SCG16-01

会場:201A

時間:5 月 28 日 12:00-12:30

Kinetics of carbide rim growth and the diffusion of carbon in the Earth’s upper mantle
Kinetics of carbide rim growth and the diffusion of carbon in the Earth’s upper mantle
STAGNO, Vincenzo1∗
STAGNO, Vincenzo1∗
1

Geodynamics Research Center, Ehime University (Japan), 2 Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo
152-8550, Japan1
Geodynamics Research Center, Ehime University (Japan), 2 Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo
152-8550, JapanThe speciation of carbon in the interior of the Earth is mainly controlled by temperature, pressure and the oxygen fugacity (fo2)buffered by the surrounding abundant Fe-bearing silicates. Within a peridotitic mineral assemblages the fo2 is thermodynamically
predicted to decrease with the depth until the precipitation of Fe-Ni metal alloy occurs at about 250-300 km down in the mantle.
In addition, the application of a recently calibrated oxybarometer for eclogites suggests that subducted carbonates will be reduced
to diamonds at about 200-250 km depth. Therefore, at such conditions the speciation of subducted carbon will be mainly affectedby the local Fe(Ni)/C ratio, with diamond, Fe3C and C-bearing Fe-Ni alloys being the most likely stable phases. To date, however,no experiments are available 1) to constrain the transport of carbon by diffusion in iron metal at pressures and temperatures of the
Earth ′ s upper mantle and 2) to test the formation of carbide phases at the interface between diamonds/graphite and Fe metal.
We performed multi-anvil experiments between 3 and 10 GPa and temperatures of 700-1200 oC with the aim of measuring C
diffusion in γ-Fe. Glassy carbon, graphite rods and synthetic diamonds were used as diffusants, placed directly in contact withpure iron rod with a thickness of 800-1400 µm. FE-SEM was used for accurate analyses of the Fe-C interface and concentration
profiles of carbon in iron were measured by electron microprobe.
Results show that the diffusion coefficient for carbon in iron metal (˜3x10-11 m2s-1) and the activation energy (˜62 kJ/mol)are similar to previous data from much lower pressures. The activation volume (˜1.5x10-6 m3/mol) obtained from isothermal
runs is in agreement with that determined for other elements for which the interstitial diffusion mechanism in iron has been
established. In addition, experiments revealed the formation of carbide as reaction rim between the diffusant and Fe metal. Time
series experiments were, therefore, performed to investigate the growth kinetics of iron carbide (Fe3C) rim. Results allow to
improve our understanding of the C storage in the Earth’s interior. In addition, our data provide an experimental constraint on
the formation of carbide phases during subduction, with implications for the deep carbon cycle and the C isotopic signature of
eclogitic diamonds.

キーワード: carbide, diffusion, diamonds, eclogites, oxygen fugacity, high pressure
Keywords: carbide, diffusion, diamonds, eclogites, oxygen fugacity, high pressure

1/1

SCG16-02

会場:201A

時間:5 月 28 日 12:30-12:45

Ferromagnesite as a Potential Deep-Mantle Carbon Carrier
Ferromagnesite as a Potential Deep-Mantle Carbon Carrier
LIN, Jung-fu1∗
LIN, Jung-fu1∗
1
1

Department of Geological Sciences, The University of Texas at Austin
Department of Geological Sciences, The University of Texas at Austin

Physical and chemical properties of the potential deep-carbon carriers such as carbonates can play a significant role in our
understanding of the deep-carbon storage as well as the global carbon cycle of the planet. Iron-bearing magnesite, ferromagnesite[(Mg,Fe)CO3 ], has been commonly proposed to be a major carbon carrier in the Earth’s mantle. Studying its elasticity andphase diagram under relevant P-T conditions of the deep mantle is thus important for our understanding of the deep-carbon
storage in the Earth’s interior. Here I will discuss our recent research results on single-crystal elasticity, the spin transition,and the high-pressure structural transition in the (Mg,Fe)CO3 carbonate system in the deep mantle [1-4]. Based on Brillouinexperimental results and thermal elastic modelling, magnesite exhibits extremely high compressional wave (Vp) anisotropy ofapproximately approximately 48 percent and shear wave (Vs) splitting of approximately 40 percent along an expected geothermof the cold subducting slab. These anisotropies are much larger than those of major constituent minerals in the Earth’s upper
mantle including olivine, pyroxene, and garnet. The modeled aggregate Vp and Vs velocities in moderately carbonated peridotite
and eclogite containing approximately 10 wt. percent magnesite (approximately 5 wt. percent CO2 ) show minimal effects ofmagnesite on the seismic profiles of these rock assemblages at upper mantle conditions, suggesting that the presence of magnesite
is likely difficult to be detected seismically in the mantle. However, due to its unusually high Vp and Vs anisotropies, magnesiterich rocks with strong preferred orientations may exhibit sufficient Vp and Vs anisotropies that can have significant influences onseismic anisotropies of the regionally carbonated upper mantle [2]. Using synchrotron X-ray diffraction and Raman spectroscopy
coupled with a diamond anvil cell, we have also studied the phase stability and compressional behavior of ferromagnesite atlower-mantle P-T conditions. An electronic spin transition of iron in the (Mg,Fe)CO3 system occurs at approximately 40 GPa
and can significantly affect its elasticity, phase stability, and chemistry at high P-T [3-4]. Our high-pressure results further showthat rhombohedral ferromagnesite transforms into an orthorhombic high-pressure phase following the spin transition of iron at
mid-lower mantle P-T conditions [1]. The high-pressure orthorhombic phase is found to be in the low-spin state that can becomea stable deep-carbon carrier at deeper parts of the lower mantle below 2000 km in depth. These findings suggest that deepmantle carbonates can exhibit unique physical and chemical properties than that at shallower mantle conditions, affecting ourunderstanding of the deep carbon cycle at extreme environments.
References:
1. J. Liu, J. F. Lin, and V. B. Prakapenka, High-pressure orthorhombic ferromagnesite as a potential deep-mantle carbon
carrier, Scientific Reports, 5, 7640.
2. J. Yang, Z. Mao, J. F. Lin, and V. B. Prakapenka, Single-crystal elasticity of the deep-mantle magnesite at high pressure andtemperature, Earth Planet. Sci. Lett., 392, 292-299, 2014.
3. J. Liu, J. F. Lin, Z. Mao, and V. B. Prakapenka, Thermal equation of state and spin transition of magnesiosiderite at highpressure and temperature, Am. Miner., 99, 84-93, 2014.
4. J. F. Lin, J. Liu, C. Jacobs, and V. B. Prakapenka, Vibrational and elastic properties of ferromagnesite across the electronic
spin-pairing transition of iron, Am. Miner., 97, 583-591, 2012.
キーワード: Ferromagnesite, Carbonate, Mineral Physics, High Pressure, Deep Carbon Cycle, Lower Mantle
Keywords: Ferromagnesite, Carbonate, Mineral Physics, High Pressure, Deep Carbon Cycle, Lower Mantle

1/1

SCG16-03

会場:201A

時間:5 月 28 日 14:15-14:30

Equation of state of Fe3 C under high pressure and temperature with implications for carbon in the Earth’s core.
Equation of state of Fe3 C under high pressure and temperature with implications for carbon in the Earth’s core.
高橋 豪 1 ; 大谷 栄治 1∗ ; 平尾 直久 2 ; 大石 泰生 2
TAKAHASHI, Suguru1 ; OHTANI, Eiji1∗ ; HIRAO, Naohisa2 ; OHISHI, Yasuo2
1

Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, 2 Japan Synchrotron
Radiation Research Institute, SPring-8
1
Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, 2 Japan Synchrotron
Radiation Research Institute, SPring-8

The densities and sound velocities of the Earth’s interior have been known based on the seismological observations, as wellknown as Preliminary Reference Earth Model (PREM). Although the Earth’s core is regarded as an Fe(-Ni) alloy, its density
is lower than that of Fe, and sound velocities of the core could not be explained by those of pure Fe at the core conditions.
Therefore, the Earth’s core is supposed to contain light elements to explain the density deficit and differences of sound velocities
between Fe and the Earth’s core. Carbon is one of the most important candidates for light elements in the Earth’s core. In thisstudy, we focused on the compression behavior of Fe3 C, which is one of the Fe-carbide. We aimed to discuss the possibility of
Fe3 C as the constituent of the Earth’s inner core.
We performed in-situ X-ray diffraction experiments using the diamond anvil cell at BL10XU beamline of SPring-8 facility toobtain pressure and volume relations of Fe3 C. We obtained P -V profiles of Fe3 C at 70˜180 GPa, and ˜2300 K. The equationof state (EOS) of Fe3 C at high temperature conditions was determined using P -V -T relationships. Compressional data werefitted by the 3rd-order Birch-Murnaghan EOS at 300 K and the Mie-Gruneisen-Debye EOS at high temperature conditions. The
parameters of V0 = 152.13(8), K0 = 265.1(6), K’0 = 3.66(1), θ0 = 246(84), γ0 = 1.06(7) and q = 1.5(2) were obtained. The
density of Fe3 C at inner core condition (assuming 329 GPa and 5000 K) calculated from the EOS was compatible with PREM
profiles. Our results indicate that Fe3 C could be dominant in the Earth’s inner core.
Keywords: Earth’s core, Fe3 C, Equation of state, PREM, Density

1/1

SCG16-04

会場:201A

時間:5 月 28 日 14:30-15:00

Carbon isotope compositions in sublithospheric diamonds
Carbon isotope compositions in sublithospheric diamonds
Harte Ben1∗
HARTE, Ben1∗
1
1

CSEC, Earth Sciences, School of Geosciences, University of Edinburgh, Scotland, UK.
CSEC, Earth Sciences, School of Geosciences, University of Edinburgh, Scotland, UK.

Studies of silicate and oxide mineral inclusions in diamonds have provided evidence of a small number of diamonds formed at
depths of approximately 250 to 800 kms in the Earth’s mantle. The major source of these diamonds is kimberlites of Cretaceous
age from Juina province, Brazil; but small numbers of similar diamonds have been found on most of the world’s continents. On
the basis of their inclusions, the diamonds have been divided into three major groups (ref 1) as follows: (a) majoritic garnet suite(basic bulk compositions and relatively Ca-poor); (b) perovskite and periclase suite (dominantly ultrabasic Mg-rich bulk compositions); (c) Ca-rich suite (with Ca-Si-Ti minerals, carbonates and some aluminous silicates). The estimated principal depthsof formation these groups are respectively in the ranges of: (a) 250-500 km; (b) 650- 750km: (c) 300-550 km.
The Carbon isotope compositions of the diamonds hosting the above suites of inclusions show some marked differences. Majoritic suite inclusions of group (a) have δ 13 C in the range of -5 to -24 ‰. The ultrabasic inclusions of group (b) have δ 13 C
compositions in the range -3 to -7 ‰. However, some rare inclusions of basic composition from the same depth range as theultrabasic inclusions have δ 13 C extending to -24 ‰ (ref 2), as with the majoritic suite. In group (c) the diamonds largely range inδ 13 C from -3 to -25 ‰. The highly negative δ 13 C values have been considered to indicate carbon of organic origin and therefore
suggest derivation from subducted ocean floor protoliths (refs 3, 4, 5, 6). Other evidence of initial ocean floor protoliths is shown
by Eu anomalies in some majoritic inclusions, and the occurrence of some highly aluminous phases in group (c). A very small
number of diamonds with δ 13 C close to 0 (zero), may indicate a marine carbonate source.
The nature of the ultrabasic protoliths yielding diamonds with δ 13 C values of -3 to -7 is particularly interesting. These carbon
isotope values are regarded as typical of the mantle. But what is the petrological history of this mantle? Given the evidence ofan ocean floor origin for the protoliths of the other inclusion suites, it is suggested that the mantle protolith for the ultrabasic
inclusions also formed part of the oceanic lithosphere before being subducted. Unlike basic rock compositions forming the ocean
crust, the ultrabasic rocks of the oceanic mantle lithosphere were probably too far below the ocean floor to acquire organic carbon- thus they retained their primitive mantle carbon signatures, although they may have undergone hydration.
With subduction, the oceanic lithosphere may give rise to a stagnant slab lying close to the upper/lower mantle boundary (refs
1 and 7). During descent of the slab, dehydration reactions may give rise to fluids/melts from which the diamonds of groups (a)and (b) crystallised (ref 4). In the accompanying image for the Juina diamonds at 101 Ma, the formation of diamonds of groups(a) and (b) is indicated by the red and green diamond shapes respectively. Once formed these are represented by the solid circularshapes and transported with the stagnant slab. Diamonds with Ca-rich inclusions (group c) are suggested to form in association
with carbonatitic melts (ref 5), which also transport all diamonds towards the continental lithosphere of the Amazonion craton.

1/1

SCG16-05

会場:201A

時間:5 月 28 日 15:00-15:15

Carbon isotopes in a Juina diamond with carbonate inclusions
Carbon isotopes in a Juina diamond with carbonate inclusions
PINTI, Daniele1∗ ; ISHIDA, Akizumi2 ; TAKAHATA, Naoto2 ; SANO, Yuji2
PINTI, Daniele1∗ ; ISHIDA, Akizumi2 ; TAKAHATA, Naoto2 ; SANO, Yuji2
1
1

GEOTOP-Universite du Quebec a Montreal, Canada, 2 Atmosphere and Ocean Research Institute, The University of Tokyo
GEOTOP-Universite du Quebec a Montreal, Canada, 2 Atmosphere and Ocean Research Institute, The University of Tokyo

Juina super-deep diamonds are formed at the transition zone, between the upper and the lower mantle. They contain numerous
mineral inclusions such as carbonates. Although rare, the occurrence of carbonates in the transition zone or even the lower mantle
suggests that the Earth’s global CO2 -cycle has an ultra-deep extension. Some authors have pointed out carbonate inclusions as
an evidence of the involvement of subduction-related fluids in the formation of these super-deep diamonds, and in general of
eclogitic-type diamonds. Here we present new data obtained on three FIB-TEM prepared foils of a Juina diamond that contains
a carbonate inclusion. Carbon isotopic signature (δ 13 C in ‰) was measured together with N content in these foils and calibrated
against a carbonado standard (GM02) with a δ 13 C of -29.2 ‰, using a NanoSIMS 50 at the University of Tokyo. The δ 13 C of asynthetic diamond used for anvil cell experiments and a natural diamond of type IA have been also measured (and conventional
mass spectrometry analyses are under way) to use them as new internal standards and crosscheck the results.
A total of 14 raster analyses (1 x 1 µm) were carried out on the three foils, using a Cs+ beam. We used 2 detectors on
different 3 magnetic fields, so we could estimate and compare three 13 C/12 C ratios. N amount was also determined. Instrumental
mass fractionation (IMF effect) was calculated using the data of GM02. Quasi-simultaneous arrival (QSA) effect was taken into
account and data corrected consequently, because of the large amount of secondary ions observed (above 100,000 cps). Counting
was between 35 and 80 cycles, depending to the variable thickness of the foils (ca. 150 nm) to avoid that the Cs+ beam pierces
the foil and measures C from the TEM carbon grid.
Results showed δ 13 C values in the Juina diamond ranging from -9.1±3.8 ‰ to -0.43±2.82 ‰ with an average δ 13 C value of 4.2 ‰ and a median value of -4.0 ‰. The diamond sample contains also a small amount of nitrogen with an average concentrationof 62 ppm, similar to previously reported concentrations measured by SIMS. These results suggest a peridotitic origin for the
diamond, possibly Type IaB, which is the most abundant class among the Juina diamonds. The origin of this diamond calls foralternative processes to explain the genesis of carbonate inclusions.
キーワード: Carbon cycle, Carbon isotopes, Diamonds, Carbonate, Juina, Transition zone
Keywords: Carbon cycle, Carbon isotopes, Diamonds, Carbonate, Juina, Transition zone

1/1

SCG16-06

会場:201A

時間:5 月 28 日 15:15-15:30

カルボナドダイヤモンドの Os 同位体比と微細組織からみたマントルプロセス
Mantle processes inferred from Os isotopic compositions and micro lectures of carbonado
diamonds
鍵 裕之 1∗ ; 白石 智子 1 ; 仙田 量子 2 ; 鈴木 勝彦 2 ; 淺野 奈津子 3 ; 大藤 弘明 3
KAGI, Hiroyuki1∗ ; SHIRAISHI, Noriko1 ; SENDA, Ryoko2 ; SUZUKI, Katsuhiko2 ; ASANO, Natsuko3 ;OHFUJI, Hiroaki3
1
1

東京大学大学院理学系研究科, 2 海洋研究開発機構, 3 愛媛大学地球深部ダイナミクス研究センター
Graduate School of Science, The University of Tokyo, 2 JAMSTEC, 3 Geodynamics Research Center, Ehime University

Carbonado, a type of natural polycrystalline diamond, has characteristics distinct from those of typical natural diamonds: forexample, no genetic relations to kimberlites, low carbon isotopic ratios, and the lack of mantle-derived mineral inclusions, andso on. Based on these characteristics, several diverse hypotheses have been proposed on the origin of carbonado. At present, noconclusive evidence has been proposed to settle the controversy. The most important point we have to remind is that carbonado
had been heavily altered after the crystallization of diamonds and the grain boundaries of micro-diamonds in carbonado may
have lost the intrinsic information on the formation of diamonds consisting of carbonado.
In this study, we tried to extract geochemical and mineralogical information from inside of diamond grains and grain boundaries, independently. We conducted Os isotopic analysis and electron microscopic observation on carbonado samples collectedfrom placer deposits in the Central African Republic. We obtained very different results between inside of diamond grains andgrain boundaries both on the Os isotopic values and mineralogy of inclusions. The origin of carbonado will be discussed basedon the intrinsic information obtained from the inside of diamond grains.

キーワード: カルボナド, Os 同位体比, 白金属元素組成, 鉱物組織, 包有物, ダイヤモンド
Keywords: carbonado, Os isotopic compositions, platinum group elements, mineral texture, inclusions, diamonds

1/1

SCG16-07

会場:201A

時間:5 月 28 日 15:30-15:45

Oligomerization and carbonization of polycyclic aromatic hydrocarbons at pressures to
16 GPaOligomerization and carbonization of polycyclic aromatic hydrocarbons at pressures to
16 GPaCHANYSHEV, Artem1 ; LITASOV, Konstantin2∗ ; SHATSKIY, Anton2 ; FURUKAWA, Yoshihiro3 ;YOSHINO, Takashi4 ; OHTANI, Eiji3
CHANYSHEV, Artem1 ; LITASOV, Konstantin2∗ ; SHATSKIY, Anton2 ; FURUKAWA, Yoshihiro3 ;YOSHINO, Takashi4 ; OHTANI, Eiji3
1

Novosibirsk State University, Novosibirsk, Russia, 2 VS Sobolev Institute of Geology and Mineralogy, Novosibirsk, Russia,
Graduate School of Science, Tohoku University, Sendai, Japan, 4 Institute for Study of the Earths Interior, Okayama University,
Misasa, Tottori, Japan1
Novosibirsk State University, Novosibirsk, Russia, 2 VS Sobolev Institute of Geology and Mineralogy, Novosibirsk, Russia,
3
Graduate School of Science, Tohoku University, Sendai, Japan, 4 Institute for Study of the Earths Interior, Okayama University,
Misasa, Tottori, Japan3

We have examined the stabilities of different polycyclic aromatic hydrocarbons (PAHs) at pressures up to 16 GPa and temperatures to 1273 K. Experiments were performed using a large-volume multi-anvil apparatus. Quenched products were analyzed
by matrix-assisted laser desorption/ionization (MALDI) and Raman spectroscopy. The MALDI measurements revealed the considerable oligomerization of PAHs at 7 GPa and 773 to 873 K and insignificant PAH oligomerization at 16 GPa and 300 K. At
7 GPa and 773 K, oligomers with atomic masses up to 3400 Da and higher were found, while only a small number of dimersof the starting PAHs were detected at 16 GPa and 300 K. PAH decomposition at 7 GPa occurred from 873 to 973 K, and thedecomposition products consisted of nanocrystalline graphite. We also obtained solid-liquid-(C+H2 ) triple points by in situ Xray diffraction and X-ray radiography and found that they are located at relatively low pressures of 1-2 GPa for naphthalene,
acenaphthene, pyrene, and coronene. Previously determined melting lines to 4-5 GPa were thus subjected for revision. The
determined decomposition temperatures of the PAHs (873-973 K) are much lower than Earth’s geotherms and the subductionslab P-T profiles at 6-7 GPa; therefore, PAH inclusions in mantle-derived minerals, which can be crystallized at 6 to 7 GPa and1600 to 1700 K, should be secondary phases and could be formed by the successive polycondensation of simple hydrocarbon
molecules under natural catalysts during eruption processes at sub-ambient pressures and temperatures. We also rebutted thehigh-temperature stability of PAHs suggested by previous shock compression experiments and theoretical predictions. However,metastable formation of PAHs in shock experiments at high PT-conditions may still be possible.

キーワード: high pressure, polycyclic aromatic hydrocarbons, carbon, oligomerization
Keywords: high pressure, polycyclic aromatic hydrocarbons, carbon, oligomerization

1/1

SCG16-08

会場:201A

時間:5 月 28 日 15:45-16:00

沈み込み帯における水素の発生源と有機炭素の空間分布
Spatial distribution of hydrogen production zone and organic carbon in the oceanic crust
安藤 祐美 1∗ ; 岡本 和明 1
ANDO, Yumi1∗ ; OKAMOTO, Kazuaki1
1
1

埼玉大学教育学研究科
Graduate school of education, Saitama University

Hydrothermal activity in the Archean-Ridge system has been considered to play a major role to maintain the oldest biospherein early Earth. In the present ridge-system, hydrogen production in the serpentinized peridotite layer, is considered as majorenergy source. However, low temperature hydrothermal zone in the lower crust layer in the ridge has been recognized as hydrogen producing zone. Then what is the hydrogen source in the oceanic lower crust? Accreted oceanic plateau is one of thebest sample to describe hydration process due to deep-sea-hydrothermal alteration because it is easy to observe huge outcrops
and collect samples systematically in whole section. We have collected rock samples from the Mikabu high P/T rocks in Toba
area, central Japan and from Ootoyo area, central Shikoku, Japan because there are large scale trench cliffs in the mine. Here, wereport mineral composition surrounding organic carbon that was found in metabasaltic rocks from Otoyo area. The metabasalt
underlies metachert, and exhibit extensive plagioclase veins. Carbonaceous material and FeS are concentrated near the veins.
Serpentinization of olivine gabbro was recognized in the metabasalt layer as lensoid body. In the Toba area, wehrlite and hornblende gabbro are dominant as the oceanic lower crustal material, subsequently suffered high P/T metamorphism. Abundant
serpentine with magnetite are along olivine grain boundaries. Cr-spinel and epidote are occasionally recognized. That is, hydrogen was produced due to hydration reaction in the intruded wherlite from the lower crust of the large plateau. Thus the graphiteprobably from organic carbon in the metabasalt suffered high P/T subduction zone metamorphism. In order to know the fate of
the graphite in deep subduction zone, we have observed the Sanbagawa eclogite (Tonaru eclogite) accompanying cupper-ironsulfides (so called Besshi mine type Cu-Fe sulfides). In the eclogite, Cu-Fe sulfides contain silicate with graphite as inclusion.
The graphite crystallization temperature calibrated using laser Raman peak shift, is estimated as 300-340 ℃. It is obviously
lower than that of the metamorphic temperature of the eclogite 550-600 ℃. It clearly suggests that graphite was probably fromthe micro-bacteria with Cu-Fe sulfides in the hydrothermal zone in the Mid-oceanic ridge system. In summary, the lower crustmight be significant zone producing hydrogen, and provide bacteria cluster above, and subsequently the organic carbon would
be recycled down deep in the mantle via subduction zone.
キーワード: 沈み込み帯, 有機炭素
Keywords: deep subduction zone, organic carbone

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SCG16-09

会場:201A

時間:5 月 28 日 16:15-16:30

弾性波速度を用いた海底泥火山の炭化水素ガスフラックス推定の試み
Hydrocarbon gas efflux from an active deep-water mud volcano constrained by seismic
velocity profiles
喜岡 新 1∗ ; 大塚 宏徳 1 ; 辻 健 2 ; 芦 寿一郎 1
KIOKA, Arata1∗ ; OTSUKA, Hironori1 ; TSUJI, Takeshi2 ; ASHI, Juichiro1
1

東大・大気海洋研, 2 九大・カーボンニュートラル・エネルギー研
Dept. Ocean Floor Geosci., Atmos. Ocean Res. Inst., UTokyo, Japan, 2 CO2 Stor. Res., Int’l. Inst. Carbon-Neutral EnergyRes., Kyushu Univ., Japan1

泥火山は地球上の地質現象の中で最も多量の炭化水素ガスを大気中に放出するソースであると考えられている。海底
泥火山から放出されるガスの組成や起源の解明について様々な研究が行われており、生物起源と熱分解起源のメタンが主であることがわかっている。そして近年の長期観測によって、海底泥火山から放出されるメタン量は予想された以上に多いことがわかってきた。しかしながら、深部掘削や in-situ での測定等が必要なため、海底泥火山内部に潜在するメタン量の推定は困難である。そこで本研究では、弾性波速度からガス量を算出するスキームを考えた。このモデルにより、例えば構造探査で得られるデータを用いて、海底泥火山火道内に存在するメタンガス量を推定することが可能となる。また、海底泥火山からの平均的なメタンガスフラックスを近似的に見積もることもできるであろう。さらに本研究
は、泥火山山体内のメタンガス量の評価だけでなく、泥火山がプレート沈み込み帯ウェッジ内の物質循環に果たす役割
や Missing methane の解明などにも大いに貢献するであろう。本発表では、熊野沖南海付加プリズムに発達する活動
的な海底泥火山へのアプリケーションを紹介する。
キーワード: 海底泥火山, メタンガス量, 弾性波速度
Keywords: Submarine mud volcanoes, methane gas fraction, seismic velocity

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SCG16-10

会場:201A

時間:5 月 28 日 16:30-16:45

Fluid emission along the Nankai Trough: Insights from noble gases in the sediment porewater
Fluid emission along the Nankai Trough: Insights from noble gases in the sediment pore
water
TOMONAGA, Yama1∗ ; ASHI, Juichiro1 ; TAKAHATA, Naoto1 ; YAGASAKI, Kazuhiro1 ; TOYODA, Shin2 ;SANO, Yuji1
TOMONAGA, Yama1∗ ; ASHI, Juichiro1 ; TAKAHATA, Naoto1 ; YAGASAKI, Kazuhiro1 ; TOYODA, Shin2 ;SANO, Yuji1
1

Atmosphere and Ocean Research Institute, The University of Tokyo, 2 Department of Applied Physics, Faculty of Science,
Okayama University of Science
1
Atmosphere and Ocean Research Institute, The University of Tokyo, 2 Department of Applied Physics, Faculty of Science,
Okayama University of Science

Noble-gas geochemistry is known to change in response to the terrigenic fluid emission triggered by major seismic events, as
observed, for instance, in the recent case of the Tohoku-Oki earthquake occurred in 2011. Therefore, characterizing the terrigenic
fluid emission in tectonically active regions is a prerequisite to understand future geochemical changes.
In the present contribution we report the results of the noble-gas and carbon isotope measurements conducted in water andsediment samples collected along the Nankai Trough using the ROV HyperDolphin during RV Natsushima cruises NT13-08 andNT14-07.
In general, sediment cores acquired at active cold seeps at the splay fault off shore Kumano are characterized by the presenceof crustal He and the respective He concentration gradients are highly variable. Sediment cores collected at shallower water
depths show relatively low He concentration gradients and high 3 He/4 He ratios suggesting the presence of mantle He.
The fluid transport dynamics in the investigated area are discussed in the light of the new insights provided by the spatial
distribution of the fluxes and the isotope signature of terrigenic He provided by the present study.
キーワード: He fluxes, subduction zones, terrigenic fluids, transport processes
Keywords: He fluxes, subduction zones, terrigenic fluids, transport processes

1/1SCG16-11

会場:201A

時間:5 月 28 日 16:45-17:00

Geochemical characteristics of submarine hydrothermal plumes near Tokara Islands
Geochemical characteristics of submarine hydrothermal plumes near Tokara Islands
WEN, Hsinyi2∗ ; SANO, Yuji1 ; TAKAHATA, Naoto1 ; ISHIDA, Akizumi1 ; TANAKA, Kentaro1 ;TOMONAGA, Yama1 ; KAGOSHIMA, Takanori1 ; SHIRAI, Kotaro1 ; ISHIBASHI, Jun-ichiro3 ;YOKOSE, Hisayoshi4 ; TSUNOGAI, Urumu5 ; YANG, Tsanyao F.2
WEN, Hsinyi2∗ ; SANO, Yuji1 ; TAKAHATA, Naoto1 ; ISHIDA, Akizumi1 ; TANAKA, Kentaro1 ;TOMONAGA, Yama1 ; KAGOSHIMA, Takanori1 ; SHIRAI, Kotaro1 ; ISHIBASHI, Jun-ichiro3 ;YOKOSE, Hisayoshi4 ; TSUNOGAI, Urumu5 ; YANG, Tsanyao F.2
1

Atmosphere and Ocean Research Institute, The University of Tokyo, Japan, 2 Department of Geosciences, National Taiwan University, Taiwan, 3 Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Japan, 4 Graduate Schoolof Science and Technology, Kumamoto University, Japan, 5 Graduate School of Environmental Studies, Nagoya University, Japan
1
Atmosphere and Ocean Research Institute, The University of Tokyo, Japan, 2 Department of Geosciences, National Taiwan University, Taiwan, 3 Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Japan, 4 Graduate Schoolof Science and Technology, Kumamoto University, Japan, 5 Graduate School of Environmental Studies, Nagoya University, Japan
Recently a new submarine volcano has been discovered near the Tokara Islands (South of Kyushu, Japan) by a multi-beamecho sounder survey. However, only a few geochemical data are available for the investigated area. Therefore, the aim of thisstudy is to characterize the volatile geochemistry of shallow hydrothermal system of volcano in the adjacent region of Tokara Islands. Seawater sampling was carried out by CTD-CMS hydrocasts during the RV Shinsei Maru KS-14-10 research cruise (25thJune ‒ 5th July, 2014) in the region stretching from Kagoshima bay to Daiichi-Amami Knoll. In the vicinity of Tokara Islands(Daiichi-Amami Knoll and Ko-Takara Shima), higher turbidity and lower pH values together with excess 3 He were observed at
the same depth, suggesting the presence of a strong hydrothermal signal. 3 He and CH4 fluxes in this region are estimated to be
0.99-2.6×104 atoms/cm2 /sec and 6-60 ton/year, respectively. There is a positive relationship between the excess 3 He and theexcess 4 He/20 Ne ratio relative to the air saturated seawater value at the ambient temperature, suggesting binary mixing between
atmospheric and volcanic noble gases. The end member for Wakamiko (in Kagoshima bay) samples shows subduction-type
mantle He signature with about 7 RA , while that for Tokara Islands indicates more crustal He share with a value of about 4 RA
(RA is the atmospheric 3 He/4 He ratio of 1.382×10−6 ). The estimated end-member of the carbon isotopic composition of CH4
in Daiichi-Amami Knoll and Ko-Takara Shima are -29.25 ‰ PDB and -23.53 ‰ PDB, respectively. Based on the measured
δ 13 CCH4 values and CH4 /3 He ratios, it is possible to estimate the origin of methane. There show mixing between East Pacific
Rise type abiogenic and thermogenic methane in Tokara Islands, while Wakamiko samples may have been fractionated throughrapid microbial oxidation in the water column.
キーワード: helium, methane, flux, Tokara Islands, shallow submarine hydrothermal plumes
Keywords: helium, methane, flux, Tokara Islands, shallow submarine hydrothermal plumes

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SCG16-12

会場:201A

時間:5 月 28 日 17:00-17:30

ロゼッタ彗星ミッションで得られた知見による地球の炭素と揮発性元素の起源
Origin of carbon and other volatile elements on Earth in the light of the Rosetta cometary
missionマーティー ベルナード 1∗ ; アルトウエグ カスリン 2 ; ロジナ チーム 2
BERNARD, Marty1∗ ; ALTWEGG, Kathrin2 ; ROSINA, Team2
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1

ナンシー岩石地球化学研究所, 2 ベルン大学物理学教室
CRPG-CNRS, 2 Physikalisches Institut, University of Bern

The origin of carbon, water, nitrogen and noble gases on Earth is debated between several cosmochemical sources including
the protosolar nebula, and volatile-rich bodies such as ”wet” asteroids (up to 15 % equivalent water and a few % C) or comets(up to 50 % water ice). Terrestrial noble gases have been interpreted as originating from the solar nebula or from the solar wind.
However, the H and N stable isotope compositions of the atmosphere and the oceans are consistent with an asteroidal, rather
than solar or cometary, contribution. For the latter, this inference is based on D and 15N enrichments in comets. However,this view was recently challenged by the discovery of a Jupiter Family comet (JFC) having a ocean-like D/H ratio. The ESA
Rosetta mission is presently analyzing the morphology, the physical parameters, and the composition of Comet 67P/ChuriumovGerasimenko (67P/CG). On board of the spaceraft, the Rosina instrument (PI. K. Altwegg, Univ. Bern, Switzerland) consistingof double focusing and time of flight mass spectrometers is analyzing gases relased by the comet [1, 2]. The analysis of noble
gases, stable isotopes, and volatile elements sheds constraints on the formation environment of this body, and seem to indicate alimited, but not necessarily negligible, contribution of 67P/CG-type material to the Earth’s oceans and atmosphere and organics.
In particular, the high Ar content of the comet and its implication for terrestrial noble gases will be discussed at the meeting.
[1] Altwegg et al., (2015), Science 347, 126952-1; [2] Hassig et al., (2015); Science 347, aaa0276-1

キーワード: 炭素, 揮発性元素, 彗星 67P/CG, ロジナ
Keywords: carbon, volatile elements, Comet67P/CG, Rosina

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SCG16-13

会場:201A

時間:5 月 28 日 17:30-17:45

月マントル中の炭素
Carbon in lunar mantle
中村 良介 1∗ ; 山本 聡 2 ; 松永 恒雄 2 ; 石原 吉明 3
NAKAMURA, Ryosuke1∗ ; YAMAMOTO, Satoru2 ; MATSUNAGA, Tsuneo2 ; ISHIHARA, Yoshiaki3
1
1

産業技術総合研究所, 2 国立環境研究所, 3 宇宙航空研究開発機構
AIST, 2 NIES, 3 JAXA

月が原始地球への巨大衝突（いわゆるジャイアントインパクト）によって形成されたとすると、その組成は地球の原始マントルの組成を反映しているはずである。衝突直後に地球の周囲に形成される円盤ではシリケイトすら蒸発しており、水や有機物といった揮発性元素の大部分はこの時に失われてしまうはずである。例外があるとすれば地球マントル中にグラファイトあるいはダイヤモンドといった揮発性が非常に低い形態で含まれていた炭素である。
一方、アポロが持ち帰った月の海の玄武岩の多くは発泡した形跡を示す。また１５号や１７号では、火山性ガラスのも採取されており、これらは揮発性の高いガスによってマグマが表面に急激に噴出することで形成されたと考えられている。このガスは月のマントル中に含まれる炭素が、上昇中に酸化されて形成された一酸化炭素ではないかと考えられている（Sato 1979)。
日本の月探査機かぐやに搭載されていたスペクトルプロファイラーは、月で最大の火山性ガラス噴出地帯が、熱の入江に存在することを発見した（Yamamoto 2014)。この火山性ガラスが一酸化炭素のみから生成されたと仮定すれば、必
要なガスの量を見積もり、それを月マントル中の炭素量と結びつけることができる。その総量から、月マントル中の炭素が（１）巨大衝突を得て地球マントルから引き継がれたものであるのか（２）あるいは月形成後にもたらされたものであるのか、について議論する。

キーワード: 地球, 月, マントル, 炭素, リモートセンシング, かぐや
Keywords: Earth, Moon, mantle, carbon, Remote sensing, Kaguya

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