研究者詳細 - 道林　克禎

論文 - 道林　克禎

分割表示 158 件中 21 - 40 件目／全件表示 >>

Cataclastic and crystal-plastic deformation in shallow mantle-wedge serpentinite controlled by cyclic changes in pore fluid pressures 査読有り国際誌

Hirauchi, K; Nagata, Y; Kataoka, K; Oyanagi, R; Okamoto, A; Michibayashi, K

EARTH AND PLANETARY SCIENCE LETTERS 576 巻頁： 117232 - 117232 2021年12月

記述言語：英語出版者・発行元：Earth and Planetary Science Letters

Episodic tremor and slip (ETS) events in the forearc mantle wedge of a warm subduction zone may reflect mixed brittle–ductile deformation of serpentinite in association with high pore fluid pressures. To understand deformation mechanisms and processes occurring in the hydrated mantle wedge, we examined in the Sanbagawa metamorphic belt, SW Japan, an antigorite serpentinite shear zone derived from mantle wedge that was formed under pressure and temperature conditions that correspond to the ETS regions. The serpentinite underwent multiple extensional (mode I) and extensional–shear (mode I–II) failure events at supralithostatic pore fluid pressures (Pf). Such failure events led to drops in Pf (several MPa) and formation of a distributed ‘fault–fracture mesh’. Antigorite precipitation in the fracture openings contributed to an increase in Pf until the failure condition was reached again, and thereby antigorite kinetics controlled the recurrence interval of seismic events. We also suggest that under the low-Pf conditions that facilitate intracrystalline plasticity rather than cataclasis, the newly precipitated antigorite aggregates (localized along shear bands) deform by dislocation creep at a high strain rate and high shear stress, resulting in the transient, accelerated viscous creep that may characterize slow slip transients.

DOI： 10.1016/j.epsl.2021.117232

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Hadal aragonite records venting of stagnant paleoseawater in the hydrated forearc mantle 査読有り

Ryosuke Oyanagi, Atsushi Okamoto, Madhusoodhan Satish-Kumar, Masayo Minami, Yumiko Harigane, Katsuyoshi Michibayashi

Communications Earth & Environment 2 巻 ( 1 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Science and Business Media LLC

<title>Abstract</title>The hadal zone at trenches is a unique region where forearc mantle rocks are directly exposed at the ocean floor owing to tectonic erosion. Circulation of seawater in the mantle rock induces carbonate precipitation within the deep-sea forearc mantle, but the timescale and rates of the circulation are unclear. Here we investigated a peculiar occurrence of calcium carbonate (aragonite) in forearc mantle rocks recovered from ~6400 m water depth in the Izu–Ogasawara Trench. On the basis of microtextures, strontium–carbon–oxygen isotope geochemistry, and radiocarbon analysis, we found that the aragonite is sourced from seawater that accumulated for more than 42,000 years. Aragonite precipitation is triggered by episodic rupture events that expel the accumulated fluids at 10−2–10−1 m s−1 and which continue for a few decades at most. We suggest that the recycling of subducted seawater from the shallowest forearc mantle influences carbon transport from the surface to Earth’s interior.

DOI： 10.1038/s43247-021-00317-1

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その他リンク： https://www.nature.com/articles/s43247-021-00317-1

Major Mineral Fraction and Physical Properties of Carbonated Peridotite (Listvenite) From ICDP Oman Drilling Project Hole BT1B Inferred From X-Ray CT Core Images 査読有り国際共著

Okazaki K., Michibayashi K., Hatakeyama K., Abe N., Johnson K.T.M., Kelemen P.B.

Journal of Geophysical Research: Solid Earth 126 巻 ( 12 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Solid Earth

We quantified mineral proportions in listvenite (completely carbonated peridotite) in Hole BT1B drilled across the basal thrust of the Samail ophiolite by the International Continental Scientific Drilling Project Oman Drilling Project using 3D X-ray Computed Tomography (XCT). We analyzed >250,000 XCT images from a continuous ∼200 m listvenite core. Histograms of the intensity of X-ray attenuation of each XCT core-slice image were fitted assuming that the listvenites are composed of magnesite, quartz, and dolomite. The XCT mineral peaks were confirmed by comparison with chemical mapping data obtained using an X-ray fluorescence (XRF) core scanner. Listvenite matrix is composed almost entirely of magnesite and quartz, consistent with discrete XRD and XRF data. Veins are composed mostly of dolomite. The mean abundance of dolomite in listvenite from BT1B is 11 vol.%, whereas that in core sections within 15 m of the basal thrust is >50 vol.%, suggesting the basal thrust acted as a source of Ca- and CO2-rich fluids. The SiO2:MgO:CaO molar ratio in the entire core from BT1B is 42:52:6, similar to that of onboard XRF data for discrete samples (41:54:5), whereas average Oman peridotites have ratios of (39:60:1), indicating Ca addition perhaps during carbonation. P- and S-wave velocities and density of listvenite are close to those of peridotite and are higher than those of serpentinites. These results suggest that limited material transfer during carbonation and hydration of the Samail ophiolite, except for Ca, CO2, and H2O. Listvenites formed in the mantle wedge above subduction zones may be an overlooked reservoir for carbon in the Earth's interior.

DOI： 10.1029/2021jb022719

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JB022719

Initial Results From the Oman Drilling Project Multi-Borehole Observatory: Petrogenesis and Ongoing Alteration of Mantle Peridotite in the Weathering Horizon 査読有り国際共著

Kelemen P.B., Leong J.A., Carlos de Obeso J., Matter J.M., Ellison E.T., Templeton A., Nothaft D.B., Eslami A., Evans K., Godard M., Malvoisin B., Coggon J.A., Warsi N.H., Pézard P., Choe S., Teagle D.A.H., Michibayashi K., Takazawa E., Al Sulaimani Z.

Journal of Geophysical Research: Solid Earth 126 巻 ( 12 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Solid Earth

The Oman Drilling Project “Multi-Borehole Observatory” (MBO) samples an area of active weathering of tectonically exposed peridotite. This article reviews the geology of the MBO region, summarizes recent research, and provides new data constraining ongoing alteration. Host rocks are partially to completely serpentinized, residual mantle harzburgites, and replacive. Dunites show evidence for “reactive fractionation,” in which cooling, crystallizing magmas reacted with older residues of melting. Harzburgites and dunites are 65%–100% hydrated. Ferric to total iron ratios vary from 50% to 90%. In Hole BA1B, alteration extent decreases with depth. Gradients in water and core composition are correlated. Serpentine veins are intergrown with, and cut, carbonate veins with measurable 14C. Ongoing hydration is accompanied by SiO2 addition. Sulfur enrichment in Hole BA1B may result from oxidative leaching of sulfur from the upper 30 m, coupled with sulfate reduction and sulfide precipitation at 30–150 m. Oxygen fugacity deep in Holes BA3A, NSHQ14, and BA2A is fixed by the reaction 2H2O = 2H2 + O2 combined with oxidation of ferrous iron in serpentine, brucite, and olivine. fO2 deep in Holes BA1A, BA1D, and BA4A is 3–4 log units above the H2O-H2 limit, controlled by equilibria involving serpentine and brucite. Variations in alteration are correlated with texture, with reduced, low SiO2 assemblages in mesh cores recording very low water/rock ratios, juxtaposed with adjacent veins recording much higher ratios. The proportion of reduced mesh cores versus oxidized veins increases with depth, and the difference in fO2 recorded in cores and veins decreases with depth.

DOI： 10.1029/2021jb022729

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JB022729

Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results From Drilling at OmanDP Hole BT1B 査読有り国際共著

Godard M., Carter E.J., Decrausaz T., Lafay R., Bennett E., Kourim F., de Obeso J.C., Michibayashi K., Harris M., Coggon J.A., Teagle D.A.H., Kelemen P.B.

Journal of Geophysical Research: Solid Earth 126 巻 ( 12 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Solid Earth

The transition from the Semail ophiolite mantle to the underlying metamorphic sole was drilled at ICDP OmanDP Hole BT1B. We analyzed the bulk major, volatile and trace element compositions of the mantle-derived listvenite series and metamorphic rocks, with the aim to constrain chemical transfers associated with peridotite carbonation along the ophiolite basal thrust. The listvenite series comprise variously carbonated serpentinites and (fuchsite-bearing) listvenites. They have high CO2 (up to 43 wt.%) and variable H2O (0–12 wt.%). Yet, they have compositions close to that of the basal banded peridotites for most major and lithophile trace elements, with fuchsite-bearing listvenites overlapping in composition with amphibole-bearing basal lherzolites (e.g., Al2O3 = 0.1–2.2 wt.%; Yb = 0.05–1 x CI-chondrite). The protolith of the listvenite series was likely similar in structure and composition to serpentinized banded peridotites which immediately overlie the metamorphic sole elsewhere in Oman. The listvenite series are enriched in fluid mobile elements (FME) compared to Semail peridotites (up to ∼103–104 x Primitive Mantle), with concentrations similar to the underthrusted metabasalts and/or metasediments for Cs, Sr and Ca and sometimes even higher for Pb, Li, As, and Sb (e.g., Li up to 130 μg/g; As up to 170 μg/g). We also observe a decoupling between Sr-Ca enrichments and other FME, indicating interactions with several batches of deep CO2-rich fluids transported along the basal thrust. These results suggest that peridotite carbonation could represent one of the major trap-and-release mechanisms for carbon, water and FME along convergent margins.

DOI： 10.1029/2021JB022733

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Geochemical characteristics of back-arc basin lower crust and upper mantle at final spreading stage of Shikoku Basin: an example of Mado Megamullion 査読有り

Akizawa, N; Ohara, Y; Okino, K; Ishizuka, O; Yamashita, H; Machida, S; Sanfilippo, A; Basch, V; Snow, JE; Sen, A; Hirauchi, KI; Michibayashi, K; Harigane, Y; Fujii, M; Asanuma, H; Hirata, T

PROGRESS IN EARTH AND PLANETARY SCIENCE 8 巻 ( 1 ) 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress in Earth and Planetary Science

This paper explores the evolutional process of back-arc basin (BAB) magma system at final spreading stage of extinct BAB, Shikoku Basin (Philippine Sea) and assesses its tectonic evolution using a newly discovered oceanic core complex, the Mado Megamullion. Bulk and in-situ chemical compositions together with in-situ Pb isotope composition of dolerite, oxide gabbro, gabbro, olivine gabbro, dunite, and peridotite are presented. Compositional ranges and trends of the igneous and peridotitic rocks from the Mado Megamullion are similar to those from the slow- to ultraslow-spreading mid-ocean ridges (MOR). Since the timing of the Mado Megamullion exhumation corresponds to the very end of the Shikoku Basin opening, the magma supply was subdued and highly episodic, leading to extreme magma differentiation to form ferrobasaltic, hydrous magmas. In-situ Pb isotope composition of magmatic brown amphibole in the oxide gabbro is identical to that of depleted source mantle for mid-ocean ridge basalt (MORB). In the context of hydrous BAB magma genesis, the magmatic water was derived solely from the MORB source mantle. The distance from the back-arc spreading center to the arc front increased away through maturing of the Shikoku Basin to cause MORB-like magmatism. After the exhumation of Mado Megamullion along detachment faults, dolerite dikes intruded as a post-spreading magmatism. The final magmatism along with post-spreading Kinan Seamount Chain volcanism were introduced around the extinct back-arc spreading center after the opening of Shikoku Basin by residual mantle upwelling. [Figure not available: see fulltext.].

DOI： 10.1186/s40645-021-00454-3

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Effects of Alteration and Cracks on the Seismic Velocity Structure of Oceanic Lithosphere Inferred From Ultrasonic Measurements of Mafic and Ultramafic Samples Collected by the Oman Drilling Project 査読有り国際共著

Hatakeyama K., Katayama I., Abe N., Okazaki K., Michibayashi K.

Journal of Geophysical Research: Solid Earth 126 巻 ( 11 ) 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Solid Earth

Seismic velocity structures of the oceanic lithosphere are variable due to the variation of alteration and heterogeneities in porosity. In order to interpret geophysically determined velocity structures, it is necessary to understand how the seismic velocity of the oceanic lithosphere is affected by alteration and porosity. We conducted petrological analysis and elastic wave velocity measurements at 200 MPa on mafic and ultramafic rocks drilled from the Samail ophiolite. The elastic wave velocity calculated from the mineral abundances of the ultramafic rocks was sensitive to serpentinization, whereas that of the mafic rocks was nearly independent of the alteration, suggesting that velocity changes with depth in the oceanic crust are mainly due to porosity reduction. Based on the effective medium theory and pressure dependence of the experimentally determined velocity, the change in the porosity was estimated to be 0.04%–0.42% at 200 MPa, indicating porosity reduction by the increase of lithostatic pressure in the oceanic crust in the fast-spreading system such as the Pacific plate. We estimated the degree of hydration in the mantle to account for the geophysical observations based on the laboratory experiments. Both the crustal porosity and mantle serpentinization increase towards the trench due to fracture related plate bending, indicating extensive hydration of the oceanic lithosphere close to the trench. From these estimates, water contents in the oceanic lithosphere were calculated to be as high as 3 wt.% in the shallow crust and 6 wt.% in the upper most mantle, which is significant for water transport into Earth's interior.

DOI： 10.1029/2021jb021923

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JB021923

Transmission Kikuchi diffraction study of submicrotexture within ultramylonitic peridotite 査読有り

Igami Y., Michibayashi K.

Physics and Chemistry of Minerals 48 巻 ( 10 ) 2021年10月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physics and Chemistry of Minerals

Deformed polycrystalline rocks show various crystallographic textures reflecting their imposed deformation histories. However, the textures of ultrafine grains, which are in the submicrometer to nanometer order, may be overlooked depending on the analytical technique used. Thus, we report the first application of transmission Kikuchi diffraction (TKD), which is capable of high-spatial-resolution crystallographic texture analysis, to a fine-grained ultramylonitic peridotite sample in a scanning electron microscope. We successfully obtained TKD maps with an effective spatial resolution of ~ 80 nm and with highly reliable indexing using a conventional W-filament scanning electron microscope with a standard electron backscattered diffraction (EBSD) system. Olivine grains, which were clearly visualized by TKD, were slightly elongated in a direction subparallel to the macroscopic lineation texture. Their shapes were nonuniform with serrated grain boundaries, strongly indicating that the sample has been deformed dominantly by dislocation activity, even though the grain size is in the order of several micrometers or smaller. The combined TKD–transmission electron microscope (TEM) analysis indicated that a slip-system transition from the [100] slip to the [001] slip might have occurred, although the crystals’ preferred orientation patterns were not completely overwritten. The transition might have been sufficiently affected by water infiltration, high differential stress, or both along the transform fault. Thus, TKD efficiently analyzed the crystallographic textures and characterized the subgrain boundaries of polycrystalline rocks consisting of submicrometer-order grains. Moreover, combining the EBSD, TKD, and TEM methods allowed us to perform multiscale analyses of the crystallographic textures of ultrafine-grained deformed rocks, seamlessly linking the millimeter- to nanometer-order scales.

DOI： 10.1007/s00269-021-01161-7

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Crack geometry of serpentinized peridotites inferred from onboard ultrasonic data from the Oman Drilling Project 査読有り国際共著国際誌

Katayama I., Abe N., Okazaki K., Hatakeyama K., Akamatsu Y., Michibayashi K., Godard M., Kelemen P.

Tectonophysics 814 巻頁： 228978 - 228978 2021年9月

記述言語：英語出版者・発行元：Tectonophysics

To assess the geometry of cracks in highly altered peridotites, we analyzed the ultrasonic velocity of serpentinized dunites and harzburgites collected by the Oman Drilling Project (Holes BA1B, 3A, and 4A). First, we estimated the hydrated fraction from grain density to obtain the porosity-free matrix velocity, which indicated complete serpentinization at shallow depths and decreasing hydration at greater depths. We assume that the difference between the solid matrix and measured onboard ultrasonic velocity is attributed to cracks with a spheroidal shape in the samples. Application of the effective medium theory to onboard data, such as P-wave velocity and porosity, indicates that the average pore aspect ratio is mostly between 0.1 and 0.01, and crack density varies from 0.58 to 0.02. We found a positive relationship between aspect ratio and hydrated fraction, suggesting a change in crack shape related to dissolution–precipitation processes during hydration. The relatively high aspect ratio and hence high fluid flux at shallow depths are also consistent with the onboard resistivity data and present-day hydration processes inferred from the borehole fluid chemistry. The inversion of ultrasonic data provides a series of elastic moduli that can be used to make a rough approximation of Poisson's ratio from the onboard data, which is a key physical property for interpreting geophysical observations in the oceanic lithosphere.

DOI： 10.1016/j.tecto.2021.228978

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Metasomatism of the off-cratonic lithospheric mantle beneath Hangay Dome, Mongolia: Constraints from trace-element modelling of lherzolite xenoliths 査読有り国際共著

Kourim F., Wang K.L., Beinlich A., Chieh C.J., Dygert N., Lafay R., Kovach V., Michibayashi K., Yarmolyuk V., Iizuka Y.

Lithos 400-401 巻頁： 106407 - 106407 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Lithos

Interactions of hydrous fluid and melt with dry mantle rocks are known to result in metasomatic alteration of the lithospheric mantle. Here we investigate such interactions that occurred beneath the Hangay Dome, Mongolia, in 22 mantle xenoliths, which were recovered from Cenozoic basalts at the Tsagan, Zala, Horgo, and Shavaryn-Tsaram localities near the village of Tariat. The xenoliths are medium- to coarse-grained spinel lherzolites that exhibit variable degrees of reaction with silicate melt and fluid (indicated by their Fe- and LREE-enrichment and the presence of secondary clinopyroxene, amphibole, phlogopite, apatite, and sulfide). According to their normalized REE patterns and microstructures, the spinel lherzolites were divided into three groups. Group 1 lherzolites contain LREE-depleted clinopyroxene and whole-rock compositions, exhibit a greater number of preserved deformation textures, and are the least affected by metasomatism. These lherzolites are interpreted to represent the sub-continental lithosphere before the rejuvenation processes that occurred during the Cenozoic. Group 3 lherzolites are characterized by partial annealing of pre-existing textures, and LREE-enrichment in clinopyroxenes and whole-rock compositions compared to Group 1 lherzolites. Group 3 lherzolites are interpreted to be the result of the interaction of depleted lithospheric mantle with a basaltic melt during the Cenozoic. The lack of correlation between the intensity of metasomatism, the degree of annealing, and the calculated temperatures of the lherzolites suggests that the Cenozoic basaltic melt percolation postdates the static recrystallization. Group 2 lherzolites exhibit characteristics from both Groups 1 and 3. Numerical modelling of the interaction between depleted lherzolites and basaltic melts evidences that: (i) a single initial liquid may fractionate to produce a range of element patterns: the observed spectrum of REE compositions of the Tariat lherzolites cannot have resulted from simple mixing of basaltic melt with a depleted mantle rocks; instead, it can be explained by chromatographic fractionation during reactive porous melt flow; (ii) highly fractionated element patterns are derived from conventional initial melt compositions and do not imply the existence of exotic melts; and (iii) strong element fractionation can be produced along short distances even at the thin section and mineral scale; this opposes the view that long percolation distances are required to produce significant chromatographic effects: the clinopyroxene core-rim disequilibrium demonstrates that REE variations in clinopyroxene rims were acquired in response to interactions with a more evolved REE-rich melt.

DOI： 10.1016/j.lithos.2021.106407

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Rheological contrast between quartz and coesite generates strain localization in deeply subducted continental crust 査読有り

Asano K., Michibayashi K., Takebayashi T.

Minerals 11 巻 ( 8 ) 2021年8月

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

Deformation microstructures of peak metamorphic conditions in ultrahigh-pressure (UHP) metamorphic rocks constrain the rheological behavior of deeply subducted crustal material within a subduction channel. However, studies of such rocks are limited by the overprinting effects of retrograde metamorphism during exhumation. Here, we present the deformation microstructures and crystallographic-preferred orientation data of minerals in UHP rocks from the Dabie–Shan to study the rheological behavior of deeply subducted continental material under UHP conditions. The studied samples preserve deformation microstructures that formed under UHP conditions and can be distinguished into two types: high-strain mafic–ultramafic samples (eclogite and garnet-clinopyroxenite) and low-strain felsic samples (jadeite quartzite). This distinction suggests that felsic rocks are less strained than mafic–ultramafic rocks under UHP conditions. We argue that the phase transition from quartz to coesite in the felsic rocks may explain the microstructural differences between the studied mafic–ultramafic and felsic rock samples. The presence of coesite, which has a higher strength than quartz, may result in an increase in the bulk strength of felsic rocks, leading to strain localization in nearby mafic–ultramafic rocks. The formation of shear zones associated with strain localization under HP/UHP conditions can induce the detachment of subducted crustal material from subducting lithosphere, which is a prerequisite for the exhumation of UHP rocks. These findings suggest that coesite has an important influence on the rheological behavior of crustal material that is subducted to coesite-stable depths.

DOI： 10.3390/min11080842

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Temporal and spatial mineralogical changes in clasts from Mariana serpentinite mud volcanoes: Cooling of the hot forearc-mantle at subduction initiation 査読有り国際共著

Ichiyama Y., Tsujimori T., Fryer P., Michibayashi K., Tamura A., Morishita T.

Lithos 384-385 巻 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Lithos

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

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Upper mantle seismic anisotropy beneath the Northern Transantarctic Mountains inferred from peridotite xenoliths near Mt. Melbourne, northern Victoria Land, Antarctica 査読有り国際共著

Kim D., Park M., Park Y., Qi C., Kim H., Lee M.J., Michibayashi K.

Journal of Structural Geology 143 巻 2021年2月

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

Microstructural investigations of mantle xenoliths from the Mt. Melbourne area were undertaken to reveal the origin of S-wave splitting beneath northern Victoria Land, Antarctica. The six analyzed peridotites contain various deformation features. The rotated olivine maxima of [100] and [010] into horizontal and vertical orientations, respectively, are classified into five samples with a D-type crystallographic preferred orientation (CPO) and one sample as an A-type CPO. The D-type olivine fabric can be explained by multiple slip systems of {0kl}[100] at low-temperature and high-stress conditions; therefore, both compressional and extensional regimes during subduction and rifting, respectively, could be applied in this study. With an assumption that olivine a-axes are aligned along the direction of mantle flow to form maximum S-wave splitting, the observed delay time of 0.9–1.3 s beneath northern Victoria Land can be partially explained by the anisotropy in the mantle peridotites. The remaining seismic anisotropy can be explained by the presence of melt pockets trapped along tectonic faults that developed perpendicular to the fast S-wave splitting direction. This study therefore demonstrates that the NE–SW-trending S-wave splitting beneath northern Victoria Land, Antarctica, results from the existence of both mantle peridotites as well as melt pockets trapped along the tectonic faults.

DOI： 10.1016/j.jsg.2020.104237

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中部地方渋川地域三波川帯におけるヒスイ輝石の再確認:ダナイト中の細脈構成鉱物としての産出

塩谷輝, 道林克禎, 纐纈佑衣, 榎並正樹

地質学雑誌 127 巻 ( 1 ) 頁： 59 - 65 2021年1月

Orthopyroxene-magnetite symplectite in olivine gabbros from the lower crustal Oman Ophiolite: Oman Drilling Project, Hole GT2A 査読有り

Chatterjee S., Bandyopadhyay D., Takazawa E., Michibayashi K.

Journal of Mineralogical and Petrological Sciences 116 巻 ( 3 ) 頁： 170 - 175 2021年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Mineralogical and Petrological Sciences

Oxidation states within the planetary interior are intrinsically linked with the broad scale tectonism; however, it is difficult to estimate the actual oxidation conditions. Orthopyroxene-magnetite symplectite formed by olivine oxidation may provide a significant clue into such oxidation events. Here we report detailed mineralogical and petrological synthesis of such orthopyroxene-magnetite symplectites from olivine gabbros of Oman Ophiolite (Hole GT2A, ICDP Oman Drilling Project). In order to understand how oxidation affects different olivine compositions, we employed a phase equilibria approach and computed several temperature-composition diagrams at a fixed pressure (1 kbar). Our experiments predict the coexistence of olivine with Fo75-76 and Fo71 with the orthopyroxene (En79 and En76), respectively, which is remarkably similar to the mineral chemistry obtained from the Oman lower crustal gabbros. From the magnetite content, we also infer that the symplectite formation may have taken place over a range of temperatures (600-1000 °C) via subsolidus olivine oxidation and/or melt (oxidizing)-olivine interaction. The latter is more probable, considering the partial occurrence of orthopyroxene and clinopyroxene rim adjacent to the symplectites.

DOI： 10.2465/jmps.201130f

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マントル掘削でのみ解明される地球科学問題 -生命惑星海洋プレートの今を理解する- 査読有り

森下知晃, 森下知晃, 藤江剛, 平内健一, 片山郁夫, 纐纈佑衣, 黒田潤一郎, 岡本敦, 小野重明, 道林克禎, 道林克禎, 諸野祐樹, 山本伸次

地学雑誌 130 巻 ( 4 ) 2021年

中部地方渋川地域三波川帯におけるヒスイ輝石の再確認:ダナイト中の細脈構成鉱物としての産出査読有り

塩谷輝, 道林克禎, 纐纈佑衣, 榎並正樹

地質学雑誌 127 巻 ( 1 ) 2021年

深海掘削計画における基盤岩掘削科学の貴種流離譚査読有り

道林克禎

地学雑誌 130 巻 ( 4 ) 2021年

オマーンオフィオライト陸上掘削試料を用いたハードロック掘削における空隙率測定法の再検討査読有り

長瀨薫平, 片山郁夫, 畠山航平, 赤松祐哉, 岡﨑啓史, 阿部なつ江, 道林克禎, 横山正

地質学雑誌 126 巻 ( 12 ) 頁： 713 - 717 2020年12月

Crustal Accretion in a Slow Spreading Back-Arc Basin: Insights From the Mado Megamullion Oceanic Core Complex in the Shikoku Basin 査読有り国際共著

Basch V., Sanfilippo A., Sani C., Ohara Y., Snow J., Ishizuka O., Harigane Y., Michibayashi K., Sen A., Akizawa N., Okino K., Fujii M., Yamashita H.

Geochemistry, Geophysics, Geosystems 21 巻 ( 11 ) 2020年11月

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

Oceanic core complexes (OCCs) represent tectonic windows into the oceanic lower crust and mantle; they are key structures in understanding the tectono-magmatic processes shaping the oceanic lithosphere. We present a petrological and geochemical study of gabbros collected at the Mado Megamullion, a recently discovered OCC located in the extinct Shikoku back-arc basin. Bathymetry of the Mado Megamullion reveals spreading-parallel corrugations extending 25 km from the breakaway to the termination. Samples from several locations include peridotites, gabbros, dolerite, and rare pillow basalts. Gabbros range from granular to varitextured olivine gabbros and oxide gabbros. The emplacement of these gabbroic rocks within the oceanic lithosphere was followed by a multiphase tectono-metamorphic evolution including (i) dynamic recrystallization within shear zones, developed under granulite- to upper-amphibolite-facies conditions, and (ii) intrusion of highly evolved melts forming felsic segregations. This tectono-metamorphic evolution recalls that of the lower crust from other OCCs worldwide, demonstrating that this OCC exposes deep-seated intrusions progressively exhumed by detachment faulting. Nonetheless, the Mado Megamullion lower crustal gabbros show an unusual crystal line of descent, different from what is reported from mid-ocean ridge lower crustal rocks. We infer that the water-bearing character of the primary melts in this back-arc basin triggered the early precipitation of clinopyroxene, soon followed by amphibole and Fe-Ti oxides. Such modifications in phase saturation are likely to be directly related to the back-arc setting of the Mado Megamullion. If so, the phase assemblages of oceanic gabbros may be a diagnostic for the tectonic setting of lower crustal rocks in ophiolites.

DOI： 10.1029/2020gc009199

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GC009199

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