suggest cooling of the hot forearc-mantle at the initiation of Mariana subduction in the Eocene. The ultramafic clasts in the mud volcanoes distant from the trench frequently contain Ca amphibole and talc, which indicates hot mantle hydration by metasomatic fluids released from the slab at subduction initiation.

DOI： 10.1016/j.lithos.2020.105941

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Tokyo Geographical Society  

<p> In the 1950s, the aim of the original mantle drilling projects was to obtain oceanic mantle samples in order to address the unanswered question of what constitutes the Earth's mantle. However, in the 21st century, it is widely accepted that the uppermost mantle is mainly composed of peridotite. Now, the challenge of mantle drilling is to understand crucial unsolved issues of earth science. Today's Earth is different from other planets due to the existence of life and plate tectonics. It is emphasized that mantle drilling is the only way to obtain the oceanic crust from top to bottom and an active mantle sample from an oceanic plate. The crucial issues that can only be addressed by mantle drilling are: (1) limits of life in an oceanic plate and its controlling factors, and (2) formation process of an oceanic plate and its modification. Modification of an oceanic plate, especially the weakening of plate strength, is required for plate tectonics. These two issues are interrelated. Long seismic profiles of oceanic plates reveal the diversity of Moho seismic reflection regions: clear, unclear, diffuse and non-Moho regions. Faults and/or fracturing in oceanic plates and subsequent seawater flow can modify oceanic plates locally, probably causing the diversity of oceanic Moho, as well as the rheological behavior of oceanic plates. Fluid flows along faults/fractures also extend the biosphere of oceanic plates. The first drilling sample should be a reference to the oceanic crust and the uppermost mantle, and define the nature of the Moho at the site, as well as constrain reasons for the diversity of the Moho in other areas. Deep sampling, such as mantle drilling in an old oceanic plate, can penetrate the biosphere/non-biosphere boundary, which tells us about the controlling factors of the limit of life. This information may help us find extraterrestrial life. After mantle drilling is completed, the borehole is the only window from the ocean floor to the mantle. An in-situ mantle observatory in the mantle hole to monitor plate movement and fluid flow with biological activity within an oceanic plate is also suggested. Detecting geoneutrinos at the mantle site allows the amounts and distributions of radioactive elements from the Earth's mantle to be measured. These provide basic information on the Earth's heat sources and the evolutionary history of the mantle.</p>

DOI： 10.5026/jgeography.130.483

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

DOI： 10.2465/jmps.201130f

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.5575/geosoc.2020.0043

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2020gc009199

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GC009199

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ASSOC MINERALOGICAL SCIENCES  

Attenuated total reflection infrared (ATR-IR) spectroscopy allows measurements to be made directly from the surface of one-sided, diamond polished thin sections of geological samples. This method greatly reduces the sample preparation time when compared to other IR spectroscopy methods and opens the possibility of using infrared spectroscopy to study thin-section scale microstructures. ATR-IR spectroscopy of antigorite, chrysotile, and lizardite in samples from the Mt. Shiraga serpentinite body, central Shikoku, SW Japan, reveals clear spectral differences in the 650-1250 cm(-1) region associated with the vibration of the Si-O bonds in SiO4 tetrahedra and in the 3300-3750 cm(-1) region associated with the vibration of the O-H bond in MgO2(OH)(4) octahedra. A data-processing algorithm developed in this study allows the absorbance intensity and wavenumber of a particular absorbance peak to be used to create serpentine mineral phase maps based on the highest intensity Si-O absorbance bands for antigorite, chrysotile, and lizardite. Our methodology can be used to map serpentinite microstructures in thin sections illustrating the potential of ATR-IR as a relatively un-explored analytical tool in petrological studies. A combination of ATR-IR and electron microprobe data shows that for antigorite the wavenumber of the O-H absorbance band is correlated with the Fe content. Metamorphic reactions of serpentine minerals play a key role in the hydrodynamics of the earth's lithosphere, and the new information on serpentine mineral hydroxyl group behavior obtained by applying the technique outlined in this study are of great potential interest to researchers in a wide range of different fields.

DOI： 10.2465/jmps.190807

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2019jb018698

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019JB018698

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

DOI： 10.1098/rsta.2018.0425

PubMed

Language：English   Publishing type：Research paper (international conference proceedings)  

Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

© 2019 Elsevier B.V. Multiple generations of amphibole may form in the lower crust due to magmatism and metamorphism during the development of oceanic core complexes. We investigated the occurrence and chemical compositions of amphibole in gabbro mylonites from the medial area of the Godzilla Megamullion along the Parece Vela Rift in the Philippine Sea. The samples contain brown and green amphiboles with a variety of different textures that may have different origins. The brown amphibole occurs mainly as blebs in clinopyroxene porphyroclasts (Bleb amphibole), the rims around clinopyroxene porphyroclasts (Coronitic amphibole), and as porphyroclasts and fine-grained amphibole within the matrix (Matrix amphibole). The trace element and Cl contents of the bleb and green amphiboles indicate magmatic and metamoprhic origins, respectively. The bleb amphibole is interpreted to have crystallized from a hydrous silicate melt derived from an oxide gabbro-forming melt prior to retrograde metamorphism. In contrast, the compositions of the coronitic amphibole and matrix amphibole vary between those of typical magmatic and metamorphic amphiboles, suggesting that the amphibole-forming reactions were continuously retrogressive. Retrograde metamorphism is generally interpreted to have involved seawater-derived fluids, but the trace element contents of the coronitic and matrix amphiboles do not differ significantly from those of the original minerals (i.e., clinopyroxene and plagioclase). One sample of gabbro mylonite (KH07–02-D18–1) contains amphiboles with high concentrations of light rare earth elements, indicating a large influx of externally derived LREE-enriched fluids. These fluids are interpreted to have formed from an interaction between hydrous silicate melt with LREE-enriched composition and seawater-derived fluid. Our results suggest that multiple phases of melt–fluid infiltration occurred during the development of the detachment fault at the Godzilla Megamullion.

DOI： 10.1016/j.lithos.2019.06.019

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Scopus

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

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2019.0_399

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2019.0_98

CiNii Research

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

© 2018 Elsevier Ltd Depth-sensing indentation tests were performed to obtain the loop energy (equivalent to the energy consumed to produce the indentation) and the residual depth of the indentation using a triangular pyramidal diamond indenter for the minerals in Mohs hardness scale except for diamond, as well as other minerals (apophyllite, forsterite, and tourmaline), at a maximum load ranging from 30 to 100 mN. A new graphic presentation is proposed that shows the hardness of minerals in log(penetration depth)−log(loop energy) space. The data for each mineral under different loads give a straight regression line with a slope of 2.6–2.9 (except for talc, which yields a slope of 2.2), while the data for different minerals under a given load yield a straight regression line with a slope of 1.1–1.2. A theoretical analysis of ideal materials, in terms of log(penetration depth)−log(loop energy) space, shows the existence of two series of parallel regression lines with slopes of 3 (data for each mineral at different loads) and 1 (data for different minerals under a given load). The results show a slight deviation between the measured and theoretical slopes, probably reflecting a progressive change in the mechanical properties of the minerals during the indentation tests.

DOI： 10.1016/j.jsg.2018.09.004

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Geological Society of America  

The deep submergence research vehicle Shinkai 6500, diving on the Challenger segment of the Mariana forearc, encountered a superstructure of nascent arc crust atop a younger mantle with entrained fragments of metamorphosed crust. A plutonic block from this crust collected at 4900 m depth has a crystallization age of 46.1 Ma and mixed boninitic-arc tholeiitic geochemical signatures. A hornblende garnetite and two epidote amphibolites were retrieved from depths between 5938 m and 6277 m in an area dominated by peridotite. The garnetite appears to represent a crystal cumulate after melting of deep arc crust, whereas the amphibolites are compositionally similar to enriched mid-ocean ridge basalt (MORB). The initial isotopic compositions of these crustal fragments are akin to those of Eocene to Cretaceous terranes along the periphery of the Philippine plate. The garnetite achieved pressures of 1.2 GPa or higher and temperatures above 850 °C and thus could represent a fragment of the delaminated root of one of these terranes. This sample has coeval Sm-Nd, Lu-Hf, and 40Ar-39Ar ages indicating rapid ascent and cooling at 25 Ma, perhaps in association with rifting of the Kyushu-Palau arc. Peak P-T conditions were lower for the amphibolites, and their presence on the ocean floor near the garnetite might have resulted from mass wasting or normal faulting. The presence of relatively fusible crustal blocks in the circulating mantle could have contributed to the isotopic similarity of Mariana arc and backarc lavas with Indian Ocean MORB.

DOI： 10.1130/GES01536.1

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Scopus

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

Here we provide an appraisal of the Poisson's ratios (υ) for natural elements, common oxides, silicate minerals, and rocks with the purpose of searching for naturally auxetic materials. The Poisson's ratios of equivalently isotropic polycrystalline aggregates were calculated from dynamically measured elastic properties. Alpha-cristobalite is currently the only known naturally occurring mineral that has exclusively negative υ values at 20–1,500°C. Quartz and potentially berlinite (AlPO4) display auxetic behavior in the vicinity of their α-β structure transition. None of the crystalline igneous and metamorphic rocks (e.g., amphibolite, gabbro, granite, peridotite, and schist) display auxetic behavior at pressures of &gt
5 MPa and room temperature. Our experimental measurements showed that quartz-rich sedimentary rocks (i.e., sandstone and siltstone) are most likely to be the only rocks with negative Poisson's ratios at low confining pressures (≤200 MPa) because their main constituent mineral, α-quartz, already has extremely low Poisson's ratio (υ = 0.08) and they contain microcracks, micropores, and secondary minerals. This finding may provide a new explanation for formation of dome-and-basin structures in quartz-rich sedimentary rocks in response to a horizontal compressional stress in the upper crust.

DOI： 10.1002/2017JB014606

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2018.0_93

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

Infrared spectroscopy is one of effective analytical methods for detecting water in minerals, but there was a disadvantage that it takes time to prepare samples. In this study, we used a ATR method that can analyze using ordinary rock polished thin sections. Water of several to several hundred ppm order in olivine and garnet grains was not detected, but the sharp peak at ~3700 cm^-1 was detected within the olivine porphyroclast in the ultra-mylonite. Further improvement is necessary, but it is expected that the ATR method will develop as a useful analytical method in the future.

DOI： 10.14824/jakoka.2018.0_21

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

[Program canceled for a disaster] Program canceled for the 2018 Hokkaido Eastern Iburi earthquake. However, This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2018.0_172

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2018.0_99

CiNii Research

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

DOI： 10.1016/j.egypro.2018.07.013

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

Recent geophysical surveys indicate that hydration (serpentinization) of oceanic mantle is related to outer-rise faulting prior to subduction. The serpentinization of oceanic mantle influences the generation of intermediate-depth earthquakes and subduction water flux, thereby promoting arc volcanism. Since the chemical reactions that produce serpentinite are geologically rapid at low temperatures, the flux of water delivery to the reaction front appears to control the lateral extent of serpentinization. In this study, we measured the permeability of low-temperature serpentinites composed of lizardite and chrysotile, and calculated the lateral extent of serpentinization along an outer-rise fault based on Darcy's law. The experimental results indicate that serpentinization extends to a region several hundred meters wide in the direction normal to the outer-rise fault in the uppermost oceanic mantle. We calculated the global water flux carried by serpentinized oceanic mantle ranging from 1.7 x 10(11) to 2.4 x 10(12) kg/year, which is comparable or even higher than the water flux of hydrated oceanic crust.

DOI： 10.1038/s41598-017-14309-9

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Scopus

PubMed

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

Hayachine-Miyamori ophiolite is an Ordovician arc ophiolite located in the northwestern margin of the South Kitakami Massif. The ophiolite has been divided into an aluminous spinel ultramafic suite (ASUS) and a chromite-bearing ultramafic suite (CRUS) depending on petrographic and mineral chemical features. The Hayachine complex is mostly composed of ASUS. The Miyamori complex is mostly composed of CRUS peridotites and pyroxenites with 1–2 km-size patchy domains of ASUS. In this study, structural analysis of the Hayachine-Miyamori ophiolite was carried out in order to examine the origin of peridotite. The peridotite samples were taken from the Hayachine ASUS and Miyamori ASUS. These peridotites are harzburgites-lherzolites and show coarse grained textures (1–3 mm), undulatory extinction, irregular grain boundaries and exsolution lamellae in pyroxene crystals. There is no distinct difference in the chemical compositions and olivine crystal-fabrics between the Hayachine ASUS and the Miyamori ASUS peridotites, though they are geochemically distinct. Spinel compositions have relatively low Cr# (0.13–0.31) and lower Ti contents (0.02–0.05). The olivine crystal-fabrics were quantified using V_P-Flinn Diagram and show A-type and AG-type patterns (Fabric Index Angle: 7°–53°, VP anisotropy: 5.7–8.9%). J-index values show relatively weak concentrations less than 3.5, possibly due to dynamic recrystallization. It shows that the studied ASUS peridotites preserve textures and crystal-fabrics deformed under higher temperature such as solidus condition in the uppermost mantle.

DOI： 10.51053/shizuoka.44.0_31

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The uppermost mantle in back arc regions is the site of complex interactions between partial melting, melt percolation, and fluid migration. To constrain these interactions and evaluate their consequences on geochemical cycles, we carried out an in situ trace element and water study of a suite of spinel peridotite xenoliths from two regions of the Japan back arc system, Ichinomegata (NE Japan) and Oki-Dogo (SW Japan), using LA-ICPMS and FTIR spectrometry, respectively. This study provides the first full dataset of trace element and hydrogen compositions in peridotites including analyses of all their main constitutive silicate minerals: olivine, orthopyroxene and clinopyroxene. The Ichinomegata peridotites sample a LREE-depleted refractory mantle (Mg# olivine = 0.90; Cr# spinel = 0.07-0.23; Yb clinopyroxene = 7.8-13.3 x C1-chondrite, and La/Yb clinopyroxene = 0.003-0.086 x C1-chondrite), characterized by Th-U positive anomalies and constant values of Nb/Ta. The composition of the studied Ichinomegata samples is consistent with that of an oceanic mantle lithosphere affected by cryptic metasomatic interactions with hydrous/aqueous fluids (crypto-hydrous metasomatism). In contrast, the Oki-Dogo peridotites have low Mg# olivine (0.86-0.93) and a broad range of compositions with clinopyroxene showing "spoon-shaped" to flat, and LREE-enriched patterns. They are also characterized by their homogeneous compositions in the most incompatible LILE (e.g., Rb clinopyroxene = 0.01-0.05 x primitive mantle) and HFSE (e.g., Nb clinopyroxene = 0.01-2.16 x primitive mantle). This characteristic is interpreted as resulting from various degrees of melting and extensive melt-rock interactions. FTIR spectroscopy shows that olivine in both Ichinomegata and Oki-Dogo samples has low water contents ranging from 2 to 7 ppm wt. H2O. In contrast, the water contents of pyroxenes from Ichinomegata peridotites (113-271 ppm wt. H2O for orthopyroxene, and 292-347 ppm wt. H2O for clinopyroxene) are significantly higher than in Oki-Dogo peridotites (9-35 ppm wt. H2O for orthopyroxene, and 15-98 ppm wt. H2O for clinopyroxene). This indicates a relationship between melt-rock interaction and water concentrations in pyroxenes. Our study suggests that the water content of the Japan mantle wedge is controlled by the late melt/fluid/rock interactions evidenced by trace element geochemistry: a mechanism triggered by magma-rock interactions may have acted as an efficient dehydrating process in the Oki-Dogo region while the Ichinomegata mantle water content is controlled by slab-derived crypto-hydrous metasomatism. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2017.03.042

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

<b> [Program canceled for typhoon]</b> Program canceled for typhoon. However, This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2017.0_336

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench recovered boninites and related rocks. Drilling in both areas ended in dolerites inferred to be sheeted intrusive rocks. The basalts apparently erupted immediately after subduction initiation and have compositions similar to those of the most depleted basalts generated by rapid sea-floor spreading at mid-ocean ridges, with little or no slab input. Subsequent melting to generate boninites involved more depleted mantle and hotter and deeper subducted components as subduction progressed and volcanism migrated away from the trench. This volcanic sequence is akin to that recorded by many ophiolites, supporting a direct link between subduction initiation, fore-arc spreading, and ophiolite genesis.

DOI： 10.1080/00206814.2016.1276482

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

<b> [Program canceled for typhoon]</b> Program canceled for typhoon. However, This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2017.0_161

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2017.0_100

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

Program canceled for typhoon. However, This presentation was performed on the special session. This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2017.0_113

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

Program canceled for typhoon. However, This presentation was performed on the special session. This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2017.0_160

CiNii Research

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

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 A(f) across cracks. A(f) 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

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

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 0 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 (&gt;10(22) 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 degrees C and 500 degrees C. For comparison, we also exposed reference specimens of conventional powder metallurgy warm-rolled and ITER-grade tungsten at 300 degrees 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 D-2 gas, a common surface degradation mechanism associated with plasma exposure. Thermal desorption spectrometry indicated moderately higher trapping of Din 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. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijrmhm.2016.05.006

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024538

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

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 V-p/V-s ratios and understand the origin of seismic anisotropy. The crusts beneath the Yangtze and Cathaysia blocks have different average thicknesses (H = 35.4 +/- 63 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 V-p/V-s 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. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2016.07.017

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Scopus

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

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 {0k1}[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 degrees and 180 degrees. The six olivine fabric types have unique values of FIA: 63 degrees for A type, -28 degrees for B type, 158 degrees for C type, 90 degrees for D type, 106 degrees for E type, and 0 degrees 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 degrees to 150 degrees for the ophiolites, 40 degrees to 80 degrees for the ridge peridotites, -40 degrees to 100 degrees for the trench peridotites, 0 degrees to 100 degrees for the peridotite xenoliths, and 40 degrees to 10 degrees 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. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.03.019

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Scopus

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

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 approximate to 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 approximate to 8 Ma.

DOI： 10.1002/2016GC006429

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024556

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

Measurements of crystallographic preferred orientations (CPO) and calculations of P- and S-wave velocities,(V-p and V-s) 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 V-p anisotropy (AV(p)) ranging from 16.4% to 25.5% and maximum V-s anisotropy [AV(s)(max)] between 21.6% and 37.8%. The mylonite has lower AV(p) and AV(s)(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 V-p 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. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2016.04.024

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

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., similar to 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. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.02.029

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Scopus

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

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 similar to 800-970 degrees 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 V-p anisotropy patterns with Vp (X)&gt; V-p(Y)&gt; V-p(Z), V-p(Y)&gt; V-p(X)&gt; V-p(Z), V-p(Z)&gt; V-p(X)&gt; V-p(Y), V-p(X)&gt; V-p(Y) approximate to V-p(Z), and V-p(X) &gt; V-p(Z)&gt; 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, &lt; 300 degrees C) serpentinization (lizardite and chrysotile) decreases V-p by similar to 6-10% and V-s by similar to 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

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

DOI： 10.1111/iar.12157

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

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 x Mg/(Mg + Fe)] in olivine (&gt; 90 center dot 5), high Cr# [Cr/(Cr + Al)] in chromian spinel (&gt; 0 center dot 50), and low Al2O3 (&lt; 3 center dot 5 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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2016.0_449

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2016.0_139

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2016.0_233

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2016.0_137

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2016.0_345

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2016.0_138

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024562

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

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 V-p 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 V-p 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 V-p(X)&gt;V-p(Y)&gt;V-p(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 degrees around the east Himalayan Syntaxis, without finite eastward or southeastward extrusion, in responding to progressive indentation of India into Asia.

DOI： 10.1002/2015JB012209

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：AMER INST 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 x 10(22) m(-2) s(-1)) at temperatures ranging between 103 and 554 degrees C. Retention of deuterium trapped in the bulk, assessed through thermal desorption spectrometry, reached a maximum at 230 degrees C and diminished rapidly thereafter for T&gt;300 degrees C. Post-mortem examination of the surfaces revealed non-uniform growth of bubbles ranging in diameter between 1 and 10 mu m 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 &lt; 111 &gt; directions. Focused ion beam profiles suggest that these bubbles nucleated as platelets at depths of 200 nm-1 mu m 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. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4928184

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024571

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IODP-MI  

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

Scopus

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

A series of simple-shear experiments on blueschist was performed at 400-500 degrees 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 &gt;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 similar to 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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_403

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2015.0_157

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_113

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_512

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_216

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_112

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2015.0_410

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Tokyo Geographical Society  

&emsp;Olivine crystal grains have various crystallographic orientations within a peridotite, resulting in a crystallographic fabric as well as a texture. Six types of fabrics have been identified in mantle peridotites: A, B, C, D, E and AG types. These fabric types have unique seismic properties such as P-wave and S-wave velocity anisotropy. A new method is proposed to classify olivine fabrics based on P-wave velocity structure on a Vp-Flinn diagram. Three P-wave velocities (<i>V₁</i>, <i>V₂</i>, <i>V₃</i>) are used, two of which are the maximum (<i>V₁</i>) and minimum (<i>V₃</i>) velocities, and the third (<i>V₂</i>) is the velocity perpendicular to the orientations of these two velocities. Relationships between <i>V₁</i>/<i>V₂</i> and <i>V₂</i>/<i>V₃</i> classify fabrics into three types: A type (equivalent to B, C and E types), D type and AG type. Moreover, taking into account structural framework such as foliation and lineation, the Vp-Flinn diagram can be expanded to identify all types of fabrics. This method is successfully applied to fabrics previously studied in Oman ophiolite.

DOI： 10.5026/jgeography.124.397

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

DOI： 10.1016/j.epsl.2014.10.026

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

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 similar to 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 degrees 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 x 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 similar to 0.1 to similar 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 mu m in a temperature range between 650 and 850 degrees 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 (similar to 1000 m) zone at high temperatures. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.10.005

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

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 650MPa. Anorthosites and gabbroic anorthosites containing &gt;80vol% plagioclase and gabbros consisting of nearly equal modal contents of plagioclase and pyroxene display distinctive seismic anisotropy patterns: V-p(Z)/V-p(Y)1 and V-p(Z)/V-p(X)1 for anorthosites while 0.8&lt;V-p(Z)/V-p(Y)1 and 0.8&lt;V-p(Z)/V-p(X)1 for gabbros. Amphibolites lie in the same domain as gabbros, but show a significantly stronger tendency of V-p(X)&gt;V-p(Y) than the gabbros. Laminated anorthosites with V-p(X)approximate to V-p(Y)&lt;&lt;V-p(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 V-p(X)approximate to V-p(Y)&gt;V-p(Z) and V-p(X)&gt;V-p(Y)&gt;V-p(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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024581

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

Scopus

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

Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024596

Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024589

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

Seismic velocity is one of the most important sources of information about the Earth's interior. For its proper interpretation, we must have a thorough understanding of the dependence of seismic velocity on microstructural elements, including the modal composition, the crystal preferred orientation (CPO), the grain shape, the spatial distribution of mineral phases, etc. The conventional Voigt, Reuss and Hill averaging schemes take into account only the modal composition and the CPO. The information about the Earth's interior is thus poorly constrained. For a better interpretation, it is critical to have a calculation method which accounts for the grain shape and the spatial distribution of mineral phases, etc. We propose a calculation method which accounts for the grain shape of strongly dimensionally anisotropic minerals like micas and serpentines. Our method can be applied to a distributed geometrical orientation of mineral grains. Comparison was made between calculated and measured velocities in three antigorite-serpentinite mylonites. Judging from the root mean square relative error, our method provides velocities closer to measured values than the Voigt, Reuss and Hill averaging schemes. The input of the grain shape considerably improves the prediction of seismic properties. However, large discrepancies (&gt;0.1 km/s) between measured and calculated velocities can be seen in some directions. The discrepancies might come from microstructural elements which were not considered in the calculation (layer structures and cracks). (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.01.025

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

The present study, which is a follow-up of the Journal of Geophysical Research paper by Ji et al. (2013a), provides a new calibration for both seismic and fabric properties of antigorite serpentinites. Comparisons of the laboratory velocities of antigorite serpentinites measured at high pressures with crystallographic-preferred orientation data measured using electron backscatter diffraction techniques demonstrate that seismic anisotropy in high T serpentinite, which is essentially controlled by the antigorite c axis fabric, is independent on the operating slip system but strongly dependent on the regime and magnitude of finite strain experienced by the rock. Extrapolation of the experimental data with both pressure and temperature suggests that V-p anisotropy decreases but shear wave splitting (Delta V-s) and V-p/V-s increase with increasing pressure in either cold or hot subduction zones. For a cold, steeply subducting slab, antigorite is most likely deformed by nearly coaxial flattening or trench-parallel movements, forming trench-parallel seismic anisotropy. For a hot, shallowly subducting slab, however, antigorite is most likely deformed by simple shear or transpression. Trench-normal seismic anisotropy can be observed when the subducting dip angle is smaller than 30 degrees. The geophysical characteristics of the Tibetan Plateau such as strong heterogeneity in Vp, Vs and attenuation, shear wave splitting and electric conductivity may be explained by the presence of strongly deformed serpentinites in lithospheric shear zones reactivated along former suture zones between amalgamated blocks, hydrated zones of subducting lithospheric mantle, and the crust-mantle boundary if the temperature is below 700 degrees C in the region of interest.

DOI： 10.1002/2013JB010661

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Scopus

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

Spinel peridotite xenoliths from the Ichinomegata Volcano (NE Japan) have distinct foliations defined by compositional layering between olivine-rich and pyroxene-rich layers as well as lineations defined by elongated spine! grains. Crystallographic preferred orientations (CPOs) of olivine are consistent with slip on (010)[100] and {0kl} [100]. The angles between the foliation and the olivine slip planes decrease with increasing values of the J-index (i.e. CPO strength). Such composite planar relationships within the peridotite xenoliths could result from shearing in the uppermost mantle, so that shear strains can be estimated by the angles between the foliation and the olivine slip plane in terms of simple shear strain (0.31-4.26). From these observations, we argue that a suite of the peridotite xenoliths recorded a rare snapshot of uppermost-mantle flow related to back-arc spreading during the opening of the Japan Sea. The peridotite xenoliths with higher J-indices (i.e. higher shear strain) tend to have slightly lower minimum temperatures, possibly defining a vertical strain gradient in the uppermost mantle section at the time of the volcano's eruption. The CPO data have been used to calculate the seismic properties of the xenoliths at PT conditions obtained from geothermobarometry, and are compared to field geophysical data from the literature. Our results are consistent with a roughly EW-oriented fastest P-wave propagation direction in the uppermost mantle beneath the northeast part of the Japan arc. Average samples are calculated based on three different structural reference frames; horizontal plane parallel to 1) foliation, 2) the plane containing the maximum concentration of olivine [100], and 3) P-wave maximum direction. S-wave anisotropy deduced from CPOs requires a reasonable thickness of the anisotropic layer (24.1-26.6 km), and the structural reference frame does not have significant effect on the estimation of thickness. Consequently, Ichinomegata peridotites record a long and complicated tectonic history; they preserve deformation 'frozen in' during back-arc spreading and this deformation also has an effect on present-day mantle flow. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2013.10.035

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Scopus

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

Peridotite formed by contact metamorphism and dehydration breakdown of an antigorite schist from the Happo area, central Japan shows a strong olivine crystallographic preferred orientation (Ol CPO). The lack of mesoscale deformation structures associated with the intrusion and the lack of microstructural evidence for plastic deformation of neoblastic grains suggest that olivine CPO in this area did not form as a result of solid-state deformation. Instead, the good correspondence between the original antigorite orientation and the orientation of the newly formed olivine implies the CPO formed by topotactic growth of the olivine after antigorite. Ol CPO is likely to develop by a similar process in subduction zone environments where foliated serpentinite is dragged down to depths where antigorite is no longer stable. The Happo Ol CPO has a strong a-axis concentration perpendicular to the lineation and within the foliation commonly referred to as B-type Ol CPO. Seismic fast directions parallel to the ocean trench are observed in many convergent margins and are consistent with the presence of B-type Ol CPO in the mantle wedge of these regions. Experimental work has shown that B-type CPO can form by dislocation creep under hydrous conditions at relatively high stresses. There are, however, several discrepancies between the characteristics of natural and laboratory samples with B-type Ol CPO. (I) The formation conditions (stress and temperature) of some natural examples with B-type CPO fall outside those predicted by experiments. (2) In deformation experiments, slip in the crystallographic c-axis direction is important but has not been observed in natural examples of B-type CPO. (3) Experimental work suggests the presence of H2O and either high shear stress or relatively low temperatures are essential for the formation of B-type CPO. These conditions are most likely to be achieved close to subduction boundaries, but these regions are also associated with serpentinization, which prevents strong olivine CPO patterns from forming. We show B-type Ol CPO can form as a result of static topotactic growth of olivine after high-temperature breakdown of foliated serpentinite. These results resolve the discrepancies between experimental and natural examples of B-type CPO and show the need to rethink the formation process of olivine CPO in convergent margins. Topotactic growth of olivine after antigorite can account for the inferred distribution of B-type Ol CPO in the mantle wedge more successfully than dislocation creep. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2013.11.025

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

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

Microstructures of a layered peridotite ultramylonite from the Oman ophiolite are compared with that of experimentally deformed samples. Average grain sizes and grain size ratios of olivine and pyroxene from each layer are compared with respect to the fraction of pyroxene (f(px)) in the layer. Grain size of the pyroxene is almost constant among different f(px) layers, whereas olivine grain size decreases significantly with increasing f(px), both of which were characteristic features found in forsterite+enstatite aggregates after grain growth experiments (Tasaka and Hiraga, ). Furthermore, the Zener relationship (log d(ol)/d(px) versus log f(px)) found in the ultramylonite is remarkably comparable to that observed in our experiments. These observations indicate effective pinning of olivine grain growth due to the presence of pyroxene grains during the deformation of the rocks. Olivine grains in layers with f(px)0.03 do not exhibit lattice-preferred orientation (LPO), whereas the grains in layers with f(px)&lt;0.03 exhibit LPO, indicating that deformation proceeded via diffusion- and dislocation-accommodated creep in the former and the latter layers, respectively. We simulated the evolution of grain size and viscosity in the shear zone based on our grain growth and flow laws obtained for diffusion creep of forsterite+enstatite (Tasaka and Hiraga, ; Tasaka et al., ) and successfully reproduced the observed grain sizes in the ultramylonite. We therefore conclude that the relative values of the kinetic parameters, some of which are functions of the f(px), are applicable to nature.

DOI： 10.1002/2013JB010619

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

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：COPERNICUS GESELLSCHAFT MBH  

DOI： 10.5194/se-5-509-2014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2014.0_174

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2014.0_095

CiNii Research

Language：English  

DOI： 10.1016/j.epsl.2013.06.031

Scopus

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

A large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase. We have measured P and S wave velocities (V-p and V-s) and anisotropy of 17 amphibole-rich rock samples containing 34-80vol% amphibole at hydrostatic pressures (P) up to 650MPa. Combined petrophysical and geochemical analyses provide a new calibration for mean density, average major element contents, mean V-p-P and V-s-P coefficients, intrinsic V-p and V-s anisotropy, Poisson's ratios, the logarithmic ratio R-s/p, and elastic moduli of amphibole-rich rocks. The V-p values decrease with increasing SiO2 and Na2O+K2O contents but increase with increasing MgO and CaO contents. The maximum (0.38-0.40km/s) and minimum S wave birefringence values occur generally in the propagation direction parallel to Y and normal to foliation, respectively. Amphibole plays a critical role in the formation of seismic anisotropy, whereas the presence of plagioclase, quartz, pyroxene, and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations (CPOs). The CPO variations cause different anisotropy patterns illustrated in the Flinn diagram of V-p(X)/V-p(Y)-V-p(Y)/V-p(Z) plots. The results make it possible to distinguish, in terms of seismic properties, the amphibolites from other categories of lithology such as granite-granodiorite, diorite, gabbro-diabase, felsic gneiss, mafic gneiss, eclogite, and peridotite within the Earth's crust. Hence, amphibole, aligned by dislocation creep, anisotropic growth, or rigid-body rotation, is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs, which contains rather little phyllosilicates such as mica or chlorite.

DOI： 10.1002/jgrb.50352

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Scopus

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

Investigations of microstructures are crucial if we are to understand the seismic anisotropy of subducting oceanic crust, and here we report on our systematic fabric analyses of glaucophane, lawsonite, and epidote in naturally deformed blueschists from the Diablo Range and Franciscan Complex in California, and the Hida Mountains in Japan. Glaucophanes in the analyzed samples consist of very fine grains that are well aligned along the foliation and have high aspect ratios and strong crystal preferred orientations (CPOs) characterized by a (1 00)[001] pattern. These characteristics, together with a bimodal distribution of grain sizes from some samples, possibly indicate the occurrence of dynamic recrystallization for glaucophane. Although lawsonite and epidote display high aspect ratios and a strong CPO of (001)[010], the occurrence of straight grain boundaries and euhedral crystals indicates that rigid body rotation was the dominant deformation mechanism. The P-wave (AV(P)) and S-wave (AV(S)) seismic anisotropies of glaucophane (AV(P) = 20.4%, AV(S) = 11.5%) and epidote (AV(P) = 9.0%, AV(S) = 8.0%) are typical of the crust; consequently, the fastest propagation of P-waves is parallel to the [001] maxima, and the polarization of S-waves parallel to the foliation can form a trench-parallel seismic anisotropy owing to the slowest V-S polarization being normal to the subducting slab. The seismic anisotropy of lawsonite (AV(P) = 9.6%, AV(S) = 19.9%) is characterized by the fast propagation of P-waves subnormal to the lawsonite [001] maxima and polarization of S-waves perpendicular to the foliation and lineation, which can generate a trench-normal anisotropy. The AV(S) of lawsonite blueschist (5.6-9.2%) is weak compared with that of epidote blueschist (8.4-11.1%). Calculations of the thickness of the anisotropic layer indicate that glaucophane and lawsonite contribute to the trench-parallel and trench-normal seismic anisotropy beneath NE Japan, but not to that beneath the Ryukyu arc. Our results demonstrate, therefore, that lawsonite has a strong influence on seismic velocities in the oceanic crust, and that lawsonite might be the cause of complex anisotropic patterns in subduction zones. (c) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.06.011

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Scopus

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

The Fizh massif, Oman Ophiolite, contains a ductile shear zone at the Moho Transition Zone. The dunites in the shear zone are classified based on microstructures into coarse granular texture, medium-grained texture, mylonite, and ultramylonites toward a gabbro contact. The average grain size of olivine decreases toward the shear zone, which contains a zone of high strain (~15 m wide). The proportion of hydrous minerals (amphibole and chlorite) in the shear zone show an increase toward the gabbro contact, suggesting that water infiltrated the shear zone from the gabbro contact. Equilibrium temperatures indicate a higher deformation temperature (~900°C) outside of the high strain zone compared with inside this zone (~750°C). Under these geochemical and temperature conditions, the temporal evolution of olivine crystal-preferred orientations (CPO) indicates the following continuous deformation scenario. First, deformation by dislocation creep under higher temperatures resulted in slip by D-type {0. kl}[100] and then weak E-type (001)[100] slip. Next, deformation by dislocation creep under lower temperatures and higher stress conditions produced a C-type (100)[001] CPO. Finally, superplastic deformation by grain boundary sliding resulted in a random CPO. © 2013 Elsevier B.V.

DOI： 10.1016/j.epsl.2013.07.009

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Scopus

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

Harzburgites obtained from the oldest crust-mantle section in the Philippine Sea plate (similar to 52 Ma) along the landward slope of the southern lzu-Ogasawara Trench, preserve mantle fabrics formed during the infancy of the subduction zone; that is during the initial stages of Pacific plate subduction beneath the Philippine Sea plate. The harzburgites have relatively fresh primary minerals despite of their heavy serpentinizations, and show inequigranular interlobate textures, and crystal preferred orientation patterns in olivine (001)1100] and Opx (100)1001]. The harzburgites have the characteristics of residual peridotites, whereas the dunites, obtained from the same location as the harzburgites, provide evidence for the earliest stages of arc volcanism during the inception of subduction. We propose that the (001)1100] olivine patterns began forming in immature fore-arc mantle with an increase in slab-derived hydrous fluids during the initial stages of subduction in in situ oceanic island arc. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.eps1.2013.06.031

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

The whole-rock chemistries of the mafic rocks in the Moho Transition Zone, Fizh Massif, the Oman ophiolite have been analyzed by X-ray fluorescence spectrometry. The mafic rocks were classified into three texture types based on their microstructures: weakly deformed gabbro, moderately deformed gabbro and ultramylonites. There is no systematic variation of the whole-rock chemistries among the three texture types. The ultramylonites show various chemistries, although they consist mostly of very fine-grained matrix with minor relatively coarser porphyroclasts. It may suggest the effect of fluid-rock interaction during ductile shearing in the Moho Transition Zone or variation of the mafic rock chemical compositions.

DOI： 10.51053/shizuoka.40.0_13

CiNii Research

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

DOI： 10.14945/00007428

Language：English   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024613

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

DOI： 10.1016/j.tecto.2012.11.027

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Scopus

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

Intense serpentinization within the Machinoyama ultramafic body, eastern-most part of the Yakuno ophiolite in the Paleozoic Maizuru belt, SW Japan, resulted in the development of block-in-matrix structure in the brittle regime, possibly associated with exhumation along a fault. Various microstructures are heterogeneously distributed throughout peridotite blocks in a serpentinite matrix. The microstructures are classified into four domains according to olivine grain size: coarse (1.0-1.5. mm), medium (0.5-1.0. mm), small (0.2-0.5. mm), and fine-grained (0.01. mm). Even in a single peridotite block, the medium-, small- and fine-grained domains occur at various scales. In particular, the fine-grained domain occurs in thin zones that cut across the other domains. These observations suggest that deformation in the peridotites before the serpentinization was partitioned into anastomosing zones during progressive inhomogeneous non-coaxial shear, resulting in the simultaneous development of a range of microstructures from the coarse-grained domain to the small-grained domain. Olivine crystal-preferred orientations tend to be weaker with decreasing olivine grain size, indicating a change in deformation mechanism from dislocation creep to grain-size-sensitive creep. Moreover, the fine-grained domains contain much more second phase than the small-grained domain even in the same sample, suggesting the role of the second phases on strain localization during dynamic recrystallization of olivine. © 2012 Elsevier B.V.

DOI： 10.1016/j.tecto.2012.07.008

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Deformation microstructures for a lawsonite blueschist from the New Idria serpentinite body, Diablo Range, are investigated to clarify rheological behaviors of glaucophane and lawsonite, which are main mineral assemblages of subducting oceanic crust at relatively cold geotherm. Developments of crystal-preferred orientations (CPOs) with small grain size, irregular grain boundary and high aspect ratio of glaucophane indicate deformation mechanism as recovery and dynamic recrystallization possibly accommodated by dislocation creep, while lawsonite deforms by rigid body rotation based on euhedral grains with angular or straight grain boundaries. Higher aspect ratios, lower angle to foliation, and stronger CPOs of both minerals in the glaucophane-rich layer rather than those in the lawsonite-rich layer suggest the strain localization into the glaucophane-rich layer. Additionally fabric strength (the degree of crystal alignment) and seismic anisotropy are higher in the glaucophane-rich layer than that of the lawsonite-rich layer, which is consistent with the microstructural analyses. All our results imply, therefore, the dominant role of glaucophane rather than lawsonite for rheological behavior and seismic anisotropy of blueschist.

DOI： 10.1111/iar.12003

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Scopus

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

DOI： 10.2204/iodp.sd.15.10.2013

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2013.0_106

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2013.0_426

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2013.0_427

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

The elemental X-ray maps of a layered gabbro sample obtained by a scanning X-ray analytical microscope have been used to produce mineral-distribution maps of the layered gabbro. These element-distribution maps have been transformed into mineral-distribution maps by Michibayashi <i>et al.</i> (2002)ʼs method. To examine the mineral-distribution maps, we tested two texture analyses: spatial distribution method and Hough transform method. As a result, the spatial distribution method could have a possibility to reveal anisotropic characters of the layered gabbro, whereas the Hough transform method would be partially able to show its anisotropic nature. Further study will be required to develop a realistic texture analysis for the mineral-distribution maps obtained by this procedure.

DOI： 10.51053/shizuoka.39.0_7

CiNii Research

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

DOI： 10.14945/00007130

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

We have investigated K-feldspar recrystallisation in granitoid mylonites within a ductile shear zone from the Ryoke metamorphic belt, SW Japan. Fine-grained K-feldspar (20 mu m on average) occurs in the matrix and in pull-apart areas within fractured K-feldspar porphyroclasts. These fine grains are elongated and oriented parallel to the main foliation in the matrix, and their grain surfaces, observed with the scanning electron microscope, are not smooth, but rough due to the development of very fine (&lt;1 mu m) round grains of K-feldspar on the surface of each grain. In pull-apart areas, the crystallographic orientation of fine-grained K-feldspar, as measured by electron backscatter diffraction (EBSD), is strongly controlled by that of the host porphyroclast, and shows rotations with shear components parallel to fractures. In the matrix, the crystallographic orientation of fine-grained K-feldspar is not consistent with intracrystalline plasticity, but rather with a growth rate that is slightly controlled by nearby porphyroclasts. All this, together with the growth features on grains, suggests that solution-precipitation of K-feldspar from K-rich aqueous fluid occurred during progressive deformation. Infrared (IR) mapping was performed to evaluate the distribution of water in pull-apart areas and the matrix. Water is heterogeneously distributed within K-feldspar porphyroclasts, which contain 150-2200 ppm H2O. In contrast, the water content is low (150-300 ppm H2O) and homogeneously distributed in fine-grained K-feldspar in the matrix and pull-apart areas, even though included in these analyses are grain boundaries that can generally contain abundant aqueous fluid. The results of EBSD analysis and IR mapping indicate that water is released during solution-precipitation of K-feldspar under mid-crustal conditions. The solution-precipitation process under a water-rich environment in the middle crust results in the formation of fine grains, possibly deforming dominantly by grain-size-sensitive creep, and with the release of aqueous fluid involved in the process. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2012.01.033

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

Annealing experiments on agate were performed to investigate grain growth kinetics and the effect of crystallographic anisotropy on normal grain growth of quartz. The experiments were conducted using a piston-cylinder apparatus at 700-800A degrees C and 0.5 GPa for 0-66 h. The grain growth rate was expressed by D (n) -D (0) (n) = kt with k = k (0) exp(-H*/RT) where D (0) is the initial grain size at t = 0, with n = 4.4 +/- A 0.3, and H* = 191.3 +/- A 11.0 kJ/mol is the activation enthalpy and logk (0) = 19.8 +/- A 1.4. While the grain aspect ratios are nearly constant at similar to 0.7 (short/long) during grain growth, the longest axis in individual grains tends to be oriented parallel to their c-axis, indicating that a primary crystal-preferred orientation of c-axis of the agate could result in the development of a weak shape-preferred orientation during grain growth.

DOI： 10.1007/s00269-011-0476-6

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Language：English  

DOI： 10.1073/pnas.1112005109

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Scopus

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

Peridotite xenoliths from Northeast Tasmania, Australia, consist of spinel lherzolites and minor dunites that originated from the uppermost mantle at depths of less than 40 km, based on the geothermal gradient beneath Tasmania, where the depth of the Moho is 29 km. The crystal preferred orientations (CPOs) of olivine and pyroxene were measured in 5 of 13 collected samples (1 dunite and 4 lherzolites) that were large enough to enable measurements. Olivine CPOs indicate the dominance of (010) [100] slip. Geothermobarometric analyses of the xenoliths yield temperatures of 950-1050 degrees C and pressures of 0.7-1.1 GPa. Using these data, we calculated changes in the seismic properties of a rock with ideal volume fractions of olivine and pyroxene under conditions of 1000 degrees C and 1 GPa, for various orientations of the structural reference frame in the case of three geodynamic models (extension, shear, and upwelling). The model of horizontal extension performs best in explaining the structure of the uppermost lithospheric mantle beneath Northeast Tasmania. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2011.12.002

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

The understanding of olivine fabric has dramatically been progressed during the last~10 years by both natural and experimental studies along with the major technological improvement. Crystal-preferred orientations (CPO) are the expression of crystallographic fabrics of grains within the rock with respect to the structural frame (X-,Y- and Z-axes). CPO patterns can be interpreted based on the plane of plastic flow and the flow direction. Olivine fabrics, which are olivine CPO patterns, have been classified into five types: A, B, C, D and E types by a series of experimental studies. An additional AG type has also been proposed in recognition of its common occurrence in nature. New results have already required major modiications to the geodynamic interpretation of the upper mantle, although some uncertainties still remain regarding the olivine fabrics and their development. © 2012, Japan Association of Mineralogical Sciences. All rights reserved.

DOI： 10.2465/gkk.120712b

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.5575/geosoc.118.11.IX_X

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2012.0_379

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2012.0_425

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2012.0_149

CiNii Research

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

CiNii Research

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

CiNii Research

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

CiNii Research

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

CiNii Research

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

Peridotite xenoliths from the Kilbourne Hole maar, New Mexico, consist of spinet lherzolite, harzburgite, and dunite. Because Kilbourne Hole erupted at approximately 10 ka, these xenoliths represent essentially current conditions beneath the Rio Grande rift. In this study, we present detailed petrofabric data and seismic properties obtained from peridotite xenoliths from Kilbourne Hole to illuminate the origin and significance of shear-wave splitting in the uppermost mantle beneath this active rift. Using phase relations and the temperature of equilibration, we infer that these xenoliths were derived from the uppermost mantle, from depths of 35-60 km. Their crystallographic preferred orientations indicate the preservation of olivine b-axis fiber fabrics with a strong concentration of [010] with girdles of [100] and [001]. We consider three geodynamic models for the source region of these xenoliths: horizontal extension, lateral shear, and upwelling. After calculating seismic properties using a volume fraction of olivine, orthopyroxene and clinopyroxene appropriate to each model, we conclude that these xenoliths are derived from a lateral shear zone (vertical foliation (XY plane) and horizontal lineation within the plane of the foliation (X-axis)). However, the degree of seismic anisotropy generated by peridotite xenoliths alone is limited, so that the existence of melt in thin cracks or dikes could be required to cause a significant increase: the orientation of such melt pockets parallel to the XY plane in either model would result in an increase in anisotropy. These results indicate that the shear-wave splitting observed in the Rio Grande rift is a reflection of the lithospheric fabric and the presence of melts as thin cracks or dikes. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.09.013

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

Machinoyama ultramafic body is the eastern most part of the Yakuno ophiolite in the Maizuru belt. Outcrops of its southeastern margin show various block-in-matrix structures towards the fault boundary to the Ultra-Tanba belt. The blocks consist of serpentinites and serpentinized peridotites and were fragmented into multiple parts, with the spaces between blocks being infilled by scaly serpentinites (<i>i.e.</i> chrysotile). The blocks decreased their sizes and formed phacoidal-shapes towards the fault boundary, whereas serpentinite matrix becomes dominant with intense foliations. These structural developments in Machinoyama body could be related to the fault activity at the boundary with the Ultra-Tanba belt.

DOI： 10.51053/shizuoka.38.0_21

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Antigorite (Atg) is stable throughout large parts of the wedge mantle of most subduction zones. Atg shows strong acoustic anisotropy and crystallographic preferred orientation (CPO) patterns of this mineral may contribute significantly to seismic anisotropy in convergent margins. Atg CPO patterns from the Higashi-Akaishi (HA) forearc mantle body of southwest Japan adds to the data set suggesting the most common Atg CPO pattern has a c-axis perpendicular to the foliation and a b-axis parallel to the stretching lineation. Statistical analysis using the eigenvector method of Atg CPO from two mutually perpendicular directions in the same sample (YZ-section and XZ-section) shows no significant differences implying sample preparation has no significant affect on the resulting Atg CPO. Reuss (uniform stress) averages of anisotropy for the Higashi-Akaishi samples are approximately treble the values for Voigt (uniform strain) averages. When comparing calculated anisotropy of hydrated mantle peridotite samples-such as the Higashi-Akaishi unit-with observed S-wave delay times in convergent margins, the appropriate averaging method needs to be considered. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2011.08.006

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

DOI： 10.14945/00006209

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

Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100-220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45 rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises ∼70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JB007931

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J-GLOBAL

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024731

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

Microstnictural and petrologic analyses of 7 gabbroic rocks sampled from the medial area of the Godzilla Megamullion (site KH07-02-D18), located along the Parece Vela Basin spreading ridge (Parece Vela Rift), Philippine Sea, reveal the development of a high-temperature ductile shear zone associated with hydrothermal metamorphism in the lower crust. The deformed gabbroic rocks are petrographically classified into mylonites and an ultramylonite, and are characterized by porphyroclastic textures consisting mainly of coarse plagioclase and clinopyroxene/amphibole porphyroclasts in a fine-grained matrix. Plagioclase crystallographic-preferred orientations vary from (010)[100] and (001)[100] patterns in the mylonites to a weak (001)[100] pattern in the some mylonites and ultramylonite, suggesting a change in the deformation mechanism from dislocation creep to grain-size-sensitive creep with increasing intensity of deformation. The chemical composition of matrix plagioclase is generally more sodic than that of porphyroclasts. Secondary amphibole is ubiquitous, consisting mainly of pargasite and magnesiohomblende (brown hornblende) and actinolite (green hornblende). The mineral assemblage is consistent with the hydrothermal metamorphic reaction: clinopyroxene + calcic plagioclase + fluid -&gt; amphibole + sodic plagioclase. Compared with deformed gabbroic rocks from the breakaway and termination areas of the Godzilla Megamullion, the samples record ductile shearing under high temperature conditions, possibly related to the development of the Godzilla Megamullion, although hydrothermal activity in the medial area appears to have been less intense than in both the breakaway and termination areas. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2011.02.001

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Relicts of deformed lithospheric mantle have been identified within serpentinites and weathered peridotites recovered from nine dredge sites and one submersible dive site from across the Godzilla Megamullion, which was emplaced at the now-extinct Parece Vela Rift in the Parece Vela Basin, a back-arc basin in the Philippine Sea. The serpentinites consist dominantly of lizardite +/- chrysotile and magnetite with minor relict primary minerals that include pyroxene, spinel, and rare olivine. The weathered peridotites consist of pyroxene, spinel, lizardite +/- chrysotile, and magnetite as well as weathering products of olivine. These rocks were classified in hand specimen into three types with different structures: massive, foliated, and mylonitic. In thin-section the serpentine minerals show no sign of deformation, whereas relict primary minerals show evidence of plastic deformation such as undulose extinction, kink bands, dynamic recrystallization, and weak to moderate crystallographic preferred orientations. Therefore, the serpentinites and weathered peridotites result from the static replacement and weathering of previously ductile-deformed peridotite. Given their location close to or on the detachment surface that exposed them, the relicts of peridotite provide evidence of deformation in the lithospheric mantle that could be related to the formation and emplacement of the Godzilla Megamullion in the Parece Vela Rift.

DOI： 10.1111/j.1440-1738.2011.00759.x

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

Petit-spots, the late Miocene alkali basaltic volcanoes on the Early Cretaceous NW Pacific Plate, originate at the base of the lithosphere. The petit-spot volcanic rocks enclose fragments of tholeiitic basalt, dolerite. gabbro. and mantle peridotite, providing a unique window into the entire section of subducting oceanic lithosphere. We provide here the first direct observations on the deep structure of the Pacific lithosphere using microstructural analyses of a petit-spot peridotite xenolith. The xenolith is a lherzolite that consists mainly of coarse- and medium-grained olivine. orthopyroxene, and clinopyroxene, as well as fine-grained aggregates of spinel and orthopyroxene that probably represent replaced pyrope-rich garnet. A strong deformational fabric is marked by a parallel alignment of millimeter-sized elongate minerals and their crystallographic preferred orientation. The olivine displays a [010] fiber pattern with a girdle of [100] axes and a maximum of [010] perpendicular to the foliation, a pattern which is consistent with a transpressional deformation in high temperature conditions at the base of oceanic lithosphere. Our microstructural observations and seismic data indicate that the lower part of the NW Pacific lithosphere possess an early stage structure of mantle flow at the asthenosphere. This interpretation is compatible with a conventional model in which oceanic lithosphere is thickened during cooling and plate convection. A discrepancy between the weak anisotropy in the petit-spot peridotite and the strong azimuthal anisotropy from the seismic data in the NW Pacific plate implies the existence of a highly anisotropic component in the deep oceanic lithosphere. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.12.011

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

Garnet clinopyroxenites occur within foliated dunite in the Higashi-akaishi peridotite mass, located within the subduction-type high-pressure/low-temperature Sanbagawa metamorphic belt. The garnet clinopyroxenites contain 3-80% garnet, and garnet and clinopyroxene are homogeneously distributed. Garnet crystals contain extensive, regular dislocation arrays and dislocation networks, suggesting that dislocation creep was the dominant deformation mechanism. Analyses of crystallographic orientation maps indicate similar grain sizes and aspect ratios for garnet and clinopyroxene, regardless of modal composition, indicating that these minerals deformed with similar degree of plasticity. Moreover, indexes of crystallographic fabric intensity (i.e., J-index and M-index) for both garnet and clinopyroxene tend to increase with increasing modal composition of garnet. Fourier-transform infrared spectroscopy analysis revealed that water content in garnet is similar to 60 ppm, whereas that in clinopyroxene is similar to 70 ppm. Olivine crystal-preferred orientations in the Higashi-akaishi peridotite mass, characterized by [0 0 1] (0 1 0), are thought to have developed during deformation under wet conditions. Consequently, we argue that the presence of water could act to enhance garnet plasticity during deformation. The results reveal contrasting influences of water on the deformation of garnet and diopside: under wet conditions compared with dry, the strain rate increases by two orders of magnitude for garnet but by an order of magnitude for diopside. Given the influence of water on the creep strength of garnet, garnet within the Higashi-akaishi mass may have become significantly as weak as clinopyroxene during deformation. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.10.008

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

The relationships between elastic wave velocities and petrofabrics were studied in two antigorite-bearing serpentinite mylonites. Rock samples with antigorite content of 37 and 80 vol% were collected from the Happo ultramafic complex, Central Japan. Compressional and shear-wave velocities were measured by the pulse transmission technique at room temperature and confining pressures of up to 180 MPa. Petrofabrics were examined by optical microscopy and scanning electron microscopy with electron backscattered diffraction (SEM-EBSD). Olivine a- and c-axes are weakly oriented perpendicular to the foliation and parallel to the lineation, respectively. Antigorite b- and c-axes are distinctly oriented parallel to the lineation and perpendicular to the foliation, respectively. Both samples show strong anisotropy of velocity. The compressional wave velocity is fastest in the direction parallel to the lineation, and slowest in the direction perpendicular to the foliation. The shear wave oscillating parallel to the foliation has higher velocity than that oscillating perpendicular to the foliation. As the antigorite content increases, the mean velocity decreases but both azimuthal and polarization anisotropies are enhanced. Measured velocities were compared with velocities calculated from petrofabric data by using Voigt, Reuss and Voight-Reuss-Hill (VRH) averaging schemes. All averaging schemes show velocity anisotropy qualitatively similar to measurements. There are large velocity differences between Voigt and Reuss averages (0.7-1.0 km/s), reflecting the strong elastic anisotropy of antigorite. Measured velocities are found between Reuss and VRH averages. We suggest that the relatively low velocity is due to the platy shape of antigorite grains, the well-developed shape fabric and their strong elastic anisotropy. The configuration of grains should be an important factor for calculating seismic velocities in an aggregate composed of strongly anisotropic materials, such as sheet silicates. © The Geological Society of London 2011.

DOI： 10.1144/SP360.6

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Water contents estimates based on infrared spectroscopy and deformation microstructures are used to constrain the origin of textural variations observed in mantle xenoliths from Kimberley, South Africa. Infrared spectra indicate water contents of 10-370 ppm (H(2)O by weight) in olivine, 20-370 ppm in orthopyroxene, up to 340 ppm in garnet and 30-550 ppm in clinopyroxene, although no systematic differences are detected among texturally distinct xenoliths (i.e. granular and sheared peridotites). In contrast, active slip systems in olivine, as inferred from tilt boundaries, are different between the granular and sheared peridotites; the former deformed via the [100](010) slip system, which is commonly active under hot, dry conditions, whereas the latter deformed via the [001](100) slip system, which is commonly activated in water-rich environments. The discrepancy in water contents estimates based on infrared spectroscopy and deformation microstructures may reflect different stages of fie evolution of water content: the present water contents, as analysed by infrared spectroscopy, may have been modified by the most recent events (e.g. eruption by kimberlite magma), whereas the water contents inferred from tilt boundaries may have resulted from the various deformation processes in the deep cratonic mantle. Accordingly, we suggest that the observed heterogeneity in water content within cratonic roots facilitates local deformation, and gives rise to the range of textures seen in cratonic mantle xenoliths. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/gj.1216

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

The Godzilla Megamullion, the largest oceanic core complex, is located at the extinct Parece Vela Basin spreading ridge in the Philippine Sea. Fault rocks are common on the surface of the Godzilla Megamullion, indicating the presence of a detachment fault exposed on the seafloor (Harigane et al., 2011a). Based on a study of deformed gabbroic rocks at the breakaway region, Harigane et al. (2008) showed that the hydrothermal metamorphism occurred retrogressively, associated with deformation in the lower crust related to the detachment fault. But the origins of fluids and the fluid/rock ratio during deformation are still unsolved. Here, we present trace element geochemical analyses of amphibole and clinopyroxene of the gabbroic rocks sampled from the medial area of the Godzilla Megamullion.

DOI： 10.14824/jakoka.2011.0.56.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2011.0.202.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

We calculated the variation of the seismic properties with two ideal mineral compositions: plagioclase 50% + clinopyroxene 50% (pl50cpx50) and plagioclase 50% and amphibole 50% (pl50amp50). These two compositions could explain a P-wave velocity model for the Godzilla megamullion from 6 km/s for pl50amp50 to 7 km/s for pl50cpx50, suggesting that this oceanic crust may be significantly hydrated.

DOI： 10.14824/jakoka.2011.0.118.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2011.0.416.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2011.0.191.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2011.0.190.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2011.0.154.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2011.0.153.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

We show that a simple plagioclase flow law can be employed to explain the microstructural evolution of gabbroic mylonites and ultramylonites that occur extensively along the surface of fault-induced asymmetric spreading over the &sim;125 km length of the Godzilla megamullion, at a temperature of 650 to 900 degree C and a remarkably higher strain rate of &sim;10E-9 s-1 to 10E-10 s-1. Our results indicate that superplastic flow within the lower crust played a significant role in movement along the detachment fault that formed the megamullion during asymmetric back-arc rifting.

DOI： 10.14824/jakoka.2011.0.39.0

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Gabbroic rocks and amphibolites were collected from the KR03-01-D10 dredge site located on the West Arm Rise of the Godzilla Megamullion, close to the Parece Vela Rift which appears to correspond to the termination area of a detachment fault, the Philippine Sea. The gabbroic rocks and amphibolites reveal the occurrence of a high hydrothermal activity in the lower crust close to a paleo-ridge. In the gabbroic rocks, plagioclase compositions of both porphyroclasts and matrix were transformed into sodium-rich compositions close to albite. Amphiboles are of secondary rather than igneous origin based on their microstructural occurrences. In the amphibolites, anorthite contents of porphyroclasts and matrix plagioclase are relatively lower than those of the gabbroic rocks, whereas the chemical compositions of amphibole within the amphibolites are similar to those of amphibole within the gabbroic rocks. Amphibolites represent the product of retrograde metamorphism associated with hydrothermal alteration of the gabbroic body by the reaction: clinopyroxene + calcic plagioclase + fluid -&gt; amphibole + sodic plagioclase. The estimated temperatures of the amphibolites derived from the amphibole thermobarometer and the gabbroic rocks derived from the hornblende-plagioclase geothermometer show similar to 700-950 degrees C and 650-840 degrees C, respectively. The hydrothermal alteration recorded in the gabbroic rocks possibly occurred under high-T conditions; the rocks were then metamorphosed to the amphibolites during a retrogressive stage. Our study indicates that amphibolitization took place with various degrees of deformation. It may imply that the hydrothermal activity increased as the Godzilla Megamullion developed as an oceanic core complex in the paleo-ridge.

DOI： 10.1111/j.1440-1738.2010.00741.x

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

Peridotite xenoliths from southern Texas consist of spinel lherzolite, harzburgite and minor dunite. Based on phase relations and temperature of equilibration, Knippa xenoliths come from the uppermost mantle, 40-70 km deep. Knippa xenoliths provide rare snapshots of upper mantle processes and compositions beneath south-central Laurentia. They preserve olivine a-axis fiber fabrics with a strong concentration of [100] and girdles of [010] and [001]. Assuming a lithospheric mantle having a horizontal flow direction parallel to fast directions, the mantle lithospheric fabric revealed by the xenoliths mostly explains the magnitude of observed shear-wave splitting observed along the southern margin of the Laurentian craton. Citation: Satsukawa, T., K. Michibayashi, U. Raye, E. Y. Anthony, J. Pulliam, and R. Stern (2010), Uppermost mantle anisotropy beneath the southern Laurentian margin: Evidence from Knippa peridotite xenoliths, Texas, Geophys. Res. Lett., 37, L20312, doi:10.1029/2010GL044538.

DOI： 10.1029/2010GL044538

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

We conducted a microstructural study of samples from a natural serpentinite shear zone in the Ohmachi Seamount, Izu-Bonin frontal arc. The serpentinite samples consist mainly of columnar antigorite grains that show marked variations in texture from two approximately orthogonal sets of grains (interpenetrating) to aligned (schistose) forms. Because the two types of grains have similar compositions, these textural differences are interpreted to reflect the existence of a strain gradient toward a plate interface in a subduction zone. The crystal-preferred orientation (CPO) of antigorite with interpenetrating texture is almost randomly oriented, whereas in the case of schistose texture the CPO shows a typical [010](001) pattern. We also found that with increasing intensity of schistosity, the polarization plane of Vs(1) for antigorite grains becomes aligned parallel to the flow plane, consistent with a plane oriented normal to the maximum concentration of slow antigorite c-axes. This configuration results in seismic anisotropy that is approximately five times higher than that for olivine grains. These findings indicate that if a serpentinite layer on the plate interface attains large bulk shear strains (gamma&gt;similar to 2), the resultant alignment of antigorite grains within the layer strongly influences the orientation and magnitude of seismic anisotropy in the mantle wedge, depending on the dip angle of the subducting slab. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.08.035

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

To identify the dominant deformation mechanism in continental middle crust at an arc-trench system, we used an SEM-EBSD system to measure the lattice-preferred orientations of quartz grains in fine-grained metachert from the low-grade (chlorite and chlorite-biotite zones) part of the low-P/high-T Ryoke metamorphic belt, SW Japan. Quartz c-axis fabrics show no distinct patterns related to dislocation creep, although the strain magnitudes estimated based on deformed radiolarian fossils are high enough that a distinct fabric might be expected to have formed during deformation. Fabric intensities are very low, indicating a random distribution of quartz c-axes. Quartz grains are equant in shape and polygonal, and free of intracrystalline plasticity. These observations suggest that the dominant deformation mechanism in the metacherts was grain-size-sensitive flow (diffusion creep accompanied by grain-boundary sliding) rather than dislocation creep, possibly reflecting the relatively low strain rate or low flow stress compared with that in high-strain zones. The development of grain-size-sensitive flow in metamorphic tectonites at mid-crustal conditions would result in a significant decrease of the rocks strength of the continental middle crust. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2010.06.002

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Language：Japanese   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   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

We investigated grain growth process of quartz aggregates in agate. The agate samples were annealed in a piston-cylinder solid medium apparatus (MK65S) of Shizuoka University. The experiments were performed at temperature of 800°C, confining pressure of 0.5 GPa for 0.5 hr, 24 hr and 66 hr, respectively. The agates were well crystallized during experiments. Mean grain sizes increased from a few to ten microns with increasing time. Aspect ratios were nearly constant at around 0.7 (<i>b/a; b</i> < <i>a</i>). Shape preferred orientation (SPO) of quartz grains were developed with increasing time. Crystal-preferred orientation of <i>c</i>-axes, which were primarily girdled, appears to control the development of SPO with time.

DOI： 10.51053/shizuoka.37.0_13

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

Elastic wave velocities were measured on a deep seafloor serpentinite sample at room temperature and confining pressures of up to 180 MPa, using a high-pressure apparatus at University of Toyama. The sample was collected from a dredge site D17 at the Godzilla Megamullion, Parece Vela Rift, Phillipine Sea during the cruise KR07-02 (R/V Kairei). The serpentinite sample has the density of 2.37 g/cm³ and consists mainly of lizardite, chrysotile and magnetite, showing a banded structure with a moderately developed lineation and foliation. Mutually orthogonal axes were set for velocity measurements; the <i>x</i>-axis is parallel to the lineation, and the <i>z</i>-axis normal to the foliation. Lizardite mainly has a mesh texture, whereas fibrous chrysotile fills veins, most of which are subperpendicular to the lineation. The compressional wave velocity at 180 MPa is the fastest (4.56 km/s) in the <i>y</i>-axis direction, the slowest (3.97 km) in the direction parallel to the lineation (<i>x</i>-axis direction), and intermediate (4.25 km/s) normal to the foliation (<i>z</i>-axis direction). The azimuthal anisotropy is 13.85% at 180 MPa. The shear wave velocity at 180 MPa is 2.07~2.35 km/s. The shear waves oscillating parallel to the <i>yz</i>-plane have the fastest velocity, and that normal to the <i>yz</i>-plane the slowest. The polarization anisotropy is thus strong along the <i>y</i>- (9.35%) and <i>z</i>- (12.24%) axes, whereas weak along the <i>x</i>-axis (1.39%). Based on microstructural examinations, observed velocity anisotropy may be mainly controlled by the orientation of chrysotile veins rather than the banded structure.

DOI： 10.51053/shizuoka.37.0_27

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

We investigated grain growth process of quartz aggregates in flint. The agate samples were annealed in a piston-cylinder solid medium apparatus (MK65S) of Shizuoka University. The experiments were performed at temperature of 800°C, confining pressure of 1 GPa for 8 hr, 12 hr and 36 hr, respectively. The flints were well crystallized during experiments. Mean grain sizes increased from 1 to 5 µm with increasing time. Aspect ratios were nearly constant at around 0.7 (<i>b/a; b</i> < <i>a</i>). Neither shape preferred orientation nor crystal-preferred orientation of quartz grains occurred with increasing time. Comparing with grain growth experiments for agate in previous studies, the grain growth rate of quartz in flint was faster than that of quartz in agate.

DOI： 10.51053/shizuoka.37.0_21

CiNii Research

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

DOI： 10.14945/00005290

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

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

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

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

DOI： 10.14945/00005288

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Geoscience Reports of the Shizuoka University  

We investigated grain growth process of quartz aggregates in flint. The agate samples were annealed in a piston-cylinder solid medium apparatus (MK65S) of Shizuoka University. The experiments were performed at temperature of 800°C, confining pressure of 1 GPa for 8 hr, 12 hr and 36 hr, respectively. The flints were well crystallized during experiments. Mean grain sizes increased from 1 to 5 μm with increasing time. Aspect ratios were nearly constant at around 0.7 (b/a; b < a). Neither shape preferred orientation nor crystal-preferred orientation of quartz grains occurred with increasing time. Comparing with grain growth experiments for agate in previous studies, the grain growth rate of quartz in flint was faster than that of quartz in agate.

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Geoscience Reports of the Shizuoka University  

We investigated grain growth process of quartz aggregates in agate. The agate samples were annealed in a piston-cylinder solid medium apparatus (MK65S) of Shizuoka University. The experiments were performed at temperature of 800°C, confining pressure of 0.5 GPa for 0.5 hr, 24 hr and 66 hr, respectively. The agates were well crystallized during experiments. Mean grain sizes increased from a few to ten microns with increasing time. Aspect ratios were nearly constant at around 0.7 (b/a; b < a). Shape preferred orientation (SPO) of quartz grains were developed with increasing time. Crystal-preferred orientation of c-axes, which were primarily girdled, appears to control the development of SPO with time.

Scopus

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

DOI： 10.14945/00005289

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

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Calcite-dolomite solvus geothermometry is a versatile method for the estimation of metamorphic temperature because of its simplicity. However, in medium- to high-grade metamorphic rocks the accuracy of estimating temperature by the integration of unmixed dolomite and calcite is hampered by the heterogeneous distribution of unmixed dolomite, difficulties in distinguishing between preexisting and exsolved dolomite and demarcating grain boundaries. In this study, it is shown that calcite-dolomite solvus thermometry can be applied to calcite inclusions in forsterite and spinel for the estimation of peak metamorphic temperature in granulite facies marbles from Skallevikshalsen, East Antarctica. The marbles are comprised of a granoblastic mineral assemblage of calcite + dolomite + forsterite + diopside + spinel + phlogopite +/- apatite, characteristic of granulite facies metamorphic conditions. Forsterite, spinel and apatite frequently contain 'negative crystal' inclusions of carbonates that display homogeneously distributed dolomite lamellae. On the basis of narrow ranges of temperature (850-870 degrees C) recorded from carbonate inclusions compared with the range from matrix carbonate it is regarded that the inclusion carbonates represent a closed system. Furthermore, this estimate is consistent with dolomite-graphite carbon isotope geothermometry, and is considered to be the best estimate of peak metamorphic temperature for this region. Matrix calcite records different stages of retrograde metamorphism and re-equilibration of calcite that continued until Mg diffusion ceased at similar to 460 degrees C. Electron backscattered diffraction (EBSD) results together with morphological features of unmixed coarse tabular dolomite suggest anisotropic diffusion and mineral growth are influenced by crystallographic orientation. Identification of sub-grain boundaries and formation of fine-grained unmixing in calcite rims suggest the presence of grain boundary fluids in the late retrograde stages of metamorphic evolution. These results, thus, demonstrate the usefulness of carbonate inclusion geothermometry in estimating the peak metamorphic temperatures of high-grade terranes and the application of EBSD in understanding the unmixing behaviour of minerals with solid solutions.

DOI： 10.1111/j.1525-1314.2010.00877.x

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The Mohelno peridotite is a medium-sized ultramafic body (2 km x 4 km in size) enclosed in the Gfohl granulites in the eastern part of the Bohemian Massif. It consists mainly of coarse spinel peridotite (harzburgite and dunite); garnet peridotite occurs only in the sheared and deformed margins of the body. To decipher the origin and history of this mantle-derived peridotite, we determined the mineral chemistry by electron microprobe analysis and olivine fabric patterns by the electron backscattered diffraction method for each rock type. We found two distinct types of olivine fabric (crystal-preferred orientation; CPO) in the peridotite, which can be correlated with the mineralogy and thermal history of each. The olivine CPO in coarse-grained spinel peridotite shows a strong concentration of [100] slightly oblique to the lineation and [010] and [001] girdles normal to the lineation (which is the so-called {0kl}[100] pattern typical of medium-temperature deformation). Olivine in coarse-grained garnet peridotite, on the other hand, shows a strong concentration of [010] normal to the foliation and a concentration of [100] parallel to the lineation (which is the so-called (010)[100] pattern typical of high-temperature deformation). These fabric patterns become diffuse as the grain size is reduced for each mineralogical type. We interpret the development of these contrasting fabric patterns and mineralogical types based on the pressure-temperature history of each rock type determined by applying published geothermometers and geobarometers to the constituent minerals. Starting from a high-temperature (&gt; 1200 degrees C) spinel peridotite, during exhumation and cooling in contact with surrounding granulites, the marginal part of the body was transformed to garnet peridotite, whereas the interior remained in the spinel-peridotite facies because cooling was slower inside the body. Because of the slow cooling and continuous deformation in the interior of the body, the original high-temperature fabric pattern in the spinel peridotite was converted to a lower-temperature type. The high-temperature fabric was preserved only at the margin of the body where cooling was more rapid. Reduction of grain size that occurred during later, low-temperature, deformation partly obliterated the high-temperature fabric patterns for both garnet and spinel peridotites. The initial rapid cooling at high temperatures associated with deformation probably occurred after the mantle peridotite was emplaced within the crustal granulites, which implies that the spinel- to garnet-peridotite transformation took place in the continental crust.

DOI： 10.1093/petrology/egp092

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2010.0.280.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2010.0.446.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2010.0.517.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2010.0.197.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2010.0.279.0

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DOI： 10.1038/nature08513

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

Peridotite xenoliths derived from the low velocity zone beneath the Avacha frontal volcano, Kamchatka, preserve a-axis slip fabrics, comparable with those in xenoliths from the back-arc region of the NE Japan. Although low-velocity zones are commonly attributed to zones of partially melted mantle, migration of the melt does not erase the existing olivine fabrics and related seismic anisotropies. These anisotropies may counteract the anisotropies associated with c-axis slip fabrics, if they exist, along the slab or in the high-pressure zone. Citation: Michibayashi, K., T. Oohara, T. Satsukawa, S. Ishimaru, S. Arai, and V. M. Okrugin (2009), Rock seismic anisotropy of the low-velocity zone beneath the volcanic front in the mantle wedge, Geophys. Res. Lett., 36, L12305, doi:10.1029/2009GL038527.

DOI： 10.1029/2009GL038527

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

Two N-S fault zones in the southern Mariana fore arc record at least 20 km of left-lateral displacement. We examined the eastward facing slope of one of the fault zones (the West Santa Rosa Bank fault) from 6469 to 5957 m water depth using the submersible Shinkai 6500 (YK06-12 Dive 973) as part of a cruise by the R/V Yokosuka in 2006. The dive recovered residual but still partly fertile lherzolite, residual lherzolite, and dunite; the samples show mylonitic, porphyroclastic, and coarse, moderately deformed secondary textures. Crystal-preferred orientations of olivine within the peridotites show a typical [100](010) pattern, with the fabric intensity decreasing from rocks with coarse secondary texture to mylonites. The sampled peridotites therefore represent a ductile shear zone within the lithospheric mantle of the overriding plate. Peridotites were probably exposed in association with a tear in the subducting slab, previously inferred from bathymetry and seismicity. Furthermore, although the dive site is located in the fore arc close to the Mariana Trench, spinel compositions within the sampled peridotites are comparable to those from the Mariana Trough back arc, suggesting that back-arc basin mantle is exposed along the West Santa Rosa Bank fault.

DOI： 10.1029/2008GC002197

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

P- (Vp) and S-wave (Vs) velocities of garnet-free (two-pyroxene granulite) and garnet-bearing (garnet granulite and garnet pyroxenite) lowermost crustal rocks collected from the Kohistan arc, northern Pakistan, were measured at 0.1-1.0 GPa and 25-400 degrees C. Garnet granulite had higher Vp (+0.31 km/s) and Vs (+0.27 km/s) than two-pyroxene granulite. Although Vp and Vs increased with increasing volume percent of garnet, plagioclase-free garnet pyroxenite showed significantly higher Vp and Vs than plagioclase-rich garnet granulite mainly due to the low Vp and Vs of plagioclase. In contrast, we observed two quasi-linear relationships between Vp (Vs) and SiO(2) content for the garnet-bearing and garnet-free rocks. The garnet-bearing rocks had relatively higher Vp and VS and stronger SiO(2) dependences than the garnet-free rocks. The stronger SiO(2) dependences of Vp and Vs in the garnet-bearing rocks suggest that the garnet formation in mafic to ultramafic rocks (e.g., pyroxenite and hornblendite), having relatively lower SiO(2), leads to more pronounced increases in Vp and Vs than that of relatively felsic rocks (e.g., felsic-to-mafic granulite). Indeed, the Vp and Vs of the garnet pyroxenite were significantly higher than those of garnet granulite but comparable to those of dunite. The significantly high Vp and Vs of the garnet pyroxenite yielded high reflection coefficients between the garnet granulite and garnet pyroxenite of up to 0.13 for P-waves and 0.14 for S-waves, comparable to values expected for Moho reflection. Thus the lithological boundary between plagioclase-rich garnet granulite and plagioclase-free garnet pyroxenite in the lowermost crust of the Kohistan arc corresponds to the seismic Moho discontinuity. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2008.12.010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.107.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.364.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.513.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

In this study of peridotite xenoliths from Ichinomegata volcano, Oga peninsula, NE Japan, we used electron backscattered diffraction to assess the validity of two methods of identifying the olivine slip system that operated during deformation. The xenoliths are harzburgite in composition and contain a distinct foliation and lineation defined by aligned spinel and pyroxene grains. Using the first method, the dominant slip system in olivine was estimated based on the crystallographic preferred orientation (CPO) of olivine with respect to the foliation and lineation. The second method was based on an analysis of subgrain rotation: given that intracrystalline subgrain boundaries were observed within several olivine grains, we measured the misorientation angles across these boundaries to define sets of slip planes, slip directions, and rotation axes. The olivine slip systems estimated using the two methods are essentially identical. The CPO pattern provides an important constraint on the dominant slip system that operated during deformation, whereas the analysis of subgrain rotation yields the slip system responsible for the development of individual subgrain boundaries composed of edge dislocations. The two methods are therefore complementary.

DOI： 10.5575/geosoc.115.288

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.272.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.273.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.511.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.108.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2009.0.363.0

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

Analysis of an in situ fault zone within the Atlantis Massif oceanic core complex (Mid-Atlantic Ridge) provides clues to the relevant deformation mechanisms and their temporal evolution within oceanic crust. IODP EXP304/305 drilled a succession of gabbroic lithologies to a final depth of 1415 m below the sea floor (mbsf), with very high recovery rates of up to 100% (generally similar to 80%). We identified an intra-crustal fault zone between 720 and 780 mbsf in a section of massive gabbro, olivine gabbro, oxide gabbro units, and minor diabase intrusions of particular interest is the section between 744 and 750 mbsf, which unfortunately was marked by low recovery rates (17%). Electrical borehole-wall images show a I-m-thick zone of east-dipping fractures within this interval, which is otherwise dominated by N-S dipping structures. Despite the high fracture density in this section, the hole walls are smooth, with rare breakouts, suggesting that the low recovery rate was due to a change in lithology rather than well conditions. The recovered rocks include ultracataclasite and possibly incohesive fault gouge that formed in the upper amphibolite regime, with mostly amphibole infill. Logging data suggest that the gabbroic rocks in this interval are rich in hydrous phases, consistent with increased amounts of amphibole found in the core. Equilibration temperature conditions of about 640 degrees C were obtained for plagioclase clasts and aluminous actinolite, assuming a pressure of 200 MPa. The permeability of the fault zone is in the range of 10(-19) to 10(-17) m(2). Although the permeability appears to be high within the fault zone relative to other parts of the section, it is no higher than that in typical lower crustal material. As a consequence, because brittle failure occurred at high temperatures, the fault zone was subsequently completely sealed by hydrous minerals, thereby preventing further fluid circulation and preserving water in the crust. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2008.08.033

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

Microstructural and petrological analyses of gabbroic rocks sampled from the Godzilla Mullion, located along the Parece Vela Basin spreading ridge (Parece Vela Rift), Philippine Sea, reveal the development of a ductile shear zone in the lower crust. The shear zone is interpreted to represent a detachment fault within an oceanic core complex. Microstructures indicative of intense deformation. characterized by porphyroclastic textures consisting dominantly of coarse plagioclase porphyroclasts and lesser clinopyroxene porphyroclasts in a fine-grained matrix, are observed within samples of gabbroic rocks dredged near the breakaway area of the Godzilla Mullion (dredge site D6). Samples are classified into three types based upon the grain-size of fine-grained plagioclase in the matrix: coarse (80-130 mu m), medium (25 mu m), and fine (similar to 10 mu m). Although the chemical composition of plagioclase porphyroclasts is consistently An 40-50 among all sample types, the compositions of fine grains in the matrix vary with decreasing grain-size, being An 40-50 for the coarse-type, An 30-40 for the medium-type, and An 5-30 for the fine-type. This finding implies that the composition of fine-grained plagioclase in the matrix is related to the following retrograde reaction that occurred during deformation: clinopyroxene+plagioclase+Fe-Ti oxide+fluid -&gt; hornblende+plagioclase. Plagioclase crystal-preferred orientations also show a gradual change with grain-size, varying from a (010)[100] pattern for the coarse-type, (010)[100] and (001)[100] patterns for the medium-type, and a weak (001)[100] pattern or random orientations for the fine-type. These patterns are interpreted to result from a change in the deformation mechanism of plagioclase from dislocation creep to grain-size-sensitive creep with decreasing temperature, thereby leading to strain softening and localization during cooling. Although secondary amphibole occurs ubiquitously within all samples, the chemical composition of amphibole varies from pargasitic hornblende (i.e. brown hornblende) to actinolite (i.e. green hornblende) within each of the sample types. However, amphibole in the coarse-type shows no evidence of deformation, whereas brown hornblende in the medium- and fine-types is plastically deformed. As a consequence, we argue that the microstructural development of the gabbroic rocks occurred during uplift-related cooling of the gabbro body and that a primary shear zone developed near the breakaway area at depth under anhydrous conditions at high temperatures above 850 degrees C; the shear zone subsequently evolved during progressive retrogression in association with hydration of the shear zone, possibly resulting in the development of the detachment fault that gave rise to the Godzilla Mullion. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2008.06.009

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Various ZnO morphologies with hexagonal cross sections were fabricated by a thermal oxidation method. Depending on the growth temperature, the lateral lengths of the hexagonal cross section varied from several hundred nanometers to the micrometer order. Comparing the cathodoluminescence (CL) of the synthesized ZnO to that of commercial ZnO:Zn phosphor revealed that a strong luminescence can be realized in undoped ZnO by fabricating one-dimensional structures. Specifically, in the micropyramid and towerlike structures, the CL intensity is locally concentrated near the hexagonal boundary. The enhanced green emission in these structures can be qualitatively explained by whispering gallery resonance modes produced in the hexagonal microcavity. (c) 2008 American Institute of Physics. [DOI:10.1063/1.2990050]

DOI： 10.1063/1.2990050

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

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

B-type olivine fabrics are pervasive within highly depleted dunites of the small-sized Imono peridotite body located within the subduction-type Sanbagawa metamorphic belt of the southwest Japan arc. The dunites contain various microstructures, ranging from porphyroclastic to fine-grained intensely sheared textures. The Mg/(Mg+Fe) atomic ratios (Fo number) of olivine within these dunites are consistently around 0.9, as are the Cr/(Cr+Al) atomic ratios (Cr number) of chromian spinel, suggesting their evolution from a highly depleted magma (boninite). These data provide strong thermal constraints on the formation of the highly depleted dunites,as their formation requires hot, hydrous, shallow mantle (&gt; 1250 degrees C at &lt; 30 km depth) in the mantle wedge. Because the Sanbagawa metamorphic belt finally entrained these peridotites during progressive retrogression, B-type olivine fabrics probably developed in the fore-arc side of the subduction zone, above or along the subducting slab, possibly in association with dehydration fluids derived from the slab. The previously documented small magnitude of S-wave splitting can be explained by the seismic properties of B-type peridotites within an anisotropic layer of approximately several kilometers in thickness, oriented by flow parallel to the subducting slab, under maximum temperatures of 880-1030 degrees C depending on the flow stress. These findings indicate that such a B-type layer could constitute a dominant source of seismic S- and P-wave anisotropy in mantle wedge regions. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2008.06.014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Geosciences, Faculty of Science, Shizuoka University  

Synthetic quartz aggregates as a starting material for high-temperature / high-pressure deformation experiments were prepared using a high-temperature / high-pressure apparatus. Silica gel was prepared using a sol-gel method and subsequently dried and heated in air for three days at temperatures between 700 and 1000°C Various sets of the gels were then packed into Pt-Ni capsules with 0–2 wt% water and were sintered to form quartz aggregates at 800°C and 1 GPa for 5 hours. As a result, synthetic quartz aggregates with polygonal textures and very weak crystallographic preferred orientations were formed from a 1:4 mixture of two silica gels dried at 700°C and 1000°C, respectively.

DOI： 10.51053/shizuoka.35.0_45

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

DOI： 10.14945/00003618

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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Tokyo Geographical Society  

&emsp;Peridotites derived from the uppermost mantle consist dominantly of olivine and subsequently of pyroxene, spinel, garnet, and plagioclase. Crystal-plastic flow of mantle rocks results in various types of structure within peridotite being developed to varying degrees, depending upon the structure sensitivity of the different mineral phases. Plastic deformation leads to the simultaneous development of shape-preferred orientations and crystal-preferred orientations. A shape-preferred orientation is the expression of the average orientation of flattening (foliation) and elongation (lineation) directions, as defined by the orientations of individual grains. A crystal-preferred orientation (CPO) is the expression of crystallographic orientations of grains within the rock, as developed via dislocation creep and recrystallization. During intense homogeneous plastic deformation of a peridotite composed of minerals with a dominant slip system, the preferred orientation of the slip plane and slip direction tends to coincide with the plane of plastic flow and the flow direction, respectively. Recently, a new olivine CPO classification (A, B, C, D, and E types) has been proposed by Karato and co-workers to illustrate the roles of stress and water content as controlling factors of olivine slip systems. An additional CPO type (AG) has also been proposed in recognition of its common occurrence in nature. Given that olivine and the other constituent minerals in peridotites contain intrinsic elastic anisotropies, the development of CPO within peridotite during plastic deformation gives rise to seismic anisotropy in the upper mantle. Thus, the anisotropic properties of mantle rocks derived from the upper 100 km of the mantle, such as Ichinomegata peridotite xenoliths from the northeast Japan arc, have been calculated and applied with the aim of understanding the seismic anisotropy of the Earth's mantle.

DOI： 10.5026/jgeography.117.93

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2008.0.489.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2008.0.485.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2008.0.251.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2008.0.490.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2008.0.247.0

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2008.0.249.0

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CiNii Research

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CiNii Research

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CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024798

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

We retrieved samples of peridotite from a dredge haul (K1192-1-D2) collected during Cruise KE92-1 undertaken by the research vessel (R/V) Hakuho in 1992 at the landward trench slope of the southern Mariana Trench (11 degrees 41.16'N, 143 degrees 29.62'E; depth 6594-7431 m), which is the deepest ocean in the world. Ten of 30 retrieved samples possessed both a foliation and lineation, as assessed from 46 thin sections of various orientations and observations of hand samples. The samples showed marked variation in microstructure, ranging from coarse (&gt; 5 mm) equigranular and intensely elongated textures to finer (&lt; 1 mm) porphyroclastic and fine-grained equigranular textures. Olivine fabrics also varied among the different samples, with (010)[100] and (010)(001] patterns (termed A- and B-type, respectively) observed in samples with coarse textures and no clear patterns observed in samples with fine textures. Even though the peridotite samples were retrieved from a single dredge site, some contain primary tectonic microstructures and some contain secondary microstructures. Recent bathymetric and topographic analyses indicate that the lithosphere in this region is as thin as 20 km. Such a thin lithosphere may have been intensely deformed, even perhaps in the ductile regime, during fore-arc extension; consequently, the observed variations in microstructure within the peridotite samples probably reflect the complex tectonic evolution of the southern Mariana region. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2007.08.010

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

CiNii Research

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

Oceanic core complexes expose gabbroic rocks on the seafloor via detachment faulting, often associated with serpentinized peridotite. The thickness of these serpentinite units is unknown. Assuming that the steep slopes that typically surround these core complexes provide a cross section through the structure, it has been inferred that serpentinites compose much of the section to depths of at least several hundred meters. However, deep drilling at oceanic core complexes has recovered gabbroic sequences with virtually no serpentinized peridotite. We propose a revised model for oceanic core complex development based on consideration of the rheological differences between gabbro and serpentinized peridobte: emplacement of a large intrusive gabbro body into a predominantly peridotite host is followed by localization of strain around the margins of the pluton, eventually resulting in an uplifted gabbroic core surrounded by deformed serpentinite. Oceanic core complexes may therefore reflect processes associated with relatively enhanced periods of mafic intrusion within overall magma-poor regions of slow- and ultra-dow-spreading ridges. ? 2007 The Geological Society of America.

DOI： 10.1130/G23531A.1

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Microstructural analyses of shear band cleavages in a centimeter-scale shear zone within a metasomatic biotite band in the Teshima granite, Ryoke metamorphic belt, southwest Japan, show that strain partitioning Occurred between quartz and biotite-feldspar domains within the shear zone. Pre-tectonic hydrothermal alteration within the granite caused biotite replacement of both plagioclase and K-feldspar, resulting in the development of biotite-feldspar domains where K-feldspar mantles dominantly biotite-plagioclase aggregates. Subsequently, the altered granite was plastically deformed in simple shear, so that intra-layer shear band cleavages were passively developed within the biotite-feldspar domains, whereas intense dynamic recrystallization occurred in the quartz domains. The rotation and orientation of the intra-layer shear band cleavages can be explained by a finite strain ellipse model, which shows that strain in the biotite-feldspar domain requires only 10-20% of the bulk simple shear strain for the development of such cleavages, so that most of strain could be accommodated by deformation in the quartz domain. Consequently, the model suggests that the development of the shear zone resulted in strain partitioning between the quartz and the biotite-feldspar domains due to compositional variations via hydrothermal alteration within the granite. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2007.02.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2007.0.252.0

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024821

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

In this study, the chemistry and microstructure of garnet aggregates within a metamorphic vein are investigated. Garnet-bearing veins in the Sanbagawa metamorphic belt, Japan, occur subparallel to the foliation of a host mafic schist, but some cut the foliation at low angle. Backscattered electron image and compositional mapping using EPMA and crystallographic orientation maps from electron-backscattered diffraction (EBSD) reveal that numerous small garnet (10-100 mu m diameter) coalesce to form large porphyroblasts within the vein. Individual small garnet commonly exhibits xenomorphic shape at garnet/garnet grain boundaries, whereas it is idiomorphic at garnet/quartz boundaries. EBSD microstructural analysis of the garnet porphyroblasts reveals that misorientation angles of neighbour-pair garnet grains within the vein have a random distribution. This contrasts with previous studies that found coalescence of garnet in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation-driven rotation. As garnet nucleated with random orientation, the difference in misorientation between the two studies is due to the difference in the extent of grain rotation. A simple kinetic model that assumes grain rotation of garnet is rate-limited by grain boundary diffusion creep of matrix quartz, shows that (i) the substantial rotation of a fine garnet grain could occur for the conditions of the Sanbagawa metamorphism, but (ii) the rotation rate drastically decreased as garnet grains formed large clusters during growth. Therefore, the random misorientation distribution of garnet porphyroblasts in the Sanbagawa vein is interpreted as follows: (i) garnet within the vein grew so fast that substantial grain rotation did not occur through porphyroblast formation, and thus (ii) random orientations at the nucleation stage were preserved. The extent of misorientation-driven rotation indicated by deviation from random orientation distribution may be useful to constrain the growth rate of constituent grains of porphyroblast that formed by multiple nucleation and coalescence.

DOI： 10.1111/j.1525-1314.2006.00642.x

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

A dense network of seismic stations has been deployed across the northeast Japan arc to investigate mantle wedge structures. To attain independent petrophysical constraints, we determined the seismic properties of Ichinomegata mantle xenoliths from the back-arc region that were brought to the surface from the mantle lithosphere by volcanic eruptions. We calculated the seismic properties of the xenoliths from olivine and pyroxene crystal-preferred orientations and single crystal elastic constants. The small magnitude of measured S-wave splitting ( delay time of 0.22 s in the area where the xenoliths were entrained) can be explained by the average seismic properties of mantle xenoliths for an approximately 20-km thick horizontal anisotropic layer, indicating that the mantle lithosphere could be one of the dominant sources of seismic anisotropy; this layer is possibly related to deformation in the uppermost mantle lithosphere due to back-arc spreading along the northeast Japan arc.

DOI： 10.1029/2006GL025812

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：AIP Conference Proceedings  

The microstructure of garnet aggregates within a metamorphic vein are investigated to constrain the duration of vein formation. Garnet-bearing veins occur subparallel to the foliation of a host mafic schist in the Sanbagawa metamorphic belt, Japan. Microstructural observations using SEM, EPMA and EBSD reveal that numerous small garnets (10-100 μm diameter) coalesced to form large porphyroblasts within the vein. EBSD analysis of the porphyroblasts reveals that misorientation angles of neighbor-pair garnet grains within the vein have a random distribution. This contrasts with previous studies that found coalescence of garnets in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation-driven rotation. The random misorientation angle distribution indicates that (1) garnets within the vein grew so fast that they could not rotate within the vein, and thus (2) random orientations of garnets at the nucleation stage were preserved. On the basis of a simple kinetic model that assumes rotation of garnet is rate-limited by diffusion creep of matrix quartz, the time taken for a small garnet grain to rotate 1° is estimated to be 10 3 - 10 4 years. This duration may indicate the upper limit of the duration of garnet growth, and of vein formation. © 2006 American Institute of Physics.

DOI： 10.1063/1.2207097

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：構造地質研究会  

CiNii Books

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

Subhorizontal mantle structures subparallel to the Moho are rotated into NW-SE subvertical orientations across a shear zone in a sinistral sense of shear within the northern Fizh mantle section of the Oman ophiolite. Dynamic recrystallization resulted in grain size reduction of olivine and the development of porphyroclastic texture. Mean olivine grain size stabilized at similar to 0.7 mm within the shear zone center; this may reflect the steady-state grain size of dynamically recrystallized olivine, as determined by the deviatoric stress, which in this case was as low as 10 MPa. Crystal-preferred orientation (CPO) patterns of olivine are consistently [100]-fiber or partial fiber texture, indicating that olivine slip systems did not change during shearing. Dynamic recrystallization causes a weakening of olivine fabric intensity toward the shear zone center, but this weakening is counterbalanced by CPO strengthening due to dislocation glide. This process resulted in an abrupt decrease in seismic anisotropy at the center of the shear zone, in contrast to a gradual decrease in olivine fabric intensity and mean grain size.
The measured seismic anisotropy patterns did not change in ways that would be significantly measurable by seismological observations. Despite the development of the shear zone, dispersion of both P- and S-waves in the shear zone may be of little effect with respect to the overall seismic anisotropy. This is not only because the shear zone occurs substantially in a narrow region but also because the seismic anisotropy is weaker in the shear zone than the high-T-structure region. It suggests that a record of simple systematic seismic anisotropy observed in the upper mantle may indicate a simplified mantle flow structure, as localized structures may be obscured in the region of the observation. (c) 2006 Elsevier B.V. All fights reserved.

DOI： 10.1016/j.epsl.2006.02.019

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2006.0_95_2

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2006.0_137_2

CiNii Research

Language：English  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Rheology, Japan  

The earth consists of crust, mantle and core. The crust is the earth's surface component, upon which we live. Situated below the crust, the mantle is the dominant component consisting of the earth, making up 80 %. The rheology of the mantle is the key to understanding the working of our mother planet. Peridotite, which is derived from the uppermost mantle, preserves structures and textures that contain information on flow stress and strain (e.g., foliation, lineation and grain size), while the crystal-preferred orientations of minerals (i.e., fabric) reveal the nature of kinematic movement within the mantle. The mantle section of the Oman ophiolite is the largest section of oceanic lithosphere exposed at the earth surface. Extensive structural mapping of these rocks has been conducted throughout the Oman mountain range to unravel mantle processes associated with the generation of oceanic lithosphere. Research in this area demonstrated that the formation of oceanic mantle lithosphere at a fast-spreading ridge involves active mantle flow associated with a mantle diapir. © 2006 The Society of Rheology, Japan.

DOI： 10.1678/rheology.34.291

Scopus

CiNii Research

Language：English  

Web of Science

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The microstructure of garnet aggregates within a metamorphic vein are investigated to constrain the duration of vein formation. Gamet-bearing veins occur subparallel to the foliation of a host mafic schist in the Sanbagawa metamorphic belt Japan. Microstructural observations using SEM, EPMA and EBSD reveal that numerous small garnets (10-100 mu m diameter) coalesced to form large porphyroblasts within the vein. EBSD analysis of the porphyroblasts reveals that misorientation angles of neighbor-pair garnet grains within the vein have a random distribution. This contrasts with previous studies that found coalescence of garnets in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation-driven rotation. The random misorientation angle distribution indicates that (1) garnets within the vein grew so fast that they could not rotate within the vein, and thus (2) random orientations of garnets at the nucleation stage were preserved. On the basis of a simple kinetic model that assumes rotation of garnet is rate-limited by diffusion creep of matrix quartz, the time taken for a small garnet grain to rotate 1 degrees is estimated to be 10(3) - 10(4) years. This duration may indicate the upper limit of the duration of garnet growth, and of vein formation.

Web of Science

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

CiNii Research

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

CiNii Research

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

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024988

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

Interfacial tension (gamma) and differential stress (sigma) affect the shape of a mineral grain included within a crystalline host. We present a simple model that predicts the progressive change in aspect ratio of an ellipsoidal inclusion. Three processes are considered in the model: dislocation creep, interface diffusion creep, and rounding by interface diffusion. The model reveals that (1) the inclusion aspect ratio (L) evolves toward a steady state value, (2) the time taken to achieve a steady state aspect ratio increases with increasing grain size (R), and (3) the dominant deformation mechanism varies from diffusion creep to dislocation creep with increasing grain size and/or differential stress. The L-R distribution pattern of garnets in a granulite-facies quartzite from the Lutzow-Holm Complex, East Antarctica is compared with the model result. The garnet aspect ratio systematically varies with respect to grain size, and the most elongate ones are of intermediate grain size (similar to 250 mm). A two-stage deformation with high and low differential stresses (stage A and B) best explains for the observed L-R pattern of garnets. The duration (t(A)) at stage A is determined only when the differential stress (sigma(A)) is assumed due to the size independency of dislocation creep. Assuming gamma(grtqtz) = 1.0 N m(-1), Dg(b),(A) = 1.0 x 10(-12) m(2) s(-1), D-gb,D-B = 1.0 x 10(-11) m(2) s(-1), and sigma(A) = 1.0 MPa, the garnet data are fitted to a theoretical curve under condition of sigma(B) = 1.4 x 10(-2) MPa, t(A) = 0.5 Myr, and t(B) = 14.4 Myr.

DOI： 10.1029/2004JB003526

Web of Science

Scopus

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

DOI： 10.2204/iodp.sd.1.05.2005

Scopus

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

The Woodroffe thrust, central Australia, is a &gt; 1.5-km-wide mylonitized shear zone marked by large volumes of mm- to cm-scale pseudotachylyte veins. The pseudotachylytes display typical melt-origin features, including rounded and embayed clasts, splierulitic and dentritic microlites, and flow structures within a fine-grained matrix. Three types of pseudotachylyte are identified on the basis of deformation texture, vein morphology, and host-rock lithology: cataclasite-related (C-Pt), myloniterelated (M-Pt), and ultramylonite-related (Um-Pt). The M-Pt and Um-Pt veins intrude into mylonite and ultramylonite and are themselves overprinted by subsequent mylonitization. These pseudotachylytes contain an internal foliation defined by flattened porphyroclasts and layering of the fine-grained vein matrix, and the foliation is generally oriented parallel to foliation in the Surrounding mylonite and ultramylonite. These observations constrain the timing and environment of M-Pt and Um-Pt pseudotachylyte formation to a protracted period of deformation and mylonitization within the ductile regime of the crust. The M-Pt and Um-Pt veins, as well as the host mylonite, are overprinted by cataclasis and multiple generations of late-stage C-Pt veins that were generated in the brittle-dominated regime of the upper crust during uplift and exhumation of the shear zone.
The coexistence of multiple generations of voluminous C-Pt, M-Pt, and Um-Pt veins indicates that the pseudotachylyte veins represent a large number of large earthquakes and accompanying seismic slip over an extended period of seismicity on the Woodroffe thrust. The timing and distribution of pseudotachylyte indicate that the earthquakes nucleated at the base of the brittle-dominated seismogenic zone and propagated down through the brittle-ductile transition into the ductile-dominated regime of the crust. (c) 2005 Elsevier B.V All rights reserved.

DOI： 10.1016/j.tecto.2004.10.016

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：静岡県地学会  

DOI： 10.14945/00024997

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

Hypocenter of the Chi-Chi earthquake is located on the detachment fault distributed approximately 10 km of depth, near the boundary between continental basement and overlying continental shelf sediments. Exhumed section of the basement rocks underwent greenschist facies (350-450℃) metamorphism. Overlying Eocene-Miocene sediments (termed as Slate Belt) also underwent sub-greenschist facies (<350℃) metamorphism. We found an outcrop-scale duplex structure exposed in the Slate Belt, suggesting an outcrop of the detachment fault. The outcrop consists of alternation of sandstone and slate layers. It is notable that pegmatitic, V-shaped quartz veins in the sandstone concentrate beneath the detachment fault, suggesting cracks filled with fluid by hydrofaulting. At this time, overlying slate layers play a major role as an impermeable cap-rock. If the stored fluid beneath the detachment was expelled to the pre-existing link thrust, cracks in the fault zone would propagate and facilitate the rupture process of the earthquake.

DOI： 10.5575/geosoc.111.2.III_IV

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2005.0_178_2

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2005.0_170_1

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2005.0_123_2

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Integrated Ocean Drilling Program  

Integrated Ocean Drilling Program Expedition 305, a joint science program with Expedition 304, was designed to investigate the processes that control formation of oceanic core complexes, as well as the exposure of ultramafic rocks in very young oceanic lithosphere. Prior studies indicated that two main drill sites on Atlantis Massif, on the western rift flank of the Mid-Atlantic Ridge (MAR) at 30°N, could provide key constraints on the structure of the detachment fault zone, rock types exposed at shallow structural levels in the footwall, and their alteration history, as well as that of the volcanic succession in the hanging wall. Expedition 305 deepened Hole U1309D in the footwall of Atlantis Massif to 1415.5 meters below seafloor, with high recovery (average = 74.8%) of dominantly gabbroic rocks. Hole U1309D was logged twice, providing the opportunity for unprecedented core-logging integration for a deep borehole in the oceanic lithosphere. The recovered rocks range from dunitic troctolite, troctolite, (olivine) gabbro, and gabbronorite to evolved oxide gabbro that locally contains abundant zircon and apatite, and diabase. The texture of the dunitic troctolite suggests a cumulate origin. The gabbroic suite from Hole U1309D is among the most primitive recovered from the MAR, with Mg# ranging from 67 to 87. Although alteration mineral assemblages record cooling of gabbroic rocks from magmatic conditions to zeolite facies, a low-temperature phase that reflects alteration at temperatures <500°C is most significant. The overall trends in alteration and the changes in secondary mineralogy downhole suggest that there may be two separate secondary processes that have affected the footwall in the vicinity of Hole U1309D. In the upper ∼840 m, seawater-rock interactions may pervade the gabbroic sequence. Below that depth, the nature of and the fluctuations in degree and style of metamorphism are related to fluids of a different composition percolating along fault/ductile deformation zones. Hence, the core records an extensive history of gabbroic rock-fluid interaction, possibly including magmatic fluids. One of the prominent features of the rocks from Hole U1309D is the lack of extensive amphibolite facies alteration and deformation. This contrasts strongly with the gabbroic suite recovered from Ocean Drilling Program Hole 735B, at the Southwest Indian Ridge. The rocks recovered in Hole U1309D show very little deformation, and any deformation related to a major detachment fault system must have occurred at low temperature and must be strongly localized in the very upper part of the hole. This, together with very minor deformation in the amphibolite facies, is not consistent with the classical "core complex" interpretation of the corrugated, domal massifs on the seafloor resulting from surface exposure of a detachment fault that roots deeply at the base of the lithosphere. In addition, shipboard paleomagnetic measurements indicate there has been no significant net tectonic rotation (5°) of the footwall. This seems to preclude a rolling hinge model for the uplift of the core of Atlantis Massif along a single concave, normal fault. The ∼ 1.4 km sequence of dominantly gabbroic rocks is inconsistent with the initial prediction that the footwall was composed of an uplifted mantle section where serpentinization was responsible for lower densities/seismic velocities in the upper few hundred meters. A more complex model than that put forward before Expeditions 304 and 305 will be required. The fact that we did not reach fresh mantle peridotite, together with the known exposures of serpentinized mantle along the southern ridge of the massif, supports models of complicated lateral heterogeneity in slow-spreading oceanic crust. We have, however, placed a constraint on the magnitude of this heterogeneity - gabbro bodies in this setting can exceed 1.5 km in thickness.

Scopus

Event date： 2018.9

Language：Japanese  

Venue：北海道大学、札幌（北海道胆振東部地震のため中止）   Country：Japan  

Event date： 2018.9

Language：Japanese  

Venue：北海道大学、札幌（北海道胆振東部地震のため中止）   Country：Japan  

Event date： 2018.5

Language：Japanese  

Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Country：Japan  

Event date： 2018.5

Language：English  

Country：Japan  

Event date： 2018.5

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Event date： 2018.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2018.5

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Country：Japan  

Event date： 2018.5

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Event date： 2018.5

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Event date： 2017.11

Language：Japanese  

Venue：東京大学大気海洋研究所，柏   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：東京大学大気海洋研究所，柏   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：愛媛大学、松山   Country：Japan  

Event date： 2017.5

Language：Japanese  

Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2017.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2016.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2016.5

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Venue：幕張メッセ、千葉   Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2015.5

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Country：Japan  

Event date： 2014.4 - 2014.5

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Venue：パシフィコ横浜、横浜   Country：Japan  

Event date： 2014.4 - 2014.5

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Venue：パシフィコ横浜、横浜   Country：Japan  

Event date： 2014.4 - 2014.5

Language：English  

Country：Japan  

Event date： 2012.9

Language：Japanese  

Venue：大阪府立大学、大阪   Country：Japan  

Event date： 2012.9

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Venue：大阪府立大学、大阪   Country：Japan  

Event date： 2012.9

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Venue：大阪府立大学、大阪   Country：Japan  

Event date： 2012.5

Language：Japanese  

Venue：幕張メッセ、千葉   Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2012.5

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Venue：幕張メッセ、千葉   Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2012.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2012.2

Language：Japanese  

Venue：東京大学地震研究所，東京   Country：Japan  

Event date： 2011.9

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Venue：茨城大学、水戸   Country：Japan  

Event date： 2011.9

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Venue：茨城大学、水戸   Country：Japan  

Event date： 2011.9

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Venue：茨城大学、水戸   Country：Japan  

Event date： 2011.9

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Venue：茨城大学、水戸   Country：Japan  

Event date： 2011.9

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Venue：茨城大学、水戸   Country：Japan  

Event date： 2011.5

Language：English  

Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2011.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2011.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.9

Language：Japanese  

Venue：富山大学   Country：Japan  

Event date： 2010.9

Language：Japanese  

Venue：富山大学   Country：Japan  

Event date： 2010.9

Language：Japanese  

Venue：富山大学   Country：Japan  

Event date： 2010.5

Language：Japanese  

Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

Language：Japanese  

Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2010.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2009.9

Language：Japanese  

Venue：岡山理科大学，岡山   Country：Japan  

Event date： 2009.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2009.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2009.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2009.5

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Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2009.2

Language：Japanese  

Venue：東京大学地震研究所，東京   Country：Japan  

Event date： 2008.9

Language：Japanese  

Venue：秋田大学、秋田   Country：Japan  

Event date： 2008.5

Language：Japanese  

Venue：幕張メッセ、千葉   Country：Japan  

Event date： 2008.3

Language：English