研究者詳細 - 道林　克禎

論文 - 道林　克禎

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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 Open Access

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

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

Web of Science

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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 Open Access

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

Open Access

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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 Open Access

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

Open Access

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Geochemical Profiles Across the Listvenite-Metamorphic Transition in the Basal Megathrust of the Semail Ophiolite: Results from Drilling at Oman DP Hole BT1B 査読有り

Marguerite Godard, Elliot J Carter, Thierry Decrausaz, Romain Lafay, Emma Bennett, Fatma Kourim, Juan Carlos de Obeso, Katsuyoshi Michibayashi, Michelle Harris, Jude A. Coggon, Damon Teagle, Peter B Kelemen

Journal of Geophysical Research: Solid Earth 2021年7月

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 Open Access

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 Open Access

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

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 Open Access

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

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 Open Access

道林克禎

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 Open Access

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

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 Open Access

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

Attenuated total reflection infrared (ATR-IR) spectroscopy of antigorite, chrysotile, and lizardite 査読有り国際誌 Open Access

Sakaguchi I., Kouketsu Y., Michibayashi K., Wallis S.R.

Journal of Mineralogical and Petrological Sciences 115 巻 ( 4 ) 頁： 303 - 312 2020年8月

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

Permeability Profiles Across the Crust-Mantle Sections in the Oman Drilling Project Inferred From Dry and Wet Resistivity Data 査読有り国際共著 Open Access

Katayama I., Abe N., Hatakeyama K., Akamatsu Y., Okazaki K., Ulven O.I., Hong G., Zhu W., Cordonnier B., Michibayashi K., Godard M., Kelemen P.

Journal of Geophysical Research: Solid Earth 125 巻 ( 8 ) 2020年8月

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

Permeability profiles in the crust-mantle sequences of the Samail ophiolite were constructed based on onboard measurements of the electrical resistivity of cores recovered during the Oman Drilling Project. For each sample, we measured dry and brine-saturated resistivity during the description campaign on the drilling vessel Chikyu. Owing to the conductive brine in the pore space, wet resistivity is systematically lower than dry resistivity. The difference between dry and wet resistivity is attributed to the movement of dissolved ions in brine that occupies the pore space. We applied effective medium theory to calculate the volume fraction of pores that contribute to electrical transport. Using an empirical cubic law between transport porosity and permeability, we constructed permeability profiles for the crust-mantle transition zone and the serpentinized mantle sections in the Samail ophiolite. The results indicate that (1) the gabbro sequence has a markedly lower permeability than the underlying mantle sequence; (2) serpentinized dunites have higher permeability than serpentinized harzburgites; and (3) discrete sample permeability is correlated with ultrasonic velocity, suggesting that the permeability variations predominately reflect crack density and geometry.

DOI： 10.1029/2019jb018698

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019JB018698

Mariana serpentinite mud volcanism exhumes subducted seamount materials: implications for the origin of life. 査読有り国際共著 Open Access

Fryer P, Wheat CG, Williams T, Kelley C, Johnson K, Ryan J, Kurz W, Shervais J, Albers E, Bekins B, Debret B, Deng J, Dong Y, Eickenbusch P, Frery E, Ichiyama Y, Johnston R, Kevorkian R, Magalhaes V, Mantovanelli S, Menapace W, Menzies C, Michibayashi K, Moyer C, Mullane K, Park JW, Price R, Sissmann O, Suzuki S, Takai K, Walter B, Zhang R, Amon D, Glickson D, Pomponi S

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 378 巻 ( 2165 ) 頁： 20180425 2020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：Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences

The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes. Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life. This article is part of a discussion meeting issue ‘Serpentine in the Earth system’.

DOI： 10.1098/rsta.2018.0425

Workshop report on hard-rock drilling into mid-Cretaceous Pacific oceanic crust on the Hawaiian North Arch 査読有り

Morishita, T, Umino, S, Kimura, J.-I, Yamashita, M, Ono, S, Michibayashi, K, Tominaga, M, Klein, F, Garcia, M.O

Scientific Drilling in press 巻 2020年

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