SGC50-01

Japan Geoscience Union Meeting 2016

Trace element composition in zircons from A-type granitoids in the Cape Ashizuri, SW
Japan: Implications for new source rock index using zircon*Kazue Suzuki1, Yusuke Sawaki2, Hisashi Asanuma2, Kentaro Hattori3, Takafumi Hirata3
1.Department of Earth and Planetary Science, The University of Tokyo, 2.Department of Earth andPlanetary Sciences, Tokyo Institute of Technology, 3.Division of Earth and Planetary Sciences,
Kyoto University
Trace element composition in zircon is expected to be an important indicator of composition of hostmagma, especially of Hadean detrital zircons (e.g. Grimes et al., 2007). Some Hadean detrital
zircons are suggested to be formed in continental crustal magma (e.g. Valley et al., 2005; Grimes
et al., 2007), however, detail composition of host magma is still unveiled. Recent discoveries of
granitic clast in meteorites in Early Solar System (lunar, HED and LL meteorite) showing anhydrous,
alkali-rich A-type granitic affinities (e.g. Warren et al., 1983; Bonin et al., 2002; Terada andBischoff, 2009) implies that A-type granitic rocks were present in the Hadean Earth (Bonin et al.,2007). Therefore, it is important to know trace element characteristics in zircons from A-typegranite for exploring evidence of the ancient A-type granitic rocks.
To obtain primary features of trace element composition in zircons from A-type granite, we
conducted in-situ LA-ICP-MS trace element analysis for 47 zircon grains from 4 samples of rapakivi
granite, Qtz-syenite and melanocratic syenite in the Ashizuri complex. These alkalic granitoids in
Ashizuri complex have characteristics of A-type granite (Loiselle and Wones, 1979) and within-plate
granite (Pearce et al., 1984), and is suggested to be formed dominantly by crystal fractionation
process from OIB-type basaltic magma (Stein et al., 1996).
Zircons from the Ashizuri A-type granitoids show oscillatory zoning, homogeneous dark core,
disturbed texture and patchy texture in Cathodoluminessence images. Based on the typical igneous
REE patterns (HREE enrichment, negative Eu anomaly and positive Ce anomaly) and its similarity eachother in zircons from rapakivi granite and Qtz-syenite, it is suggested that the trace element
composition of the zircons reflect those of the host magma. On the other hand, some zircons inmelanocratic syenite show large variations of REE pattern and include obvious inherited cores,
which imply contamination of surrounding rocks to host magma. To clarify characteristics of zircons
crystallized from A-type granitic magma, we only use data from the rapakivi granite and the
Qtz-syenite for comparison with previous data from other type (S-, I-, M-type) granitic rocks.
The magmatic zircons from the Ashizuri A-type granitoids show large Eu negative anomalies (Eu/Eu* =<0.004 –0.070), high Nb contents (2.85 –236 ppm), relatively high Y (423 –13520 ppm) and U contents(171 –7908 ppm), and relatively low Sr contents (0.08 –2.38 ppm). These trace element feature in
the zircons probably reflect high HFSE, low Eu and Sr concentration in the host A-type granitic
magma. The geochemical characteristics of the zircons from Ashizuri complex become more distinct in
Eu/Eu*, Nb/Sr, U/Sr, Y/Sr closs-plot diagram, showing lower Eu/Eu*, higher Nb/Sr, U/Sr and Y/Srratio compared to those in zircons from other type granitic rocks. Previous trace element data inzircons from A-type granitoids in Delamerian Orogen, South Australia (Pankhurst et al. 2013) isalso plotted on similar area to the Ashizuri A-type granitoids in Eu/Eu*vs. Nb diagram. Because
high HFSE, low Eu and Sr contents are common feature in the A-type granitic rocks, these diagrams
are probably useful for distinguish zircons crystallized in A-type granite from those in othergranitic rocks.
Keywords: Zircon trace element composition, A-type granite, LA-ICP-MS, the Cape Ashizuri, SW Japan©2016. Japan Geoscience Union. All Right Reserved.

- SGC50-01 -SGC50-01©2016. Japan Geoscience Union. All Right Reserved.

Japan Geoscience Union Meeting 2016

- SGC50-01 -SGC50-02

Japan Geoscience Union Meeting 2016

Geochemistry of monazite in granitic rocks from Japanese island arc*Keita Itano1, Tsuyoshi Iizuka1, Mihoko Hoshino2
1.Earth and Planetary Science, The University of Tokyo, 2.National Institute of Advanced Industrial
Science and Technology
Monazite is a one of rare earth element (REE)-rich phosphate mineral and commonly occurs in pelitic
metamorphic rocks and peraluminous igneous rocks (Williams et al., 2007). Geochemistry ofmetamorphic monazite has been intensively investigated using laser ablation-inductively coupledplasma-mass spectrometry (LA-ICPMS) and its REE pattern, especially Eu negative anomaly ([Eu/Eu*]N) and heavy REE (HREE) depletion ([Gd/Lu]N), is linked to the crystallization condition (e.g.,
Rubatto et al., 2006). In contrast, the geochemical investigation of igneous monazite has been
mainly carried out using electron-microprobe analysis (EMP) (e.g., Kelts et al., 2008). Hoshino etal. (2012) analyzed the monazites in granites and pegmatites from Japan by EMP. They found that theratios of light REE (LREE) to middle REE (MREE) on the monazites are different between ilmeniteand magnetite- series granitic rocks, which was interpreted to reflect the different degree ofdifferentiation. Yet, the determination of Eu and HREE abundances have not been carried out due tothe interference and low-concentrations during EMP analysis. In this study, we have used LA-ICP-MS
to measure Eu and HREE abundances in the monazites and examined whether Eu anomaly and HREE
depletion exhibit consistent variations with LREE or not. The results of monazite REE analysis
using LA-ICPMS shows distinct REE patterns between the monazites from ilmenite-series andmagnetite-series granitic pegmatites. The Eu negative anomalies of the igneous monazites weresignificantly large ([Eu/Eu*]N < 10-3) relative to those of metamorphic monazites. This feature may
be used as indicator to distinguish between a monazite in pegmatite and a one in metamorphic rock.
Among the monazites of the two series, the [Eu/Eu*]N values of ilmenite-series monazites are larger
by one or two orders of magnitude than those of magnetite-series monazites. The REE patterns ofmonazites in ilmenite-series rocks display moderate decrease from La to Gd relative to those ofmonazites in magnetite-series rocks; in contrast, the monazite REE patterns of ilmenite-series
rocks show prominent decrease from Gd to Lu relative to those of magnetite-series rocks. These
different features in REE patterns between monazites from ilmenite-series and magnetite-series
would reflect the degree of differentiation and imply that the formation of ilmenite-series rocks
is attributed to not only assimilation of sediments but also crystal fractionation, especially thefractionation of minerals incorporating HREEs relative to MREEs. The relatively enriched MREE anddepleted HREE abundances in ilmenite-series monazite cannot be explained simply by assimilation of
subducted sediments, which are enriched in both MREE and HREE (Plank and Langmuir, 1998). This
inference is consistent with the differences of O, Sr and Nd isotopic features between two-series
granitic rocks (Takagi, 2004). We consider that fractional crystallization of the minerals enrichedin HREE relative to MREE (e.g., garnet) subsequent to sedimentary assimilation defines thecharacteristic monazite REE patterns of the magnetite-series and ilmenite-series granitic rocks inJapanese island arc.
Keywords: REE, trace element, LA-ICP-MS©2016. Japan Geoscience Union. All Right Reserved.

- SGC50-02 -SGC50-03

Japan Geoscience Union Meeting 2016

Highly siderophile element variations in the Ontong Java Plateau basalts*Akira Ishikawa1,2, Atsushi Utsunomiya3, Keiko Koshida1, Maria Luisa Tejada2, Tsuyoshi Komiya1,
Katsuhiko Suzuki2, Takashi Sano4
1.The University of Tokyo, 2.JAMSTEC, 3.Japan Geocommunications Co. Ltd., 4.National Museum of
Nature and Science
The Early Cretaceous Ontong Java Plateau is widely recognized as a product of the largest igneous
activity on the Earth, and its formation and evolution has been investigated by multidisciplinary
approaches in order to understand large igneous provinces (LIPs) in general. Recent geochemical
studies suggest that the Ontong Java Plateau has sampled a near-primitive, less degassed deep
mantle reservoir that has remained isolated from convecting upper mantle shortly after theformation of the Earth. Since such primitive reservoir is possibly only available at the base oflower mantle in the modern Earth, the plateau-forming lavas may have characteristic compositions ofhighly siderophile elements reflecting the deep-plume source likely influenced by core formation or
core-mantle interaction. Here we report comprehensive dataset of Re-Os isotopes and highly
siderophile element (HSE: Os, Ir, Ru, Pt, Pd and Re) concentrations for all three distinct
geochemical types of the Ontong Java Plateau basalts. They are comprised of 11 samples of the lessevolved Kroenke-type lavas (>8 wt.% MgO) from two deep sea drill sites (ODP Sites 1185 and 1187),
22 samples of the more dominant Kwaimbaita-type basalts (<8 wt.% MgO) from three drill sites (ODP
Sites 1183, 1185 and 1186) and on-land exposure in Malaita, Solomon Islands and 22 samples of lessvoluminous Singgalo-type basalts (<8 wt.% MgO with a few exceptions) forming younger cover on the
Kwaimbaita-types lavas at an ODP Site 807 and Malaita. All of Kroenke- and most of Kwaimbaita-typebasalt data yield a linear array on the Re-Os isochron diagram corresponding to an age of 121.5 ±3.1 Ma and initial 187Os/188Os ratio of 0.1304 ±0.0049, almost identical to those reported inprevious studies. Singgalo-type basalts tend to show variably radiogenic initial 187Os/188Os ratios,
indicating contributions of enriched components either derived from surficial environments or fromradiogenic pyroxenitic source. Significant contributions of pyroxenitic source is inferred from theobservation that Singgalo-type lavas have distinctively lower platinum-group element (PGE)
abundances when compared with similarly evolved Kwaimbaita-type basalts, althoughsulfide-fractionation may have played a role on their depletions. The chondrite-normalized HSE
patterns of Kroenke- and Kwaimbaita-type basalts show broadly similar IPGE-depleted and
PPGE-enriched patterns typical of sulfer-undersaturated tholeiitic basalts. However, the two types
can be distinguished by contrasting Os and Ru abundances (Kroenke: high, Kwaimbaita: low) probably
reflecting the different degrees of olivine/spinel fractionation. Since the observed HSE
fractionation trend (particularly Ir variation) is significantly different from those identified
for Hawaiian picrites or Archean komatiites, further constraints on HSE behavior during magma
evolution are clearly required for estimating HSE compositions of primitive magma and source
mantle.
Keywords: Large Igneous Provinces, basalt, Platinum-group elements©2016. Japan Geoscience Union. All Right Reserved.

- SGC50-03 -SGC50-04

Japan Geoscience Union Meeting 2016

Os isotope ratios and PGE abundances of the Pitcarn basalts: Implication for the EM-1
source*Ryoko Senda1, Akira Ishikawa2, Takeshi Hanyu1, Hiroshi Kawabata3, Toshiro Takahashi4, KatsuhikoSuzuki5
1.Department of solid earth geochemistry, Japan Agency for Marine-Earth Science and Technology,
2.Department of Earth Science and Astronomy, The University of Tokyo, 3.Faculty of Science, Kochi
Univeristy, 4.Department of Geology, Niigata University, 5.Research and Development Center for
Submarine Resources, Japan Agency for Marine-Earth Science and Technology
It is widely known that subduction recycled materials are involved in producing the chemical andisotopic heterogeneities observed in oceanic island basalts (OIB). The type of recycled materialpresent in the Enriched Mantle 1 (EM-1) source, which have radiogenic Sr, unradiogenic Nd, andunradiogenic Pb isotope compositions compared to those of depleted mantle source, has been widely
debated. Oceanic crust with pelagic sediment (e.g., Chauvel et al., 1992), delaminatedsubcontinental lithospheric mantle (SCLM) (e.g., Hauri and Hart, 1993), subducted oceanic plateaus(Gasperini et al., 2000) and just single melting process involving pristine mantle (Collerson etal., 2010) have all been invoked as the EM-1 source. The rocks from Pitcairn hotspot are well known
to have a strong EM-1 flavor. Recently, Garapic et al. (2015) suggested that the high Ti abundancesin the Pitcairn basalts are possibly related to recycled pyroxenites in the Pitcairn mantle source.
We have measured Os isotope ratios and major and trace element abundances including the platinumgroup elements (PGE) in the basalts from Pitcairn Island to elucidate the origin of the EM-1
signature of these basalts.
The Os isotope ratios for the samples with Os > 20 pg/g range from 0.135 to 0.152 and are similar
to those measured in previous studies on EM-1-type basalts (~0.150 for samples with Os > 50 pg/g
and ~0.180 with Os > 20 pg/g from Reisberg et al., 1993; Eisele et al., 2002; Garapic et al.,2015). The Os, Ir and Ru concentrations of the Pitcairn basalts are roughly correlated with MgO andNi contents and tend to be lower than those of other OIB such as Hawaii and Canary Islands. Whereas
Pd and Re concentration are similar to those for other OIBs. The chondrite-normalized PGE patternsof studied samples show systematic variation with or against the degree of the EM-1 flavor (e.g.,decreasing of the 206Pb/204Pb and 143Nd/144Nd isotope ratios). Since crustal materials normally show
large fractionation between I-PGE and P-PGE and the crustal materials have higher Os isotope ratios
than mantle, the simple assimilation of crustal materials cannot explain our data. We carefully try
to make an assumption of the source magma components to explain the genesis of Pitcairn Island
basalts based on our data combined with previous studies.
Keywords: PGE abundances, Os isotope ratio, EM-1

©2016. Japan Geoscience Union. All Right Reserved.

- SGC50-04 -SGC50-05

Japan Geoscience Union Meeting 2016

Geochemical study of melt inclusions in Pitcairn basalts, South Pacific*Takahiro Ozawa1, Takeshi Hanyu2, Hikaru Iwamori2,1, Morihisa Hamada2, Takayuki Ushikubo3, Kenji
Shimizu3, Motoo Ito3, Jun-Ichi Kimura2, Qing Chang2, Tsuyoshi Ishikawa3
1.Tokyo Institute of Technology, 2.Department of Solid Earth Geochemistry, Japan Agency for
Marine-Earth Science and Technology, 3.Kochi Institute for Core Sample Research, Japan Agency for
Marine-Earth Science and Technology
The existence of water and volatile element is important in thinking about mantle dynamics, and a
lot of trials limiting volatile element content and distribution in mantle from the volcanic rockfrom mantle are made. In this study, we analyzed major element, trace element, volatile element,
lead isotope at local site for the olivine melt inclusions that they were thought that had volatileelement. As a result, we obtained a preliminary result about melt inclusions from the Pitcairn
island, South Pacific. The isotope composition of the volcanic rocks of Pitcairn island show
composition range to EM1 from DM. We chose two EM1-like basalt rock samples of PC-41 and PC-87A in
this study, and prepared melt inclusions more than 50μm to analyze a local site by some analyzers.
Each melt inclusion varied in a characteristic, and there were two kinds which crystallized
amphibole and ilmenite and crystallized euhedral clinopyroxene in melt inclusions of PC-41. Melt
inclusion of PC-87A includes homogeneous glass or dendritic clinopyroxene e equally. Therefore theanalysis domain set it from the mineral which crystallized to the maximum in remote glass or thefoundation stone domain. Firstly we measured volatile elements (H2O, CO2, F, P, S, Cl) at a 30μm
diameter and lead isotope at a 30μm diameter using SIMS (IMS 1280-HR). In the next place, I
measured main element at 10μm diameter using FE-EPMA. Finally I measured about a major element andtrace element at 20μm or a 30μm diameter using LA-ICP-MS. There was not the difference with PC-41
and PC-87A about lead isotope ratio, and they were in the isotope ratio range same as all rocks.
However, there was difference in both about the elementary composition. Compared with MgO and othermajor elements, PC-87A shows in same trend as all rock composition, but PC-41 clearly shows two
different trends. Because these two trends of PC-41 relate to the difference in crystallized out
minerals, they separated by crystallization after melt inclusions trapped by olivine. In adding
PC-41 is congruent with crystallization advancing to MgO being lower than PC-87A more in PC-41.
About trace elements, PC-87A accorded for the composition of all rocks, however there was different
composition from like PC-87A in PC-41. Difference of two compositions in PC-41 were not concernedwith crystallization and major elements. The latter has low HREE in characteristically, this seems
that the melt coexisted with garnet under high pressure flows into the magma reservoir and produces
heterogeneity of the composition in magma reservoir. About volatile elements, there is remarkabledifference of quantity of H2O in PC-41 and PC-87A. PC-41 has 0.03-0.10 wt.% and a low value whereas
PC-87A has 0.37-0.81 wt.% . CO2 does not maintain original value by degassing and enrichment of thegas phase. Halogen elements is hard to relatively degass, for example Cl has high 570-1700ppm andcorrelates with H2O and other trace elements, and seems reflect composition of the mantle source.
In conclusion, quenched homogeneous melt inclusions such as PC-87A seems maintain information ofdeep mantle, and are important in estimating H2O and volatile elements composition from melt
inclusions in the mantle source. Melt inclusions crystallized out well such as PC-41, however,greatly lost H2O in degassing and diffusive process and are difficult to estimate composition of
the primary magma.

©2016. Japan Geoscience Union. All Right Reserved.

- SGC50-05 -SGC50-06

Japan Geoscience Union Meeting 2016

Origin of geochemical mantle reservoirs: Roles of subduction filter and thermal evolutionof mantle*Jun-Ichi Kimura1, James B Gill2, Peter E van Keken3, Susanne Skora4, Hiroshi Kawabata5
1.Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Scienc and Technology,
2.Department of Earth and Planetary Sciences, University of California Santa Cruz, 3.Department of
Terrestrial Magnetism, Carnegie Institution for Science, 4.Institute of Geochemistry and Petrology,
ETH, 5.Research and Education Faculty, Kochi University
Upwelling mantle melts at Mid-Ocean Ridges (MOR) to form basaltic igneous oceanic crust (IOC). IOC
and overlying sediment (SED) descend into the mantle at subduction zones (SZ). The IOC, SED, andoverriding mantle melt to form stable continental crust (CC) after crustal-level processing,whereas the residual slab is recycled into the lower mantle. We quantitatively explore the element
re-distributions at MOR and SZ using numerical mass balance models, and we evaluate their roles inthe Earth’s geochemical cycle. Our models of slab residues differ from previous ones by being
internally consistent with geodynamic models of modern arcs and successful explanations of modern
arc magma genesis, and by including element fluxes from the dehydration or melting of eachunderlying slab component. We find that the upper mantle potential temperature (Tp) was 1400–1650 °C from 3.5 to 1.7 Gyr before decreasing gradually to ~1300 °C today. Hot SZs with Tp ~1600 °C havea thermal structure like modern SW Japan where high-Mg andesite is formed that is like CC.
Isotopically, residual IOC from hot SZ evolves to the HIMU OIB reservoir, residual SED to EMII, theresidual base of the mantle wedge to EMI, and the residual top of the mantle wedge to thesubcontinental lithosphere (SCLM) reservoir, after 1.7–2.5 Gyr of storage in the lower mantle. The
Common (C) or Focal Zone (FOZO) reservoir is a stable mixture of the first three residues. Older
recycled residues (~2.5 Gyr) form the DUPAL anomaly in the southern hemisphere, whereas younger
ones (~1.7 Gyr) are in the northern hemisphere. These ages correspond to major CC forming events.
We attribute the E-W heterogeneity of the depleted upper mantle (DMM) to involvement of
sub-Gondwana SCLM except in the Pacific.
Keywords: Mantle reservoir, Subduction zone filter, Thermal evolution of mantle©2016. Japan Geoscience Union. All Right Reserved.

- SGC50-06 -