Published Papers - SHINJO Ryuichi

Mixed carbonate-siliceous hydrothermal chimneys ahead of the Asal propagating rift (SE Afar Rift, Republic of Djibouti)

Moussa N.

Journal of African Earth Sciences ( Journal of African Earth Sciences )  197   104765 - 104765   2023.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The geochemical gas field in surface sediments in the Southwest sub-basin of East Vietnam Sea: distribution, origin, and comparative features with other regions of Western East Vietnam Sea

Duc Luong Le, Hoang Nguyen, Anatoly Obzhirov, Ryuichi Shinjo, Renat B. Shakirov

Vietnam Journal of Marine Science and Technology ( Publishing House for Science and Technology, Vietnam Academy of Science and Technology (Publications) )  22 ( 4 ) 337 - 362   2022.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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We analyzed 39 gas samples, including carbon dioxide, hydrocarbon gases C1–C4, hydrogen, and helium, in surface sediment from 19 gravity cores collected from the SW sub-basin of the East Vietnam Sea (EVS) using the headspace and vacuum degassing methods. Based on the result, we discussed the distribution and origin of gases in the southwest sub-basin EVS surface sediments. The sediments are mostly clay and silty clay containing methane ranging from 0.5–440 ppm. The anomalous concentrations of methane, helium, and hydrogen occur along the continental slope in the Nam Con Son basin of Southwest EVS. Methane is the dominant gas compared to other detected hydrocarbon gases, including ethylene, propane, and butane. Based on comparative results, the background methane concentrations in surface sediments decrease from South to North, from the southwestern sub-basin of the East Vietnam Sea to the Phu Khanh and the Red river basins. We propose the presence of a large-scale degassing zone of hydrocarbon gases and discuss the gases’ origin in surface sediments based on hydrocarbon gas ratios, carbon isotope compositions of carbon dioxide and methane, and the relationship between geochemical characteristics of surface sediments and fault system, and surface sediment gases.

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Development and Application of an Environmental Education Tool (Board Game) for Teaching Integrated Resource Management of the Water Cycle on Coral Reef Islands

Shimabukuro M.

Sustainability (Switzerland) ( Sustainability (Switzerland) )  14 ( 24 ) 16562 - 16562   2022.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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To solve resource issues on coral reef islands, an understanding of the water cycle is essential. Water resource management is intricately linked to diverse occupational industries and coral reef ecosystems on these islands. To effectively promote sustainable natural resource management, we developed a board game as an environmental education and communication tool for school students and people of all ages. The concept of the game is that “clean water will always be available if it is used properly”. The board game was designed based on an island with an underground freshwater lens as its main water resource. Role-playing was used to enhance islander livelihoods such as with vegetable and livestock farming, fishing, and tourism. Players, while working collaboratively, have to use the island’s groundwater adequately and conserve it for future generations. The game was developed through a transdisciplinary process in collaboration with scientists, administrative officers, civic groups, and students. Additionally, the board game was tested in diverse communities. In this study, we elaborated on the board game after it was played by students at an elementary school on Tarama Island. We observed that participants learned that cooperation is important for the sustainable use of water resources. Moreover, the participants proposed two methods for cooperation: joint discussion and ‘assembly decisions’. The board game has the potential to be used as an effective environmental education tool to promote sustainable water resource management on coral reef islands.

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Redox evolution of differentiating hydrous basaltic magmas recorded by zircon and apatites in mafic cumulates: The case of the Malayer Plutonic Complex, Western Iran

Deevsalar R.

Geochemistry ( Geochemistry )  83 ( 1 ) 125946 - 125946   2022.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Estimation of the origin of bullet lead usend in early-modern to modern Japan by lead isotope ratio

Aizawa, M, Mizota, C, Hosono, T, Shinjo, R

kinzoku, Materials Science & Technology   92 ( 11 ) 62 - 78   2022.11

Type of publication: Research paper (other science council materials etc.)

Sr isotopic ratios of hydrothermal fluids from the Okinawa Trough and the implications of variation in fluid–sediment interactions

Toki, T, Nohara, T, Urata, Y, Shinjo, R, Hokakubo-Watanabe, S, Ishibashi, J, Kawagucci, S

Progress in Earth and Planetary Science ( Progress in Earth and Planetary Science )  9 ( 59 )   2022.10 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Abstract Sr isotope ratios of hydrothermal fluids were observed at five sediment-associated sites in the Okinawa Trough to investigate the diversity of subseafloor fluid–rock–sediment interactions. The estimated ⁸⁷Sr/⁸⁶Sr ratios of the hydrothermal endmember fluids at the five sites were all higher than those at the sediment-starved sites. The endmember Sr isotopic ratios of hydrothermal fluids were diverse within the Okinawa Trough, ranging from 0.7077 at the Iheya North Knoll site to 0.712 at the Yonaguni Knoll IV site. To our knowledge, 0.712 is the highest value reported to date for seafloor hydrothermal fluids. This variation is likely attributable to the relative contributions of multiple subseafloor Sr reservoirs, which are ⁸⁷Sr-poor volcanic rock and ⁸⁷Sr-rich hemipelagic sediments containing clay minerals of terrestrial origin. These data support a model based on the carbon isotope ratio of CH₄, which indicates whether volcanic rocks or terrestrial sediments are distributed in the high-temperature reaction zone of the hydrothermal system.

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Geochemical and geochronological constraints on origin of the Sawlava ophiolite (NW Iran): Evidence for oceanic mantle evolution beneath Iran-Iraq border

Ghorbani M.R.

Lithos ( Lithos )  418-419   106695 - 106695   2022.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Drifted pumice stones at Okinawa Prefecture derived from the 2021 August eruption at Fukutokuokanoba submarine volcano

Usami, K, Shinjo, R

Bull. Mus., Okinawa Pref. Mus. Art Mus.   ( 15 ) 1 - 16   2022.03

Type of publication: Research paper (bulletin of university, research institution)

THE ORIGIN OF GEM SPODUMENE IN THE HAMADAN PEGMATITE, ALVAND PLUTONIC COMPLEX, WESTERN IRAN

Gheshlaghi, RS; Ghorbani, M; Sepahi, AA; Deevsalar, R; Nakashima, K; Shinjo, R

CANADIAN MINERALOGIST ( Canadian Mineralogist )  60 ( 2 ) 249 - 266   2022.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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ABSTRACT Pegmatite bodies with a simple mineral composition are widespread within the Sanandaj-Sirjan Zone (SaSiZ), Zagros Orogen, Iran; however, gem-bearing pegmatite bodies are rare. There is a pegmatitic vein within the Hamadan garnet (± andalusite ± staurolite) schist adjacent to the Alvand Plutonic Complex (APC), south of Hamedan city (western Iran), in which large crystals of gem spodumene occur together with quartz, amazonite, beryl, tourmaline, and apatite. This spodumene-bearing pegmatite consists of four major zones with slightly different mineral compositions from the border to the core. The wall zone of quartz-rich granitoid and the intermediate zone of alkali granite have trondhjemitic compositions near the quartzolitic gem-bearing core zone. All parts of the vein are peraluminous in composition and exhibit S-type affinity. Two types of spodumene which have been distinguished in the core zone are colorless to very pale yellow and pink, transparent with vitreous luster and inclusion-free (eye clean) under 10× magnification. The different color in these minerals can be attributed to the slightly different chemical compositions, particularly lower Fe/Mn ratios in the pink material. The δ7Li values of the spodumene (+5.58 to +6.57‰) are indicative of the incorporation of middle continental crustal components in their genesis. Change in the mineral assemblage from tourmaline-bearing in the intermediate zone to spodumene + tourmaline in the core zone of the spodumene-bearing pegmatite is consistent with increasing lithium content from the wall zone to the core. Petrographic, geochemical, and isotopic data indicate that partial melting of middle-crustal Al-rich metapelitic source was followed by fractional crystallization to generate these rocks. In this concern, the required Li for the crystallization of spodumene was probably supplied by the breakdown of staurolite of the Hamadan schist and/or subsequent fractional crystallization of the parent magma. The results also demonstrate that the regional tectonic regime exerts a primary control on the occurrence and emplacement of the miarolitic pegmatite in the upper crust and the formation of gem spodumene during late-stage magmatic activities.

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Lead isotopic characteristics of gun bullets prevailed during the 19th century in Japan: Constraints on the provenance of lead source from the United Kingdom and Japan

Aizawa M.

Journal of Archaeological Science: Reports ( Journal of Archaeological Science: Reports )  41   103268 - 103268   2022.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Provenancing Nineteenth Century Saltpetre From British India Using Nitrogen, Oxygen, and Strontium Isotope Ratios

Chitoshi Mizota, Robin Hansen, Takahiro Hosono, Azusa Okumura, Ryuichi Shinjo, Masataka Aizawa

Collections: A Journal for Museum and Archives Professionals ( SAGE Publications )  18 ( 2 ) 155019062110729 - 155019062110729   2022.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Highly purified specimen of saltpetre, kept in two glass jars are stored in the collections of the Natural History Museum, London, United Kingdom. Historic catalogs of the specimen collection record their acquisition date as 17th March, 1881. The specimen represent heritage of the saltpetre industry during the times of the colonial British India. Chemical analysis shows that they are highly refined, containing only traces of impurities. Dual isotopic composition (δ¹⁵N and δ¹⁸O) of nitrate implies their intrinsic origin as British India. In addition, relative to highly radiogenic signature of Sr widespread throughout India, less radiogenic strontium (⁸⁷Sr/⁸⁶Sr = 0.707859–0.714168) in the specimens suggests that final stages of the refining took place in western India where relevant waters containing pristine Sr were used. Stable isotope geochemistry in combination with history and socio-economy provide new insights into this research area which is not yet fully understood.

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Geochemistry and petrogenesis of intrusive rocks of Chadormalu deposit; an implication on whole-rock geochemistry and Sr-Nd-Pb isotopes

Nayebi, N, Esmaeily, D, Modabberi, S, Shinjo, R, Deevsalar, R, Lehmann, B

Scientific Quarterly Journal of Geosciences   32   29 - 42   2022 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Mantle geodynamics and source domain of the East Vietnam Sea opening- induced volcanism in Vietnam and neighboring regions

Hoang Nguyen, Ryuichi Shinjo, Thi Huong Tran, Duc Luong Le, Duc Anh Le

Vietnam Journal of Marine Science and Technology ( Publishing House for Science and Technology, Vietnam Academy of Science and Technology (Publications) )  21 ( 4 ) 393 - 417   2021.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The spreading of the East Vietnam Sea (EVS, also known as Bien Dong, or the South China Sea), leading to the occurrence of syn-spreading (33-16 Ma) and post-spreading (< 16 to present) volcanism. Syn-spreading magma making up thick layers of tholeiitic basalt with a geochemical composition close to the refractory and depleted mid-ocean ridge basalt (MORB) is mainly distributed inside the EVS basin. The post-spreading magma is widely distributed inside the basin and extended to South and SE China, Hainan island, Southern Laos (Bolaven), Khorat Plateau (Thailand), and Vietnam, showing the typical intraplate geochemistry. Basaltic samples were collected at many places in Indochina countries, Vietnam’s coastal and continental shelf areas, to analyze for eruption age, petrographical, geochemical, and isotopic composition to understand the similarities and differences in the mantle sources between regions. The results reveal that basalts from some areas show geochemical features suggesting they were derived subsequently by spinel peridotite and garnet peridotite melting, forming high-Si, low-Mg, and low-Ti tholeiitic basalt to low-Si, high-Mg, and high-Ti alkaline basalt with the trace element enrichment increasing over time. Other basalts have geochemical and isotopic characteristics unchanged over a long period. The post-spreading basalt’s radiogenic Sr-Nd-Hf-Pb isotopic compositions show different regional basalts distribute in the various fields regardless of eruption age, suggesting that their mantle source feature is space-dependent. The post-EVS spreading basalts expose the regional heterogeneity, reflecting the mixture of at least three components, including a depleted mantle (DM) represented by the syn-EVS spreading source, similar to the DUPAL-bearing Indian MORB source; an enriched mantle type 1 (EM1), and type 2 (EM2). The DM may interact and acquire either EM1 or EM2 in the sub-continental lithospheric mantle; as a result, different eruption at different area acquires distinct isotopic signature, reflecting the heterogeneous nature of the subcontinental lithospheric mantle. The study proposes a suitable mantle dynamic model that explains the EVS spreading kinematics and induced volcanism following the India - Eurasian collision from the Eocene based on the research outcomes.

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Last glacial temperature reconstructions using coupled isotopic analyses of fossil snails and stalagmites from archaeological caves in Okinawa, Japan.

Asami R, Hondo R, Uemura R, Fujita M, Yamasaki S, Shen CC, Wu CC, Jiang X, Takayanagi H, Shinjo R, Kano A, Iryu Y

Scientific reports ( Scientific Reports )  11 ( 1 ) 21922   2021.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Abstract We applied a new geoarchaeological method with two carbonate archives, which are fossil snails from Sakitari Cave and stalagmites from Gyokusen Cave, on Okinawa Island, Japan, to reconstruct surface air temperature changes over the northwestern Pacific since the last glacial period. Oxygen isotope ratios (δ¹⁸O) of modern and fossil freshwater snail shells were determined to infer seasonal temperature variations. The observational and analytical data confirm that δ¹⁸O values of fluid inclusion waters in the stalagmite can be regarded as those of spring waters at the sites where snails lived. Our results indicate that the annual mean, summer, and winter air temperatures were lower by 6–7 °C at ca. 23 thousand years ago (ka) and 4–5 °C at ca. 16–13 ka than those of the present day. Our reconstruction implies that surface air cooling was possibly two times greater than that of seawater around the Ryukyu Islands during the Last Glacial Maximum, which potentially enhanced the development of the East Asian summer monsoon during the last deglaciation. Considering the potential uncertainties in the temperature estimations, the climatic interpretations of this study are not necessarily definitive due to the limited number of samples. Nevertheless, our new geoarchaeological approach using coupled δ¹⁸O determinations of fossil snails and stalagmite fluid inclusion waters will be useful for reconstructing snapshots of seasonally resolved time series of air temperatures during the Quaternary.

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Chemical, mineralogical, and physicochemical features of surface saline muds from Southwestern sub-basin of the East Vietnam Sea: Implication for new peloids

Luong Le Duc, Hoang Nguyen, Ryuichi Shinjo, Renat B. Shakirov, Anatoly Obzhirov

Vietnam Journal of Earth Sciences ( Publishing House for Science and Technology, Vietnam Academy of Science and Technology (Publications) )    1 - 13   2021.09 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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This study presents the chemical, mineralogical and physicochemical features of 8 saline mud samples from 8 gravity cores located in the southwestern sub-basin of the East Vietnam Sea. The grain-size analysis of mud samples reveals the amount of clay and silt particles in the ranges of 65.1-89.2% and 9.5-34.2%, respectively and a very low fraction of sand. The analytical results showed that mud samples have high contents of SiO2 (32.79-48.09%), Al2O3 (11.26-13.63%), CaO (3.10-13.93%), Fe2O3 (4.15-9.45%), and low contents of TiO2, MnO, MgO, Na2O, K2O and P2O5. The XRD analysis of mud samples indicated mineral compositions with major minerals of quartz, illite, calcite, chlorite, feldspar, kaolinite, and other minor minerals like halite, smectite, fluorapatite, pyroxene, amphibole. The organic and physicochemical parameters of mud samples were also measured. Potentially toxic elements in mud samples were determined and compared with reference values and the technical standard. This study proposes that saline mud samples from the studied area are potential peloids.

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Reconstruction of ocean environment time series since the late nineteenth century using sclerosponge geochemistry in the northwestern subtropical Pacific

Asami R.

Progress in Earth and Planetary Science ( Progress in Earth and Planetary Science )  8 ( 1 )   2021.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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<title>Abstract</title>The geochemistry of calcifying marine organisms is an excellent proxy for reconstructing paleoceanographic history, but studies of hypercalcified demosponges (sclerosponges) are considerably fewer than those of corals, foraminifers, and bivalves. For this study, we first generated near-annual resolved stable carbon and oxygen isotope (δ¹³C and δ¹⁸O) and element/Ca ratios (Sr/Ca, Ba/Ca, Pb/Ca, U/Ca) time series for 1880–2015 from sclerosponge samples (<italic>Acanthochaetetes wellsi</italic>) collected at Miyako Island and Okinawa Island in the Ryukyu Islands of southwestern Japan. The δ¹³C records exhibited a typical variation of anthropogenically derived Suess effects, demonstrating that the rates of decrease of –0.0043‰/year before 1960 and – 0.024‰/year after 1960 in the northwestern subtropical Pacific were respectively similar to and about 1.4 times higher than those of the Caribbean Sea in the tropical Atlantic. Spectral analysis of the δ¹⁸O time series revealed significant periodicity of approximately 2, 3, 6.5, 7–10, and 20–30 year/cycle, indicating that sea surface conditions in the southern Ryukyu Islands had been dominated by interannual and decadal variations in temperature and seawater δ¹⁸O since the late nineteenth century. The Sr/Ca and U/Ca ratios for the species <italic>A. wellsi</italic> (high-Mg calcite) might not be a robust proxy for seawater temperatures, unlike <italic>Astrosclera willeyana</italic> and <italic>Ceratoporella nicholsoni</italic> sclerosponges (aragonite). An evident increasing Pb/Ca trend after 1950 found in the samples is probably attributable to Pb emissions from industrial activities and atmospheric aerosols in eastern Asian countries. The Ba/Ca variations differ greatly among sampling sites, which might be attributable to the respective local environments. This evidence demonstrates that more high-resolution age determinations and geochemical profilings enable delineation of secular variations in ocean environments on annual and interannual timescales. Results of our study suggest that if sclerosponges living in deeper ocean environments are collected, spatial and vertical oceanographic variations for the last several centuries will be reconstructed along with coral proxy records.

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Geochemical evidence for “cryptic amphibole fractionation" and lower crust melting for the generation of island arc tholeiitic rocks from northern Fossa Magna, central Japan

M. Aizawa, R. Shinjo, S. Okamura, T. Takahashi, N. Fujibayashi

Lithos ( Elsevier BV )  386-387   106028 - 106028   2021.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Shimajiri Group equivalent sedimentary rocks dredged from sea knolls off Kume Island, central Ryukyus: Implications for timing and mode of rifting of the middle Okinawa Trough back-arc basin

Kikunaga R.

Island Arc ( Island Arc )  30 ( 1 )   2021.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Temporal changes of source mantle compositions for Late Cenozoic volcanic rocks in Oki islands, SW Japan

Aizawa Masataka, Shinjo Ryuichi, Okamura Satoshi, Hirai Yasuhiro

Annual Meeting of the Geological Society of Japan ( The Geological Society of Japan )  2021 ( 0 ) 059   2021

Type of publication: Research paper (research society, symposium materials, etc.)

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Spatial distribution and pollution assessment of trace elements Pb, Cu, Ni, Fe and as in the surficial water of Staring Bay, Indonesia

Armid A.

Journal of the Brazilian Chemical Society ( Journal of the Brazilian Chemical Society )  32 ( 2 ) 299 - 310   2021 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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