著者

Junji Yamamoto Hidemi Ishibashi Yuuki Hagiwara Lena Yokokura Kiyoaki Niida

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.56, no.1, pp.31-39, 2022 (Released:2022-02-28)

参考文献数

36

被引用文献数

1

---

In the Horoman peridotite complex, the peridotite containing olivine-filled channels is known to exist. To examine the distribution pattern of the channel olivine, we performed non-destructive microanalyses of Raman spectra at 51 points of the olivine with 5 mm intervals along the channel. Compared with the Raman spectra of a reference euhedral olivine, for which the crystallographic orientation is known, there is no abrupt change in the crystallographic orientation in the 250 mm line analysis region of the channel. Moreover, Mg/Fe ratios of the channel olivine show gradual change over the entire measured area. If the channel olivine is an aggregate of olivine grains crystallized from magma infiltrating into the channel, then there should be olivine grains with both uneven crystallographic orientation and a homogeneous Mg/Fe ratio. Therefore, the olivine in the channel is regarded as a single crystal with slight growth zoning. The peridotite with the channel had been a part of mantle that was uplifted by the collision of plates. Therefore, the channel is a trace of magma migrating in the mantle. Magma migration in mantle drives the material–thermal circulation system connecting the Earth’s interior and surface. Furthermore, the size of the mineral in mantle reflects its stress field. Therefore, the magma channel involving such a large olivine is a unique specimen that reveals the particular characteristics of magmatism occurring in the Earth’s interior.

著者

Aiko Nakato Shiori Inada Shizuho Furuya Masahiro Nishimura Toru Yada Masanao Abe Tomohiro Usui Hideto Yoshida Takashi Mikouchi Kanako Sakamoto Hajime Yano Yayoi N. Miura Yoshinori Takano Shinji Yamanouchi Ryuji Okazaki Hirotaka Sawada Shogo Tachibana

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

pp.GJ22017, (Released:2022-10-21)

被引用文献数

9

---

The Hayabusa2 spacecraft explored C-type near-Earth asteroid (162173) Ryugu and returned asteroidal materials, collected during two touchdown operations, to the Earth as the first sample from carbonaceous-type asteroid. The sample container, in which ~5 g of Ryugu sample was enclosed, was safely opened in the clean chamber system with no severe exposure to the terrestrial atmosphere. In the course of preparation operation of the sample container, two dark-colored millimeter- to sub-millimeter-sized particles were found outside the sealing part of the sample container. Because they look similar to the Ryugu particles inside the sample container, the particles were named as Q particles (Q from questionable). In this study, we investigated Q particles (Q001 and Q002) mineralogically and petrographically to compare them with potential contaminants (the ablator material of the reentry capsule and fine sand particles at the capsule landing site), Ryugu sample, and CI chondrites. The Q particles show close resemblance to Ryugu sample and CI chondrites, but have no evidence of terrestrial weathering that CI chondrites experienced. We therefore conclude that the Q particles are originated from Ryugu and were expelled from the sample catcher (sample storage canister) in space prior to the enclosure operation of the sample catcher in the sample container. The most likely scenario is that the Q particles escaped from the sample catcher during the retrieval of the sample collection reflector, which was the necessary operation for the sample container closing.

著者

Toshitaka Gamo Harue Masuda Toshiro Yamanaka Kei Okamura Junichiro Ishibashi Eiichiro Nakayama Hajime Obata Kiminori Shitashima Yoshiro Nishio Hiroshi Hasumoto Masaharu Watanabe Kyohiko Mitsuzawa Nobukazu Seama Urumu Tsunogai Fumitaka Kouzuma Yuji Sano

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.38, no.6, pp.527-534, 2004-12-20 (Released:2008-04-08)

参考文献数

31

被引用文献数

12 32

---

This paper reports a series of studies leading to the discovery of a submarine hydrothermal field (called Nakayama Field) at an arc seamount (12°43′N, 143°32′E) in the southernmost part of the Mariana Trough, western Pacific Ocean. We first detected hydrothermal plumes characterized by water column anomalies of temperature, light transmission, Mn, Fe, Al, O2, CH4, and δ13C of CH4 above the summit caldera of the seamount. Then deep-tow camera surveys confirmed the existence of hydrothermal activity inside the caldera, and an ROV dive finally discovered white smoker-type fluid venting associated with vent fauna. A high concentration of aluminum in the plume and white smoker-type emissions imply acidic hydrothermal activity similar to that observed at the DESMOS Caldera in the eastern Manus Basin, Papua New Guinea. Anomalously low δ13C (CH4) of −38‰ of a vent fluid sample compared to other arc hydrothermal systems along the Izu-Bonin and Mariana Arcs suggests an incorporation of biogenic methane based on a subsurface microbial ecosystem.

著者

Kenta Yoshida Yoshihiko Tamura Tomoki Sato Chalermrat Sangmanee Ratchanee Puttapreecha Shigeaki Ono

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

pp.GJ22011, (Released:2022-08-06)

被引用文献数

7

---

The 2021 eruption of Fukutoku-Oka-no-Ba (FOB) in the northwest Pacific on 13 August 2021 produced a large volume of pumice that drifted westward for ~1300 km to the Nansei Islands, Japan, and some extent. In February 2022, pumice with similar characteristics to the FOB pumice was deposited along the Gulf of Thailand. The pumice clasts deposited in Songkhla Province, Thailand, were fine-grained with <4 cm in size and rounded. Most of the clasts consisted of clinopyroxene, plagioclase (andesine), and olivine phenocrysts in a vesiculated grey groundmass, with black-coloured spots exhibiting signatures of a basaltic magma. The whole-rock compositions of the pumice are trachytic, with 61 mass% SiO2 and 9 mass% total alkali (Na2O + K2O). The overall characteristics in the pumice from Thailand are similar to those in FOB pumice. These pumice in Thailand were from the 2021 FOB eruption, and drifted >2800 km south-westward across the South China Sea.

著者

Kentaro Nakamura Shinsuke Kawagucci Kazuya Kitada Hidenori Kumagai Ken Takai Kyoko Okino

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.49, no.6, pp.579-596, 2015-11-26 (Released:2015-12-05)

参考文献数

40

被引用文献数

37 58

---

Polymetallic sulfides deposited in seafloor hydrothermal vents have recently attracted attention as potential deep-sea mineral resources for base, rare, and precious metals such as Cu, Zn, Pb, In, Ga, Ge, Au, and Ag. For future exploitation of this type of deep-sea mineral resources, development of effective methods for exploring seafloor hydrothermal activity is a key to provide the most promising list of fields. However, conventional exploration methods are likely laborious and time-consuming, and a more efficient methods for exploration of seafloor hydrothermal vents are to be further developed. In the last decade, water column observation using multibeam echo souder (MBES) systems have become successfully applied to exploration of seafloor hydrothermal vents. In 2013 and 2014, we conducted extensive water column surveys using MBES systems in the mid-Okinawa Trough. During the surveys, we detected 10 hydrothermal vent sites, including previously known sites, belonging to four relatively large hydrothermal vent fields, located at the Izena Hole, Iheya North Knoll, Iheya Small Ridge, and a seamount 15 km northwest of the Izena Hole. All of the hydrothermal vent sites are in groups of 2–3 vent sites belonging to a hydrothermal field. Morphological features of the acoustic water column anomalies (rising vertically up to ~1000 m from the seafloor without a significant change of width) implied that the acoustic water column anomalies were not caused directly by hydrothermal vent fluid flows. The depth of the top of the acoustic water column anomalies (~500 m) corresponded rather well to the depth of the CO2 phase transition from liquid/clathrate-hydrate to vapor. This suggests that the acoustic water column anomalies are attributed to water mass including dense liquid CO2 droplets with clathrate-hydrate crusts, which are originally derived from the seafloor hydrothermal fluid discharges.

著者

JUN-ICHIRO ISHIBASHI TAKUROH NOGUCHI TOMOHIRO TOKI SHUNSUKE MIYABE SHOSEI YAMAGAMI YUJI ONISHI TOSHIRO YAMANAKA YUKA YOKOYAMA ERIKO OMORI YOSHIO TAKAHASHI KENTA HATADA YUZURU NAKAGUCHI MOTOKO YOSHIZAKI UTA KONNO TAKAZO SHIBUYA KEN TAKAI FUMIO INAGAKI SHINSUKE KAWAGUCCI

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.48, no.4, pp.357-369, 2014-07-20 (Released:2014-07-31)

参考文献数

48

被引用文献数

23 67

---

Two active hydrothermal fields, Jade and Hakurei fields have been discovered within the Izena Hole, a rectangular 6 km × 3 km shape depression located in the middle Okinawa Trough back arc basin. In both fields, intense hydrothermal activity is represented by venting of high-temperature fluid (>300°C) and occurrence of sulfide/sulfate ore deposits. We collected hydrothermal fluids during dive expeditions of ROV Hyper Dolphin conducted in 2003, 2010 and 2011, in order to analyze both elemental and gas species. The geochemistry of high temperature hydrothermal fluids collected from the Jade and Hakurei fields is very similar to each other with exceptions in minor gas composition. Little temporal variation was observed in geochemistry of the high-temperature hydrothermal fluid of the Jade field over two decades, since a previous study carried out in 1989. These results suggest that these fluids are derived from a common fluid reservoir where fluid chemistry is basically controlled by fluid-mineral equilibria and gas species are dominantly contributed from the same magma. Venting of low temperature fluid (about 104°C) was discovered in the distal part of the Jade field, which was named as the Biwako vent. Chemical composition of the Biwako vent fluid was distinctive from that of the high temperature fluid in the proximal part of the Jade field, and could not be explained by simple dilution or cooling. This intra-field chemical diversity could be caused by phase separation and segregation during fluid upwelling, based on relationships in concentrations of Cl and major cations. On the other hand, the chemical diversity recognized in minor gas composition between the Jade and Hakurei fields is in accordance with results from previous plume survey. Difference in concentrations of minor gases such as H2 is attributed to contribution from thermal degradation of organic matter in the sediment, during fluid upwelling.

著者

Yukihiko Satou Keisuke Sueki Kimikazu Sasa Hideki Yoshikawa Shigeo Nakama Haruka Minowa Yoshinari Abe Izumi Nakai Takahiro Ono Kouji Adachi Yasuhito Igarashi

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.52, no.2, pp.137-143, 2018-03-30 (Released:2018-04-19)

参考文献数

14

被引用文献数

36 77

---

Two types of radioactive particles were isolated from environmental samples collected at various distances from the Fukushima Dai-ichi Nuclear Power Station. “Type A” particles are 2–10 μm in diameter and display characteristic Cs X-ray emissions when analyzed using energy-dispersive X-ray spectrometry (EDS). “Type B” particles are considerably larger, up to 400 μm in diameter, with Cs concentrations too low to be detectable with EDS. These larger particles were isolated from the region north of the nuclear reactor site, which was contaminated on March 12, 2011. The specific activity of Type B particles is much lower than Type A, and the mean 134Cs/137Cs ratios are ~0.93 and 1.04, respectively. The Type B ratio indicates that power station Unit 1 is the source, implying that these larger radioactive particles were discharged on March 12. This study found that different type of radioactive particles were released not only on March 15 but also on March 12.

著者

Asako Takamasa Katsuhiko Suzuki Yusuke Fukami Tsuyoshi Iizuka Maria Luisa G. Tejada Wataru Fujisaki Yuji Orihashi Takuya Matsumoto

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.54, no.3, pp.117-127, 2020 (Released:2020-06-22)

参考文献数

33

被引用文献数

1 5

---

The extinct, relatively short-lived nuclide 182Hf produced 182W as a decay product. Fractionation of Hf-W in the very early Earth led to variations in the 182W/184W ratios of terrestrial rocks; however, because these variations are very small, quantifying 182W/184W ratios requires an extremely precise method. Here, we propose an improved method for highly precise and accurate method for measuring the 182W/184W ratios of terrestrial rocks. Samples were extracted with 4-methyl-2-pentanone and purified by cation and anion exchange chromatography prior to determination of the W isotope ratio by multiple collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) system coupled with a desolvating nebulizer. Sample preparation removed matrix elements (e.g., Hf, Ta, Os, and dimers of Nb and Mo) with masses similar to those of W isotopes, resulting in these elements having a negligible influence on the measured 182W/184W ratios. A W standard solution processed by ion exchange chromatography and/or solvent extraction showed a 183W deficiency, even after mass fractionation correction of the measured isotope data. As reported previously, mass-independent fractionation increases the 182W/184W ratio if the 183W/184W ratio is used to correct for mass fractionation to for better precision in natural samples. However, accurate 182W/184W ratios for a basalt reference material (JB-2) were obtained, even if 183W was used for mass fractionation correction. Our results show that it is also possible to correct for the effects of mass-independent fractionation on the 183W/184W ratio by sample-standard bracketing using a W standard solution subjected to the same preparation procedure used for the samples. A major advantage of the newly developed method is that it requires a smaller amount of sample (0.2–0.3 g; 50–80 ng W for JB-2) compared with that needed for other reported methods (typically 0.7–15 g; 500–1000 ng W). This decrease in sample amount was possible by removing matrix elements from the sample solutions, and cleaning the membrane of the desolvating nebulizer between analyses also contribute to enhancing the W ion beam intensity and to high precision. Analysis of different basalts from the Loihi, Kilauea islands and Ontong Java Plateau with various W isotopic compositions consistent with the previous studies demonstrated the reliability of the method.

著者

Kanoko Kurihara Norika Numa Sota Niki Mai Akamune Masaki Nakazato Shuji Yamashita Shoichi Itoh Takafumi Hirata

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.57, no.5, pp.e9-e16, 2023 (Released:2023-10-24)

参考文献数

35

---

Elemental and isotopic analyses of individual submicron-sized particles in chondrite matrix were made by an inductively coupled plasma time-of-flight mass spectrometer (ICP-TOF-MS) and a multiple collector ICP-MS equipped with high-time-resolution ion counters (HTR-MC-ICP-MS). The particles were collected from Allende CV3 chondrite through a laser ablation-in-liquid (LAL) technique. Firstly, the abundances for four major elements (Si, Al, Mg, and Fe) were determined on total 6086 particles, indicating that the Allende matrix is a mixture of submicron-sized particles made mainly of olivine, pyroxene, spinel, Fe–Ni sulfide, and Fe–Ni metal, consistent with the predicted major constituent minerals by a nebular condensation model. The major elemental compositions revealed that Fe–Ni particles are minor components (about 0.3% in number fraction) in the Allende matrix. Then, to estimate the origin of these metallic particles, abundances for Ni and two minor elements (Os and Pt) were measured. Total 10417 particles of Ni–Os–Pt bearing particles were also found in the chondrite matrix. Majority of the particles were enriched in Ni. Os and Pt were present as separated particles, and no particles with presence of both the Os and Pt were found. Finally, with the HTR-MC-ICP-MS technique, 195Pt/194Pt value was measured on total 1545 particles. The resulting 195Pt/194Pt values agree with the solar composition within analytical uncertainties. This lack in isotopic anomalies of the 195Pt/194Pt can be explained either by majority of the Pt nuggets being produced from uniform reservoir in the solar system or by Pt being isotopically homogenized prior to the formation of the solar nebula.

著者

S. TACHIBANA M. ABE M. ARAKAWA M. FUJIMOTO Y. IIJIMA M. ISHIGURO K. KITAZATO N. KOBAYASHI N. NAMIKI T. OKADA R. OKAZAKI H. SAWADA S. SUGITA Y. TAKANO S. TANAKA S. WATANABE M. YOSHIKAWA H. KUNINAKA THE HAYABUSA2 PROJECT TEAM

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.48, no.6, pp.571-587, 2014-11-20 (Released:2014-12-19)

参考文献数

99

被引用文献数

59 101

---

Hayabusa2 is an asteroid exploration mission to return surface samples of a near-Earth C-type asteroid (162173) 1999 JU3. Because asteroids are the evolved remnants of planetesimals that were the building blocks of planets, detailed observation by a spacecraft and analysis of the returned samples will provide direct evidence regarding planet formation and the dynamic evolution of the solar system. Moreover, C-type asteroids are expected to preserve the most pristine materials in the solar system, a mixture of minerals, ice, and organic matter that interact with each other. Space missions are the only way to obtain such pristine materials with geologic context and without terrestrial contamination. Hayabusa2 will launch off in 2014, arrive at 1999 JU3 in mid-2018, and fully investigate and sample the asteroid at three different locations during its 18-month stay. The concept and design of the Hayabusa2 sampler are basically the same as that on-board Hayabusa, and impact sampling with a 5-g Ta bullet will be made at three locations of the asteroid. The sample container has three separate chambers inside to store samples obtained at different locations separately. The spacecraft will return to Earth with samples in December 2020. Returned samples will be investigated by state-of-the-art analytical techniques in 2020 to understand the evolutionary history of the solar system from 4.56 Gyr ago to the present by combining results from laboratory examinations of the returned samples with remote-sensing datasets and comparing all results of observations of meteorites, interplanetary dust particles, and future returned samples.

著者

Naoto Takahata Yama Tomonaga Yuichiro Kumamoto Masatoshi Yamada Yuji Sano

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.52, no.2, pp.211-217, 2018-03-30 (Released:2018-04-19)

参考文献数

24

被引用文献数

1 21

---

In this work we report tritium concentrations determined in seawater samples collected offshore of Fukushima in the northwestern Pacific Ocean, immediately after the Fukushima Dai-ichi Nuclear Power Plant (F1-NPP) accident. We found surface seawater to have high concentrations of tritium (3H) and cesium-137 (137Cs) with respect to the concentrations expected for the investigated region. Tritium concentrations were up to six times the pre-accident level. However, these concentrations were found to be relatively low compared to those of 137Cs and 129I. This is most likely because of the very low production ratio of tritium to 137Cs in the F1-NPP, and the inherently high background concentration of tritium in these environmental waters (mainly ascribed to global fallout from nuclear weapons tests conducted during the 1960s). The tritium distribution in surface seawater showed higher concentrations close to the shore and lower concentrations offshore. Higher tritium concentration areas had spread both northward and southward from the F1-NPP along the coast, indicating that large amounts of tritium were carried by coastal currents. A positive correlation was found to exist between 3H and 137Cs concentrations in the seawater. The calculated 3H/137Cs ratio was similar to the production ratio of these isotopes reported for the broken reactors in the F1-NPP, which indicates that both radionuclides might have originated from the F1-NPP. Direct emission of tritium to the ocean from the F1-NPP was estimated to be approximately 0.05 PBq immediately after the accident, which is much smaller than the total inventory in the environment.

著者

Yuki Inoue Reo Okiyama Yuuki Hagiwara Junji Yamamoto

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.57, no.2, pp.92-99, 2023 (Released:2023-04-14)

参考文献数

24

被引用文献数

1

---

We measured the Raman spectra of CO2 fluid at 30 MPa and room temperature (19.1–21.3°C). The spectra showed peaks attributed to the CO2 combining various isotopes such as 12C16O2, 13C16O2, and 12C16O18O. The relative ratio of 12C16O2 to 12C16O18O peaks represents the oxygen isotope ratio of CO2. To evaluate the precision of the peak ratios, we measured the CO2 Raman spectra at different exposure times. We examined the standard deviation (1 σ) of the peak intensity ratios and area ones for 20 measurements at each exposure time. The standard deviations of the intensity ratios and area ones were 2.7 and 3.1%, respectively, at a maximum exposure time of 494 s, conversion to peak intensity of 12C16O2 yields about 2,000,000 counts. The uncertainties are 2.5–3 times greater than expected from the noise of a CCD camera and photon statistics. The oxygen isotope ratios (δ18O) of natural samples have a range of variation of about 16.6%. Compared to that value, the precision we obtained from this study is very small. Raman spectroscopy can be combined with microscopy to analyze areas as small as approx. 1 μm in diameter. Therefore, oxygen isotope measurement using Raman spectroscopy has potential for application to natural samples as a new method for small CO2 fluids such as fluid inclusions.

著者

SHINSUKE KAWAGUCCI KOTARO SHIRAI TEFANG FAITH LAN NAOTO TAKAHATA URUMU TSUNOGAI YUJI SANO TOSHITAKA GAMO

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.44, no.6, pp.507-518, 2010-12-20 (Released:2013-03-23)

参考文献数

60

被引用文献数

14 35

---

Hydrothermal plumes above the HAKUREI and JADE sites, two high-temperature hydrothermal vent sites in the Izena Cauldron at the mid-Okinawa Trough, were investigated in order to gain a preliminary understanding of gas geochemical characteristics at underlying hydrothermal vent sites. Three geochemical tracers, H2, CH4 and δ3He, covary with each other above the HAKUREI site but only CH4 and δ3He are correlated above the JADE site. The carbon isotope ratio of methane within the Izena Cauldron can be accounted by a combination of the fluid dilution by ambient seawater and microbial consumption with the kinetic carbon isotope effect (KIE) of 1.007. An estimated endmember δ13C value of -32‰ in the HAKUREI fluid was obtained. Both the plumes above the HAKUREI and JADE sites showed C1/C2 ratios between 103∼104. Only the bottom water around the HAKUREI site showed significant N2O excess with isotopically light δ15N and δ18O, suggesting N2O input from microbial activity in the sediment. A linear correlation between H2 and CH4 in the HAKUREI plume gives a H2/CH4 ratio of the HAKUREI fluid of more than 0.022. The estimated H2/CH4 ratio in the HAKUREI fluid is significantly higher than that of the JADE fluid, comparable with those of fluids venting at other sediment-related hydrothermal systems, and also comparable with those of thermogenic gases produced by hydrothermal sediment experiments. These facts suggest that fluid-sediment interaction during fluid upwelling appears to modify gas geochemical characteristics at the HAKUREI site but have little influence at the JADE site. This study demonstrates the availability of the Izena Cauldron hydrothermal field and the HAKUREI and JADE sites as a natural laboratory for investigating the fluid-sediment interaction during fluid upwelling.

著者

Hidenori Genda

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.50, no.1, pp.27-42, 2016 (Released:2016-02-04)

参考文献数

167

被引用文献数

26 54

---

The presence of water on Earth has played important roles in shaping the solid regions of the planet as well as in the origin and evolution of life. This paper addresses three fundamental aspects of Earth’s water; (1) the quantity of water on the surface and in the interior that Earth possesses, (2) the length of time that surface oceans have been present, and (3) the mechanism(s) by which this water was supplied or generated. From geochemical and geophysical analysis, and high-pressure experimental works, the water content in the Earth’s mantle can be estimated to be from one to ten times the present ocean mass. Although it is difficult to estimate the water content in the Earth’s core, recent high-pressure experimental work indicates copious amounts of hydrogen in the core. From geological and geochemical evidence, the Earth’s surface oceans appear to have existed since very early in the Earth’s history, perhaps even since the Earth’s formation. However, changes in the ocean volume throughout the Earth’s history have not been well determined. Several possible water sources and supply mechanisms have been proposed, in association with theories regarding planet formation in our solar system. Since there are several uncertainties concerning the process of planet formation, the origin of the Earth’s water is still in question.

著者

Hikaru Sawada Tsuyoshi Iizuka Yukiyasu Tsutsumi Yukio Isozaki

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.53, no.3, pp.171-179, 2019 (Released:2019-06-11)

参考文献数

64

---

To understand the timing and mode of crustal production and reworking in the Archean, we performed U-Pb and Hf isotopic analyses of detrital zircon grains from the ca. 2.3 Ga Murmac Bay Group in the Rae Craton, central Canada. The zircon U-Pb ages range from 3.9 to 2.3 Ga with a significant gap interval of 3.6–3.3 Ga, indicating that felsic magmatism has semi-continuously within the craton since the early Archean. The combined U-Pb and Hf isotopic data define three distinct Hf isotope-age arrays that share a similar slope equivalent to that of typical 176Lu/177Hf ratio of continental crust, and the slope intersects the mantle evolution curve at 2.9–2.6, 3.3–3.2, and 3.8–3.6 Ga. The secular trends in zircon Hf isotopes illustrate episodic crust formation from depleted mantle during the three periods with subsequent reworking of pre-existing crusts into younger granitoids. Furthermore, these results infer that granitoid crust was rarely reworked for more than 800 million years after its formation. This finding is well explained by assuming that the Archean Rae block has grown outward from the interior by adding new crusts through subduction-related magmatism and/or by secondary accretion of exotic arc crusts. In such a tectonic framework, younger crusts were likely utilized more preferentially in crustal melting during subduction-related magmatism. These observations suggest that plate subduction has operated already in the early Archean, as early as 3.6 Ga Eoarchean.

著者

Haruo Tsuruta Yasuji Oura Mitsuru Ebihara Yuichi Moriguchi Toshimasa Ohara Teruyuki Nakajima

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.52, no.2, pp.103-121, 2018-03-30 (Released:2018-04-19)

参考文献数

35

被引用文献数

42

---

Using an hourly-resolution time series of the Fukushima radionuclides collected on used filter-tapes installed in suspended particulate matter (SPM) monitors, we measured the hourly radiocesium values at the SPM monitoring sites of Futaba and Naraha located within 20 km of the Fukushima Daiichi Nuclear Power Plant (FD1NPP) during March 12–25, 2011. The time-series of the 137Cs concentrations at the sites were analyzed and compared with radiation dose rates at the many monitoring posts/points of Fukushima Prefecture and the Tokyo Electric Power Company. At Futaba, nine plumes of high 137Cs concentrations were found on March 12–13, 15–16, 18–20, and 24–25, 2011, when southeasterly winds prevailed. On March 12, the first peak of the 137Cs concentrations was detected at Futaba at 9:00 Japanese Standard Time (JST) due to the first release from reactor Unit 1 (U1) in the early morning. Furthermore, the highest 137Cs concentration, i.e., 13,600 Bq m–3 was observed at 15:00 JST after a vent operation at U1, just before the hydrogen explosion of U1 at 15:36 JST. On the afternoon of March 15, plumes from the FD1NPP were observed at Futaba due to a constant southeasterly wind and were then transported to downwind, resulting in the formation of a highly deposited zone of radionuclides spanning more than 30 km from near the FD1NPP to the northwest. In contrast, seven plumes of high 137Cs concentrations were found at Naraha on March 15–16, 18, 20–21, 2011, when northerly winds prevailed. On March 15, a plume caused by the first release from Unit 2 was observed at Naraha at 1:00 JST, and the highest concentration, i.e., 8,300 Bq m–3, was observed at 3:00 JST, and then were transported southward to the Kantou area. The activity ratios of 134Cs/137Cs in the plumes were divided into two groups. The plumes at Futaba on March 12–13, which had ratios of 0.92–0.94, are identified to be released from U1, compared to its ratio of 0.94, as derived from the inventory data. All other plumes with the ratios of 1.02–1.04 at Futaba and Naraha during March 15–21 have not been determined to be released from U2 and/or Unit 3.

著者

Sheng Xu Luyuan Zhang Stewart P. H. T. Freeman Xiaolin Hou Katsuhiko Yamaguchi Alan J. Cresswell David C. W. Sanderson

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.50, no.3, pp.287-291, 2016-05-18 (Released:2016-05-30)

参考文献数

18

被引用文献数

3

---

This paper reports iodine (127I and 129I) and cesium (137Cs) isotope concentrations in groundwater of confined and unconfined aquifers in the vicinity of the Fukushima Dai-ichi nuclear power plant (FDNPP). 127I and 129I concentrations range from 2–13 μg/L and 5 × 107–8 × 1010 atom/L respectively, resulting in 129I/127I atomic ratios from 5 × 10–9 to 2 × 10–6. In all samples, 137Cs concentrations were below detection limit. The deep-sealed groundwater from the confined aquifer did not contain significant quantities of Fukushima-derived 129I compared to the groundwater in the unconfined aquifer. The minimal 129I/137Cs activity ratios in the groundwater are more than 2–500 times higher than the FDNPP source ratio. These data can be explained by rainwater infiltrating through the surface soils, with the more water-soluble 129I preferentially extracted into the aqueous phase and the 137Cs preferentially retained in the soil.

著者

Juan Yu Bokun Li Chen Sun Lingen Bian Zhouqing Xie

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.49, no.5, pp.503-512, 2015-09-30 (Released:2015-09-30)

参考文献数

41

被引用文献数

1

---

During the 5th China Arctic Research Expedition of the R/V Xuelong (June–September, 2012) total gaseous mercury (TGM) in the marine boundary layer along the route was measured. The spatial distribution of TGM was determined from Shanghai to the Bering Strait along the Northwestern-Pacific volcanic belt and around Iceland outside the Arctic Ocean. TGM ranged from 0.17 to 9.03 ng/m3 with a mean of 1.86 ± 1.21 ng/m3 (median: 1.55 ng/m3). Several peaks along the cruise exceeded 4.0 ng/m3. TGM means in leg1 and leg4 (near Japan) were 1.99 ± 0.71 ng/m3 and 2.56 ± 1.39 ng/m3, respectively. In leg2 and leg3 near the Kamchatka peninsula, TGM was 1.23 ± 0.55 ng/m3 and 2.78 ± 1.42 ng/m3, respectively. In leg5 near Iceland TGM was 1.39 ± 1.02 ng/m3 with relatively high value in Reykjavik harbor (mean: 1.91 ± 1.27 ng/m3). Based upon backward air trajectory, trace gas CO, meteorological/hydrologic data, and volcanic degassing information, relatively greater TGM values were associated with the role of ocean emissions, volcanic, and other geothermal activities.

著者

Naoto Takahata Reika Yokochi Yoshiro Nishio Yuji Sano

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.37, no.3, pp.299-310, 2003-06-20 (Released:2008-04-08)

参考文献数

32

被引用文献数

9 15 12

---

Twenty three gas samples were collected from hot and mineral springs associated with Ontake volcano in central Honshu, Japan from June 1996 to June 2000. The chemical compositions, He, Ar, C and N isotopic ratios were measured using a gas chromatography, noble gas and stable isotope mass spectrometers, respectively. The 3He/4He ratio decreased with increasing distance from the central cone of the volcano to the sampling site, while δ13C value of CO2 increased with the distance. Such trends are consistent with those observed from November 1981 to June 1993 in the literature, suggesting that source of magmatic helium and carbon is located beneath the volcanic cone and they are continuously emitted into surroundings. The δ15N value of N2 increased with the distance while most 40Ar/36Ar ratios were similar to the atmospheric value. Magmatic nitrogen may also be carried by a fluid flowing through the volcanic edifice and diluted by crustal nitrogen. Significant increase of 3He/4He ratio from 1996 to 2000 was observed at the site close to the fault formed by a M6.8 earthquake that occurred in September 1984, which agrees well with the 3He/4He change from November 1981 to June 1993. Anomalous increase of δ13C value was observed at Shirakawa site from June 1993 to June 2000. The change cannot be explained by a simple two-component mixing between magmatic and crustal end-members and may require another model with three end-members, mantle, limestone and sediment.

著者

Thomas Ferrini Olivier Grandjouan Olivier Pourret Raul E. Martinez

出版者

GEOCHEMICAL SOCIETY OF JAPAN

雑誌

GEOCHEMICAL JOURNAL (ISSN:00167002)

巻号頁・発行日

vol.55, no.2, pp.51-58, 2021 (Released:2021-11-22)

---

Cyanobacteria induced biomineralization of atmospheric CO2 is a natural process leading to the formation of carbonates by spontaneous precipitation or through the presence of nucleation sites, under supersaturated conditions. As importance of basaltic rocks in the carbon cycle has already been highlighted, basaltic glass was chosen to test its ability to release cations needed for carbonate formation in presence of Synechococcus sp. cyanobacteria. Active cyanobacteria were expected to generate a local alkaline environment through photosynthetic metabolism. This process produces oxygen and hydroxide ions as waste products, raising the pH of the immediate cell surface vicinity and indirectly enhancing the carbonate CO32- concentration and providing the a degree of saturation that can lead to the formation of calcite CaCO3 or magnesite MgCO3. In the presence of active cells, the saturation index (SI) increased from -10.56 to -9.48 for calcite and from -13.6 to -12.5 for magnesite, however they remained negative due to the low Ca2+ and Mg2+ activities. Dead cells were expected to act as nucleation sites by the stepwise binding of carbonate with Ca2+ and Mg2+ on their surface. In the presence of inactive cells, SI values were closer to 0 but still negative due to the low pH and cation concentrations. Our results highlight that our current understanding of the carbon cycle suggests that Earth’s climate is stabilized by a negative feedback involving CO2 consumption and especially during chemical weathering of silicate minerals.