SGC50-01

Room:102A

Time:May 25 14:15-14:30

Geochemical connection between HIMU-FOZO-PREMA: two-stage dehydration of oceanic
crust with layered structure
SHIMODA, Gen1∗ ; KOGISO, Tetsu2
1Geological Survey of JAPAN, 2 Graduate School of Human and Environmental StudiesGraduate School of Human and Environmental Studies
Isotopic composition of the ocean island basalts (OIBs) can be explained by mixing of isolated reservoirs in the Earth (White,
1985; Zindler and Hart, 1986; Hofmann, 1997; Stracke, 2012). In early research on the mantle reservoirs, the isotopic composition of OIBs was explained by the mixing of depleted MORB mantle (DMM) and three enriched reservoirs, those are HIMU
(high-u: u = 238U/204Pb) EM1 (Enriched Mantle 1) and EM2 (Enriched mantle 2). In addition to these reservoirs, importanceof reservoirs whose isotopic compositions are common and intermediate has been pointed out, such as, FOZO (Focal Zone, Hart
et al., 1992) and PREMA (Prevalent Mantle, Zindler and Hart, 1986). Although these intermediate reservoirs have been used todescribe the isotopic distribution of OIBs, existences of the intermediate reservoirs, themselves, are still in debate. Therefore,
elucidating the origin of the intermediate reservoirs should be also important from the perspective of production of mantle heterogeneity (e.g., Hofmann, 1997; Stracke et al. 2005; Stracke, 2012).
To elucidate the origin of mantle reservoirs, geochemical modeling has been conducted, in which origin of HIMU, FOZO and
PREMA is discussed. The results suggest that MORBs with high frequency (common MORBs) without significant chemical
modification during subduction have chemical composition that is suitable for producing PREMA. It suggests the importanceof recycling of dry MORBs for the production of OIBs source. Dehydration of common MORBs in subduciton zones can produce FOZO isotopic signatures if amount of dehydrated water is close to the maximum amount (4 %) of dehydrated aqueous
fluid in subduction zones. Thus, FOZO-PREMA isotopic array can be explained by recycling of common MORBs that releasevarious amount of aqueous fluid during subduction. For the production of HIMU, additional dehydration (˜2%) at high pressure
is required. As high pressure dehydration release supercritical fluid with relatively high U/Pb and low Th/Pb ratios, chemical
fractionation during dehydration is different from the sub-arc process. This difference can explain isotopic difference between
HIMU and FOZO.

Keywords: HIMU, FOZO, PREMA, MORBs, OIBs

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SGC50-02

Room:102A

Time:May 25 14:30-14:45

Ocean Basalt Simulator version 1 : Trace element mass balance in adiabatic melting of apyroxenite-bearing peridotite
KIMURA, Jun-ichi1∗ ; KAWABATA, Hiroshi2
1

JAMSTEC, 2 Kochi University

We present a new numerical trace element mass balance model for adiabatic melting of a pyroxenite-bearing peridotite for
estimating mantle potential temperature, depth of melting column, and pyroxenite fraction in the source mantle for a primaryocean basalt/picrite. The Ocean Basalt Simulator version 1 (OBS1) uses a thermodynamic model of adiabatic melting of apyroxenite-bearing peridotite with experimentally/thermodynamically parameterized liquidus?solidus intervals and source mineralogy. OBS1 can be used to calculate a sequence of adiabatic melting with two melting models, including (1) melting of
peridotite and pyroxenite sources with simple mixing of their fractional melts (melt-melt mixing model), and (2) pyroxenite
melting, melt metasomatism in the host peridotite, and melting of the metasomatized peridotite (source-metasomatism model).
OBS1 can be used to explore (1) the fractions of peridotite and pyroxenite, (2) mantle potential temperature, (3) pressure oftermination of melting, (4) degree of melting, and (5) residual mode of the sources. In order to constrain these parameters, themodel calculates a mass balance for 26 incompatible trace elements in the sources and in the generated basalt/picrite. OBS1 iscoded in an Excel spreadsheet and runs with VBA macros. Using OBS1, we examine the source compositions and conditionsof the mid-oceanic ridge basalts, Loihi?Koolau basalts in the Hawaiian hotspot, and Jurassic Shatsky Rise and Mikabu oceanic
plateau basalts and picrites. The OBS1 model shows the physical conditions, chemical mass balance, and amount of pyroxenite
in the source peridotite, which are keys to global mantle recycling.
Keywords: Peridotite, Pyroxenite, Adiabatic melting, Trace element, Mass balance

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SGC50-03

Room:102A

Time:May 25 14:45-15:00

Geochemical Composition of Dykes along the Cameroon Volcanic Line (CVL): Constrains on CVL magmatism and tectonism
ASAAH, Asobo nkengmatia elvis1∗ ; YOKOYAMA, Tetsuya1 ; AKA, Festus tongwa2 ; USUI, Tomohiro1 ;KURITANI, Takeshi3 ; WIRMVEM, Mengnjo jude4 ; IWAMORI, Hikaru1 ; OHBA, Takeshi41Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-, 2 Institute of Mining
and Geological Research, P.O. Box 4110, Yaounde, Cameroon, 3 Graduate school of Science, Osaka City University, 3-3-138
Sugimoto, Sumi Yoshi-ku, Osaka 558-8585,, 4 Department of Chemistry, School of Science, Tokai University, Hiratsuka, 2591211, Japan
Mafic dykes along the Cameroon Volcanic Line (CVL) align in a general N 30?? - N 70?? direction. These alignments are
consistent with the tectonic lineaments and the orientation of the CVL, indicative of a time and space relationship between thedykes and CVL lavas with the tectonic activities of the African plate. However, sub-alkaline volcanic rocks studied in someareas along the CVL are thought to be older than and not related to the CVL magmatism. Mafic dykes outcrop in the Oku
Volcanic Group (OVG) but have not been studied. The aim of this study is to 1) characterize volcanic dykes in the OVG and
Mt. Bambouto, 2) constrain the geochemical relationship between the dykes and CVL alkaline lavas, and 3) establish a tectonic
history of emplacement of these dykes. Three dykes in the OVG and two along the Dschang-Santcho escarpment (flank of Mt.
Bambouto) were systematically studied. An alkaline dyke is observed intruding a sub-alkaline dyke for the first time along theCVL, indicating a time and space relation between the two series. The dykes are weathered and show chemical evidence of
crustal contamination. Contamination of less than 20 % for the alkaline dykes (BD2 and BDS alkaline) and 30 - 40% (BDS
sub alkaline, BD3 and DS), can explain the varying degrees of crustal signatures in the samples. Geochemical characteristics
suggest that the Batibo alkaline intrusions and the sub-alkaline intrusions were derived from a similar mantle source with OVG
lavas. These characteristics are similar to those of the CVL alkaline lavas and OIBs. However, the differences in elemental
concentrations and isotope composition of the sub alkaline dykes and the alkaline dykes in the OVG can be ascribed to varying
degrees of weathering, assimilation of crustal components and different degrees of partial melting. The Low MgO, Ni, Cr, and V
in the Batibo alkaline intrusion are due to the rapid rate of chemical weathering of olivine. The dykes in this study are related to
the CVL magmatism in space and time. Fractures cutting through the basement rocks, but not the dykes suggest that the dykes
are younger than the tectonic activities. The Sub-alkaline intrusion that is also intruded by the alkaline dyke in the BDS is older(43 - 422 Ma). This indicates that its emplacement was earlier than the surface expression of the alkaline CVL magmatism in the
Tertiary (<31 Ma).
Keywords: Oku volcanic group, Dykes, Crustal contamination, Cameroon Volcanic Line, Magmatism, Tectonism

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SGC50-04

Room:102A

Time:May 25 15:00-15:15

The Hf isotope evolution of the bulk silicate Earth: Evidence from meteorite zircon
IIZUKA, Tsuyoshi1∗ ; YAMAGUCHI, Takao1 ; HIBIYA, Yuki1 ; AMELIN, Yuri2
1

The University of Tokyo, 2 The Australian National University

The 176 Lu-176 Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of Earth’s crustmantle differentiation, but the interpretation of Lu-Hf isotope data requires an accurate estimation of Hf isotope evolution of thebulk silicate Earth (BSE). Because both Lu and Hf are refractory and lithophile, the isotope evolution can be potentially reconstructed from the present-day 176 Hf/177 Hf and 176 Lu/177 Hf in undifferentiated chondrite meteorites. Unfortunately, however,these ratios in chondrites are highly variable due to the metamorphic re-distribution of Lu and Hf, making it difficult to ascertain the correct reference values for the BSE. In addition, it has been proposed that chondrites contain excess 176 Hf due to theaccelerated decay of 176 Lu resulting from photoexcitation to a short-lived isomer in the early Solar System. If so, the paradigmof a chondritic BSE would no longer be valid for the Lu-Hf system. Herein we report the first high-precision Lu-Hf isotope
analysis of meteorite zircon, a mineral that is resistant to metamorphism and has low Lu/Hf. The analyzed zircon grains wereextracted from the non-cumulate eucrite Agoult. Based on the zircon Lu-Hf isotope data as well as the Agoult whole-rock Lu
isotope data, we determine the initial 176 Hf/177 Hf of the Solar System to be 0.279791 +/- 0.000018. Reconciling the Solar System initial 176 Hf/177 Hf value with Lu-Hf isotope systematics of chondrites indicates a constant decay rate of 176 Lu throughout
the history of the Solar System, thereby removing the requirement for a non-chondritic BSE. We further use the initial value toidentify chondrites that preserve the primary Lu-Hf signatures and, therefore, are the best representative of the BSE. Our newly
established Lu-Hf parameters for the BSE (176 Hf/177 Hf = 0.282793 +/- 0.000011; 176 Lu/177 Hf = 0.0338 +/- 0.0001) strengthen
the evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir
on Earth as early as 4.5 billion years ago on Earth.
Keywords: bulk silicate Earth, zircon, hafnium isotopes, crust-mantle differentiation, eucrite, early solar system

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SGC50-05

Room:102A

Time:May 25 15:15-15:30

Partitioning behavior of elements between metal and sulfide melt
SUZUKI, Toshihiro1∗ ; HIRATA, Takafumi2 ; TAKAHASHI, Eiichi1
1

Earth and Planet. Sci., Tokyo Tech., 2 Earth and Planet. Sci., Kyoto Univ.

The partitioning behavior of elements between solid and liquid metal is key information to resolving the evolution of metallic
core of the terrestrial planets. In the case of silicate mineral-melt system, it is well known that partition coefficients closely relate
to size of cation and crystal structure. Thus similar size dependences in partition coefficients were also considered in metallic
systems. For example, Van Orman et al. (2008) measured partition coefficient of Re, Os and Pt in Fe-S system under highpressure, and proposed that partition coefficients of these elements are fitted by Lattice Strain Model (Blundy & Wood, 1994)
when they are plotted against atomic radius. Stewart et al. (2009) proposed that partitioning behaviors in metallic system can be
explained by Lattice Strain Model when Neutral Atom Radius (Clementi et al. 1967) is adopted. However, it seems very strangethat maximum of partition coefficient is found in Os, whose size is considerably larger than that of iron, which constructs thefundamental framework of crystal structure. In these metallic systems, it is well known that partition coefficient strongly dependon light element contents (sulfur, phosphorus or carbon) of metallic liquid. Therefore, we have to carefully consider the chemicalaffinity of elements to find the systematics in partitioning behaviors. In this study, we performed melting experiments of FeNi-S
system under high pressure in various sulfur contents, and examined the systematic change in partitioning behaviors.
We synthesized Fe-Ni(95:5) alloy doped with 14 trace elements (Co, Cu, Ge, Mo, Ru, Ph, Pd, W, Re, Os Ir, Pt, Au, Pb) inapproximately 150 ppm, by arc-melting method. A small chip of this alloy and a small amount of FeS powder were packed in
the MgO capsule, and high pressure melting experiments were performed using Kawai-type multi-anvil press installed at Tokyo
Institute of Technology. Quenched samples were polished and major element compositions were measured by EPMA. Traceelement abundances were determined by LA-ICP-MS installed at Kyoto University.
The observed partition coefficients in the present experiments were generally in agreement with the previous works, and indicating strong dependences to sulfur content in liquid phase. When we accept that partition coefficients are mainly controlled bychemical affinity of elements, then size dependence of partition coefficients must be found in sulfur free system, which includes
no chemical affinity effects on partition coefficients. Although we have no data for such pure metallic system, partitioning behavior in the pure metal system can be predicted from the observed sulfur dependence in partitioning behaviors. It was foundthat the differences in partition coefficients between elements become smaller with sulfur content of liquid phase decreases. Thismeans that partition coefficients in pure metal system may show similar values, even if in large sized elements, such as Au or W.
Blundy & Wood(1994), Nature 372, 452-454.
Clementi et al.(1967), J. Chem. Phys., 47, 1300-1307.
Stewart et al.(2009), Earth Planet. Sci. Lett. 284, 302-309.
Van Orman et al. 2008), Earth Planet. Sci. Lett. 274, 250-257.
Keywords: element partitioning, metal, sulfide, high pressure

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SGC50-06

Room:102A

Time:May 25 15:30-15:45

Single shot laser ablation-multiple collection-ICP-mass spectrometry for U-Pb age
HATTORI, Kentaro1∗ ; SAKATA, Shuhei1 ; HIRATA, Takafumi1
1

Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University

Combination of laser ablation sample introduction technique and ICP-mass spectrometry (LA-ICPMS) has been widely used
for element and isotopic analyses for solid samples1) . One of the great advantages of LA-ICPMS is high quantitative capability
achieved by the ”post ionization” configuration. With the post ionization, ionization and atomization of the analytes in the plasma
source will be independently carried out, and therefore, the optimization of the operational conditions for both the sampling andionization can be made. This suggests that the hard ionization can be carried out even under the ”soft” laser sampling. One of the
major source of the analytical error is an elemental fractionation during the laser ablation (down-hole fractionation)2) . In fact,
the measured Pb/U ratio can change with time when the larger ablation was made with ablation spots of higher aspect ratios3) .
To overcome this, we have tried to measure U-Pb ages from the ablation spots of smaller aspect ratio (i.e., shallower pit).
The shallower ablation pit could be obtained when a smaller number of laser shots were adopted. To achieve this, a multiple
collector-ICPMS was adopted to the U-Pb age determinations. With the multiple collector system, precision in the isotope ratio
measurements can be improved even from the transient signals produced by the smaller number of laser shots. Hence, six isotopes
were monitored by the six independent multipliers ; 202 Hg (IC), 204 Pb (IC), 206 Pb (IC), 207 Pb (IC), 208 Pb (IC), 232 Th (F) and235
U or 238 U (IC).
Three natural zircons (OD-34) , Plesovice5) and GJ-16) ) were employed to evaluate the reliability of the resulting U-Pb ages.
Nancy 915007) zircon was used as a calibration standard for the Pb/U ratio measurements. The glass standard (NIST SRM 610)
was used for the calibration in the 207 Pb/206 Pb isotope ratio measurements. Laser ablation system used in this study was a New
Wave Research femto laser ablation system (Fremont, CA 94538, USA), and the ICPMS instrument used in this study was a Nu
Instruments (Wrexham, UK) Nu Plasma II multi-collector ICPMS. For comparison, U-Pb ages were also measured by the single
collector-ICPMS instrument (Nu Instruments AttoM). In our presentation, we will demonstrate the high analytical capability of
the MC-ICPMS technique from the single shot laser sampling.
References
1) J.Koch and D.Guenther, Applied Spectroscopy, 65(5), 155A-162A (2011).
2) S.Eggins, L.Kinsley and J. Shelly, Applied Surface Science, 127-129, 278-286 (1998).
3) I.Horn, R.L Rudnick and W. F. McDonough, Chemical Geology, 164, 281-301 (2000).
4) H.Iwano et al., Island Arc, 22.3, 382-394, (2013).
5) J.Sláma et al., Chemical Geology, 249, 1-35 (2008).
6) S.E.Jackson et al., Chemical Geology, 211, 47-69 (2004).
7) M.Wiedenbeck et al., Geostandard Newsletter, 19, 1-23 (1995).
Keywords: LA-MC-ICPMS, U-Pb age, zircon, single shot, elemental fractionation, aspect ratio

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SGC50-07

Room:102A

Time:May 25 15:45-16:00

Isotope analysis of ng-sized Nd samples: toward the isotopic analysis of foraminifera
extracted from deep-sea sediments
WAKAKI, Shigeyuki1∗ ; YOSHIMURA, Toshihiro2 ; KURODA, Junichiro2 ; OHKOUCHI, Naohiko2 ;ISHIKAWA, Tsuyoshi1
1

KOCHI, JAMSTEC, 2 Department of Biogeochemistry, JAMSTEC

Modern seawater has heterogeneous Nd isotopic compositions. The source rocks of Nd in the ocean, continental rocks andigneous rocks derived from the mantle, show wide range of variation in their radiogenic 143 Nd/144 Nd ratios (˜5 permil). The
short residence time of Nd in the ocean (300-500 yr: Tachikawa et al., 2003; Amakawa et al., 20004; Arouze et al., 2009)
compared with the ocean mixing timescale of 1500 yr (Broecker and Peng, 1982) prevents the homogenization of seawater Ndisotopic compositions. The Nd isotopic variation of the seawater has been used to distinguish different water masses, to trace theocean circulation and to estimate the flow rate and contribution of Nd from various sources (ca. Piepgras and Wassurburg, 1980;
Amakawa et al., 2013).
Calcareous shells of foraminifera are now drawing attention as a proxy of seawater Nd in the past, which can be used to
trace the changes of the oceanic Nd isotopic composition related with paleoclimate changes (Tachikawa et al., 2014). One ofthe difficulties in analyzing Nd isotopic composition of foraminifera comes from the low Nd concentration of the foraminiferal
shells. The low Nd concentration (up to several ppm) of foraminiferal shells requires quite large sample sizes (several mg) tomeet the minimum sample size required for Nd isotope analysis (Nd amount of 2-5 ng). Lowering the sample size limits for
Nd isotope analysis may expand the applicability of the technique to foraminifera-poor sediments derived from oceanic drillingsites.
We have developed a new technique to measure isotope ratios of ng to sub-ng sized Nd samples using total evaporation
normalization method (Wakaki et al., 2007) together with the low-blank Nd separation chemistry. Isotope ratios of Nd aremeasured using thermal ionization mass spectrometer (Thermo TRITON) at Kochi Core Center.
The 143 Nd/144 Nd values of the isotopic reference reagent JNdi-1, measured at sample sizes of 0.5, 1 and 2 ng of Nd, allagreed with the values obtained by large sample measurement (100 ng of Nd) within statistical errors. The reproducibility of
143Nd/144Nd values are 100 ppm (n = 8), 60 ppm (n = 9) and 40 (n = 8) ppm for 0.5, 1 and 2 ng measurements, respectively. The
precision and accuracy of the sample analysis, including chemical procedure, is checked by analyses of two GSJ reference rocks,
JB-2 (basalt) and JCp-1 (coral). The basalt sample was decomposed by mixed HF-HNO3-HClO4, and the coral sample wasdecomposed by HNO3. Sample aliquots, containing 0.5 and 1.2 ng of Nd, respectively, were processed by using the low-blank
Nd separation chemistry. The measured 143Nd/144Nd ratios of JB-2 (n = 9) and JCp-1 (n = 8) samples all agreed with the values
obtained by measurements with large sample sizes within statistical errors. These results demonstrate that our technique gives
reliable results even for samples as small as 0.5 ng of Nd. Preliminary results of subsurface-dwelling planktonic foraminifera
samples, Globorotalia tumida, collected from a Quaternary sediment core from the West Caroline Basin (western equatorial
Pacific Ocean) will be presented.
Keywords: paleoclimate, Nd isotopes, foraminifera

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SGC50-08

Room:102A

Time:May 25 16:15-16:30

Origin of Bowers Ridge and its Oligocene arc magmatism: Results from the IODP Expedition 323, Hole U1342
KAWABATA, Hiroshi1∗ ; SATO, Keiko2 ; KIMURA, Jun-ichi2 ; CHANG, Qing2 ; SENDA, Ryoko2 ;TAKAHASHI, Toshiro3 ; HIRAHARA, Yuka4 ; MIYAZAKI, Takashi2 ; SCHOLL, David W.5
1Faculty of Science, Kochi University, 2 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3 Faculty of Science, Niigata University, 4 Aichi University of Education, 5 U.S. Geological Survey,
The Bowers Ridge is an 800 km-long arcuate aseismic ridge extending northward from the Central Aleutian Ridge. IODP
Expedition 323 drilled a total of 41.54 m of igneous basement at site U1342 in the northwestern Bowers Ridge, where an 800
m-deep wave-eroded platform exist. The recovered basement, composed of andesitic lavas and basaltic to andesitic volcaniclastic
rocks (Kawabata et al., 2011), provide an opportunity to explore temporal change in magma composition at Bowers Ridge justbefore the cessation of arc magmatism in the Oligocene.
The recovered volcanic samples yield 26-34 Ma 40 Ar-39 Ar ages (Sato et al., 2015) and have arc signature characterized bydepletion of HFSE and enrichment of LILE on the multi-element diagrams normalized to NMORB. The trace element features,with the presence of anorthitic plagioclase phenocrysts (An93), confirm the arc-origin of the ridge that was deduced from dredge
samples around Site U1342 (Cooper et al. 1987; Wanke et al., 2012). In arc magmatism, flux from subducted oceanic crust
played an important role as suggested by high Ce/Pb and unradiogenic 206 Pb/204 Pb.
Temporal change of magma chemistry was examined from both the core and reported dredge samples. Lower units of coresamples exhibit low to middle-K series, whereas both the upper units of core and dredge samples show middle to high-K series.
In addition, the dredge samples are more enriched in LREE, Rb, and Ba, and show higher (LREE, MREE)/HREE ratios thanthe core samples. The dredge basalts and andesites fall within the adakite field on the discrimination diagrams of Sr/Y vs Y and
La/Yb vs Yb (Wanke et al., 2012), whereas all the core samples are non-adakitic basalts and andesites. These geochemical results
suggest that the difference in magma compositions between the core and dredge samples could mainly reflect the difference inthe amount of slab-derived flux and/or the flux compositions. In this context, the inferred slab melting event (Wanke et al., 2012)
may not be a unique scenario for producing the adakitic dredge basalts and andesites. Larger amount of slab-derived flux andhigher melting pressure can also explain the change in magma compositions from the non-adakitic core samples to the adakitic
dredge samples. Thus, more careful examination is required to determine whether or not the already inferred extraordinary highgeothermal gradient is essential for the Oligocene magmatism at the Bowers Ridge.

Keywords: adakite, Bowers Ridge, remnant arc

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SGC50-09

Room:102A

Time:May 25 16:30-16:45

Fluorine content reveals new insight into arc magmatism of Southern Volcanic Zone,
Chile.
TOYAMA, Chiaki1∗ ; ORIHASHI, Yuji2 ; SHINJOE, Hironao3 ; SUMINO, Hirochika4 ; MURAMATSU, Yasuyuki5
1

JAMSTEC, 2 ERI, Univ. of Tokyo, 3 Tokyo Keizai Univ., 4 Univ. of Tokyo, 5 Gakushuin University

The halogen elements have high partition coefficients in aqueous fluid (Bureau et al., 2000), but the difference in their partition
coefficients for aqueous fluid/silicate melt/silicate minerals/organic matter results in distinct elemental ratios in seawater, pore
fluid, sediment, oceanic crust and mantle (e.g., Johson et al., 2000; Burgess et al., 2002; Palme and O’Neil, 2004). For instance,
fluorine is incorporated into apatite, amphibole and phengite (Svensen et al., 2001) while iodine has a high abundance in organicrich marine sediments because it is an essential element for life. These characteristics make halogens useful to trace water cycling
in subduction zones (e.g., Fehn et al., 2003; Muramatsu et al., 2007; Sumino et al., 2010). Recently, subduction of marine pore
fluid into the mantle has been suggested based on noble gas isotopes in the mantle (Holland and Ballentine, 2006) and halogen
compositions of exhumed mantle wedge peridotites (Sumino et al., 2010). However, only a little is known about the behaviorof halogen elements during subduction processes and their fate in the earth ′ s mantle. Therefore, we newly analyzed halogen
concentrations in regional representative lavas obtained from 13 volcanoes on the Quaternary volcanic front of the Southern
Volcanic Zone (SVZ) of Andean arc in Chile. In this presentation, we focus on fluorine content that has least influence ofdegassing on volcanism.
Fluorine contents of most analyzed samples are 100-300 ppm. To understand behavior of fluorine on fractional crystallization,
the correlations of SiO2 and FeO∗/MgO with fluorine data from a volcano are plotted. This result indicates that the fluorine
dependency with these parameters changes at SiO2 = 55 wt% and FeO∗/MgO = 4.2, resulting from apatite crystallization andremoval from the magma. Thus, the evolved rock samples from which apatite crystallized were excluded from further discussion.
We compared fluorine with major and trace element data obtained by previous study (Shinjoe et al., 2013) and newly revealed
that the fluorine concentrations of selected samples were not correlated with boron concentrations. This means that fluorineshows different behavior in the subduction zone magmatism though both fluorine and boron are fluid-mobile elements. The
basaltic samples from Hudson, the southernmost volcano of SVZ, show very high fluorine concentration (∼1000 ppm). Similar
anomalies were confirmed also with Nb and Ta. The chemical characteristics suggest that the magma source of this region has
been derived from the metasomatized mantle wedge by influence of slab-derived melt (Kilian and Behrmann 2003; Shinjoe etal., 2013). The fluorine concentration possibly becomes new sensitive detector of slab-derived melt in arc volcanism.

Keywords: fluorine, subduction zone, slab melt, slab fluid

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SGC50-10

Room:102A

Time:May 25 16:45-17:00

Volatile components of apatite grains from pyroclastic flow deposits of Aso volcano
DOKYU, Marie1∗ ; SANO, Yuji2 ; TAKAHATA, Naoto2 ; ISHIDA, Akizumi2 ; KOIKE, Mizuho2 ;YOSHIDA, Kenta3 ; HIGASHINO, Fumiko3 ; KOGISO, Tetsu1
1Graduate School of Human and Environmental Studies, Kyoto University, 2 Atmosphere and Ocean Research Institute, The
University of Tokyo, 3 Graduate School of Science, Kyoto University
Water in the Earth is important for life and mantle dynamics. The amount of water in the interior of the early Earth andchondrited is one of the most essential constraints for revealing the origin of the Earth’s water. An important clue to the water
budget in the early Earth is apatite grains in chondrites and in -4.4 Ga zircon from Jack Hills in Australia. Since apatite hasvolatile components, it is expected to determine the amount of water in chondrites and the interior of the early Earth from OH
composition of the apatite. However, partitioning and exchanging of volatile components, especially water, between apatite andmelt has been unclear. Mathez and Wabster (2002) and Webster et al. (2009) tried to reveal partitioning of F and Cl between
apatite, melt, and fluid with high-temperature and high-pressure experiments, but they did not discuss the exchange relationship involatile components’ site (X site) in apatite. Pan and Fleet (2002) suggests that volatile components in apatite should be affectedby other cation components. Accordingly, the goal of this study is to reveal the relationship of volatile components between
apatite and melt, including revealing the exchange relationship in volatile components’ site in apatite and other components
which affect on it.
We analyzed volatile compositions of apatite grains and melt inclusions in plagioclase phenocrysts from pyroclastic flow
deposits of Aso volcano with EPMA and nano-SIMS. We analyzed 4 samples, ryholitic and andesitic of Aso-3 and Aso-4. EPMA
and nano-SIMS analysis revealed that F concentrations in apatite in each sample show large variations while Cl concentrations
are constant, suggesting that F and OH substitute for each other in the X site. OH concentration in apatite of mafic sample waslarger than that of silicic one.
We find that F and Cl in apatite and these in melt inclusion have no correlation, while OH in apatite and water in host magma,
which is estimated from temperature, pressure, the composition of plagioclase, and so on (Kaneko et al., 2007), have a positive
correlation.We also find that the amount of OH and that of CaO, P2 O5 and MgO in apatite have positive correlations, therefore
Ca, P, and Mg could affect on the behavior of F and/or OH. Additionally, Number of cations in M site (assuming oxygen number= 13) was 4.66-4.88, which is smaller than expected from stoichiometry, suggesting that other components, such as rare earth
elements, would be present in M site.
Keywords: apatite, volatile component, water

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SGC50-11

Room:102A

Time:May 25 17:00-17:15

Garnet-amphibole fractionation generating basalt to dacite magmas of Pre-Komitake volcano, JapanSHIBATA, Tomoyuki1∗ ; YOSHIMOTO, Mitsuhiro2 ; FUJII, Toshitsugu2 ; NAKADA, Setsuya3
1

Beppu Geothermal Research Laboratory, Kyoto University, 2 Mount Fuji Research Institute, Yamanashi Prefectural Government, 3 Earthquake Research Institute, University of Tokyo
The Pre-Komitake volcano, which was discovered by scientific drilling into Mt. Fuji, is an older volcanic body than Fuji and
Komitake volcanoes buried beneath the NE flank of Fuji volcano (Nakada et al., 2004; Yoshimoto et al., 2010). The Fuji, Komitake, and Pre-Komitake volcanoes are situated in a complex tectonic setting near the junction of three plates: the North American
Plate in the east, the Eurasian Plate in the west, and the Philippine Sea Plate in the south, under two of which the Pacific Plate
subducts from east to west. The magmas of Pre-Komitake are different from those of Fuji and Komitake (Yoshimoto et al., 2010).
According to Yoshimoto et al. (2010), the Pre-Komitake lavas are characterized by hornblende-bearing andesites and dacites,in contrast to the hornblende-free basaltic rocks of Fuji and Komitake. These authors also suggested that the concentrations ofincompatible elements increase with increasing SiO2 in the magmas of Pre-Komitake, whereas those of Fuji increase despite
SiO2 remaining fairly constant (Fujii, 2007). They suggested that the variations in magma chemistry in this area between 250 ka
and recent times might have occurred as a result of a change in regional tectonics that occurred ˜150 ka, although this remains
unproven. To our knowledge, no detailed research has yet been carried out into Pre-Komitake magma genesis on the basis ofcomprehensive major and trace elements, and isotopic compositional data sets. Therefore, we analyzed the trace element andSr-Nd isotopic compositions of the Pre-Komitake magmas in order to better understand their genesis.
The Sr and Nd isotope ratios ranged from 0.703320?0.703476, and 0.512885?0.513087, respectively, which are very similar
to those of the lavas from Fuji and Komitake volcanoes (Nagai et al., 2004) that erupted subsequently. Enrichment of large
ion lithophile elements, Pb and Sr, can be seen in the primitive mantle-normalized multi-element diagram of the Pre-Komitake,
Komitake, and Fuji lavas. These collectively show island arc lava signatures, however, the middle to heavy rare earth elements
are more depleted in the Pre-Komitake lavas, compared to those from Fuji. Positive Eu anomalies are observed, although theextents of these anomalies decrease with increasing SiO2 in the Pre-Komitake lavas, whereas this is not observed in Fuji lavas.
The Sr/Y ratios of Pre-Komitake lavas increase from basalt to basaltic andesite, but decreases through andesite to dacite. Thisoccurs in combination with a rapid increase in La/Yb ratios, followed by a more gradual increase. A gradual decrease in Dy/Yb
ratios is also seen over the entire compositional range. These data suggest deep (>12 kbar) fractionation of garnet and amphibole
followed by shallow (i.e., ˜5 kbar) fractionation of amphibole and plagioclase. Such variations are not observed in the Komitake
and Fuji lavas, for which deep fractionation of clinopyroxene and shallow fractionation of plagioclase have been suggested. All
three lavas, including those from the Pre-Komitake volcano, show similar isotopic, major, and trace element compositions in theunfractionated basalts. The differing geochemical trends found in the Pre-Komitake lavas are likely to be due to different mineral
fractionations occurring in the hydrous Pre-Komitake basalts compared to the dry Fuji and Komitake basalts.

Keywords: Pre-Komitake volcano, Fuji volcano, Trace elements, Sr-Nd isotope ratios, Garnet fractionation

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Time:May 25 17:15-17:30

Partition of the platinum group elements between Cr spinels and whole rocks in boninites
from Ogasawara islands
SENDA, Ryoko1∗
1

JAMSTEC

Abundance of the platinum group elements (PGEs) in volcanic rocks are expected to have some information about source
mantle or magma genesis as other elements. Sulfides and Cr spinel are known to important host of PGEs, for example, enrichmentof PGEs are reported in chromitites from layered intrusions, ophiolites and alpine-type peridotites (Ahmed and Arai, 2002, Buchl
et al., 2004). Among volcanic rocks, however, Cr spinel can be observed in mafic-ultramafic magmas as komatiite and boninite.
The correlation between whole rock Cr and PGEs in magmatic rocks are observed (Hamlyn et al., 1985), whether PGEs status in
Cr spinels unresolved. Experimental studies on partitioning of PGEs between spinels and silicate melts are reported and showedsignificant amounts of IPGEs (Iridium-group PGE; Ru, Os, Ir) can be held in solid solution in spinel species as Cr spinels withhigh partition coefficient under oxidized conditions (fO2 >QFM +2). In empirical studies, the partitioning of Rh, Ru and Ir into
Cr spinels increases with increasing oxygen fugacity are shown in komatiites by Jung-Woo et al. (2012). Here newly PGE data of
Cr spinels and whole rocks from boninites Ogasawara and Guam islands are shown and have a discussion about PGE partitioning
in boninite and tholeiite magma.
Keywords: platinum group element, boninite, partition

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Room:102A

Time:May 25 17:30-17:45

Determining the deep crustal composition of Japan island arc using xenoliths
NAGAO, Jun1∗ ; OZAWA, Kazuhito2
1

Department of Earth and Planetary Science Graduate School of Science, The University of Tokyo, 2 Department of Earth andPlanetary Science Graduate School of Science, The University of Tokyo
Understanding the composition of the continental crust is central for deciphering its evolutionary history. The composition of
the deep continental crust has been inferred by combining seismic data and chemical data for metamorphic rocks and xenoliths.
Seismic wave speed reflects the density of the underground which is governed by the major elements. Thus, seismic data provide
insights into the structure and major element composition of the continental crust, but no constraints on the trace element composition. By contrast, analyses of metamorphic rocks and xenoliths are the best methods to measure the major and trace elementsof the deep continental crust, but the occurrence of these rocks is restricted.
So far, the deep crustal composition has been extensively investigated for continental regions, but that for island arc remains
poorly constrained. Because seismic data show differences in the thickness and the major element composition between continental shields and island arcs, it is important to independently determine the deep crustal compositions of island arcs. For thispurpose, we have analyzed ca. 100 xenolith samples from Ichinomegata in Akita and Takashima in Saga for the major and traceelement abundances.
The major element concentrations were measured by XRF, whereas the trace element concentrations were measured by LAICPMS.
The major element measurements revealed that the analyzed xenoliths from Ichinomegata have compositions ranging fromultramafic to intermediate, whereas those from Takashima are ultramafic to felsic. The trace element data for the Ichinomegata
and Takashima mafic xenoliths indicate that these rocks are depleted in high field strength elements (HFSE) such as Nb,Ta,Zr,Hf,
and enriched in large ion lithophile elements including Pb. The observed geochemical features are well explained by the generation of the lower crust of Japan island arc by fluid-related partial melting of the mantle wedge. When the data for the Japanesemafic xenolith samples are compared with those for the average lower (mafic) continental crust that is mainly based on analysesof metamorphic rocks and xenoliths from continental regions (Fig. 1), it is evident that the Japanese xenolith samples are lessenriched in most incompatible elements, despite their similar SiO2 contents to the average lower continental crust. In addition,
the relative depletion in the Japanese samples is more relevant for HFSE. These findings may indicate a higher degree of mantle
partial melting due to more efficient fluid supply in Japanese subduction zones relative to settings where most lower continental crusts were generated. Notably, the Japanese mafic xenolith samples have similar U contents to that of the average lower
continental crust. It is well known that U behaves as a fluid-mobile element under oxidative conditions, but as a fluid-immobile
element under reducing conditions. Also, it has been indicated that about 2.2 Ga, the Earth’s surface changed from reducing tooxidative environments. Taking these into account, the agreement in U contents together with different contents in other mostincompatible elements can be interpreted as reflecting that the significant part of the lower continental crust was formed when
the Earth’s surface was under reduced conditions and, therefore, U behaved as a fluid-immobile element during dehydration
processes. We found that among the analyzed xenolith samples in this study, major and trace element abundances are weakly
correlated. Although we need to investigate more xenolith samples from various areas to verify this inference, such correlation
would be useful to combine seismic data and chemical data for rock samples to develop a model of the deep crustal compositionof Japan island arc.
Keywords: Xenolith, Ichinomegata, Takashima, Neutrino, island arc, crustal composition

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Time:May 25 17:30-17:45

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