BPT05-01

Japan Geoscience Union Meeting 2016

The progress of research on REY-rich mud within the Minamitorishima EEZ*Yasuhiro Kato1,2,3, Koichiro Fujinaga3,1, Kentaro Nakamura1,2, Kazutaka Yasukawa1,3, Junichiro Ohta1,
Yutaro Takaya4,1, Koichi Iijima2, Shiki Machida2,1, Tatsuo Nozaki2,1, Jun-Ichi Kimura2, KatsuhikoSuzuki2, Hikaru Iwamori2,5
1.Department of Systems Innovation, Graduate School of Engineering, University of Tokyo, 2.Japan
Agency for Marine-Earth Science and Technology, 3.Chiba Institute of Technology, 4.Department of
Resources and Environmental Engineering School of Creative Science and Enginerring, Waseda
University, 5.Tokyo Institute of Technology
Three years have passed since the amazingly fruitful research cruise KR13-02 resulted in a
discovery of deep-sea mud extremely enriched in rare-earth elements and yttrium (REY) within theJapanese exclusive economic zone (EEZ) surrounding Minaimitorishima Island. The mud with maximum
total REY content of ~8,000 ppm strongly attracts our attention as an unconventional and highly
promising deep-sea mineral resource. Subsequent six cruises, i.e., MR13-E02, KR14-02, MR14-E02,
MR15-E01 Leg 2 and Leg 3, and MR15-02, have highlighted that the southern part of the
Minamitorishima EEZ appears to be the unique area where the “extremely REY-rich mud” lies at very
shallow depth (2 to 4 m) below the seafloor. In the presentation, we report a general overview of
our latest findings from various approaches to REY-rich mud in the Minamitorishima EEZ including
chemical, physical, statistical and engineering techniques.
Keywords: deep-sea mineral resource, REY-rich mud, Minamitorishima Island©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-01 -BPT05-02

Japan Geoscience Union Meeting 2016

Distribution of highly/extremely REY-rich mud layers in the southern part of the
Minamitorishima EEZ: Insight from major and trace element geochemistry*Kentaro Nakamura1, Kazutaka Yasukawa1, Koichiro Fujinaga1, Yasuhiro Kato1,2,3
1.Department of Systems Innovation, School of Engineering, The University of Tokyo, 2.Frontier
Research Center for Energy and Resources (FRCER), School of Engineering, The University of Tokyo,
3.Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Since the discovery of highly/extremely REY-rich mud layer (more than 2000/6000 ppm ΣREY) within
the Japanese Exclusive Economic Zone (EEZ) around the Minamitorishima Island [1], exploitation of
REY-rich mud has attracted particular interest because of its high potential as a REY resource.
Detailed investigation by subbottom profiling and piston coring conducted over the last three years
has revealed the distribution of REY-rich mud (>400 ppm ΣREY) and overlying non-REY-rich sediments
within the Minamitorishima EEZ [Nakamura et al., in revision]. However, both lateral and vertical
distributions of the highly/extremely REY-rich mud layers are still uncertain. Here we examine
major and trace element compositions of deep-sea sediments cored from the Minamitorishima EEZ. On
the basis of geochemical characteristics, REY-rich mud can be subdivided into six types including
highly/extremely REY-rich mud, and the highly/extremely REY-rich mud layer is the second top layerof the REY-rich mud succession. In the presentation, we discuss the distribution of each layer ofthe REY-rich mud and its paleoceanographic implication.
Keywords: highly/extremely REY-rich mud layers, Minamitorishima EEZ, geochemistry©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-02 -BPT05-03

Japan Geoscience Union Meeting 2016

Distribution of extremely REY-rich mud in the southern part of the Minamitorishima EEZ*Koichiro Fujinaga1,2, Kazutaka Yasukawa2,1, Shiki Machida3,2, Tatsuo Nozaki3,2, Yutaro Takaya4,2,
Junichiro Ohta2, Kazutaka Oya2, Daiki Niikuma4, Yoshiro Nishio5, Yuka Masaki3, Yoichi Usui3, Satoru
Haraguchi3, Koichi Iijima3, Hiroshi Amakawa3, Katsuhiko Suzuki3, Kentaro Nakamura2,3, Yasuhiro Kato
2,3,1

, MR15-E02 Leg.2 cruise members

1.Chiba Institute of Technology, 2.Department of Systems Innovation, School of Engineering,
University of Tokyo, 3.Japan Agency for Marine-Earth Science and Technology, 4.Department of
Resources and Environmental Engineering School of Creative Science and Enginerring, Waseda
University, 5.Research and Education Faculty, Kochi University
Since the discovery of the “extremely REY-rich mud” (ΣREY > 5000 ppm) in the Japanese exclusive
economic zone (EEZ) surrounding Minamitorishima Island (Kato et al., 2013), we conducted sevenresearch cruises over three years. In the MR15-E01 Leg 2 cruise, one of the latest research cruises
by R/V Mirai from March 14 to 28, 2015, we focused to investigate the detailed distribution of theextremely REY-rich mud in the southern part from the Minamitorishima EEZ. During the cruise, wecollected 13 sediment cores by piston coring. Here, we report the distribution, visual coredescriptions, bulk-sediment chemical compositions of the deep-sea sediment in the southern part of
the Minamitorishima EEZ in order to clarify geological and geochemical characteristics of theextremely REY-rich mud.
Keywords: rare earth elements and yttrium (REY), REY-rich mud, Minamitorishima Island, deep-sea
mineral resource©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-03 -BPT05-04

Japan Geoscience Union Meeting 2016

Geochemical independent components constituting deep-sea sediments within the
Minamitorishima EEZ*Kazutaka Yasukawa1,2, Kentaro Nakamura1, Koichiro Fujinaga2,1, Junichiro Ohta3,1, Hikaru Iwamori3,4,
Yasuhiro Kato1,2,3
1.School of Engineering, The University of Tokyo, 2.Chiba Institute of Technology, 3.JAMSTEC,
4.Department of Earth and Planetary Sciences, Tokyo Institute of Technology
Recently, the presence of “extremely REY-rich mud”, deep-sea sediments containing extraordinarily
high concentrations of rare-earth elements and yttrium (REY), was confirmed within the Japanese
exclusive economic zone (EEZ) surrounding Minamitorishima Island (Kato et al., 2013; Fujinaga etal., 2013; Iijima et al., submitted). The maximum total REY content in the extremely REY-rich mud
exceeds 7000 ppm, which is higher than that of any other deep-sea sediment ever reported from theworld ocean.
Deciphering the genesis of the mud should provide us groundbreaking insights into both thepotential distribution of the novel resource for REY of great economic value and the mystery of
paleoceanographic event(s) that caused an anomalous concentration of specific elements in an abyss.
As a first step to achieve the goal, it is quite important to unravel the source materials andphysicochemical processes that generated the sedimentary sequence.
Here we applied Independent Component Analysis to the comprehensive data set composed of major- andtrace-elemental contents of more than 800 bulk deep-sea sediment samples collected from the
Minamitorishima EEZ. Although being a preliminary interpretation, several geochemical independent
components can be extracted from the whole data structure; e.g., biogenic calcium phosphate
associating with very high REY content, Fe-Mn oxides accompanied by characteristic metals, etc. We
report the results and interpretation of our new analysis, and statistically characterize thedeep-sea sediments within the Minamitorishima EEZ.
-- References -Fujinaga, K. et al. (2013) JpGU Meeting 2013.
Kato, Y. et al. (2013) JpGU Meeting 2013.
Keywords: deep-sea sediment, REY-rich mud, Independent Component Analysis©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-04 -BPT05-05

Japan Geoscience Union Meeting 2016

Evidence from the Acasta zircons for consistent occurrence of magmas with moderately
elevated d18O throughout the Eoarchean*Takayuki Ushikubo1, Tsuyoshi Iizuka2, Michael J. Spicuzza3, John W. Valley3
1.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology,
2.University of Tokyo, 3.University of Wisconsin-Madison
Oxygen isotope ratio of undamaged zircon is a refractory signature and useful to infer petrogenesisof its host rock [1,2]. The d18O values of zircons from primitive magmas are 5.3±0.6‰ (2 SD)[3].
Occurrence of ‘supracrustal’ d18O values (>6.3‰) in >4 Ga zircons from the Jack Hills, Western
Australia indicates existence of hydrated crustal rocks and chemically differentiated crust by 4.3
Ga [4]. However, because Jack Hills zircons are detrital and no host rock is known, it is difficult
to reconstruct crustal evolution in the early Earth. The Acasta Gneiss Complex (AGC) in the Slave
Province, Canada is one of the best places to study early crustal evolution because multiple
generations of Eoarchean rocks are preserved [5].
In this study, oxygen isotope ratios (d18O) of zircons from six felsic gneisses and one pegmatiteof the AGC [5] were measured with an ion microprobe, CAMECA IMS 1280-HR at Kochi Institute,
JAMSTEC. We selected zircons which exhibit concordant U-Pb age (mostly with 0±2% discordance) [5]and the samples can be classified into three groups based on their crystallization ages, >3.9 Ga,
ca. 3.75 Ga, and ca. 3.6 Ga zircons, respectively. A new kimberlite zircon standard: KC-KLV-Zrc1
from Kaalvallei, South Africa (d18O=5.43±0.14‰ VSMOW, 2 SD, determined by a laser fluorination andgas-source mass spectrometry at University of Wisconsin-Madison) was used as a running standard for
SIMS analysis. Typical spot-to-spot reproducibility of d18O values was ±0.26‰ (2 SD). The 16OH−/16O−
ratios of zircons, which is an indicator of radiation damage [6], were monitored during oxygenisotope analysis and analysis pits were examined by SEM after the analyses to identify disturbed d
18

O values by later alteration. We use oxygen isotope data from zircons with no evidence for later

alteration.
Multiple oxygen isotope analyses within individual zircon grains showed that some AGC zircons havevariable oxygen isotope ratios by ca. 0.5‰ correlated with growth zoning layers recognized by
Cathodoluminescence (CL). The studied AGC zircons commonly have moderately elevated d18O values(6.0 to 6.5‰) with a few exceptions of lower d18O values (down to 5.0‰) in >3.9 Ga zircons. No low
d18O values (<4.7‰), which were recognized in ca. 4.0 Ga zircons from Idiwhaa tonalitic gneiss in
the AGC [7] are observed from the samples in this study. Consistent occurrence of zircons withmoderately elevated d18O values (6.0 to 6.5‰) from ca. 4.0 Ga to 3.5 Ga indicates that productionof sediment and incorporation of sediment to magma sources consistently occurred in the Acasta
region in this period. Since zircons with low d18O values are recognized in a tonalitic gneiss at
ca. 4.0 Ga [7], interaction of crustal rocks with fluid at high temperatures would have occurred at
an earlier stage of felsic rock formation. Oxygen isotopic characteristics of AGC zircons,moderately elevated with a narrow range of d18O values (6.0 to 6.5‰), is distinct from that ofzircons from West Greenland (<6.0‰ at ca. 3.8-3.9Ga) [8]. In addition, higher d18O values arerecognized in >4.0 Ga zircons from Jack Hills [e.g., 3,4]. The distinct O isotope evolution among
the terranes indicate that crust-forming processes have been already established by Eoarchean.
References:[1] Page F. Z. et al. (2007) Am. Mineral. 92, 1772-1775. [2] Valley J. W. et al., (2014)
Nature Geosci. 7, 219-223. [3] Valley J. W. et al. (2015) Am. Mineral. 100, 1355-1377. [4] Cavosie
A. J. et al. (2005) Earth Planet. Sci. Lett. 235, 663-681. [5] Iizuka T. et al. (2007) Precam. Res.
153, 179-208. [6] Wang X.-L. et al. (2014) Chem. Geol. 389, 122-136. [7] Reimink J. R. et al.
(2014) Nature Geosci. 7, 529-533. [8] Hiess J. et al. (2009) Geochim. Cosmochim. Acta 73,4489-4516.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-05 -BPT05-05

Japan Geoscience Union Meeting 2016

Keywords: Acasta Gneiss, zircon, oxygen isotope, SIMS

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-05 -BPT05-06

Japan Geoscience Union Meeting 2016

Hadean detrital zircons in the Jack Hills metaconglomerate, Western Australia:
Implications for Hadean Earth tectonics*Shinji Yamamoto1, Tsuyoshi Komiya2, Tsuyoshi Iizuka2, Takazo Shibuya3, Kenneth D Collerson4, Shuhei
Sakata5, Hideyuki Obayashi5, Takafumi Hirata4, Yukio Isozaki5, Shigenori Maruyama6
1.Yohohama National University, 2.The University of Tokyo, 3.JAMSTEC, 4.Queensland University,
5.Kyoto University, 6.Tokyo Institute of Technology
Hadean (4.56-4.0Ga) rocks are absent on the modern Earth. Yet, the firs 600 million years is themost critical and important period of the habitable planet Earth to understand the generalinterests whether or not the habitable planet can be appeared as only one rocky planet among allplanets or satellites in solar system, as we understand through research history. The Jack Hills
metasedimentary rocks have long been investigated because of the presence of Hadean zircons back to
ca. 4.4 Ga (e.g. Wild et al., 2001; Holden et al., 2009; Valley et al, 2014). Previous research not
only for geochronology but also mineral inclusions in detrital zircons ranging in age between 3.0
Ga and 4.4 Ga have given excellent information on the Hadean surface environment. Here we described
additional information for the Hadean magma and impact evidence based on mineral inclusions,specifically apatite, to estimate the space environment and host magma which is presumably felsic
TTG magma. The result showed plate tectonics must have been operated back to 4.3 Ga because of thepresence of TTG magma and possible presence of ocean back to 4.3 Ga because mineral inclusions in
Hadean zircon cover various minerals dominated by quartz, plagioclase, K-feldspar, apatite,muscovite, biotite with subordinate amounts of hornblende, rutile, monazite, magnetite, hematite,
pyrite and goethite, indicating the host magma must have been granitic composition. To produce thefelsic magma similar to the modern Earth plate tectonics must have been already operated. Plate
tectonics also needs the presence of thick ocean to cover the mid oceanic ridge.
Keywords: Hadea, zircon, Jack Hills©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-06 -BPT05-07

Japan Geoscience Union Meeting 2016

Composition of the Hadean oceanic crust and its hydrous melting experiments: Investigation
for the composition of the Hadean oceanic and continental crust*Nozomi Kondo1, Tetsu Kogiso1
1.Graduate School of Human and Environmental Studies, Kyoto University
The process of the mantle-crust differentiation and the composition the oceanic and continental
crust in the Hadean era (before 4.0 Ga), just after the formation of the Earth, are essential tounderstand the chemical mantle evolution due to the extraction and recycling of the crust, and theeffect of the nutrients supplied from crust to hydrosphere, on the birth and evolution of the earlylife. From the analyses of the Hadean zircon, the existence of liquid water and granitic-andesitic
melt have been implied (Trail et al. 2007; Hopkins et al. 2010), but the process to generate suchgranitic-andesitic melt and the composition of the melt are still unclear. Previous studies havesuggested that the Hadean mantle would have had high potential temperature, and that the oceanic
crust generated at high mantle potential temperature (MPT) has komatiitic composition (Takahashi1985). Because the hot Hadean mantle could have generated steep thermal gradient in the crust, thiskomatiitic oceanic crust could have experienced hydrous melting upon subduction, and generated
granitic-andesitic melt which could have formed the continental crust. However, the hydrous meltingof komatiitie and the possibility for the komatiitic oceanic crust to have contributed to thegeneration of the Hadean continental crust have been scarcely investigated. This study aims todetermine the major element composition of the melt generated by hydrous melting of komatiitic
oceanic crust, and constrain the composition of the probable Hadean continental crust and theprocess of its generation.
We estimated the style of the igneous activity in Hadean and the composition of the oceanic crust,referring previous mantle convection models at high MPT (Korenaga 2009; Foley et al. 2014). The
Hadean oceanic crust would have formed form the melt generated at small melt fraction under a thick(-200km) lithosphere before the onset of the plate-tectonics, and after the onset of theplate-tectonics, formed from the melt generated at large melt fraction under oceanic ridges. Then,the composition of the oceanic crust was estimated from high pressure and high temperature melting
experiments (Kondo et al. Submitted) in the case before the onset of the plate-tectonics, and from
calculations with pMELTS in the case after the onset of the plate-tectonics. The compositions of
the melt were estimated to be komatiitic in both cases, though the MgO and FeO contents are
significantly different between the two cases. We synthesized starting powders of these komatiitic
compositions from oxide and carbonate powders, and performed hydrous melting experiments using thepiston-cylinder high pressure apparatus. In experiments, the oxygen fugacity was carefully analyzed
and assessed. In this presentation, we report the estimated compositions of the probable Hadean
oceanic crust and progress of the hydrous melting experiments.
Keywords: Hadean, continental crust, komatiite, hydrous melting experiment©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-07 -BPT05-08

Japan Geoscience Union Meeting 2016

Estimation of the ocean tide on the early Earth based on the all ocean model*Mai Motoyama1, Hideo Tsunakawa1, Futoshi Takahashi2
1.Deparment of Earth and Planetary Sciences, Tokyo Institute of Technology, 2.Deparment of Earthand Planetary Sciences, Kyushu University
The ocean tide is one of the important factors affecting the Earth’s surface environment and theevolution of the Earth-Moon system. According to the Giant impact hypothesis, the Moon was formed
at a distance of about three Earth’s radius (RE) 4.6 billion years ago. In this case, the tidal
force in the ocean of the early Earth would be more than ten to thousand times as strong as thepresent. However previous studies pointed out that severe attenuation of tidal waves might work due
to mechanical response of seawater motion to result in relatively calm state (e.g. Abe et al.,1997). In the present study, we have analyzed tidal response of the ocean on the early Earthassuming the simple model in which the constant-depth ocean covers all the surface of the rigid
Earth (called the all ocean model). The ocean depth is treated as a parameter of 1300, 2600 and
5200 m, since the present volume of the seawater gives ~2600 m depth for the all ocean model. The
tidal force is assumed to be caused by the Moon’s gravitational force since the Earth-Moon distanceshould be smaller at the early time than at present. Assuming reasonable values of the friction andthe Earth’s rotation period, we have analyzed the tidal response of mode Ynm (n, m ≤3) in the allocean model, where Ynm is the spherical harmonics of degree n and order m. We will discuss possible
resonance and estimate height of the tidal wave.
Keywords: Early Earth, Ocean, Tide

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-08 -BPT05-09

Japan Geoscience Union Meeting 2016

Occurrence and U-Pb zircon dating of the Archean Dongshan gneiss in Anshan, the North
China Craton*Hiroki Uehara1, Tsuyoshi Komiya2, Shinji Yamamoto4, Yoshiaki Kon3, Yibing Li5, Wei Jin6
1.Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo,
2.Department of Earth Science & Astronomy Graduate School of Arts and Sciences, The University ofTokyo, 3.National Institute of Advanced Industrial Science and Technology, 4.Graduate School ofEnvironment and Information Sciences, The Yokohama National University, 5.Institute of Geology,
CAGS, 6.Univ. Jilin
The Eoarchean geologic terrains are quite rare in the world. Most of them are distributed in theLaurentia, and only two terrains of Anshan, North China and Mt. Sones, Antarctica are outside theLaurentia. The Anshan area in northeastern part of North China Craton is one of a few places, where
over 3.8 Ga crustal materials are found, in the world. Previous works reported ca. 3.8 Ga zircons
from the Baijiafen and Dongshan gneisses (Liu et al., 1992; Song et al., 1996). But, Wu et al.
(2008) emphasized that the protolith of granitic gneisses were emplaced at 3.3 Ga, and that theolder zircons, up to 3.8 Ga, are inherited. The U-Pb dating and Cathodoluminescence images of thezircons from Baijiafen and Dongshan gneisses, as well as recent Hf and O isotope analyses of thezircons, shows presence of the 3.8 Ga rocks in the Anshan is still controversial(Liu et al., 2008;
Nutman et al., 2009; Wu et al.,2008, 2009).
We carried out a comprehensive investigation of detailed observation of an outcrop in the Dongshanarea, Anshan, U-Pb dating and Cathodoluminescence observations of zircons from the outcrop to
constrain the emplacement age of protoliths of the orthogneisses. The outcrop consists mainly of
two lithologies: highly altered metamorphosed mafic rock and orthogneisses with some generations.
The orthogneisses are further subdivided into pale-gray gneiss, white gneiss and white granitic
intrusion, respectively. The occurrence of the mafic rock and orthogneisses indicates that themafic rock (1) was intruded by the pale-gray gneiss (2), the pale-gray gneiss (2) was further
intruded by the white gneiss (3), and all of them were, finally, intruded by the white granitic
intrusions (4). We studied Cathodoluminescence imaging and U-Pb dating of zircons carefully
separated from each rock type. The results follow: (1) the metamorphosed mafic rock yields only
metamorphic zircons with ca. 3.3 Ga ages, (2) only the pale-gray gneiss contains 3.8 Ga zircons,(4) the white gneiss has ca. 3.3 Ga zircons and (4) the white granitic intrusion contains very
young, ca. 500 Ma, zircons.
We will report their protolith ages and the related granitic intrusion events based on the
Cathodoluminescence images, U-Pb dating with LA-ICP-MS, Hf and O isotopes and REE patterns of thezircons and whole rock compositions of the host rocks.
Keywords: Archean, zircon, Anshan©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-09 -BPT05-10

Japan Geoscience Union Meeting 2016

Tectonic setting of the Paleoproterozoic (2.1 Ga) sedimentary basins in southeasten Gabon:
A possible evolutionary hotspot of the early macrobiota*Tomohiko Sato1, Yusuke Sawaki1, Shigenori Maruyama1
1.Tokyo Institute of Technology
The Paleoproterozoic is one of the most important transition periods in the Earth’s history, marked
by the oxidation of surface environment and the appearance of eukaryotic organisms. The
centimeter-sized fossils (~17 cm in maximum), possibly multicellular organisms, were reported from
2.1 Ga black shales in southeastern Gabon (El Albani et al., 2010, Nature). These Gabon
macrofossils occur only in the restricted area and only during the short time period. The
uniqueness of the subsistence of the large organisms in the 2.1 Ga Gabon may be the key to solve
the essential requirements for evolution of life; however, the detailed tectonic settings andgeochemical conditions of the fossil occurrence are poorly constrained. In order to clarify thesesettings, we are going to conduct precise geological survey and investigate the multi-isotope
chemostratigraphy of the Paleoproterozoic sequences in Gabon.
The Paleoproterozoic sedimentary sequences are distributed widely in the Francevillian Basin insoutheastern Gabon, which consist of 4 sub-basins; Franceville, Lastoursville, Okondja, and Booue.
The ca. 2 km-thick Paleoproterozoic sedimentary sequences in these rift-basins are subdivided into
FA (sandstones with uranium-rich conglomerates), FB (black shales, siltstones and carbonates), FC(carbonates and cherts), and FD (black shales) in ascending order. The FA indicates fluvial anddeltaic depositional setting, and the FB, FC and FD suggest marine deposition during the rifting
and basin deepening. The Gabon macrofossils are reported only from the black shales of the FB in
the Franceville Basin; however, nodule-like fossils are recently found in the black shales of the
FB in the Okondja Basin (Moussavou et al., 2015, J. Geol. Geosci.), which is almost the same
horizon as the macrofossils. The difference of tectonic setting and geochemical environment between
the Franceville and Okondja Basins is essential to understand the uniqueness of the evolutionary
hotspot. The Gabon macrofossils likely inhabited in a shallow water oxygenated environment. Theremight be an evolutionary influence of the well-known Oklo nuclear reactors, which is very near to
the macrofossil site.
As a preliminary study, we analyzed strontium isotopes of the carbonate samples collected from theLastourville Basin. In this presentation, we will discuss the tectonic setting of the Francevillian
Basin at the time of Gabon macrofossil appearance.
Keywords: Paleoproterozoic, Gabon, strontium isotope©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-10 -BPT05-11

Japan Geoscience Union Meeting 2016

The stratigraphy and a new age constraint of the volcaniclastic sequence of Birimian in
Cape Three Points, Ashanti belt, southwest Ghana*Satoshi Yoshimaru1, Shoichi Kiyokawa1, Takashi Ito2, Minoru Ikehara3, Kenji Horie4, Mami Takehara4,
Takashi Sano5, Frank K Nyame6, George M Tetteh7
1.Department of Earth and Planetary Science, Kyushu University, 2.Ibaraki University, 3.Kochi
University, 4.National Institute of Polar Resarch, 5.National Museum of Nature and Science,
6.University of Ghana, 7.University of Mining and Technology
Paleoproterozoic Birimian greenstone belt, extending from eastern Guinea to western Niger, islocated in southern part of West Africa Craton. The geological structure of the Ashanti belt
occupying most of western Ghana, especially gold mines, has been revealed a little by scientificresearch. At the Cape Three Points area, there is no previous report about change in environment of
deep sea floor during paleoproterozoic period. We focused on environment and bioactivities during
deposition of protolith of the Birimian greenstones at this region. As a preliminary study, we
report the stratigraphy, structures of volcanic and volcaniclastic sequence, the depositionalsettings and age at this region.
Ashanti belt, striking NE-SW and occupying most of western Ghana, is composed of mainly basalts orandesites, volcaniclastic rocks and belt type or non-belt type granitoids, and is uncomfortably
overlain by acidic volcaniclastics and gold bearing conglomerates. The maximum depositional age ofthe cap of Birimian rocks is 2154±2 Ma (U-Pb zircon: Oberthür et al., 1998) and the youngest age ofthe intruded rock into Birimian volcanic in this region is 2174±2 Ma (U-Pb zircon: Oberthür et al.,1998).
In the Cape Three Points region facing the Gulf of Guinea, very thick volcaniclastic sequences arepresent in succession over 4000 m and about 1000 m-thick of stratigraphy of the study sites isreconstructed by detailed field investigations. The layers are running N-S, most of them dip 60-80
to the east. The stratigraphy shows fining upward. All of these sediments were affected bygreenschist facies metamorphism, and thus minerals of amphiboles, plagioclase, chlorite and epidote
are very common, while quartz grains are not so popular member here. The TiO2/Al2O3 ratio obtained
from chromites with EPMA in basaltic rocks indicates that these rocks produced in the volcanic arc
system. Trace elements compositions of whole-rock compositions tend to show low concentration ofNb, and high concentration of LREEs. These facts also indicate that they are derived from volcanicarc region. Those thick finning-upward volcaniclastic sequence, chemical compositions may besuggest that the Cape Three Points area was formed on the mid-deep sea floor beside an oceanic
volcanic arc.
We obtained new age information from the porphyritic dyke with several meters in length and <1m in
widths. This dyke is foliated and some minerals are sheared and tone off. Zircon grains collectedfrom the dyke were measured by SHRIMP at NIPR, and yielded weighted mean 204Pb-corrected 207Pb/206Pb
age of 2265.6±4.6 Ma (95% confidence), which indicates that the volcaniclastic sequences deposited
before 2265.6±4.6 Ma and deformed after that. Only four detrital zircons are dated around 2260 Ma
in this site and these age groups are the oldest in the Ghanean greenstone terrene (Loh and Hiedes
1992). Therefore, there is possibility that the early volcanic activity history of the Ghana
Birimian remains at Cape Three Points.
Keywords: Ghana Birimian greenstone belt, paleoproterozoic, volcanicrastics©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-11 -BPT05-12

Japan Geoscience Union Meeting 2016

Preliminary report of Ghana Biriman Greenstone belt drilling project (GHB): Reconstruction
Paleoproterozoic oceanic environment*Shoichi Kiyokawa1, Takashi Ito2, Minoru Ikehara3, Kosei E. Yamaguchi5, Tetsuji Onoue4, Kenji Horie6, Satoshi Yoshimaru1, Tsubasa Miki1, Tetteh M George7, Frank K Nyame8
1.Department of Earth and Planetary Sciences Faculty of sciences, Kyuushu University, 2.Dept.
Education, Ibaraki Univ., 3.Kochi Univ., 4.Kumamoto Univ., 5.Toho Univ., 6.National Polar Inst.,
7.University of Mines and Technology, Tarkwa, 8.University of Ghana, department of Geology
The Paleoproterozoic Birimian Greenstone Belt along the Cape Three Points area contains very thickvolcaniclastic and organic rich sedimentary rocks which we now refer to as Cape Three Points Groupin the lower part of Birimian Greenstone Belt. Recent field work in this area uncovered 1000m total
thickness of volcanoclastic sedimentary sequence. Stratigraphically, the lower portion contains
thick vesicular volcaniclastic rocks probably of sub-aerial origin. The middle portion is made up
of well laminated alternation of volcaniclastics and black shale with the upper portion dominatedby well laminated volcaniclastics with black shale sequence. Fining upward sequence and REE datasuggest shallow to deep sea depositional conditions at oceanic island arc setting. New SHRIMP age
data from porphyry intrusion in this sequence show about 2250Ma but sedimentation and volcanic
activity is much older than this age. 195m continuous core drilling from Dec 3-12th 2015 at theupper part of the Cape Three Points Group intersected 30 m saprolite and 30 to 195m well preserved
stratigraphy with graded bedding and lamination. Analysis of C, S isotopes would reveal deeper
oceanic conditions and biogenic activity during deposition.
Keywords: Paleoproterozoic, Birimian Greenstone belt, oceanic island arc©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-12 -BPT05-12©2016. Japan Geoscience Union. All Right Reserved.

Japan Geoscience Union Meeting 2016

- BPT05-12 -BPT05-13

Japan Geoscience Union Meeting 2016

Mid-oceanic ridge is not the birth place of life: secondary place to live
*Shigenori Maruyama1
1.Earth-Life Science Institute, Tokyo Institute of Technology
The image of Mother ocean or idea that the birth place of life is ocean is totally wrong. The
primordial ocean immediate after the formation of the Earth was extremely toxic and should not be
the place to live for any kind of life. Chemical composition of primordial ocean deduced from the
Earth formation theory is too acidic (pH less than 1), extremely high salinity (5-10SU (SU issalinity unit, 1SU is present seawater salinity) and enriched in heavy metals. Therefore the birthplace of life should have been on primordial continent which can have clean water like lacustrine
environment. Probably the first life was born at natural nuclear reactor combined with geyser(natural nuclear geyser). Numerous kinds of commonote must have appeared in such environment,
however they experienced mass extinction because of influx of toxic ocean. Lives that could endurestrong outer force and repeated influx of mass extinction could survive to be the ancestor ofanimal and plant which is archaea and eubacteria respectively. Through time, cleansing of toxic
ocean progressed by water-rock reaction between rock materials provided from continent and toxic
ocean and fixation of heavy metals as ore deposit at the mid-oceanic ridge. As a result, acidic
ocean is neutralized gradually. Salinity of ocean is thought to be dropped to 2SU by 635Ma. In
other words, it was too difficult for life to live in ocean before that time at least.
However, mid-oceanic ridge is exceptional place to reduce salinity. At immediate vicinity along
mid-oceanic ridge, salinity is low, because seawater is separated into high saline dense seawaterand lighter water closed to freshwater due to boiling. Lighter low saline water goes up and densewater move to deeper place. Due to this process, salinity around mid-oceanic ridge is kept lower,
and it became possible for life to live there. However, as explained above, mid-oceanic ridge area
is not the birth place of life. In addition to chemical composition of ocean, environment of
mid-oceanic ridge is poor in diversity. Therefore it is not suitable for life to be emerged. As aresult, birth place of life is thought to be on primordial continent with diversified surface
environment and habitable trinity. In other word, lives born on the primordial continent had
secondarily migrated to mid-oceanic ridge. The reason why lives around mid-oceanic ridge remaining
characteristics of ancient life is migration into mid-oceanic ridge occurred in very early stage oflife history.
Keywords: seawater salinity, primordial continent, mid-oceanic ridge hydrothermal system©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-13 -BPT05-14

Japan Geoscience Union Meeting 2016

Origin of hydrocarbons from serpentinite-hosted Hakuba Happo hot spring: Molecular andintramolecular 13C analyses*Konomi Suda1, Yuichiro Ueno1,2,3, Alexis Gilbert2, Naohiro Yoshida2,4
1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2.Earth-Life Science
Institute (WPI-ELSI), Tokyo Institute of Technology, 3.Precambrian Ecosystem Laboratory, JAMSTEC,
4.Department of Environmental Chemistry and Engineering, Interdisciplinary Graduate School of
Science and Engineering, Tokyo Institute of Technology
The early environment before the origin of Earth’s life remains poorly understood due to lack ofgeological records during Hadean era (>4.0 Ga). Serpentinite-hosted hot spring/hydrothermal systems
are considered to have been widespread in Hadean Earth and a potential site to synthesize organic
compounds abiotically (e.g., Russell et al., 2010). The fluid associated with low temperature(<100°C) serpentinization is characterized by strongly alkaline condition and is often rich inhydrogen (H2) and methane (CH4). Previous field studies revealed that the C1-C5 hydrocarbons werecommonly observed in serpentinite-hosted systems, regardless of continental or seafloor setting[e.g., Charlou et al., 2002; Proskurowski et al., 2008; Etiope et al., 2011; Szponar et al., 2013].
However, production mechanisms of these hydrocarbons have not been poorly understood. We reportchemical, and molecular and intramolecular carbon isotopic study of hydrocarbons for on-landserpentinite-hosted systems: Hakuba Happo hot spring in Japan. The spring water of the Hakuba Happois around 50°C and high pH (~10.5). The main gas components were N2, H2 and CH4. The CH4 in Happowater has been suggested as abiogenic origin based on the previous hydrogen isotopic study (Suda etal., 2014).
The concentrations of C1 to C4 hydrocarbons were determined by Gas Chromatograph (GC) with two
detectors of Pulsed Discharge Detector (PDD) and Thermal Conductivity Detector (TCD). Quantitative
analysis of dissolved organic acids was performed by High Performance Liquid Chromatograph (HPLC).
The δ13C values of C1 to C5 hydrocarbons were determined by using the on-line pre-concentration
system coupled with the GC-C (combustion)-IRMS (isotope ratio mass spectrometer) method. For the
first time, we apply a novel analytical method, namely intramolecular 13C analysis of propane (C3H8), to a natural sample derived from the serpentinite-hosted system. The intramolecular 13C
composition in propane was measured using the GC-pyrolysis (Py)-GC-C-IRMS system (Gilbert et al.,2016).
The isotopic trend of depletion in 13C with increasing molecular weight (δ13C1 > δ13C2 > δ13C3 > ...)
was observed in Happo sample, showing similar isotopic trend compared with that of Lost City field,
a seafloor serpentinite–hosted hydrothermal system (Proskurowski et al., 2008). We developed an
abiotic polymerization model to account for isotopic compositions of Happo hydrocarbons. The carbon
isotopic compositions of Happo hydrocarbons can be explained by the successive addition of a single
carbon compound (C1-compound) with constant isotopic fractionation. The result of theintramolecular analysis revealed that the difference of δ13C values between terminal and centralcarbon atom positions of propane (site preference; SP in ‰) for Happo sample showed a significantly
high SP value compared with that of thermogenic origin. Such a highly SP value corresponded to that
expected from a polymerization model developed in this study. Thus, both molecular andintramolecular 13C compositions of hydrocarbons for serpentinite–hosted sample suggested that the
production mechanism of these hydrocarbons was abiotic polymerization of C1-compound with aconstant isotopic fractionation. The δ13C value of methane suggested that methane was a reactant
C1-compound for polymerization reaction. On the other hand, the formate and acetate were detected
in Hakuba Happo hot spring. Formate was the second highest concentrated dissolved C1-compound after©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-14 -BPT05-14

Japan Geoscience Union Meeting 2016

methane in Happo water, implying that formate was an alternative carbon source for abiotic
polymerization in the serpentinite–hosted systems.
Keywords: Serpentinite, Abiogenic hydrocarbon, Intramolecular isotopic analysis, Stable carbon
isotope©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-14 -BPT05-15

Japan Geoscience Union Meeting 2016

Experimental study on H2 generation through reactions between komatiite and CO2-richseawater*Hisahiro Ueda1,2, Takazo Shibuya2, Yusuke Sawaki1, Masafumi Saitoh2, Ken Takai2, Shigenori Maruyama3
1.Tokyo institute of technology, 2.JAMSTEC, 3.ELSITo understand the chemical nature of hydrothermal fluids in the komatiite-hosted seafloorhydrothermal system in the Hadean, we conducted two hydrothermal serpentinization experiments
involving synthetic komatiite and a CO2-rich acidic NaCl fluid (pH = 4.9 at 25 °C) at 250 °C and
350 °C, 500 bars. During the experiments, the total carbonic acid concentration (ΣCO2) in fluids at
250 °C and 350 °C decreased from approximately values from 400 to near 30 and 170 mmol/kg,
respectively, which is consistent with the greater amount of alteration carbonate mineral at 250 °C
than at 350 °C in the serpentinized/carbonated komatiites (Shibuya et al., 2013). Furthermore, theprecipitated carbonate species strongly influenced Mg concentration in the hydrothermal fluid: Mg
concentration at 250 °C (carbonate as Fe-bearing dolomite) was 36–40 mmol/kg, which was 30–40 times
higher than that at 350 °C (carbonate as calcite). Therefore, in contrast to modern seafloorhydrothermal systems, the reactions between komatiite and CO2-rich seawater at temperatures where
dolomite was stable could have been the source of Mg for the Hadean ocean (e.g., Alt, 1995). More
importantly, the carbonation of komatiites potentially suppressed H2 generation in the fluids. The
Fe content in dolomite at 250 °C (3–8 wt%) was clearly higher than that of calcite at 350 °C (< 0.8wt%), while the steady-state H2 concentration in the fluid was approximately 0.024 and 2.9 mmol/kg
at 250 °C and 350 °C, respectively. This correlation between the Fe content in carbonate mineraland the H2 concentration in the fluid suggests that the incorporation of ferrous iron into thecarbonate mineral probably limited the magnetite formation and consequent generation of hydrogen in
the fluid during the serpentinization of komatiites. In comparison with modern H2-rich seafloorhydrothermal systems, the H2 concentration of the fluid in the experiment at 350 °C corresponds tothat of Kairei hydrothermal field (Central Indian Ridge) (Takai et al., 2004; Gallant and Von Damm,
2006; Kumagai et al., 2008; Nakamura et al., 2009), where hydrogenotrophic methanogens dominate in
the prosperous microbial ecosystem. Accordingly, the high-temperature serpentinization of komatiite
would provide the H2-rich hydrothermal environments that were necessary for the emergence and early
evolution of life in the Hadean ocean. In contrast, considering that carbonate minerals become morestable with decreasing temperature in the komatiite-H2O-CO2 system, H2-rich fluids may not have been
generated by serpentinization at temperatures below 250 °C, even in the komatiite-hostedhydrothermal systems of the Hadean Earth.
Keywords: komatiite, CO2-rich condition, hydrothermal alteration, early Earth, experiment©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-15 -BPT05-16

Japan Geoscience Union Meeting 2016

Whole-rock abundances and spatial distributions of transition elements in the Early andMiddle Archean BIFs: The mechanism of their involvement in the BIFs and reconstruction of
the chemical evolution of seawater in the Precambrian.
*Shogo Aoki1, Yasuhiro Kato2, Takafumi Hirata3, Tsuyoshi Komiya1
1.Graduate School of arts and science, University of Tokyo, 2.School of Engineering, The Universityof Tokyo, 3.Graduate School of Science, Kyoto University
Banded Iron Formations (BIFs) are chemical sediments, ubiquitously distributed in the Precambriansupracrustal belts. Therefore, their trace element compositions are helpful for deciphering
geochemical evolution on the earth through the time. However, it is necessary to elucidate factors
controlling the bulk compositions because their compositions are highly variable. We estimatedchemical evolution of seawater based on the bulk compositions of BIFs from ca. 3.8 Ga Isuasupracrustal belt, southern West Greenland, and spatial distribution of the trace element contents
within the BIFs from ca. 3.0 Ga Cleaverville area, Western Australia.
The BIFs in the Isua supracrustal belt are composed of magnetite, quartz and actinolitic
amphibole. Because the amphibole-rich BIFs are significantly enriched in Co, Ni, Cu, Zn, HREE and U
contents, their bulk compositions are not suitable for estimate of seawater composition. Moreover,the magnetite-rich and amphibole-poor samples show positive correlations of Ni, V and U contents
with Zr contents, suggesting that the elements were not derived from the seawater but from detritalmaterials. The good correlation of the trace element contents with Zr contents or with mineralogy
indicates the transition element contents such as Ni in the Archean ocean were much lower thanpreviously estimated, and comparable to those in the Proterozoic ocean.
The BIFs in the Cleaverville Formation show laminated structures from millimeter to centimeter
thick, composed of hematite and chert bands. The hematite bands are further composed of
micrometer-thick, thin hematite layers. Elemental mappings of the hematite bands with LA-ICP-MS
show that some layers or patches with higher Al, Ti and HFSE contents exist between the thin
hematite layers. Moreover, spatial distribution that Ni, Cu and Zn contents are correlated with Al
and Ti contents suggests that their elements in the BIFs were derived from detrital materials. On
the other hands, because Mo-rich areas are limited to the hematite layers, Mo in the BIFs washosted by the precursor of the hematite, providing a potential to estimate the seawatercomposition. The contrasting occurrence of Mo against Ni, Cu and Zn, which are redox-sensitiveelements, imply that the Mid-Archean oceans were slightly oxidative because of presence of Mo (Ⅵ)
in seawater.
Keywords: Banded Iron Formations, the Archean, the spatial distributions of the trace elements©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-16 -BPT05-17

Japan Geoscience Union Meeting 2016

Estimation of 3.2 Ga seawater-hydrothermal environment from sulfur isotopic analyses ofbarite crystals in Dixon Island Formation, Western Australia*Tsubasa Miki1, Shoichi Kiyokawa1, Naoto Takahata2, Akizumi Ishida2, Takashi Ito3, Minoru Ikehara4,
Kosei E. Yamaguchi5,6, Yuji Sano2
1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University,
2.Atmosphere and Ocean Research Institute, University of Tokyo, 3.College of Education, Ibaraki
University, 4.Center for Advanced Marine Core Research, Kochi University, 5.Faculty of Science,
Toho University, 6.Astrobiology Institute, NASA
Fluctuations of sulfur isotopic ratio (δ34S) and concentrations of seawater sulfate throughgeological time have a close relationship with atmospheric oxygen level and biological activity ofsulfate reducing bacteria. For example, in the Archean δ34S values of sulfate was +4.6‰ (3.47Ga;
Shen et al., 2009) and seawater sulfate concentration was <2.5 μM (>2.4Ga; Crowe et al., 2014b).
However, after major increase in oxygen levels in the Paleoproterozoic, the concentration became
larger up to 1-2mM (>1.6Ga; Kah et al., 2004). Besides, increased sulfate level promoted microbial
sulfate reduction and isotopically light 32S in sulfate was selectively used for metabolism andmoved into sulfide, resulting in high δ34S sulfate. Therefore, δ34S of Archean sulfate is low
compared to that of the Proterozoic (e.g. Canfield and Farquhar, 2009).
In this way, δ34S of past sulfate minerals is a good proxy for redox state and microbial sulfate
reducing systems in the Precambrian. However, reports of δ34S of Archean sulfate are scarce andlocalities and ages of research are partial. Therefore, we focused on newly discovered sedimentarybarite (BaSO4) layers from the 3.2Ga Dixon Island Formation, which is considered to have been
deposited in a relatively deep open sea environment (Kiyokawa et al., 2006).
The Dixon Island Formation is located in the coastal Pilbara terrane, Western Australia and shows
low metamorphic grade (Kiyokawa and Taira, 1998). Barite layers alternate with black chert layers
in the Black Chert Member of the Dixon Island Formation that overlies hydrothermal vein networks.
Barite is considered to have formed during precipitation of black chert. Though most of them aresilicified (Kiyokawa et al., 2006), there exist small crystals of barite (less than 200 μm in
diameter) which are regarded to be remnants of original barite. We crushed three rock samples fromdifferent horizons, separated twelve fine barite grains in total, and performed micro-meter scale δ34

S analyses using a NanoSIMS.

We used five sedimentary barites as working standards which are considered to have δ34S homogeneityin each crystal determined by an IsoPrime. For measuring samples, we performed raster analyses of
two or three spots for each crystal, and values were averaged. As a result, we obtained scattered δ
34

S values of -2.1 to +18.7‰ (Avg.=+6.5‰, 1σ=6.3‰) from twelve crystals. On the other hand,averages in each rock sample were +3.4, +7.8 and +8.4‰. Measurement errors were ±0.87‰ to ±3.72‰.
Average δ34S values for each rock sample are similar to literature values of Archean sulfate(+5-10‰, Canfield and Farquhar, 2009). Meanwhile, focusing on the range of values of each crystal,lower ones were near δ34S of mantle-originated sulfur (ca. 0‰), which may reflect δ34S ofhydrothermal-originated sulfate. Besides, higher ones were near δ34S of modern seawater sulfate(+22‰) and thus higher than Archean sulfate. There are two possible causes of high δ34S: 1) extreme
microbial sulfate reduction in an environment closed with respect to sulfate (Rayleighfractionation) or 2) hydrothermal fluid supplying isotopically heavy sulfate.
This study is the first attempt of in situ δ34S analyses for Archean barite microcrystals. We
detected isotopic heterogeneity in individual barite crystals within three single barite beds.
Conventional combustion method for S isotope analysis may mix this heterogeneity and provide us©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-17 -BPT05-17

Japan Geoscience Union Meeting 2016

with averaged values. There is a possibility that δ34S dispersion in each barite bed shows isotopic
heterogeneity of seawater sulfate at that time.
Keywords: Archean, sulfur isotopes, barite, SIMS

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-17 -BPT05-18

Japan Geoscience Union Meeting 2016

Ediacaran sulfur cycling reconstructed from an isotopic analysis of carbonate associatedsulfate in Doushantuo Formation*Fumihiro Matsuura1, Masafumi Saitoh2, Yusuke Sawaki1, Yuichiro Ueno1,2,3
1.Tokyo Institute of Technology, 2.JAMSTEC, 3.Earth-Life Science Institute
Carbonate associated sulfate (CAS) is useful for reconstructing sulfur isotopic composition ofseawater sulfate. However, extraction method of CAS from carbonate rocks has not been firmly
established yet. In particular, oxidation of co-existing pyrite sulfur would seriously damage
isotopic analysis of CAS during the extraction from rock samples. We have developed an improved
method to extract the pure CAS and evaluated the validity of the new method using scallop shell
powder containing modern marine CAS and pyrite powder. The results demonstrate that the new CAS
extraction method is effective for preventing unwanted sulfur components from co-existing pyrite
when the pyrite/CAS ratio in a sample is <10. We applied the new CAS extraction method to Ediacaran
drill core samples from the Three Gorges area, South China collected by a Tokyo Tech.–Xian Univ.
joint project. The studied section includes the Neoproterozoic Doushantuo Formation and theoverlying Dengying Formation. The concentrations of CAS from the Doushantuo and Dengying Fms. range
from 0 to 365 ppm with an average value of 105 ppm. The δ34S values of CAS range from +24 to +46‰
with an average value of +34‰. A previous study of the Doushantuo samples collected from outcrop
reported that the CAS concentrations range from 0 to 2159 ppm with an average value of 570 ppm(n=73), and the δ34S values of CAS range from +7 to +44‰ with an average value of +25.7‰ (n=83)(McFadden et al., 2008). The apparent differences between the present and previous data may
indicate that the careful treatment is nessesary during CAS extraction. Based on the new sulfur
isotope data of CAS and of chromium reducible sulfur (CRS) (n=44), we reconstructed the
Neoproterozoic sulfur cycle in Three Gorges area. The difference of δ34S value between CAS andco-existing CRS increased from 5‰ at the Doushantuo cap carbonate, +26‰ in the Member 2, andexceeded 40‰ in the Member 3 of the Formation. The maximum sulfur isotope fractionation between CAS
and co-existing CRS exceeded 47‰ in the Member 3. The fractionation between CAS and CRS decreased
down to -3‰ at the Dengying Formation. This suggests that sulfate concentration increased at theupper part of Doushantuo Fm.; however, decreased again before Dengying Formation. In addition, ourquadruple sulfur isotope analysis revealed that mass-dependent-exponent for 36S (lambda-36 value)
between CAS and CRS is relatively constant around 1.90, regardless of the degree of δ34S isotope
fractionation. This indicates that the Ediacaran sulfur cycle in Three Gorges area is markedly
different from modern marine sulfur cycling.
Keywords: Neoproterozoic sulfur cycle, Carbonate associated sulfate, quadruple sulfur isotope
analysis©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-18 -BPT05-19

Japan Geoscience Union Meeting 2016

The rise of oxygen in the Earth surface at 3.5–3.4 Ga and 2.7–2.2 Ga*Kunio Kaiho1, Yuki Katayama1, Tomohiro Kawase1, Wladyslaw Altermann3, Martin Van Kranendonk4,
Tsuyoshi Komiya2, Ryosuke Saito1
1.Graduate School of Science, Tohoku University, 2.University of Tokyo, 3.University of Pretoria,
4.University of New South WalesGreat oxidation event (GOE) on Earth occurred approximately 2.3 billion years ago (Ga) based oniron redox state and sulfur isotopes. However, the age of first oxidation of the Earth’s surface iscontroversial. Presence of small amount of O2 in the environment at 2.5 Ga has been suggested byredox sensitive elements and sulfur isotopes and at 2.7 Ga by nitrogen isotopes. We analyzedhydrocarbon-derived geochemical parameters diagnostic for sedimentary redox conditions, i.e., thepristane/phytane ratio (Pr/Ph), from shallow marine sedimentary rocks in Labrador, Canada, Western
Australia, and South Africa. Here, we show that anoxic shallow sea at >3.95 Ga was followed byintermediate conditions at 3.5–2.9 Ga, local oxic conditions at 2.7 Ga, and subsequently global
oxidation at 2.6–2.2 Ga. These results indicate that the rise of oxygen in the Earth surface
occurred at 3.5–3.4 Ga and 2.7–2.2 Ga.
Keywords: Archean, oxygen, organic molecules©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-19 -BPT05-20

Japan Geoscience Union Meeting 2016

Authigenic carbonate precipitation at the end-Guadalupian (Middle Permian) in China:
Implications for the carbon cycle in ancient anoxic oceans*Masafumi Saitoh1, Yuichiro Ueno2, Yukio Isozaki3, Takazo Shibuya1, Katsumi Shozugawa3, Motoyuki
Matsuo3, Naohiro Yoshida2
1.JAMSTEC, 2.Tokyo Tech, 3.Univ Tokyo
Carbonate precipitation is a major process in the global carbon cycle. It was recently proposedthat authigenic carbonate (carbonate precipitated in situ at the sediment–water interface and/or
within the sediment) played a major role in the carbon cycle throughout Earth’s history. The carbon
isotopic composition of authigenic carbonates in ancient oceans have been assumed to besignificantly lower than that of dissolved inorganic carbon (DIC) in seawater, as is observed in
the modern oceans. However, the d13C values of authigenic carbonates in the past has not been
analyzed in detail. Here, we report authigenic carbonates in the uppermost Guadalupian (Middle
Permian) rocks at Chaotian, Sichuan, South China. Monocrystalline calcite crystals <20 mm long arecommon in the black mudstone/chert sequence that was deposited on a relatively deep anoxic
slope/basin along the continental margin. Textures of the crystals indicate in situ precipitationon the seafloor and/or within the sediments. The calcite precipitation corresponds
stratigraphically with denitrification and sulfate reduction in the anoxic deep-water mass, as
indicated by previously reported nitrogen and sulfur isotope records, respectively. Relatively highd13C values of the authigenic carbonates (largely -1‰) compared with those of organic matter in therocks (ca. -26‰) suggest that the main carbon source of the carbonates was DIC in the water column.
The calcite crystals precipitated in an open system with respect to carbonate, possibly near the
sediment–water interface rather than deep within the sediments. The d13C values of the carbonates
were close to the d13C value of seawater due to mixing of 13C-depleted remineralized organic carbon(that was released into the water column by the water-mass anaerobic respiration) with the large
DIC pool in the oceans. Our results imply that d13C values of authigenic carbonates in the anoxic
oceans might have been systematically different from the values in the oxic oceans in Earth’s
history, controlled by the depth of the redoxcline in the water column and sediments. If our model
is correct, authigenic carbonates with relatively high d13C values in the ancient anoxic oceans may
have had a less substantial influence on the bulk d13C values in geologic records than has beenpreviously suggested.
[ref.] Saitoh et al. (2015) Progress in Earth and Science 2:41

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-20 -BPT05-21

Japan Geoscience Union Meeting 2016

Osmium isotope excursion in the central Panthalassa during the Toarcian Oceanic Anoxic
Event: Relationships between Karoo-Ferrar volcanism and climatic-biologic changes*Wataru Fujisaki1, Yusuke Sawaki1, Hisahiro Ueda1, Konomi Suda1, Tomohiko Sato2, Manabu Nishizawa3,
Tetsuya Yokoyama1
1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2.Earth-Life Science
Institute, Tokyo Institute of Technology, 3.Laboratory of Ocean-Earth Life Evolution Research(OELE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)The Toarcian Oceanic Anoxic Event (T-OAE) represents one of the most severe paleo-environmental
turbulences in the Mesozoic. The volcanic activities in the Karoo-Ferrar Large Igneous Provinces(LIPs) have been considered as the most fundamental trigger for the Toarcian perturbation, although
the connection between the Karoo-Ferrar LIPs and the T-OAE remains unclear. Consequently, thedebate on the influence of large volcanic activities on the global environmental changes is still
controversial. Radiogenic Os isotopes of sedimentary rocks are useful for estimating the influxfrom both ancient basaltic magmatism and continental weathering, making this tracer suitable forunderstanding the cause of T-OAE. Because of the lack of detailed Os isotopes across the T-OAE, therelationship between biotic crisis, anoxia, and the volcanism in the central Panthalassa is still
ambiguous. To clarify the relationship between the Karoo-Ferrar LIPs and their turbulences to theglobal environmental changes across the T-OAE, we determined the Re and Os concentrations, seawater187

Os/188Os values, and organic carbon isotopes in Plinsbachian to Toarcian deep-sea cherts from the

Inuyama area, southwest Japan. Unlike shallow marine regions, two bedded black chert intervals(T-OAE1 and T-OAE2 in stratigraphic ascending order) were recognized in the central Panthalassa.
The rock powder was spiked with 190Os and 185Re prior to acid decomposition. The sample was digested
by a mixture of CrO3 and H2SO4 in a sealed Carius tube at 240 ºC for more than 48 h. Subsequently,
Os was separated by solvent extraction using CCl4 and back-extracted from CCl4 into HBr, followedby the final purification using the micro-distillation method. The Os isotopes were determined by
N-TIMS at Tokyo Tech. The solution remaining after the CCl4 extraction was transferred to a Teflon
vessel, in which Cr6+ was completely reduced to Cr3+ by ethanol to avoid the disturbance of Re
separation with ion exchange chromatography. Subsequently, Re was purified by passing the sample
solution through an anion exchange resin. The Re isotopes was determined using a quadrupole-type
ICP-MS at Tokyo Tech. The Os and Re concentrations were determined by the isotope dilution method.
The Re and Os abundances in 27 chert samples across T-OAE intervals varied from 0.006 to 213.1
ng/g, and from 2.0 to 2078 pg/g, respectively. The initial 187Os/188Os ratios in the samples
decreased from the Plinsbachian to the Toarcian, and reached the minimum value of 0.11 at the onsetof T-OAE1. Afterward, the seawater 187Os/188Os values increased to 0.56 towards the end of T-OAE1,
and decrease down to 0.24 at the interval between T-OAE1 and T-OAE2. During the T-OAE2, theseawater 187Os/188Os values abruptly increased up to 1.22. Our seawater 187Os/188Os values varied
preceding the variation of organic carbon isotopes, most likely reflecting the difference ofresidence time between Os (20 kyr) and organic carbon (75-100 kyr). From these observations, we
propose the following scenario for the perturbation in the T-OAE intervals. The Karoo-Ferrar
volcanic activities induced an anoxic condition, which resulted in unradiogenic 187Os/188Os inseawater followed by negative δ13Corg ratios before the T-OAE intervals. The Karoo-Ferrar volcanism
released significant amount of CO2, which triggered the global warming and enhanced the magnitude
of continental weathering during both T-OAE intervals. Subsequent gradual increases of Os isotopes
likely reflect their aftermaths. To conclude, the Karro-Ferrar volcanism played an important rolefor induing anoxic condition and global warming during Toarcian in the central Panthalassa.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-21 -BPT05-21

Japan Geoscience Union Meeting 2016

Keywords: Toarcian Oceanic Anoxic Event , central Panthalassa, bedded chert, osmium isotope,organic carbon isotope, Karoo-Ferrar volcanism©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-21 -BPT05-22

Japan Geoscience Union Meeting 2016

Cretaceous to Paleogene deep-water agglutinated foraminifers in the western North Pacificpelagic sediments*Junichiro Ohta1,2, Kentaro Nakamura2, Kazutaka Yasukawa2,3, Koichiro Fujinaga3,2, Koichi Iijima1,
Hikaru Iwamori1,4, Yasuhiro Kato2,1,3
1.Japan Agency for Marine-Earth Science and Technology, 2.School of Engineering, the University ofTokyo, 3.Chiba Institute of Technology, 4.Graduate School of Engineering, Tokyo Institute ofTechnology
Deep-water agglutinated foraminifers (DWAF) are often composed of the only microfossils
well-preserved in pelagic sediments without calcareous and siliceous fossils. DWAF have beenstudied for a long time for determining a stratigraphic succession and obtaining paleoecologicalinformation. While their quantitative distributions in sediments from the Atlantic Ocean were
well-documented (e.g., Kuhnt et al., 1992), those from the Pacific Ocean have not been studied
sufficiently enough to establish the stratigraphy. Wightman and Kuhnt (1992) investigated DWAF in
the sediment cores drilled at Deep Sea Drilling Project Sites 196 and 198, and Ocean Drilling
Program Sites 800 and 801 in the western North Pacific Ocean. They reported that the faunal densityand diversity of DWAF rapidly declined across the horizon that approximately corresponds to theCretaceous/Paleogene (K-Pg) boundary.
Recently, we constructed lithological description, including microfossils, for a pelagic sedimentcore of KR13-02 PC05 collected from the western North Pacific Ocean, and recognized a rapid declineof the density and diversity of DWAF across a spherule-rich layer. The spherules have a very
similar appearance to those associated with the Chicxulub impact at the K-Pg boundary. We present a
distribution of DWAF across the spherules-rich layer in the core and discuss its paleoceanographic
implications.
Keywords: deep-water agglutinated foraminifers, K-Pg boundary, pelagic sediments, western North
Pacific Ocean©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-22 -BPT05-23

Japan Geoscience Union Meeting 2016

Oceanic anoxic event at the Carnian/Norian boundary interval in the Black Bear Ridge
section, British Columbia, Canada*Tetsuji Onoue1, John-Paul Zonneveld2, Michael J Orchard3, Katsuyuki Yamashita4, Honami Sato5,
Soichiro Kusaka6
1.Kumamoto University, 2.University of Alberta, 3.Geological Survey of Canada, 4.Okayama
University, 5.JAMSTEC, 6.Museum of Natural and Environmental History, Shizuoka
The Black Bear Ridge section in northeastern British Columbia consists of a continuously exposed
succession through the upper Carnian and lower Norian, and has been proposed as a candidate Global
Stratotype Section and Point (GSSP) for the Carnian/Norian boundary (CNB). In order to infer thelate Carnian to early Norian environmental changes in the western Canadian continental margin, thestratigraphic variations of isotope 87Sr/86Sr, δ13C, and δ18O values and redox sensitive elements (V,Ni and Cr) in the CNB interval of the Black Bear Ridge section were examined. The study section is
located along the north shore of Williston Lake in northeastern British Columbia. The Black Bear
Ridge section represents a distal ramp facies deposited in a passive margin environment along thewestern margin of the North American craton. The stratigraphic interval across the CNB displays atemporal positive shift in the δ13C values, with a synchronous increase in the redox indices(V/V+Ni and V/Cr ratios). The coincidence of the increase in δ13C values and V/V+Ni and V/Cr
indices suggests that positive carbon isotope shift in the CNB interval is attributed to theincreasing of marine organic carbon burial rates in response to the anoxic conditions. Increased δ
13C values for carbonate rocks at the CNB has been also reported from the Upper Triassic sections

in Europe (e.g., Pizzo Mondello section, Sicily), which suggests the more widespread development ofanoxic conditions in the CNB interval between the Pacific and the Tethyan Oceans. The present
geochemical data and recent conodont biostratigraphic works at Black Bear Ridge show that the onsetof oceanic anoxic event may have been responsible for the faunal turnover event at the CNB. The
cause of this anoxic event is enigmatic but the 87Sr/86Sr and δ13C isotope data largely excludes thepossible cause of the oceanic anoxic event triggered by dissociation of methane hydrates anddegassing due to large-scale volcanic activity.
Keywords: Limestone, Triassic, Canada©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-23 -BPT05-24

Japan Geoscience Union Meeting 2016

Carbon dioxide emission during OAE 1a from the oil reservoir in Brazilian offshore*Akihiro Kano1
1.Graduate School of Social and Cultural Studies, Kyushu University
Development of a huge oil field has been unveiled in Brazilian offshore during the last decade. It
consists of ~150 m thick porous carbonate distributed in an area of half Honshu, which was formedin ~1 million years. Depositional setting was likely a saline lake developed in the onset ofcontinental rifting between South America and Africa. However, laminated texture and rapid
depositional rate are supportive alternative view that it was deposited from carbonate spring(travertine). Since this discovery, travertine researchers have been focusing the origin of thiscarbonate oil reservoir. The Brazilian carbonate rock comprises a huge carbon mass of 1.23 x 1019
mole, when we take the porosity and the carbonate content similarly 50%.
Travertine is a rapid CO2-degassing system as well as a carbonate-depositing system. Our results inJapan and Indonesian travertines indicated the degassing surpassed the carbonate deposition with
G/P ratio of 7-18. When we introduce this to the carbon mass of the Brazilian carbonate, thedegassed CO2 is calculated 1.2-2.7 x 1015 ton as carbon, which is equivalent to 2-5% of crustal
inorganic carbon of Berner (1990). If the degassing had occurred in a period of 1 myr, the averagedegassing rate corresponds to 14-32% of the modern emission from fossil fuel.
Depositional age of the Brazilian carbonate was 123 Ma during the Ocean Anoxic Event (OAE) 1a. The
most likely climatic background was warming due to increase in CO2 concentration, and its potential
source might be superplume forming the Pacific oceanic rises or accelerated volcanism in subduction
zones. However, an enormous degassing from the Brazilian carbonate calculated here could be morethan a candidate trigger of OAE 1a if it was a travertine system.
Keywords: Cretaceous, OAE, carbon dioxide©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-24 -BPT05-P01

Japan Geoscience Union Meeting 2016

The distribution of the oldest rocks at the Acasta gneiss complex*Keiko Koshida1, Akira Ishikawa2,3, Shinji Yamamoto4, Shogo Aoki2, Hiroki Uehara2, Tsuyoshi Komiya2
1.Department of Earth and Planetary Science, The University of Tokyo, 2.Department of Arts andSciences, University of Tokyo, 3.Japan Agency for Marine-Earth Science and Technology, 4.YOKOHAMA
National University
The Hadean from birth of the Earth to 4.03 Ga is the earliest period of the history of the Earth,and defined by no preservation of rock records in the Earth. The oldest rock, which defines the
Hadean era, is present in the Acasta Gneiss Complex (AGC). The AGC, located in the western part of
the Slave Province, Canada, is one of the Early Archean terranes, and mainly consists of 3.6-4.0 Ga
felsic and layered gneiss suites with minor mafic rocks. Based on a zircon U-Pb geochronology,
Bowring et al. (1999) reported 4.03 Ga granodioritic gneiss, which is, so far, considered as theoldest terrestrial rock. Recent studies try to more quantitatively elucidate the emplacement agesof the Acasta gneisses by combining the zircon U-Pb geochronology with whole rock and mineral(zircon) geochemistry. Mojzsis et al. (2014) classified an orthogneiss sample into some components
based on cross-cutting relationship, and reported U–Pb geochronology and trace element compositions(REE, Ti) of zircons from the components and compositions of the components themselves. The
apparent calculated partition coefficients for REEs between the components and zircons separated
from the components were compared with the theoretical partition coefficients. They concluded thatall AGC zircons older than 4.0 Ga were inherited and AGC emplacement age was 3.92 Ga because theapparent calculated partition coefficients for the >4.0 Ga zircons are inconsistent with thetheoretical values. On the other hand, Reimink et al. (2014) discovered well-preserved
4.02-billion-year-old tonalitic gneiss in the northern part of the AGC and named “Idiwhaa Tonalitic
Gneiss (ITG)”. The ITG is garnet-biotite-hornblende tonalitic gneiss, and has intermediate major
element compositions. It contains abundant igneous zircons with a U-Pb crystallization age of 4.02
Ga and their REE compositions are consistent with the host whole rock compositions. Notably, the
ITG is characterized by their high total iron, low Mg-numbers, flatter REE patterns and negative Eu
anomalies, and is distinct from the typical Archean TTGs. They concluded that the oldest tonalite
was formed in a plume-related tectonic setting. However, Reimink et al. (2014) identified the ITG
unit only in the northern part of the East Acasta Gneiss Complex. In order to more comprehensively
obtain the distribution of ITG unit over the AGC, we carried out geological survey in the Acasta
gneiss complex, and conducted major and trace element analysis of the orthogneisses and U-Pb datingof zircons. Preliminary results indicated the orthogneiss, which shares some geochemical featuresof the ITG, is also present in the southern part of the AGC, implying that the ITG unit isextensively distributed over the AGC.
Keywords: oldest rock, Acasta gneiss complex©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P01 -BPT05-P02

Japan Geoscience Union Meeting 2016

U–Pb dating of zircon grains from the North Pole Adamellite in the eastern Pilbara Craton*Hisashi Asanuma1, Shuhei Sakata2, Yusuke Sawaki1, Kazue Suzuki2, Takafumi Hirata3, Shigenori
Maruyama1
1.Tokyo institute of Technology, 2.The University of Tokyo, 3.Kyoto University
Supracrustal rocks around the North Pole Dome, Western Australia provide valuable geologicalevidences in the early Archean. Since the oldest known microfossils were discovered from chertbeds, the North Pole area has attracted interests from many researchers. The stratigraphic section
belongs to the lowermost group (Warrawoona Group) in the Pilbara Supergroup, and predominantly
consists of greenstone-chert successions that have been well described by previous workers. These
successions were mainly dated by U-Pb geochronology of zircon. Thorpe et al. (1992) and Kitajima etal. (2008) reported the U-Pb ages of zircon grains separated from tuffaceous chert, felsic lava,
and intrusive adamellite. Most of dated zircons, however, exhibited anomalously high abundance ofcommon lead, and their U-Pb ratios were plotted far away from a concordia curve. These problems
should be resolved for better age constraints on the strata in the North Pole area, which is
crucial for understanding the timing of the early life evolution on Earth.
In the North Pole area, mafic-ultramafic greenstones are capped by bedded cherts, and include
zircon-bearing tuffaceous chert layers and felsic lavas. These successions were regionally upliftedby later adamellite intrusion. This study focuses on the adamellite to determine thecrystallization age based on U-Pb geochronology of zircon. We separated and handpicked more than
1000 zircon grains from two adamellites (95NP207 and 96NP208). These zircon grains have euhedral
shapes, and also exhibit oscillatory zoning under cathodoluminescence observation. On the otherhands, most of the zircon rims are enriched in non-formula elements such as Ca and Al, whichindicates that the zircons partially experienced metamictization. In this study, non-metamictizeddomain in oscillatory zoned zircon was selected for in-situ U-Pb analysis, and the U-Pb ratio wasmeasured with LA-MC-ICP-MS at University of Kyoto.
7 and 4 zircons were plotted on the Tera-Wasserburg concordia curve within their analytical errors
from 95NP207 and 96NP208, respectively. Moreover these concordant zircons have low contents ofcommon lead (204Pb/206Pb values < 0.0005). Based on weight mean 207Pb/206Pb ages of the concordantzircons, 95NP207 and 96NP208 were respectively dated at 3486 ±52 Ma and 3449 ±17 Ma. The larger
error of the former data was attributed to two older zircons of 3523 ±17 Ma and 3567 ±14 Ma. We
concluded that the adamellite intrusion had occurred before 3449 ±17 Ma, and that the intrusive age
gave the minimum depositional age of the greenstone-chert successions in the North Pole area.
Keywords: North Pole area, Paleoarchean adamellite, U-Pb zircon dating, Concordia age©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P02 -BPT05-P03

Japan Geoscience Union Meeting 2016

Subduction geotherm of mid-Archean collision zone: metamorphism of the
granitoid-greenstone region south of the Barberton greenstone belt, South Africa*Kazumasa Aoki1, Shinji Yamamoto2, Tsuyoshi Komiya3
1.Department of Applied Science Okayama University of Science, 2.Graduate School of Environment andInformation Sciences, Yokohama National University, 3.Department of Earth and Astronomy, The
University of Tokyo
The approximately 3.5-3.2 Ga Barberton greenstone belt surrounded by TTG plutons and gneiss is oneof the oldest and best-preserved examples of Archean geology in the world. Over the past fifteen
years, migmatitic amphibolites, amphibolite and eclogite facies metamorphic rocks associated withca. 3.23 Ga collisional event were reported from the granitoid-greenstone domain to the south of
the Barberton greenstone belt (Dziggel et al., 2002; Moyen et al., 2006, Nédélec et al., 2012).
Although it was pointed out that these rocks formed under geothermal gradients of ca. 12-20°C/km,
which is similar to those found in recent subduction zone, the specific subduction geotherm at thepeak-P metamorphism has not yet been clarified. In this study, in order to constrain the subduction
geotherm at the time, we have examined the metamorphic P-T conditions of the highest-grade rocks in
the granitoid-greenstone region near Badplaas by focusing on the petrology and thermodynamics ofquartz-rich layers in metamorphosed Banded Iron Formations (sample no. BF152 and 153) at the Inyoni
shear zone.
The studied samples contain the minerals quartz, garnet, grunerite, hornblende, hematite andepidote. Garnet porphyroblasts are commonly round shape and almandine-rich components. They are
divided into two types based on the chemical analyses. The first-type has a chemical zoning. Thesegrains are generally characterized by a decrease of Mn from core (GRT1: XSps = 0.06-0.08) to mantle(GRT2: 0.04-0.07), and an increase of that from mantle to rim (GRT3: 0.1-0.2). On the other hand,
the Ca contents slightly increase from core (GRT1: Xgrs = 0.20) to mantle (GRT2: 0.22-0.24), andthen slightly decrease to rim (GRT3: 0.20-0.21). The second-type shows no-chemical zoning. Chemicalcompositions of the type are quite similar to those of GRT2 or GRT3. Hornblendes (HBL1) show anematoblastic texture and the chemical compositions plot in the ferrohornblende field. Some grains
are overgrown by actinolite with increasing Si contents (pfu) (HBL2). Grunerites (GRU1) occur asanhedral grains and have Mn (pfu) values of 0.27-0.89. Some grains (GRU2) are slightly zoned fromcore to rim. The cores have Mn (pfu) values of 0.52–0.55 decreasing to 0.27-0.30 at the contact
with retrograde actinolite. Epidotes occur as anhedal grains and the XFe3+ (= Fe3+/Al+Fe3+) ranges
from 0.20 to 0.22. Hematite grains are ahnedral. The petrography and mineral compositions ofstudied samples indicate that peak mineral assemblage was GRT2 + HBL1 + GRU1 + Qtz + Hem andchanged to GRT3 + HBL2 + GRU2 + Act + Qtz + Hem at a late stage.
The metamorphic P-T conditions were estimated by garnet-hornblende geothermometer (Graham &Powell, 1984 and Perchuk et al., 1985) using the program THERMOBAROMETRY ver. 2.1 (Spear & Kohn,
1999) and the average P calculations of THERMOCALC ver. 3.3.3 with the computer program AX (Holland
and Powell, 1998 and its update). These results show that the investigated rocks underwent eclogite
facies metamorphism at P= ca. 11-15 kbar and T = ca. 680-710 °C, and subsequently they underwent
greenschist facies metamorphism at P= ca. 5-10 kbar and T = ca. 450-470 °C during exhumation. The
estimated peak P-T conditions correspond to previous works for the highest-grade rocks in the same
area (Moyen et al., 2006).
Integration of our new results with published data suggests that the subduction geotherm at thepeak-P metamorphism associated with 3.23 Ga collisional event was ca. 20-30°C/km and the trajectory
was an anticlockwise with kinkpoint at around 10 kbar. This gradient gives close agreement with

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P03 -BPT05-P03

Japan Geoscience Union Meeting 2016

those of other collision-type HP-UHP metamorphic belts such as Himalaya and Kokchetav Massif. Thesefeatures suggest the possibility that the mid-Archean crust was sufficiently cool and rigid, andsome of the crustal materials were subducted to at least eclogite facies depths without melting
during the continent evolution of the early Earth.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P03 -BPT05-P04

Japan Geoscience Union Meeting 2016

In-situ U-Pb dating of zircons from the Eoarchean Itsaq Gneiss and supracrustal rocks in
the Isua area, southern West Greenland: Reappraisal of geochronology and tectonics of theIsua supracrustal belt
Naoki Sato1, Shinji Yamamoto2, Hiroki Uehara1, Shuhei Sakata1, Yoshiaki Kon4, Kazuaki Okamoto5,
Takafumi Hirata3, *Tsuyoshi Komiya1
1.Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University ofTokyo, 2.Graduate School of Environment and Information Sciences, Yohohama National University,
3.Graduate School of Science, Kyoto University, 4.National Institute of Advanced Industrial Scienceand Technology, 5.Faculty of Education, Saitama University
It is considered that emergence of life and operation of plate tectonics date back to the Eoarcheanor Hadean. But, the Archean rocks are preserved only in few blocks; thus it is important todetermine the age of the Isua supracrustal belt (ISB) in the Itsaq Gneiss Complex because previous
works reported evidence for the plate tectonics and vestige of life from the ISB. Previous works of
U-Pb dating of zircons from orthogneisses in the Isua area suggested that northern part of the ISB
and an orthogneiss batholith in the northern area have younger ages of ca. 3700 Ma whereas thesouthern part and orthogneiss rocks in the southern area have older ages of ca. over 3800 Ma.
Nutman et al. (2009) proposed that they were separately formed and subsequently collided andamalgamated with each other around 3690 to 3660 Ma because of the difference in the ages between
the northern and southern areas. They also suggested that in this case, the suture zone was locatedalong a chert layer at the center of the belt.
We separated zircons from three northern orthogneisses, five southern orthogneisses and two felsic
sedimentary rocks in the ISB, and conducted Cathodoluminescence (CL) observations, U-Pb dating with
LA-ICP-MS, and LA-Raman analyses to estimate the influence of metamictization. The CL observations
showed that some zircons still preserve magmatic oscillatory zoning in the core, and that zircons
from the northern area have relatively darker CL intensity than those from southern area. The
zircons from the felsic sedimentary rocks have relatively bright CL intensity, and oscillatory
zoning with ambiguous boundaries. The CL observations suggest that influence of secondary thermal
events increased from for the zircons in southern orthogneisses through ISB to northern
orthogneisses. The LA-Raman analyses can constrain the degree of recrystallization or restorationof mineral structures during later thermal events. The zircons from the northern orthogneisses are
more restored than those from the southern orthogneisses. In contrast to the CL observations, thezircons in the ISB suffered the most severely from the later restoration than any others. The
combination of the CL and LA-Raman observations indicates especially, the zircons from the ISB had
suffered severe secondary thermal events, but the mineralogical structures were partially restored
possibly due to thermal events of granitoid intrusions so that their CL images and LA-Raman
analyses are inconsistent each other. Because both the mineralogical restoration and destruction
resulted in Pb loss, it is considered that the zircons in the ISB underwent more significant Pbloss. The U-Pb ages of the zircons from the northern orthogneisses range from ca. 3660 to 3780 Ma
whereas the zircons from the southern orthogneisses have ages from ca. 3750 to 3850 Ma. The zircons
from the ISB range from 3660 to 3750 Ma. The relationship between zircons from the northern
orthogneisses and ISB is inconsistent with geological relationship, which the orthogneisses were
intruded into the ISB. The geochronological data of zircons should be reconsidered in the points ofthe mineralogical restoration and destruction; thus the accretionary model for the formation of ISB
is still valid.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P04 -BPT05-P04

Japan Geoscience Union Meeting 2016

Keywords: Isua supracrustal belt, U-Pb dating of zircons©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P04 -BPT05-P05

Japan Geoscience Union Meeting 2016

Alkaline hydrothermal metamorphism in the Archean: Implications for behavior ofchalcophile elements and the deposits*Tsuyoshi Komiya1
1.Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University ofTokyo
Coevolution of the surface environment and life through the time is one of the most significant
features of the earth. Decoding of ocean chemistry in the early Earth is a key issue to understandthe origin and evolution of life. Copper is one of chalcophile elements and the 27th most abundantelement in a crust. Zinc and cobalt also belong to the chalcophile elements. The copper is an
essential element for oxygen-producing photosynthesis because the Cu is utilized for plastocyanin.
The plastocyanin is used by higher plants whereas cytochrome (an iron-protein) is used by red andbrown algae. And, some of green algae and cyanobacteria can use both plastocyanin and cytochrome
depending on the cupper contents. The copper is essential for cyanobacteria, green algae and higher
plants. Because another copper protein, Hemocyanin, is a protein that transports oxygen throughout
the bodies, Cu is also important for some invertebrate animals such as Arthropoda and some of
Mollusca. It is also well-known that chalcophile elements possibly played an important role onprebiotic evolution because presence of Co and Zn promotes formation of oligomers. The behavior of
the chalcophile elements in the hydrothermal environments influenced formation of copper deposits
in the Eoarchean.
Comparison of copper contents between modern unaltered and hydrothermally-altered ocean floor
basalts indicates that the altered basalts have more copper contents than the unaltered basalts. On
the other hand, zinc contents of the altered basalts increase with the increasing alteration.
Although both the copper and zinc belong to chalcophile elements, their behaviors are different
during the hydrothermal alteration of basalts.
The North Pole and Mable Bar greenstone belts in Pilbara, Western Australia, are characterized byocean plate stratigraphy and duplex structures so that they originate from accretionary complexes
in the Archean. We classified the greenstones into MORB- and OIB-types based on the relationship of
the greenstones with cherts: the greenstones on thick cherts are classified into MORB-type whereas
the greenstones interlayered with thin chert layers into OIB-type, respectively (Komiya et al.,2002). Moreover, a previous work classified the hydrothermally-altered MORBs into Type I withmagmatic texture, Type II without magmatic texture and Highly silicified groups, and reported theirgeochemical compositions (Nakamura & Kato, 2004).
Comparison of the copper contents between the unaltered and hydrothermally-altered MORBs in the
Paleoarchean shows that the highly silicified group has lower Cu contents than the unaltered MORBs.
The Type-I and II groups are highly scattered in Cu contents. On the other hand, the highly
silicified group has lower Zn contents than the unaltered MORBs, but the Type-I and II groups arehigher Zn contents.
A pH-Eh diagram of the copper shows that the copper can be dissolved only in a narrow pH-Eh
condition, namely relatively acidic and oxic condition because Cu forms sulfide under anoxic (Eh <0.3) condition whereas forms oxides and metal of CuO, Cu2O and Cu under high (>7) pH condition. On
the other hand, zinc has a large stability field of dissolved zinc under lower pH (<8) and higher
Eh (>0.2) condition.
As a result, it is considered that the behavior of zinc in seawater and hydrothermal fluid in theArchean was similar that in the Phanerozoic. On the other hand, the behavior of copper in theArchean was different from that in the Phanerozoic because the Archean seawater was anoxic and a©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P05 -BPT05-P05

Japan Geoscience Union Meeting 2016little acidic to neutral whereas hydrothermal fluid was more alkaline. The difference possibly
accounts for the difference in behaviors of copper of the hydrothermally-altered basalts between in
the Archean and Phanerozoic. Hydrothermal fluid unrelated with silicification in the Archeanpossibly supplied more copper than that in the Phanerozoic.
Keywords: Chalcophile elements, Archean, Biological evolution, Economic Geology©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P05 -BPT05-P06

Japan Geoscience Union Meeting 2016

Carbon isotope and chemical compositions of the metasedimentary rocks from Saglek Block(>3.95 Ga), Labrador, Canada: Discovery of the oldest life and its habitat environment
Takayuki Tashiro1, Akizumi Ishida2, Masako Hori2, Motoko Igisu3, Yuji Sano2, *Tsuyoshi Komiya1
1.Department of Earth Science & Astronomy, Graduate School of Arts and Sciences, The University ofTokyo, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.Japan Agency for
Marine-Earth Science and Technology
The Earth is the only planet where liquid water and organisms are present. However, our knowledgeof early earth as well as origin of life is still poor because of little preservation of Eoarcheansupracrustal rock. This study first presents geological, petrological and geochemical features of
the 3.95 Ga supracrustal rocks including pelitic rocks, conglomerates, carbonate rocks, cherts,
chert nodules and ultramafic rocks from 3.95 Ga Saglek Block. This presentation is composed of two
topics. The first topic aims at revealing the origin of graphite in the metasedimentary rocks basedon petrographic observation and carbon isotope analyses. The purpose for the second topic is
elucidating the protolith of the carbonate rocks, and estimating the redox condition of the
Eoarchean seawater on the basis of petrographic observation and major and trace element analyses.
We obtained carbon isotope compositions of graphite (δ13Corg) from -28.2 to -11.0‰ in pelitic rocks,
from -27.6 to -20.8‰ in conglomerates, from -9.9 to -6.9‰ in carbonate rocks and from -10.3 to-9.9‰ in chert nodules, respectively. The maximum δ13Corg values of the graphite in pelitic rocks ofeach locality increase with increasing metamorphic grade from amphibolite to granulite facies,
indicating that the variation of the δ13Corg values is due to later metamorphism so that a primary δ
13Corg value is lower than the minimum δ13Corg value. The crystallization temperature of the graphite,

estimated from Raman spectroscopic analyses, is consistent with metamorphic temperature of the hostrocks except for chert nodules, suggesting that the graphite does not originate from latercontamination. On the other hand, the carbon isotope compositions of carbonates range from -3.8 to-2.6‰. The large fractionation (δ13Ccarb - δ13Corg), up to 25‰, implies the presence of autotroph
utilizing the reductive acetyl-CoA pathway or Calvin cycle at least 3.95 Ga, ca. 110 Ma earlier
than previous records.
We analyzed major element compositions of the carbonate rocks, pelitic rocks, conglomerates, chert
nodules and ultramafic rocks and their trace element compositions except for conglomerates andchert nodules are reported. The origins of the carbonate rocks in the Eoarchean metamorphic
terrains are always controversial because of severe later carbonate metasomatism and presumption ofacidic seawater condition (so-called a soda ocean model) due to quite high CO2 atmosphere. The rareearth element + yttrium (REE + Y) patterns of some carbonate rocks are obtained in order to reveal
the origins of the carbonate rocks, namely metasomatized mafic rock or chemical sedimentary rock.
They are disrupted by input of crustal detritus or post-depositional disturbance. However, thecarbonate rocks, which preserve seawater-like REE + Y patterns, still exist in all of our studied
areas, indicating the chemical sedimentary origin of the carbonate rocks. All carbonate rocks in
Saglek Block have no Ce anomalies, supporting the reduced condition of the Eoarchean ocean. The
combination of carbon isotope values of the graphite and REE patterns of the carbonate rocks
suggest the presence of the autotroph using the reductive acetyl-CoA pathway or Calvin cycle except
for cyanobacteria at least 3.95 Ga.
Keywords: The oldest evidence for organism, Eoarchean, Saglek Block in Labrador, Carbonate rock©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P06 -BPT05-P07

Japan Geoscience Union Meeting 2016

Occurrence and geochemical study of the basalts, komatiites and cherts from the silica
alteration zones in the Barberton greenstone belt, South Africa*Saori Umeda1, Akira Ishikawa1, Tsuyoshi Komiya1
1.Graduate school of Arts and Sciences, The University of Tokyo
The Early Archean Barberton Greenstone Belt (BGB), South Africa, comprises three groups of theOnverwacht, Fig Tree and Moodies Groups. The Komati and Hooggenoeg formations in the Onverwacht
Group contain a well-exposed volcanosedimentary sequence of komatiitic and basaltic volcanic rocks
and cherts. It is known that the komatiite and basalt underwent both severe carbonation andsilicification. However, the relationship of the timing, order, and geological distribution between
the silicification and carbonation and the extent of the elemental movement during their events arestill ambiguous. This work presents distribution of the silicified and carbonated volcanic rocks,
and the petrological and geochemical sequences from unaltered though carbonated to silicified
volcanic rocks.
The silicified volcanic rocks from the basalts and komatiites widely underlie the bedded cherts,
whereas the carbonated rocks are sporadically and rarely distributed all over the thick volcanic
sequences. Only the carbonated rocks are found within the volcanic sequences. On the other hand,the silicification is dominated, but both the silicified and carbonated volcanic rocks occur underthe bedded cherts. In addition, an ultramafic komatiite flow underwent both carbonization andsilicification in the middle Hooggenoeg Formation, but the silicification is limited to the upper
part of the flow whereas the lower part avoids the severe silicification and preserves muchcarbonate minerals, suggesting the silicification postdated the carbonation.
We analyzed major and trace element contents of the carbonated, silicified and not-silicified
volcanic rocks including five basalts and eleven peridotitic and basaltic komatiites and fiveoverlying cherts. The fresh basalt has ca. 47% in SiO2 contents whereas the silicified basalts
range from 57 to 78% in SiO2. Their Mg, Fe, Na, Mn and P contents progressively decrease withincreasing SiO2 contents. Their TiO2, Al2O3 and K2O contents decrease for moderately silicifiedbasalts, and then increase for severely silicified basalts with increasing SiO2 contents. On theother hand, their Ca contents increase for moderately silicified basalts, and then decrease forseverely silicified basalts with increasing SiO2 contents. Fresh peridotitic komatiites have ca.
45% in SiO2 contents whereas the silicified komatiites range from 55 to 84% in SiO2. A moderately
silicified komatiite with ca. 55% in SiO2 content has distinct compositions rather than others, andare highly enriched in Al2O3, MgO, and K2O contents. However, TiO2, Al2O3, FeO and MgO contents ofthe silicified ultramafic komatiites progressively decrease with increasing SiO2 contents. Their
MnO, CaO and Na2O contents basically decrease but are fluctuated with increasing SiO2 contents.
The PAAS-normalized rare earth element (REE) patterns are quite distinct between the silicifiedbasalts and ultramafic komatiites. All of the silicified basalts and ultramafic komatiites have
LREE-depleted REE patterns and large to faint positive Eu anomalies. Some ultramafic komatiites
have obvious negative Ce anomalies, positive Eu and Y/Ho anomalies whereas silicified basalts have
no Ce anomalies. Both positive and negative Y/Ho anomalies are found for both the silicifiedbasalts and komatiites. The REE patterns of cherts apparently depend on the underlying silicified
volcanic rocks. The cherts overlying the silicified basalts have no Ce anomalies whereas those overthe silicified komatiites have obvious negative Ce anomalies. The systematic change of the REE
patterns implies the elemental mobility depends on the host rocks during the silicification andcarbonation.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P07 -BPT05-P07

Japan Geoscience Union Meeting 2016

Keywords: Silicification, Barberton greenstone belt, Hydrothermal process©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P07 -BPT05-P08

Japan Geoscience Union Meeting 2016

PIXE and microthermometric analyses of fluid inclusions in hydrothermal quartz from the
2.2 Ga Ongeluk Formation, South Africa: implications for ancient seawater salinity*Takuya Saito1, Takazo Shibuya2, Tsuyoshi Komiya3, Shigenori Maruyama1, Masanori Kurosawa4
1.Earth-Life Science Institute, Tokyo Institute of Technology, 2.Precambrian Ecosystem Laboratory,
Japan Agency for Marine-Earth Science and Technology, 3.Department of Earth Science & Astronomy
Graduate School of Arts and Sciences The University of Tokyo, 4.Graduate School of Life andEnvironmental Sciences, University of Tsukuba
Seawater salinity is a critically important component because of the control it exerts on thechemical species in the seawater in that the chlorine concentration limits the concentrations ofother cations and chloro-complexes. The analyses of fluid inclusions in hydrothermal quartz
precipitated during seafloor hydrothermal alteration are useful for estimating the salinity ofancient seawater. We performed microthermometry and PIXE analyses on fluid inclusions in quartz
from the 2.2 Ga Ongeluk Formation, which consists mainly of submarine basaltic andesite volcanics(pillow lavas and sheet flows) erupted during a period of global glaciation, and these analyses
were used to estimate the seawater salinity during the glaciation.
The hydrothermal quartz contains many primary and secondary liquid-vapor fluid inclusions as wellas inclusions that are randomly distributed without a trace of secondary healed cracks. These fluidinclusions were individually analyzed with microthermometry to obtain the concentrations of Na, Ca
and Cl and with PIXE methods to obtain the concentrations of Cl, K, Ca, Mn, Fe, Cu, Zn, Br, andother elements.
Our obtained results show a different model salinity between primary (high-salinity) and secondary(relatively low-salinity) fluid inclusions, wide Na/Ca variation in the primary fluid inclusions
and wide variation in transition metal concentrations (excluding Fe) in the Na-rich primary
inclusions. Based on a comparison with modern seafloor hydrothermal vent fluids, these patterns canbe explained by the two distinct mixing process: one process involves 1) a Na-rich, Ca- andtransition metal-poor endmember mixing with 2) a Ca-rich, Na- and transition metal-poor
hydrothermal fluid affected albitization (Ca-Na exchange reaction), and the other mixing process
involves 1) a Na-rich, Ca- and transition metal-poor endmember mixing with 3) a Na- and transition
metal-rich, Ca-poor hydrothermal fluid affected high temperature water/rock reactions. The Na-rich,
Ca- and transition metal-poor endmember (1) in the primary inclusions is considered to represent
the 2.2 Ga Ongeluk seawater composition.
The estimated seawater salinity is approximately six times greater than the modern value and 3–4
times higher than the value estimated for the early seawater based on the total amount of theextant continental salt deposits and saline groundwater (1.5–2 times the present seawatersalinity). The difference between these estimates may result from the presence of unknown salt
deposits and saline ground water in the modern continental crust or the formation of ice from muchas two thirds of the ocean water during the 2.2 Ga global glaciation.
Keywords: fluid inclusion, seafloor hydrothermal alteration, salinity, PIXE, Ongeluk Formation©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P08 -BPT05-P09

Japan Geoscience Union Meeting 2016

Constraints on the surface environments and the ocean biological activities in the Archean*Yuusuke Nakagawa1, Peng K. Hong2, Kazumi Ozaki3, Eiichi Tajika1
1.Graduate School of Frontier Sciences,University of Tokyo, 2.The University Museum, The Universityof Tokyo, 3.AORI, The University of Tokyo
In the Archean, the climate of the Earth may have been warmer than that of today in spite of thelower luminosity of the Sun at that period [1]. The greenhouse effect of methane, in addition tothat of carbon dioxide, is considered to have maintained the warm climate [2, 3], however, previous
studies do not support the methane flux required for the warm climate [4]. In this study, wedeveloped a coupled model of 1-D atmospheric chemistry –ocean ecosystem –biogeochemical cycle inorder to investigate the biogenic methane flux in the Archean. We found that the biogenic methane
flux could have been high enough to maintain warm climate if we assume ecosystem composed ofmultiple anoxygenic phototrophs which uses hydrogen and iron, with acetogen and methanogens,because of the H2–CH2O–CH4 and CO–CH3COOH–CH4 biogeochemical cycles driven by Fe-CH2O-CH4
biogeochemical cycle could amplify the methane production nonlinearly through the recycling
processes of organic matters.
[1] Walker et al., 1982, Palaeogeography, Palaeoclimatology, Palaeoecology, 40, 1. [2] Pavlov etal., 2001, Journal of Geophysical Research: Planets, 106, 23267. [3] Haqq-Misra et al., 2008,
Astrobiology, 8, 1127. [4] Kharecha et al., 2005, Geobiology, 3, 53.
Keywords: Archean, faint young Sun paradox, anaerobic organism, methane greenhouse effect, 1-D
atmospheric chemistry - ocean ecosystem - biogeochemical cycle model©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P09 -BPT05-P10

Japan Geoscience Union Meeting 2016

Chronological constraints on Paleoproterozoic strata in Gabonese Republic*Yusuke Sawaki1, Tomohiko Sato1, Hisashi Asanuma1, Shuhei Sakata2, Takafumi Hirata2
1.Tokyo Institute of Technology, 2.The University og Tokyo
The Paleoproterozoic is one of the most important periods through the Earth history and ischaracterized by numerous geological events such as emergence of eukaryote, Snowball Earth, andrise of oxygen level in the ocean-atmosphere system. Recently macroscopic structures, which can beinterpreted as colonial organisms by some researchers, have been reported from Paleoproterozoic
sedimentary rocks in Gabonese Republic. Many kinds of geochemical proxies in the sediments havebeen measured in order to decipher surface environment at that time. In spite of their importance,
chronological constraints on the rocks are still insufficient. Previous workers reposted Rb-Sr
isochron ages of intrusive syenites and zircon U-Pb ages from basement gneisses. The errors anduncertainties of the Rb-Sr isochron ages, however, were over 100 million years. The previous studyof the zircon U-Pb age was devoid of description of internal structures in zircons under acathode-luminescence observation, therefore the metamorphic age of the basement gneiss has not been
evaluated in a rigorous manner.We got some syenite rocks and a powdery sample prepared from abasement gneiss from research collaborators in Gabonese Republic. The syenites are mainly composedof K-feldspar and aegirine, and include quartz, siderite, and fluorite as accessary minerals.
SEM-EDS observation demonstrates that fluorine is also enriched in the aegirine. In addition tothat, the alkaline elements-rich chemical compositions of the syenites imply that these rocks
belong to A-type granite. We tried to separate zircon grains from the syenites, but could identify
little zircons. On the other hand, many subhedral zircons were picked up from the powdery sample.
Under the cathode-luminescence observation, many zircon grains show oscillatory zoning from core torim, except for metamictized parts. Newly grown metamorphic rims could not be identified in thesezircon grains.We will present the preliminary results and advances for more precise chronologicalconstraints on sedimentary ages of Paleoproterozoic strata in Gabonese Republic.
Keywords: Paleoproterozoic, Gabonese Republic, U-Pb geochemistry©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P10 -BPT05-P11

Japan Geoscience Union Meeting 2016

Organic Nitrogen/Carbon isotope ratios from the Middle Proterozoic sedimentary rocks,
McArthur Basin, Northern Australia*Kazumi Yoshiya1, Yusuke Sawaki2, Manabu Nishizawa3, Tsuyoshi Komiya4, Shigenori Maruyama1
1.Earth-life Science Institute, Tokyo Institute of Technology, 2. Earth & Planetary Sciences, Tokyo
Institute of Technology, 3.JAMSTEC, 4.The University of Tokyo
Oxygenation of Earth's surface is expected to be deeply linked to evolution of life. Many of
independent evidence suggest that the Earth’s atmospheric oxidation state is increased in two
steps: from 2,400 to 2,300 million years ago, and around 600 million years ago (Holland, 2006). On
the other hand, ocean was mostly dominated by reducing conditions during the Archean, whereas theocean-atmosphere system in the Phanerozoic was as oxygenated as it is now. It has been generally
assumed that the middle Proterozoic ocean was globally oxic at the surface and sulfidic (euxinic)
at depth. Nitrogen limitation caused by trace metal scarcity has been proposed as an explanation
for why eukaryotic diversification is delayed (Canfield, 1998; Anbar & Knoll, 2002).
Here we show nitrogen and carbon isotope compositions of middle Proterozoic sediments, mainly
carbonate rocks, mudstones and black shales prepared from six drillcore samples (Mount Young 2,
McArthur River 2, Urapunga 4, Urapunga 5, Jamison-1 and 14MCDDH002) in McArthur Basin, Northern
Australia.
δ15NTN values of the black shale in the Wollogorang and Barney Creek formations are relatively
high, ranging from +4 to +7 ‰. The high δ15NTN values likely reflect the predominance of partial
denitrification in the water-column. δ15NTN values gradually decrease from +7 to +1 ‰stratigraphically upward, and the average δ15NTN value is 3.5 ‰.
An increasing nitrate reservoir may have been responsible for the decreasing δ15NTN value, which
implying an ocean oxygenation in the middle Proterozoic.
.
Keywords: Nitrogen isotope ratio, Middle Proterozoic, McArthur Basin©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P11 -BPT05-P12

Japan Geoscience Union Meeting 2016

Stratigraphy of banded iron formation in El Dabbah, Eastern Egypt*TAISHI SUZUKI1, Shoichi Kiyokawa1, Minoru Ikehara2, Takashi Sano3, Dawood Maher4, Mohamed
Abouelhassan4
1.Kyushu Univ., 2.Kochi Univ., 3.National Museum of Nature and Science, 4.Menoufia Univ.
In the Eastern Desert of Egypt c. 700 Ma-old, Iron formations are present within greenstone belts(El-Gaby et al., 1990). Since detailed stratigraphy of the iron formation and its sedimentary
environment are not well understood, we have conducted detailed geological research at Wadi El
Dabbah in the middle of the Eastern Desert greenstone belt. The middle area is characterized by low
metamorphic grade compared to the north and south areas that have high metamorphism with upper
greenschist to amphibolite facies conditions (Khalil and El-Shazly 2011).
The El Dabbah area has been divided into four geological sections by a left-lateral fault (N-S
strike) and reverse fault (E-W strike). In the northeast and northwest areas, volcaniclastic rocks
are deposited horizontally, which include thin BIF in the northwest area. In addition, this area iscovered unconformably by the Hammamat Group which is a continental sedimentary succession showing adome-like fold structure. In the southeastern area, the main rock types are gabbro, massive basalt
and coarse-grained volcaniclastic rocks. BIF are randomly occurs in several places. In thesouthwest area, coarse-grained volcaniclastic rocks, pillow lava, black shale and BIF makealternating layers. Strata are mostly dipping to the north at around 40-60 degrees. In thesouthwest area, gabbro and thick lava mainly comprises the basement. In the central unit of thesouthwest area, the continuity of stratigraphy is preserved, and BIF and black shale areinterbedded with pillow lava and volcaniclastic rocks.
Our study focused on two well-preserved areas. We performed XRF and REE chemical analysis for
powdered rock samples from both areas. We also analyzed Corg and δ13Corg of black shales overlying
BIF at the other section. Corg is 0.07 ~ 0.12 wt % and δ13Corg is -22.5 ~-23.5 ‰. Trace elements involcaniclastic rocks around the BIF are indicative of a volcanic arc basalt origin in terms of a
Nb−Zr−Y discrimination diagram. The volcanic rocks consist of sparsely vesicular pillow and massive
lavas, and sediments of continental origin are not present except for the BIF and black shale. In
conclusion, these formations were likely formed near island arc setting. BIF of this area wasdeposited repeatedly during a resting stage of the volcanic activity.
Keywords: banded iron formation, Neoproterozoic©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P12 -BPT05-P13

Japan Geoscience Union Meeting 2016

Chemical mapping of the Ediacaran phosphatized microfossils from Doushantuo Formation,
South China and extant organisms of animals and algae: Toward establishment of chemical
paleontology*Ayano Ohkawara1, Shuhei Sakata2, Takeshi Ohno3, Nami Okubo4, Shin Kubota5, Tsuyoshi Komiya2
1.Department of Earth and Planetary Science, The University of Tokyo, 2.Graduate School of Arts andSciences, The University of Tokyo, 3.Department of Chemistry, Faculty of Science, Gakushuin
University, 4.Department of Economics, Tokyo Keizai University, 5.Field Science Education andResearch Center, Kyoto University
The Ediacaran is a period when the living biota was born. Thus, its fossil records are important,especially phosphatized ones, that are elaborately preserved. Various kinds of the Ediacaran
phosphatized microfossils have been found from the Doushantuo Formation, South China. The
Doushantuo Formation is comprised of alternative layers of phosphorite and dolomite, and was
deposited just after the Marinoan glaciation in the Cryogenian. Most of the Doushantuo spheroidal
microfossils are several hundreds µm across, and some are divided into 2 to 100 cells, and others
have chorion on which spiny ornaments are distributed. Some specimens have both. It was consideredthat the Doushantuo microfossils have affinity with dormant metazoan embryos or algae based on
those shapes, but their phylogenetic position is still controversial.
Previous studies focused only on morphological structures of the Doushantuo microfossils by
microscopic, SEM and μCT observations, and inferred the phylogenetic position based onmorphological comparison between the microfossils and living organisms. For example, Chen et al.
(2009) pointed out that some of the microfossils resemble living bilaterians at cleavage stages
when they are divided into some macromeres and micromeres, and postulated that the Doushantuo
microfossils were derived from bilaterian embryos. However, generally speaking, the shapes offossils are easily modified through diagenesis or taphonomy so that it is difficult to obtainrobust evidence only from the physical structures. On the other hand, combination of chemical
analyses and morphological observations of the fossils provides a powerful method to morequantitatively obtain the phylogenetic position of Doushantuo microfossils. The geochemical
identification of fossils is named as chemical paleontology hereafter. A purpose of this work is
finding key elements to identify the origin of Doushantuo microfossils toward establishment of thechemical paleontology.
We performed chemical mapping of the Doushantuo microfossils and extant organisms on thin sections
with LA-ICP-MS at the Gakushuin University and The University of Tokyo. The extant organisms
comprise multicellular rhodophyta and some species of cnidarian embryos. The latters, especially,
are selected at various developmental stages because it is considered that the morphologicalvariations of the Doushantuo microfossils are partially due to the difference in theirdevelopmental stages. The living organisms were cast into methacrylate-resin disks and cut intosome thin sections.
We obtained chemical mapping of 10 bioessential elements, which comprise three major elements (Mg,
P and Ca) and seven trace elements (B, Al, Fe, Cu, Zn, Sr, Ba and Pb), on three developmental
stages of the coral embryos and three embryo-like microfossils from the Doushantuo Formation.
Identical elemental distribution and concentration between the living organisms and Doushantuo
microfossils were not obtained yet, but some new findings have been obtained.
First, some elements (Sr, Ba, and Pb) are concentrated on their outer membranes of the living coralembryos, and the distribution patterns become homogenized with the developmental stages. Second,the elemental distribution patterns in brown phosphate parts vary among the microfossil specimens©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P13 -BPT05-P13

Japan Geoscience Union Meeting 2016

whereas the patterns in gray phosphate parts are almost similar among the specimens. The
compositional variation is possibly due to vestiges of the precursors because the brown phosphateparts contain more organic matter so that they possibly preserve more primitive elemental
distribution than the gray phosphate parts.
The good correlation between elemental distributions and tissues provides a potential for chemical
paleontology. But, further analyses of more microfossils on brown phosphates with much organic
matter as well as various extant organisms should be necessary to find the key elements to identify
the Ediacaran microfossils.
Keywords: Ediacaran, microfossil, chemical paleontology©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P13 -BPT05-P14

Japan Geoscience Union Meeting 2016

Cu chemostratigraphy of the Ediacaran in the Three Gorge area, South China*Yechuan Geng1, Tsuyoshi Komiya1, Takeshi Ohno2
1.Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University ofTokyo, 2.Gakushuin University
The earth is only the planet, where higher forms of life exist. The Ediacaran-Cambrian transition
is characterized by numerous events such as emergence of metazoans and disturbances of surface
environment like Snowball Earth. The appearance and evolution of metazoans are the most important
issue of the evolution of the earth and life, but the causes are still obscure. The stable isotope
geochemistry of Cu is poorly known because of the lack of a suitable analytical technique. Thus, we
try to establish the analytical technique of sedimentary rocks and obtain the secular change of the
Cu isotope ratios of sedimentary rocks through the time.
Copper is one of the essential elements for life, especially for the hemocyanins in metazoans. The
hemocyanins (also spelled haemocyanins) are proteins that transport oxygen throughout the bodies ofsome invertebrate animals including arthropods and some of molluscs. We study the copper cycle ofseawater from the Ediacaran to early Cambrian because its sensitivity to redox allows us to obtainsome new data about the evolution of the life. However, data of the copper isotope ratios from the
Ediacaran to Cambrian ocean are quite limited.
We carried out on-land drilling of the sedimentary succession in Three Gorges area, South China.
The drill core samples of black shales and carbonate rocks will be used for the chemical analyses.
Now, we try to establish the copper isotope analysis using some standards. At first, samples are
dissolved with aqua regia. Each sample was subsequently dissolved in 1 ml of 7 N HCl and insoluble
particles were centrifuged out. The separation of transition elements on strongly basic anion
exchange resins in hydrochloric media is a classical procedure (Kraus and Moore, 1953). Van derWalt et al. (1985) demonstrated that the macroporous form (AG MP-1) of strongly basic anion
exchange resins has higher distribution coefficients for Cu(II), Fe(III) and Zn(II) in concentrated
HCl.
At first, we will analyze Cu concentrations of the sedimentary rocks with ICP-MS, and we will
analyze the Cu isotopic data in order to establish a new tool of Cu isotope chemostratigraphy in
the Ediacaran.
Keywords: copper, concentration, chemostratigraphy, Three Gorges©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P14 -BPT05-P15

Japan Geoscience Union Meeting 2016

The origin of deep-sea sediments within the Minamitorishima EEZ inferred from elemental
composition and isotopic ratios*Erika Tanaka1, Kazutaka Yasukawa1,2, Kentaro Nakamura1, Takashi Miyazaki3, Junichiro Ohta3, Koichiro
Fujinaga2,1, Hikaru Iwamori3,4, Yasuhiro Kato1,3
1.School of Engineering, The University of Tokyo, 2.Chiba Institute of Technology, 3.JAMSTEC,
4.Department of Earth & Planetary Sciences, Tokyo Institute of Technology
Recently, the deep-sea sediments containing a high concentration of rare-earth elements and yttrium(REY) were discovered in the Pacific Ocean [1]. In 2013, the presence of "extremely REY-rich mud"was confirmed within the Japanese exclusive economic zone (EEZ) surrounding Minamitorishima Island[2]. The downhole variations of total REY content of the bulk sediments demonstrate that a few
specific layers constitute distinct peaks of REY content. Such an extraordinary concentration
implies a possible link between an episodic environmental change and formation of marine mineral
resources, which strongly attracts our attention from both paleoceanographic and resource-geologic
view points. However, the origin of deep sea sediments including REY-rich mud within the
Minamitorishima EEZ has not been completely elucidated yet.
In order to unravel the origin of these sediments, it is necessary to decipher geochemical
end-members characterized by distinctive compositions and to specify their sources, fluxes andprocesses of supply. The most powerful tool for this approach is isotopic compositions such as Nd,
Sr, Pb and so on. [3, 4].
Here, as the first step for the comprehensive elucidation of the origin of the deep sea sedimentsin the Minamitorishima EEZ, we analyzed the modern, uppermost sediment samples collected from thesouthern part of the Minamitorishima EEZ. We investigated (1) mineralogical compositions by smear
slide observation and XRD analysis and (2) bulk chemical compositions by XRF and ICP-MS analyses,
in addition to (3) bulk Nd isotopic ratios using Thermal Ionization Mass Spectrometry (TIMS). We
report the results and interpretation of the analysis, and discuss the origin of the uppermost
sediments in the study area.
References[1] Kato et al. (2011) Nature Geoscience 4, 535-539.
[2] Fujinaga et al. (2013) JpGU2013[3] Goldstein, O’Nion and Hamilton (1984) Earth and Planetary Science Letters 70,221-236.
[4] Grousset and Biscaye (2005) Chemical Geology 222, 149-167.
Keywords: Deep-sea sediments, Rare Earth Sediments and Yttrium, Minamitorishima EEZ, Nd isotpes©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P15 -BPT05-P16

Japan Geoscience Union Meeting 2016

Pb isotope ratios of the Akeshi Au deposit, Kagoshima, Japan: Implication for gold
mineralization*Shumpei Murakami1, Koichiro Fujinaga2,1, Junichiro Ohta3,1, Kazutaka Yasukawa1,2, Kentaro Nakamura1,
Yasuhiro Kato1,2,3, Kurokawa Kyouhei4, Hikaru Iwamori3,5, Nagaishi Kazuya6, Tsuyoshi Ishikawa3
1.School of Engineering the University of Tokyo, 2.Chiba Institute of Technology, 3.JAMSTEC,
4.Mitsui Kushikino Mining Co., Ltd., 5.Tokyo Institute of Technology, 6.Marine Work Japan Co., Ltd.
Elucidating the origin of the deposits can provide a crucial key constraint in exploration for new
mineral deposits. It is previously considered that the epithermal deposits are formed byore-forming fluids originated from hydrous magmas and/or created by the circulation of meteoric
water within the shallow crust. The fluids extract metals from magmas and/or host rocks and thenmove to the shallower part of the crust, resulting in deposition of valuable metals due toreduction of pressure and temperature [1]. The previous mineralization model has been proposed on
the basis of isotopic study of relatively light elements (e.g., H and O) in ore-forming fluid.
However, recent isotopic studies on heavy metals (e.g., Pb, Sr and Nd) suggest the involvement ofanother important component, i.e., slab-derived fluid, to the formation of epithermal ore deposits[2]. For example, based on Pb-Sr isotopic compositions, Hosono and Nakano [3] suggested that deep
crustal fluid contributes to the formation of Hishikari gold deposits. In addition, Fujinaga et al.
[2] pointed out a possibility that slab-derived fluid contributes to the formation of hydrothermal
deposits in Japan, based on Pb isotope compositions of ore samples.
In the present study, to detect direct information of source of metals contributing to theformation of epithermal gold deposits, we study Pb isotopic compositions of sulfide ores from theHishikari and Akeshi gold deposits. The Hishikari and Akeshi gold deposits both in Kagoshima
prefecture, Japan, are the typical of the Hokusatsu-type and Nansatsu-type gold deposits,
respectively. Especially, the Hishikari deposit is known as one of the world's highest-grade gold
deposits [4].
Analytical result shows that the ore samples have three trends centering the host rock in 206Pb/204
Pb–207Pb/204Pb–208Pb/204Pb isotopic compositional space. Trend-1 constitutes a mixing trend between thehost rock and the bed rock (Shimanto Supergroup), which is consistent with the previous ore-forming
model. Trend-2 extends from host rock to an inferred composition of PHS-fluid (slab-derived fluid
from Philippine Sea plate [5]). This trend implies that the slab-derived fluid contributes tomineralization of hydrothermal ore deposits as suggested recently [2]. Trend-3 cannot be explainedby any geochemical end-member considered here, so more detailed investigation is required. A
relationship between Pb isotopic ratio and Au concentration suggests that both the bed rock and thePHS-fluid contribute to Au mineralization.
References[1] Hedenquist and Lowenstern (1994) Nature 370, 519-527.
[2] Fujinaga et al. (2013) GEOFLUID 3.
[3] Hosono and Nakano (2004) Earth Planet. Sci. Lett. 222, 61-69.
[4] Izawa et al. (1990) J. Geochem. Explor. 36, 1-56.
[5] Nakamura et al. (2008) Nat. Geosci. 1, 380-384.
Keywords: Akeshi gold deposit, slab-fluid, Pb isotopic ratio, ore-forming fluid, hydrothermal
deposits©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P16 -BPT05-P17

Japan Geoscience Union Meeting 2016

Chemostratigraphic correlation of deep-sea sediments in the western North Pacific Ocean:
Insight into the origin of REY-rich mud*Kazuhide Mimura1, Kentaro Nakamura1, Kazutaka Yasukawa1,3, Junichiro Ohta2,1, Koichiro Fujinaga3,1,
Shiki Machida2, Yasuhiro Kato1,2,3
1.School of Engineering, the University of Tokyo, 2.JAMSTEC, 3.Chiba Institute of Technology
REY-rich mud, a deep-sea sediment containing high concentrations of rare-earth elements and yttrium(REY), is expected to be a new resource for the critical elements due to its multiple advantages
such as huge resource potential and paucity of radioactive elements [1]. It has been confirmed that
REY-rich mud also exists in the Japanese exclusive economic zone (EEZ) around MinamitorishimaIsland [2], followed by the discovery of “extremely REY-rich mud” that contains more than 6000 ppm
of total REY from the Minamitorishima EEZ [3].
Due to detailed investigation by subbottom profiling and piston core sampling, the surficial
distribution of REY-rich mud within the Minamitorishima EEZ has been almost revealed recently[Nakamura et al., in revision]. However, piston coring cannot obtain sediment samples from thedeeper part of the sediment layer (at most ~13 m bellow sea floor (mbsf)). This hampers detailed
discussion of sediment stratigraphy in the Minamitorishima EEZ that is an important key toelucidate the genesis and distribution of the new resource.
In order to overcome this problem, we focused on the Ocean Drilling Program (ODP) Hole 1149
located in the Japanese EEZ, 600 km to the south-southeast from Tokyo. The sediment layer of ODP
Hole 1149 was almost continuously cored from the seafloor surface to ~180 mbsf (~97% of recovery)[4]. The sediments were classified into three units: ash- and biogenic silica-bearing clay of Unit
I (from the core top to 118.2 mbsf), pelagic brown clay of Unit II (118.2 to 179.1 mbsf), and chert
layer of Unit III [4].
Chemical analyses of 210 bulk sediment samples show that REY-rich mud is presented only in lower
part of the Unit II, whereas sediments in upper part of the Unit II and Unit I are all non-REY-richmud. Moreover, we found extremely REY-rich mud containing 7500 ppm of total REY in the Unit II.
This is the first report of extremely REY-rich mud from outside the Minamitorishima EEZ. By
comparing the newly analyzed data of ODP Hole 1149 and those from the Minamitorishima EEZ [5], thesediment stratigraphy in the Minamitorishima EEZ has been well reconstructed.
References[1] Kato et al. (2011) Nature Geoscience 4, 535-539.
[2] Kato, Y. et al. (2012) Abstract with programs, the society of Resource Geology.
[3] Fujinaga, K. et al. (2013) JpGU Meeting 2013.
[4] Plank et al. (2000) Proc. ODP. Init. Repts. 185[5] Oya, K. et al. (2015) JpGU Meeting 2015.
Keywords: deep-sea sediment, REY-rich mud, whole-rock chemical analyses, ODP Hole 1149,
Minamitorishima EEZ©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P17 -BPT05-P18

Japan Geoscience Union Meeting 2016

Chemical leaching of rare-earth elements from highly REY-rich mud with carbonated water*Yutaro Takaya1,2,3, Koichiro Fujinaga4,3,2, Yasuhiro Kato3,2
1.Department of Resources and Environmental Engineering School of Creative Science and Enginerring,
Waseda University, 2.Research and Development (R&D) Center for Submarine Resources, Japan Agency
for Marine-Earth Science and Technology, 3.Department of Systems Innovation, Graduate School ofEngineering, University of Tokyo, 4.Chiba Institute of Technology
During the research cruise KR13-02 of R/V Kairei, highly and extremely REY-rich mud (total REY
concentration exceeds 3,000 ppm and 5,000 ppm, respectively) were collected within the Japanese
exclusive economic zone surrounding Minamitorishima Island, northwestern Pacific Ocean. Due to its
great economic value, the REY-rich mud has received attention as a newly promising resource forrare-earth elements.
Takaya et al. (2015) reported that the optimum conditions for chemical leaching of rare-earth
elements from highly REY-rich mud with strong acid (HCl and H2SO4). The study shows that theapatite grains, the main host mineral of REY, dissolve easily in the diluted acid solution underroom temperature. We have conducted the chemical leaching experiments with carbonated water which
may enable to integrate the leaching and recovery processes (the recovery of rare-earth elementsfrom the leaching solution as a carbonate minerals). Here, we explain the concept of thishydrometallurgical processes and report the preliminary results of our experiments.
Keywords: REY-rich mud, Chemical leaching, Deep-sea mineral resources©2016. Japan Geoscience Union. All Right Reserved.

- BPT05-P18 -