SGC16-01

日本地球惑星科学連合2016年大会

Research of Helium Isotopes in Taiwan: The Legacy of Dr. Tsanyao Frank Yang
Tsanyao Frank Yang1, *Tefang Lan2, Hsiao-Fen Lee2, Ching-Chou Fu2, Pei-Chuan Chuang1, Wei-Li Hong1,
Vivek Walia3, Hsuan-Wen Chen1, Hsin-Yi Wen1, Ai-Ti Chen1, Hsiao-Chi Chen1, Chun-Ming Chiu1, Chun-Yuan
Cheng1, Nian-Ru Wu1, Yu-Chen Cheng1, Jin-Lun Chuang1, Li-Hsin Kao1, Cheng-Hong Chen1, Yuji Sano1,4
1.Dept. Geosciences, National Taiwan University, Taiwan, 2.Institute of Earth Sciences, Academia
Sinica, Taiwan, 3.National Center for Research on Earthquake Engineering, Taiwan, 4.Atmosphere andOcean Research Institute, University of Tokyo, Japan
Helium isotope systematics is a powerful proxy to distinguish fluid origins and conveys fruitfulgeological information. In the past several decades, this robust isotope systematics had offered
pivotal knowledge on many key issues in Earth and planetary sciences. It revealed essential
geological information of Taiwan as well. Taiwan is located on the junction of two subduction
systems–Ryukyu Arc and Luzon Arc. The geotectonic setting is complex and intriguing.
Dr. Tsanyao Frank Yang was the pioneer of gas geochemistry studies in Taiwan. He established thefirst gas geochemistry laboratory in National Taiwan University in 1998 and started exploring all
possible research topics on and around this tectonic-active island. In the past two decades, his
research covered volcanic/hydrothermal gas studies, volcanic activity monitoring, gas hydrate
exploration, soil gas as a tool to locate fault traces, soil gas flux measurement, earthquake
precursory, mud volcanoes, low-temperature geochronology and many more. He died of pancreas cancer
in March 2015. He was a warm and enthusiastic mentor, a prolific scientist and a great friend. He
will always be remembered.
Here we present Dr. Yang’s achievement on helium isotopes studies in Taiwan throughout his research
career. We integrate all the research results from his team and summarize the observations. We willshow the distribution of helium isotope ratios in Taiwan and its implications on tectonic settings.
Keywords: Tsanyao Frank Yang, Taiwan, Helium isotopes©2016. Japan Geoscience Union. All Right Reserved.

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日本地球惑星科学連合2016年大会

Volatile behaviors at an immature stage of subduction zone inferred from volcanic glasses
in the Bonin fore-arc (IODP Expedition 352)
Volatile behaviors at an immature stage of subduction zone inferred from volcanic glasses
in the Bonin fore-arc (IODP Expedition 352)
*清水 健二1、牛久保 孝行1*Kenji Shimizu1, Takayuki Ushikubo1
1.海洋研究開発機構

高知コア研究所

1.Kochi Core Center, Japan Agency for Marine-Earth Science and Technology
IODP Expedition 352 was targeted to drill the entire magmatic sequence comprising the outer Bonin
fore-arc to elucidate early subduction dynamics. During the expedition, a total of 1.22 km of
igneous basement related to subduction initiation was cored from four sites (U1439, U1440, U1441,
U1442). Two sites (U1440 and U1441) located nearer to the trench (stratigraphically lower and older
sequence than U1439 and U1442), recovered igneous rocks at the basement that are mostly fore-arc
basalts (FABs). From other two sites (U1439 and U1442) located ~15 km west from U1440 and U1441,
boninites were recovered.
From all sites, we recovered fresh volcanic glasses manifest as chilled margins of pillow lavas,
massive lavas, hyaloclastites and pyroclastic deposits. In order to constrain behaviors ofvolatiles at an immature stage of subduction zone, we analyzed volatile (H2O, CO2, F, Cl, S) and P2O
5concentrations of 100 volcanic glasses (31, 23, 1 and 45 samples from U1439, U1440, U1441 andU1442, respectively) using SIMS (CAMECA IMS 1280-HR) at JAMSTEC.
Glasses from the boninite sites (U1439 and U1442) are higher in H2O (~1.9 wt%) at the lower partsof the holes and slightly lower in H2O (~1.6 wt%) at the upper parts of the holes and are
remarkably in low CO2 (< several ppm: below detection limit, DL) and S (7-130 ppm). Their F and Cl
contents are 66-166 ppm and 357-981 ppm, respectively.
On the other hand, most glasses from the FAB sites (U1440 and U1441) have various H2O contents(0.11-0.57 wt%) and measurable CO2 contents (67-151 ppm) with high S contents (776-1250 ppm). Their
F and Cl contents are 62-111 ppm and 101-597 ppm, respectively. Three highly evolved glasses (MgO
3.3 wt%) probably from the same glassy layer from U1440 are high in H2O (0.80 wt%), F (300 ppm) andCl (2900 ppm). We also found a boninitic glass between FAB lavas from U1440, in terms of H2O (1.95wt%), CO2 (below DL) and S (301 ppm).
F/P ratios of glasses, which reflect their original source mantle, are 0.49±0.03 (1 standard
deviation) for boninites and 0.28±0.02 for FABs. Since the F/P ratio of the depleted upper mantle(DM) is 0.27±0.11, those of FABs have not been influenced by subducting materials. However, 10-50
times higher Cl/K (0.6-4) and 2-4 times higher H2O/F (24-56) ratios of FABs than those of DM
indicate influx of a small amount of Cl-rich fluid to the mantle wedge at the very beginning of
subduction formation. Boninites are highly enriched in H2O (H2O/F: 110-298), but not in Cl (Cl/K:
0.1-0.4) relative to FABs, indicating that contribution and composition of subducting materials
have changed with time.
キーワード：沈み込み帯、揮発性元素、IODP
Keywords: subduction zone, volatiles, IODP

©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-02 -SGC16-03

日本地球惑星科学連合2016年大会

伊豆-マリアナ弧火山岩中かんらん石斑晶の分析からみた希ガスとハロゲンの沈み込み過程
Noble gas and halogen subduction processes constrained by the analysis of olivines from
Izu-Mariana arc lavas*角野 浩史1、小林 真大2、Burgess Ray3、Jepson Lisa3、町田 嗣樹4、清水 綾5、Hilton David6、Ballentine
Chris7*Hirochika Sumino1, Masahiro Kobayashi2, Ray Burgess3, Lisa Jepson3, Shiki Machida4, Aya Shimizu5,David Hilton6, Chris Ballentine7
1.東京大学総合文化研究科広域科学専攻、2.東京大学理学系研究科地殻化学実験施設、3.マンチェスター大学、4.海洋研究開発機構、5.東京都立産業技術研究センター、6.スクリプス海洋研究所、7.オックスフォード大学
1.Dept. Basic Science, Univ. Tokyo-Komaba, 2.GCRC, Grad. Sch. Sci., Univ. Tokyo, 3.SEAES, Univ.
Manchester, 4.JAMSTEC, 5.Tokyo Metro. Ind. Tec. Res. Inst., 6.Scripps Inst. Ocean., UC San Diego,
7.Dept. Earth Sciences, Univ. Oxford
The presence of noble gases and halogens with seawater and sedimentary pore-fluid signatures inexhumed mantle wedge peridotites and eclogites from the Sanbagawa-metamorphic belt, southwest Japan[1,2], mantle-derived xenoliths from Kamchatka and Luzon arcs [3], and in seafloor and forearc
serpentinites [4] along with seawater-like heavy noble gases (Ar, Kr, and Xe) in the convecting
mantle [5] strongly suggest the subduction of sedimentary-pore-fluid-like noble gases and halogens.
The noble gas and halogen compositions of olivines in arc lavas of the Izu-Mariana subduction zone
were determined to develop a better understanding of the processes that control the return of thesevolatile and highly incompatible elements into the mantle. Trace amounts of halogens (Cl, Br, andI) in the olivine samples were measured using a combination of neutron irradiation and noble gas
mass spectrometry [6].
The 3He/4He ratios of samples are in the range of the mid-ocean ridge basalt (MORB) value. This isconsistent with helium isotope ratios of the subduction zone mantle xenolith [3], which indicates aconsiderably low contribution to the mantle wedge beneath the arc of radiogenic 4He in the
subduction fluids observed in the Sanbagawa samples exhumed from depths in the range from 30 to 100
km [1,2]. In contrast, the 40Ar/36Ar ratios for each volcano (299–620) are significantly lower thanthe MORB source (up to 32,000 [5]), which indicates significant involvement of atmospheric Ar (40Ar/36Ar = 296) in the arc magmas. Systematically higher 40Ar/36Ar ratios in the rear arc than in the
volcanic front suggest that subduction of seawater-derived Ar has a significant effect on the noble
gas composition of the magma-generation region. Although the halogen compositions of most of theolivines are close to that of MORB-source mantle, some samples from the rear-arc regions show asignificant contribution from pore-fluid-derived halogens. Combined with the noble gas results,
halogen-poor fluid associated with atmospheric noble gases may be dominantly released from thesubducting slab beneath the arc, while halogen supply from the subducted slab is limited to themagma generation region beneath some volcanoes in the rear arc. This implies the relative
persistence of halogens in the subducting slab compared with noble gases.
A simple mass balance calculation of subducted and mantle-derived Ar isotopes reveals that higher
subduction flux than that of seawater-derived Ar in the pore fluids of the subducting
sediment/crust is required. Although the serpentinized lithosphere in the subducting slab has been
regarded as the best candidate for the carrier of seawater-derived Ar with high subduction flux[4], the ratios of halogens and noble gases to water of slab-derived fluids preserved in the fluidinclusions of subduction zone mantle peridotites are inconsistent with the ratios in serpentinites
collected from the Earth’s surface. This requires strong coupling behavior of halogens and noble©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-03 -SGC16-03

日本地球惑星科学連合2016年大会

gases with their host water during hydration of the subducting materials, release of aqueous fluids
from subducted slab, and upward migration of the fluids in the mantle wedge. It remains unclear
whether noble gases and halogens in the subducting materials are completely released beneath the
Izu-Mariana rear arc. However, the presence of seawater-like noble gases in the convecting mantle[3] implies that a small portion of seawater-dissolved atmospheric noble gases may be transported
to greater depths in the deeper mantle, and then incorporated into the mantle convection.
[1] Sumino et al. EPSL 2010. [2] Sumino et al. Mineral. Mag. 2011. [3] Kobayashi et al. Mineral.

Mag. 2013. [4] Kendrick et al. Nature Geosci. 2011. [5] Holland & Ballentine Nature 2006. [6]Turner JGR 1965.
キーワード：ハロゲン、希ガス、沈み込み、マントル、揮発性元素循環
Keywords: halogen, noble gas, subduction, mantle, volatile recycling©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-03 -SGC16-04

日本地球惑星科学連合2016年大会

高Mg安山岩と超マフィック火山岩の共存について
On the coexistence of high-Mg andesites and ultramafic volcanic rocks*三部 賢治1、川本 竜彦2、小野 重明3*Kenji Mibe1, Tatsuhiko Kawamoto2, Shigeaki Ono3
1.東京大学地震研究所、2.京都大学大学院理学研究科附属地球熱学研究施設、3.独立行政法人海洋研究開発機
構
1.Earthquake Research Institute, University of Tokyo, 2.Institute for Geothermal Sciences, Graduate
School of Science, Kyoto University, 3.Japan Agency for Marine-Earth Science and Technology
In order to understand the origin of magmas in the hydrous upper mantle, we have been investigating
the phase relation and compositions of phases in the system peridotite-H2O. Using X-ray radiography
technique together with Kawai-type multi-anvil high-pressure apparatus (SPEED-1500, SPring-8,Japan), the second critical endpoint in the peridotite-H2O system was determined to be at around
3.8 GPa and 1000 ºC (corresponding to a depth of ~ 110 km) [1]. It is possible that two fluid
phases (i.e., aqueous fluid and hydrous silicate melt) coexist up to 3.8 GPa. Above 3.8 GPa,
however, hydrous silicate melt and aqueous fluid in upper mantle becomes indistinguishable fromeach other and the melting temperature of hydrous mantle peridotite can no longer be defined beyond
this critical condition. Using the quenched recovered samples obtained by Mibe et al. [1], chemicalcompositions of aqueous fluid, silicate melt, and supercritical fluid magma in the vicinity of
second critical endpoint were determined by the electron microprobe analyzer. In the run at 3.6
GPa, the composition of aqueous fluid was high-Mg andesitic, whereas the composition of hydrous
silicate melt was komatiitic. Our experimental results indicate that high-Mg andesitic magma andkomatiitic magma can be generated at the same time as the liquid-fluid immiscibility near thesecond critical endpoint in the peridotite-H2O system. Some natural examples on the coexistence ofhigh-Mg andesites and ultramafic volcanic rocks from various tectonic settings and locations aroundthe world will also be presented.
[1] Mibe, K., M. Kanzaki, T. Kawamoto, K. N. Matsukage, Y. Fei, and S. Ono (2007), Second critical
endpoint in the peridotite-H2O system, J. Geophys. Res., 112, B03201, doi:10.1029/2005JB004125.
キーワード：高温高圧
Keywords: high pressure and high temperature©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-04 -SGC16-05

日本地球惑星科学連合2016年大会

マントル遷移層の還元反応による脱水融解
Redox dehydration melting of mantle transition zone deduced from the H2O storage capacity*芳野 極1、櫻井 萌2、坂本 直哉3、圦本 尚義4*Takashi Yoshino1, Moe Sakurai2, Naoya Sakamoto3, Hisayoshi Yurimoto4
1.岡山大学地球物質科学研究センター、2.東京工業大学地球惑星科学科、3.北海道大学創成研究機構、4.北海道大学大学院理学研究院 自然史科学部門 地球惑星システム科学分野
1.Institute for Study of the Earth's Interior, Okayama University, 2.Department of Earth andPlanetary Sciences, Tokyo Institute of Technology, 3.Isotope Imaging Laboratory, Creative ResearchInstitution, Hokkaido University, 4.Department of Natural History Sciences, Hokkaido University
Knowledge of the H2O storage capacities of minerals forming mantle peridotite provides essential
constraints on estimation of H2O content and the onset of hydrous partial melting in the mantle. In
the mantle transition zone, wadsleyite can store significant amount of H2O in their crystal
structures under extremely high oxygen fugacity. However, the H2O storage capacity has not been
determined under the low oxygen fugacity predicted from the mantle transition zone7. Here we reportthat the H2O storage capacity of wadsleyite in equilibrium with the peridotite assemblage underlower oxygen fugacity is much smaller than that under higher one. Very low H2O storage capacity ofwadsleyite can attribute to the low H2O activity in the melt. Considering the more reducing statein the deep mantle, dominant speciation of volatile phases is not H2O but H2. Low H2O activity inthe reduced deep mantle requires that H2O storage capacity in the Earth’s mantle is much smaller
than that predicted from the maximum H2O concentration determined under the high oxygen fugacity.
The hydrated and oxidised subducted slab will induce “redox dehydration melting” through decreaseof oxygen fugacity by the surrounding reduced mantle transition zone. H2O in the generated melt
will be reduced to hydrogen through the oxidation of iron-bearing minerals. Fe-H melt or FeHx
trapping the released hydrogen would become the main carrier of hydrogen into the deep mantle.
キーワード：酸化還元、水の溶解度、脱水
Keywords: redox condition, water storage capacity, dehydration©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-05 -SGC16-06

日本地球惑星科学連合2016年大会

Noble gas incorporation into the deep Earth*Andrew P Jephcoat1
1.Institute for Study of the Earth's Interior, Okayama University
The present state of the Earth evolved from energetic events that were determined early in thehistory of the solar system. A key process in reconciling this state and the observable mantle
composition with models of the original formation relies on understanding the planetary processingthat has taken place over the past 4.5Ga and the range of most relevant P-T conditions governing
primary segregation and mixing. Recent developments with the laser-heated diamond anvil cell havemade possible extension of the conventional pressure limit for solubility and partitioning
experiments as well as the direct study of volatile trace elements. In particular, selected resultsof liquid–liquid, metal–silicate (M–Sil) partitioning are presented for several noble gas andmolecular elements in a synthetic chondritic mixture, spanning a wide range of atomic number helium to iodine The application of these methods is new and allows extension of geochemical
studies performed in larger-volume apparatus. Not only is the attainment of uniform and equilibrium
mixing important in this small-sample environment (perhaps 10-100 micrometers in linear dimension
depending on the pressure), but also the microanalysis of quenched samples to determine the
distribution of minor and trace elements. Systematic results on the solubility of He, Ne and Ar
suggests that their incompatibility in solid silicate and metallic phases may not have been as
great as previously thought -- and hence are candidates for storage in the deep Earth. Helium
solubility in the metal phase relative to that of the silicate suggests the core should beconsidered a deep Earth reservoir for example. If the core is a reservoir, then the mechanisms forinteraction with the lower mantle become important requiring examination of the processes ofmaterial exchange at the core-mantle boundary. The interpretation of the results depended on
precise microanalysis of LHDAC samples, and the application of UV laser ablation,
mass-spectrometric techniques that provided for the first time a spatially resolved depth profile
in samples. Attention needs to be paid to the likely mode of solubility - entrapment versus bonded
and non-bonded host environments for example - and we attempt to consider the real implications for
the Earth in either case.
Keywords: Noble gases, Laser-heated diamond-anvil cell, core-mantle, element partitioning,solubility©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-06 -SGC16-07

日本地球惑星科学連合2016年大会

含水ブリッジマナイト：下部マントルにおける貯水能力
Hydrous bridgmanite: Water storage capacity in the lower mantle*井上 徹1、柿澤 翔1、藤野 清志1、栗林 貴弘2、長瀬 敏郎2、Greaux Steeve1、肥後 祐司3、坂本 直哉4、圦本
尚義4、服部 高典5、佐野 亜沙美5
*Toru Inoue1, Sho Kakizawa1, Kiyoshi Fujino1, Takahiro Kuribayashi2, Toshiro Nagase2, Steeve Greaux1, Yuji Higo3, Naoya Sakamoto4, Hisayoshi Yurimoto4, Takanori Hattori5, Asami Sano5
1.愛媛大学地球深部ダイナミクス研究センター、2.東北大学、3.JASRI, SPring-8、4.北海道大学、5.JAEA
1.Geodynamics Research Center, Ehime University, 2.Tohoku University, 3.JASRI, SPring-8, 4.Hokkaido
University, 5.JAEA
Recently hydrous ringwoodite was found in a natural diamond inclusion, which includes ~1.5 wt% H2
O. In addition, the experimental studies show that wadsleyite and ringwoodite, which are the mostabundant minerals in the mantle transition zone, can contain water up to 2.2–2.7 wt% [e.g. Inoue etal., 1995, 1998, Kohlstedt et al., 1996]. These results show that the mantle transition zone is astrong water reservoir in the Earth’s interior, and at least locally, hydrous. On the other hand,
the water storage capacity in the lower mantle is a matter of debate.
We have been conducting the study for the stability and water solubility of hydrous and nominallyanhydrous minerals, and the recent target is the effect of Al. In this process, we found that
Al-bearing bridgmanite (Mg-silicate perovskite) can contain significant amount of water. The
possible H substitution mechanism can be proposed by means of chemical compositional relationshipbetween Mg, Si, Al and H. In addition, we clarified the possible H position in the bridgmanite bymeans of the powder neutron diffraction analysis in J-PARC, together with the single crystal X-ray
structural analysis in PF. This shows that the significant amount of H (water) can be stored in the
Earth’s lower mantle.
Because of the H in the bridgmanite, the physical properties of the bridgmanite can be changed. The
information is very important to discuss the water content and the composition in the lower mantle.
We have also conducted the equation of state and the ultrasonic wave velocity measurements ofhydrous bridgmanite in BL04B1, SPring-8 to determine the elastic wave velocities and the elastic
properties under high pressure and temperature condition. In this talk, I will introduce about our“hydrous bridgmanite” project.
キーワード：含水ブリッジマナイト、下部マントル、放射光Ｘ線その場観察実験、中性子回折、弾性的性質
Keywords: hydrous bridgmanite, lower mantle, Synchrotron X-ray in situ experiment, neutron
diffraction, elastic property©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-07 -SGC16-08

日本地球惑星科学連合2016年大会

マントル最下部における含水領域の形成
Formation of a hydration zone at the bottom of the lower mantle*大谷 栄治1、増野 いづみ1、大平 格1*Eiji Ohtani1, Izumi Mashino1, Itaru Ohira1
1.東北大学大学院理学研究科地学専攻
1.Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku
University
One of the major water carriers into the lower mantle is delta-AlOOH-phase H MgSiO2(OH)2 solid
solution (aluminous phase H) [1]. Our experiments revealed that the solid solution containing water
can be stable to the core-mantle boundary region, 120 GPa and 2500 K [2, 3], which is the condition
along the normal mantle geotherm. The core-mantle boundary is the region with a large temperature
gradient, thus dehydration or dehydration melting is inevitable at the core-mantle boundary.
There are three possibilities on the roles of this hydrous phase at the core-mantle boundary
region: First, the reaction of this hydrous phase with the metallic core to introduce hydrogen into
the core. Second, dehydration melting at the core-mantle boundary which might create a partial
molten low velocity zone at the core-mantle boundary. Third, formation of a hydrated zone at thebase of the lower mantle by suppling fluid dehydrated at the hot core-mantle boundary. Here, we
consider a possible role of this hydrous phase for formation of a hydration region at the base of
the lower mantle, the third process listed above.
Ohira et al. [2] revealed that hydration of aluminous bridgmanite creates delta-AlOOH phase and
MgSiO3 bridgmanite containing smaller amount of Al2O3. This hydration reaction can occur by suppling
fluid dehydrated at the hot core-mantle boundary. Mashino et al. [4] measured the sound velocity ofdelta-AlOOH at high pressure and revealed that both Vp and Vs of this phase is greater than the
major transition zone minerals such as ringwoodite and majorite, whereas the velocities are lower
than bridgmanite at the bottom of the lower mantle. Drop of sound velocities can be expected byformation of delta-AlOOH phase by consuming Al2O3 in bridgmanite at the base of the lower mantle.
Decrease of the sound velocity can be accounted for the low velocity nature at the core-mantle
boundary. Thus, the bottom of the lower mantle may be a second largest water reservoir next to themantle transition zone.
References:[1] Ohtani (2015). Hydrous minerals and the storage of water in the deep mantle. Chemical Geology
418, 6–15.
[2] Sano et al. (2008). Geophys. Res. Lett., 35, L03303, doi:10.1029/2007GL031718[3] Ohira et al. (2014). Earth Planet. Sci. Lett., 401, 12–17, doi:10.1016/j.epsl.2014.05.059[4] Mashino, I., M. Murakami, E. Ohtani (2016). Jour Geophys. Res., 10.1002/2015JB012477
キーワード：下部マントル、核マントル境界、delta-AlOOH、含水H相、加水、低速度領域
Keywords: Lower mantle, Core-mantle boundary, delta-AlOOH, Phase H, Hydration, Low velocity region©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-08 -SGC16-09

日本地球惑星科学連合2016年大会

Global water cycle constrained by the evolution of dynamic hypsometry*Jun Korenaga1
1.Department of Geology and Geophysics, Yale University
The presence of liquid water on the surface is one of the important characteristics that make theEarth a unique planet, and it is usually considered to be critical for a planet to be habitable.
Also, surface water is often believed to be essential for the operation of plate tectonics, which
in turn enables the return of surface water to the planetary interior. The amount of surface water
is thus a time-dependent variable that is controlled by the dynamics of Earth's interior. The Earth
not only has surface water but also has just a right amount of it to allow the subaerial exposureof continental crust, which is important for the modulation of the atmospheric composition as wellas various biogeochemical cycles. To better understand the role of water in the Earth history,
therefore, we need to decipher how the distribution of water between the surface and the deep
interior has changed with time and how it has affected the surface environment. In thiscontribution, we focus on reconstructing the history of surface water by assembling relevant
observational constraints and theoretical considerations. It is now possible to derive a fairly
robust constraint on the history of surface water, at least back to around 3 Ga, by examining theconstancy of continental freeboard in light of the evolution of dynamic hypsometry. We also discuss
its implications for the coevolution of Earth's interior and surface environment.
Keywords: oceans, mantle convection, plate tectonics©2016. Japan Geoscience Union. All Right Reserved.

- SGC16-09 -SGC16-10

日本地球惑星科学連合2016年大会

Global fluxes of fluorine and sulfur efficiently released at mid-ocean ridges
Global fluxes of fluorine and sulfur efficiently released at mid-ocean ridges
鹿児島 渉悟1、*佐野 有司1、高畑 直人1Takanori Kagoshima1, *Yuji Sano1, Naoto Takahata1
1.東京大学大気海洋研究所
1.Atmosphere and Ocean Research Institute, the University of Tokyo
Fluorine and sulfur are major components of high temperature volcanic gases, and significantly
affect surface environments due to high chemical activity. Therefore their fluxes between the
mantle and surface environments are important to elucidate evolutionary histories of Earth’s
atmosphere and ocean. We estimated fluorine and sulfur fluxes at mid-ocean ridges (MOR) based on
chemistry of submarine vent fluids and MORB vesicles which may reflect components efficiently
released from magmas through upward propagation of film ruptures by bubble expansions duringdecompression[1]. Fluorine flux was constrained by two methods as follows:
1) Multiplication of fluorine concentrations in submarine hydrothermal fluids and the fluid flux at
MOR may provide an estimate of fluorine flux at MOR. A worldwide vent chemistry research[2]suggested that vent fluids are depleted in fluorine (<0.74 ppm F) relative to seawater (1.29 ppm
F). The global flux of vent fluids of (8.0+/-2.1)x1015 g/y was calculated using a numerical
Bayesian inversion procedure to explain the relationship between compositions of hydrothermal
fluids and altered sheeted dikes[3]. This value is not consistent with the flux of (3.1+/-0.7)x1016
g/y obtained based on the 3He concentration of (1.7+/-0.2)x10-14 mol/g (1σ) in 10 high temperature(>200°C) hydrothermal fluids at EPR and MAR[4], and the MOR 3He flux of (527+/-102) mol/y[5]. These
two fluid fluxes, when multiplied by the maximum fluorine concentration of 3.88x10-8 mol/g,
provides fluorine fluxes ranging from 3.1x108 mol/y to 1.2x109 mol/y with an average of(7.6+/-4.5)x108 mol/y.
2) Multiplication of F/3He ratios in MORB vesicles and 3He flux will provide another fluorine flux.
We analysed eight MORB vesicles (13°N,17°S on EPR; 15°N,30°N,37°N on MAR; 24°S-25°S on CIR) with acrushing technique extracting fluorine and helium simultaneously[6]. Fluorine was extracted into
alkaline solution and measured by an ion chromatography (ICS-2100; Thermo Fisher Scientific Inc.),
while helium was measured by a noble gas MS (VG5400; Waters Corp.), both housed at AORI. F/3He
ratios in vesicles range from 2.0x105 to <2.8x107 with an average of (1.2+/-0.5)x106 (1σ), providing
a global fluorine flux of (6.4+/-3.1)x108 mol/y by multiplying the MOR 3He flux.
One might calculate a weighted mean of two MOR fluorine fluxes to be (6.8+/-2.5)x108 mol/y. However
it should be noted that the actual MOR fluorine flux may be lower than this flux because theapplied fluorine concentration in hydrothermal fluids is an upper limit, and seawater contamination
was not deconvolved for MORB vesicles. We also note that this flux is much lower than flux (1.13x10
12mol/y) estimated using the F/CO2 ratio in the MORB source and CO2 flux from the mantle[7],implying that the most part of fluorine resides in the melt and is not released immediately after
the oceanic crust production.
Sulfur flux, together with carbon, will be estimated based on chemistry of vent fluids and MORB
vesicles, which is similar approach as for fluorine. In addition, comparing MOR and arc fluxes, theglobal cycles of fluorine, sulfur, and carbon will be discussed in the presentation.
[1]Namiki & Kagoshima (2014)JGR Solid Earth 119, 919-935. [2]German & Von Damm (2004)Treatise On

Geochemistry 6 (eds Holland & Turekian)181-222. [3]Coogan & Dosso (2012)EPSL 323-324, 92-101.
[4]Kagoshima et al. (2015)Sci. Rep. 5, 8330. [5]Bianchi et al. (2010)EPSL 297, 379-386.
[6]Kagoshima et al. (2012)Geochem. J. 46, e21-e26. [7]Fischer (2008)Geochem. J. 42, 21-38.

©2016. Japan Geoscience Union. All Right Reserved.

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日本地球惑星科学連合2016年大会

キーワード：fluorine flux、sulfur flux、carbon flux、mid-ocean ridge basalt、hydrothermal
fluid、volcanic gas
Keywords: fluorine flux, sulfur flux, carbon flux, mid-ocean ridge basalt, hydrothermal fluid,
volcanic gas©2016. Japan Geoscience Union. All Right Reserved.

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日本地球惑星科学連合2016年大会

Redistribution of noble gases during magma ocean crystallization*Colin Jackson1, Neil Bennett1, Zhixue Du1, Yingwei Fei1, Curtis Williams2, Sujoy Mukhopadhyay2
1.Carnegie Institution of Washington, 2.UC Davis
Recent measurements of Xe isotopes place the formation of high 3He/4He mantle to within the first
80 Ma of solar system history. This timeframe coincides with Earth’s accretion, leading to the
hypothesis that a magma ocean concentrated materials that now comprise the high 3He/4He source. We
have initiated an experimental study to better constrain the distribution of noble gases within thesolid Earth during magma ocean crystallization and the petrogenesis of high 3He/4He mantle. We
report the Ar contents of minerals (bridgmanite, periclase) and liquids (silicate and Fe metallic
melts) salient to magma ocean crystallization that were synthesized in the presence of Ar-richfluids at high pressure. Our initial experiments are conducted with Ar because it is the middle
noble gas, so its behavior is most representative of the bulk elemental group. Experiments wereconducted using laser-heated diamond anvil cells (DAC) and multi-anvil (MA) apparatus and wereanalyzed by microprobe and laser ablation techniques.
The Ar contents of the large majority of bridgmanite and periclase analyses in the MA experiments
were at or below the WDS detection limit. Detection limits are calculated from counting statistics
and nominally approached 20 ppm Ar for longer duration analyses. Saturation of an Ar-rich fluid in
the MA experiments was confirmed by high Ar concentration blebs throughout the recovered samples.
Laser ablation analyses on a MA experiment yielded highly variable Ar concentrations inbridgmanite, ranging from 450 to 10 ppm. Given the observation of Ar-rich blebs in the MA
experiments, we interpret the lower range in Ar concentration as our current best estimate of Ar
solubility in bridgmanite. The Ar contents of samples from DAC experiments were more variable, butlarge areas of laser-heating spots on bridgmanite contain Ar contents at or below the detection
limit by EDS microprobe (~100 ppm Ar). Bridgmanite disproportionated to (Mg,Fe)O and SiO2 in somehigher temperature heating spots. These phases also had undetectable Ar concentrations. In aparallel series of experiments, we have also quantified the concentration of Ar dissolved into
silicate and Fe metallic liquids at 15 GPa using a DAC. Preliminary measurements by EDS yield Ar
concentrations of 4000 ppm for the silicate liquid and Ar concentrations below detection in the Femetallic liquid. This concentration is similar to previous determinations of Ar solubility insilicate liquids at transition zone pressures.
Our results imply that noble gases are strongly concentrated in silicate liquids over minerals andliquid Fe during magma ocean episodes. High 3He/4He mantle is associated with unradiogenic noble
gas signatures. Given this, we suggest that the petrogenesis of high 3He/4He mantle is related to
the fractionation of a silicate liquid during a magma ocean episode.
Keywords: noble gases, magma ocean, volatiles©2016. Japan Geoscience Union. All Right Reserved.

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