研究者詳細 - 中村　栄三

MISC - 中村　栄三

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In-situ U-Pb zircon age dating deciphering the formation event of the omphacite growth over relict edenitic pargasite in omphacite-bearing jadeitite of the Itoigawa-Omi area of the Hida-Gaien belt, central Japan

Keitaro Kunugiza, Eizo Nakamura, Atsushi Goto, Katsura Kobayashi, Tsutomu Ota, Hiroshi Miyajima, Kazumi Yokoyama

JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 112 ( 5 ) 256 - 270 2017年10月

記述言語：英語出版者・発行元：JAPAN ASSOC MINERALOGICAL SCIENCES

Omphacite replacing after relic edenitic pargasite has been found in an omphacite-bearing jadeitite block of the Itoigawa-Omi area in the Hida-Gaien belt. Omphacite occurs sporadically as fine-grained aggregate reaching a few cm in length in a jadeite-albite matrix, and sometimes contains edenitic pargasite as a core. The edenitic pargasite is chemically and optically homogeneous and does not show direct contact with jadeite and albite. An irregular shaped omphacite-diopside mixed area occurs near edenitic pargasite in a coarse omphacite aggregate. The texture suggests that the breakdown of edenitic pargasite was triggered by the addition of a hydrothermal fluid, from which jadeite and albite were precipitated later, passing through diopside and omphacite by the reaction:
NaCa2Mg5(AlSi7)O-22(OH)(2) -> (NaAlSi2O6 + CaMgSi2O6) + CaMgSi2O6+ Mg3SiO5 + H2O.
At the periphery of pseudomorphic omphacite, a hydrothermal fluid removed the breakdown components of the reaction other than omphacite.
New in-situ LA-ICP-MS U-Pb dating revealed that zircons in edenitic pargasite yield apparent age up to similar to 590 Ma, with mean ages of 560 +/- 16 Ma, interpreted as the minimum age of a precursor rock. A zircon age of 519 +/- 21 Ma from jadeitite without omphacite corresponds to a timing of crystallization of omphacite, jadeite, and albite. The studied jadeitite is a typical R-type jadeitite, and the nearly total replacement from a precursor rock to the omphacite-bearing jadeitite has been attributed to hydrothermal activity at Middle Cambrian times.

DOI： 10.2465/jmps.170402a

Silicate-SiO reaction in a protoplanetary disk recorded by oxygen isotopes in chondrules

Ryoji Tanaka, Eizo Nakamura

NATURE ASTRONOMY 1 ( 7 ) 1523 - 1529 2017年7月

記述言語：英語出版者・発行元：NATURE PUBLISHING GROUP

The formation of planetesimals and planetary embryos during the earliest stages of the solar protoplanetary disk largely determined the composition and structure of the terrestrial planets. Within a few million years of the birth of the Solar System, chondrule formation and the accretion of the parent bodies of differentiated achondrites and the terrestrial planets took place in the inner protoplanetary disk(1,2). Here we show that, for chondrules in unequilibrated enstatite chondrites, high-precision Delta O-17 values (where Delta O-17 is the deviation of the delta O-17 value from a terrestrial silicate fractionation line) vary significantly (ranging from -0.49 to + 0.84%) and fall on an array with a steep slope of 1.27 on a three-oxygen-isotope plot. This array can be explained by the reaction between an olivine-rich chondrule melt and an SiO-rich gas derived from vaporized dust and nebular gas. Our study suggests that a large proportion of the building blocks of planetary embryos formed by successive silicate-gas interaction processes: silicate- H2O followed by silicate-SiO interactions under more oxidized and reduced conditions, respectively, within a few million years of the formation of the Solar System.

DOI： 10.1038/s41550-017-0137

Petrologic and geochemical characterization of rift-related magmatism at the northernmost Main Ethiopian Rift: Implications for plume-lithosphere interaction and the evolution of rift mantle sources

D. H. Feyissa, R. Shinjo, H. Kitagawa, D. Meshesha, E. Nakamura

LITHOS 282 240 - 261 2017年6月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

In this paper, we present petrography, K-Ar ages, whole-rock major- and trace-element concentrations, and Sr-Nd-Hf-Pb isotopic ratios of volcanic rocks from Debre Birhan area in the northernmost Main Ethiopian Rift (MER). The K-Ar ages of the mafic series range from 27 to 0.25 Ma, and two felsic rocks yield ages of 0.93 and 0.23 Ma. The mafic volcanics are classified into older and younger series based on their K-Ar ages. The Mg-numbers (Mg# < 60) of both mafic series, along with low Ni and Cr contents, clearly indicate that these lavas have undergone fractionation en route to the surface. Geochemical and isotopic compositions of the older and younger mafic lavas indicate that crustal contamination did not play a significant role in the evolution of their magmas, hence reflect the geochemical characteristics of the sources. The older and younger mafic volcanic rocks display contrasting trace element and isotopic signatures. The older lavas have higher La/Nb, Zr/Nb, Ba/Nb and Sr-87/Sr-86(i) (0.70445-0.70681) and lower epsilon(Hf) (-2.58 to + 6.01) and epsilon(Nd) ( -1.25 to +3.43) and less radiogenic Pb isotopic ratios (Pb-206/(204)Pbi = 17.82-18.64, except TG-54 = 19.1) relative to the younger mafic lavas. Correlations among isotopic ratios and trace element concentrations provide evidence for the involvement of at least three major end-member components (C-1, C-2, and C-3) in the petrogenesis of these mafic lavas. The C-1 end-member component contributes dominantly to younger mafic lavas, and has isotopic composition similar to the common component 'C' deduced from oceanic basalts. The second end-member component (C-2) is represented by lavas near the transition between older and younger, and has isotopic composition similar to that of the seafloor basalts of the Red Sea and the Gulf of Aden. The third end-member component (C-3) is prominent in the older mafic series, and similar isotopically to Pan-African lithosphere. The younger felsic volcanic rocks generally have higher Sr-87/Sr-86(i) (0.70395-0.70689) than younger mafic series (0.70366-0.70454) but Nd, Hf and Pb isotopic ratios similar to those of the younger mafic lavas. The element concentrations and Sr, Nd, Hf and Pb isotopic compositions of the younger felsic rocks are explained by fractional crystallization of mafic melts in shallow-level magma chambers accompanied by limited assimilation of crustal material. Low degrees of partial melting of existing mafic underplate can account for the genesis of the least differentiated (intermediate) lavas, but failed to explain highly evolved younger felsic rocks. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2017.03.011

Post-collisional magmatism of western Chukotka and Early Cretaceous tectonic rearrangement in northeastern Asia

P. L. Tikhomirov, V. Yu Prokof'ev, I. A. Kal'ko, A. V. Apletalin, Yu N. Nikolaev, K. Kobayashi, E. Nakamura

GEOTECTONICS 51 ( 2 ) 131 - 151 2017年3月

記述言語：英語出版者・発行元：MAIK NAUKA/INTERPERIODICA/SPRINGER

The paper presents new data on the isotopic age and chemical composition of volcanic rocks from the Tytyl'veem and Mangazeika basins of western Chukotka superposed on Mesozoides of the Verkhoyansk-Chukotka Tectonic Region. The results of SIMS U-Pb zircon dating (121.4 +/- 2.8 and 118.0 +/- 2.0 Ma) corroborate the Aptian age of the Tytyl'veem Formation. This age, in turn, indicates its formation after closure of the South Anyui ocean (Neocomian), but before origination of the Okhotsk-Chukotka Belt (Albian-Campanian). Post-collisional Aptian igneous rocks are widespread in the northern Verkhoyansk-Chukotka Tectonic Region; the legth of the corresponding igneous province is no less than 1400 km. In geochemical characteristics, the post-collisional volcanic rocks occurring in Western Chukotka are similar with the rocks from Andean-type igneous belts.

DOI： 10.1134/S0016852117020054

Trace element and isotopic geochemistry of Cretaceous magmatism in NE Asia: Spatial zonation, temporal evolution, and tectonic controls

Petr L. Tikhomirov, Elena A. Kalinina, Takuya Moriguti, Akio Makishima, Katsura Kobayashi, Eizo Nakamura

LITHOS 264 453 - 471 2016年11月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

Results of a comprehensive geochemical study (major and trace elements, and isotopes of Sr, Nd, Pb, Hf) of Cretaceous volcanic rocks from the Chukotka area in northeastern Russia are presented. Synthesis of available geological and geochronological data suggests diachronous onset of activity of the Okhotsk-Chukotka volcanic belt (OCVB), the largest magmatic province in the region. The OCVB consists of ca. 10(6) km(3) of volcanic rocks. At 106-105 Ma, subduction-related magmatism initiated in the southern and central segments of the OCVB. In the Central and Northern Chukotka areas, where the northern OCVB is exposed, onset of arc magmatism occurred ca. 10 m.y. after extension-related magmatism of the Chaun igneous province at 109-104 Ma. Mafic rocks from the OCVB yield (Sr-87/Sr-86)(80) (Ma) of 0.7033 to 0.7047, epsilon Nd-80 (Ma) of 0.0 to 7.10, epsilon Hf-80 (Ma) of 4.12 to 12.88, ((206)pw(204)pb)(80 Ma) of 18.11 to 18.42, and ((208)pb/(204)pb)(80 Ma) of 37.96 to 38.21. Volcanic rocks from the Chaun province, as well as OCVB rocks from Northern Chukotka, originate from a relatively enriched source and have (Sr-87/Sr-86)(80) (Ma) of 0.7088 to 0.7100, epsilon Nd-80 (Ma) of -5.81 to -3.42, epsilon Hf-80 (Ma) of -3.40 to -0.25, ((206)pb/(204)pb)(80 Ma) of 18.69 to 18.90, and ((208)pb/(204)pb)(80 Ma) of 38.65 to 38.86. No definitive across-arc elemental or isotopic zonation of the OCVB has been revealed, probably because of wide-scale crustal melting and subsequent contamination of mantle-derived melts. However, there is a clear along-arc isotopic zonation. In our interpretation, this results from heterogeneity of the subcontinental lithospheric mantle, which likely was a major contributor to the magma source. The similar isotopic signatures of silicic (dominantly crust-derived) and mafic (mantle-derived) volcanic rocks in each OCVB segment imply that remelting of juvenile mafic underplated material was the main process responsible for the crust-derived magma generation. These data from the major Cretaceous magmatic provinces of northeast Asia are synthesized in context of existing plate tectonic reconstructions. (C) 2016 Elsevier B.V. All rights reserved:

DOI： 10.1016/j.lithos.2016.08.009

The oxygen isotope composition of San Carlos olivine on the VSMOW2-SLAP2 scale

Andreas Pack, Ryoji Tanaka, Markus Hering, Sukanya Sengupta, Stefan Peters, Eizo Nakamura

RAPID COMMUNICATIONS IN MASS SPECTROMETRY 30 ( 13 ) 1495 - 1504 2016年7月

記述言語：英語出版者・発行元：WILEY-BLACKWELL

RATIONALE: The precise determination of Delta'O-17 values in terrestrial material is becoming increasingly important to understand the mass-dependent fractionation processes that cause variations in oxygen isotope ratios. San Carlos olivine is widely used as the reference material for oxygen isotope measurements of terrestrial and extraterrestrial materials. We report new Delta'O-17 values for San Carlos olivine that were independently determined in two different laboratories (Geoscience Center [GZG], University of Gottingen) and Institute for Study of the Earth's Interior [ISEI], Okayama University, Misasa) in direct comparison with VSMOW2 and SLAP2 water standards.
METHODS: The delta O-17 and delta O-18 values of VSMOW2, SLAP2, GISP, and San Carlos olivine were determined relative to reference gas. In both laboratories, water and San Carlos olivine samples were prepared by BrF5 fluorination. In both laboratories, the O-2 released from water and olivine samples was passed through the same purification system and measured using the same mass spectrometer relative to the same reference gas.
RESULTS: In both laboratories, the delta O-17(VSMOW2) and delta O-18 (VSMOW2) scales were slightly compressed with respect to the recommended composition of VSMOW2 and SLAP2. The new Delta'O-17(0.528) value (calculated from the VSMOW2-SLAP2 scaled 6 values) of San Carlos olivine from GZG was -36 +/- 9 ppm and, from ISEI, a value of -40 +/- 7 ppm (1(7 standard deviation) was determined. These values are similar to 50 ppm higher than previously reported from the same laboratories. Possible causes for the observed discrepancies are discussed.
CONCLUSIONS: The results of this study in comparison with previous data from the same laboratories demonstrated that for high accuracy determination of Delta'O-17 values: (i) calibration of the reference gas relative to O-2 released from primary standards (VSMOW2, SLAP2) in the same laboratory is highly recommended, (ii) non-linearity of the mass spectrometer may not only affect delta O-17 and delta O-18 values but also Delta'O-17 values, and (iii) the VSMOW2-SLAP2 scaling should also be applied to analyses of rocks and minerals. Studies that are concerned with small differences in Delta'O-17 at similar delta O-18 values, however, are not affected by non-linearity of the mass spectrometer. Copyright (C) 2016 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.7582

Comment on "Diverse magmatic effects of subducting a hot slab in SW Japan: Results from forward modeling'' by J.-I. Kimura et al.

Ivan Pineda-Velasco, Tai T. Nguyen, Hiroshi Kitagawa, Eizo Nakamura

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 16 ( 9 ) 2848 - 2852 2015年9月

Geochemical heterogeneities in magma beneath Mount Etna recorded by 2001-2006 melt inclusions

Federica Schiavi, Alberto Rosciglione, Hiroshi Kitagawa, Katsura Kobayashi, Eizo Nakamura, Pasquale Mario Nuccio, Luisa Ottolini, Antonio Paonita, Riccardo Vannucci

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 16 ( 7 ) 2109 - 2126 2015年7月

記述言語：英語出版者・発行元：AMER GEOPHYSICAL UNION

We present a geochemical study on olivine and clinopyroxene-hosted melt inclusions (MIs) from 2001 to 2006 Etna basaltic lavas and pyroclastites. Three MI suites are distinguished on the basis of trace element fingerprinting. Type-1 MIs (from 2001 Upper South and 2002 Northeast vents) share their trace element signature with low-K lavas erupted before 1971. Critical trace element ratios (e.g., K/La, Ba/Nb), along with Pb isotope data of Type-1 MIs provide evidence for a heterogeneous mantle source resulting from mixing of three end-members with geochemical and isotopic characteristics of EM2, DMM, and HIMU components. Type-1 MIs composition does not support involvement of subduction-related components. Type-2 (from 2001 Lower and 2002 South vents) and Type-3 (2004 eruption) MIs reveal ghost plagioclase signatures, namely lower concentrations in strongly incompatible elements, and positive Sr, Ba, and Eu anomalies. Both Type-1 and Type-2 MIs occur in 2006 olivines, which highlight the occurrence of mixing between Type-1 and Type-2 end-members. Type-2/Type-3 MIs testify to en route processes (plagioclase assimilation and volatile fluxing) peculiar for deep dike fed eruptions. The latter are strongly controlled by tectonics or flank instability that occasionally promote upraise of undegassed, more radiogenic primitive magma, which may interact with plagioclase-rich crystal mush/cumulates before erupting. Type-2/Type-3 MIs approach the less radiogenic Pb isotopic composition of plagioclase from prehistoric lavas, thus suggesting geochemical overprinting of present-day melts by older products released from distinct mantle sources. Our study emphasizes that MIs microanalysis offers new insights on both source characteristics and en route processes, allowing to a link between melt composition and magma dynamics.

DOI： 10.1002/2015GC005786

Evaluation of the applicability of acid leaching for the U-238-Th-230 internal isochron method

Ryoji Tanaka, Tetsuya Yokoyama, Hiroshi Kitagawa, Demissie Bizuneh Tesfaye, Eizo Nakamura

CHEMICAL GEOLOGY 396 255 - 264 2015年3月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

The U-238-Th-230 internal isochron method has great potential for determining eruption ages of young volcanic materials if the separated groundmass phases have a sufficiently wide range of U/Th ratios. We examined the fractionation behavior of U and Th in aged (i.e., >0.5 Ma) basaltic samples by 6 M hydrochloric acid leaching to evaluate the applicability of acid-leaching treatment for the U-238-Th-230 internal isochron method. Acid leaching of aged basaltic rocks in U-238-U-234-Th-230 secular equilibrium at the bulk-rock scale results in Th-230-U-238 and U-234-U-238 radioactive disequilibria for both leachates and residues. These radioactive disequilibria can be explained by redistribution of Th-234 (parent of U-234) and Th-230 between acid-soluble and acid-resistant phases due to alpha-recoil. The number of Th-230 atoms redistributed by alpha-recoil can be calculated by using a mass conservation equation for U-234 atoms and by the relative amount of recoiled Th-230 and Th-234, the latter proportional to the kinetic energy of the recoiled nuclide. When the fraction of daughter nuclide U-234 remaining in either the residue or leachate, after alpha-recoil redistribution of U-238, is large enough (>95%), the corrected (Th-230/U-238) values of leachate and residue show radioactive equilibria. This result demonstrates that preferential fractionation between U and Th does not occur during acid leaching for basaltic samples if there is no selective etching of the alpha-recoil track. This study implies that acid-leaching can be used in conjunction with the U-238-Th-230 internal isochron method for dating young volcanic rocks by evaluating the degree of the alpha-recoil redistribution of U-234. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2014.12.025

In situ ion-microprobe determination of trace element partition coefficients for hornblende, plagioclase, orthopyroxene, and apatite in equilibrium with natural rhyolitic glass, Little Glass Mountain Rhyofite, California

James G. Brophy, Tsutomu Ota, Tak Kunihro, Tatsuki Tsujimori, Eizo Nakamura

AMERICAN MINERALOGIST 96 ( 11-12 ) 1838 - 1850 2011年11月

記述言語：英語出版者・発行元：MINERALOGICAL SOC AMER

Partially crystalline hornblende gabbro inclusions from the Little Glass Mountain Rhyolite contain euhedral plagioclase, orthopyroxene, hornblende, and apatite crystals in contact with interstitial rhyolitic (71-76% SiO(2)) glass. Textural and mineral compositional data indicate that the gabbros crystallized sufficiently slowly that surface equilibrium was closely approached at the interface between crystals and the liquid. This rare occurrence represents a natural dynamic crystallization experiment with a "run time" that is not realistically achievable in the laboratory. SIMS analysis of mineral rim-glass pairs have permitted the determination of high-quality, equilibrium trace-element partition coefficients for all four minerals. These data augment the limited partition coefficient database for minerals in high-SiO(2) rhyolitic systems. For all minerals, the D values are consistent with those anticipated from crystal-chemical considerations. These data further support a liquid SiO(2) control on the REEs (and presumably other elements) partitioning wherein D values systematically increase with increasing liquid SiO(2) content.

DOI： 10.2138/am.2011.3857

Mineralogical and geochemical constraints on magmatic evolution of Paleocene adakitic andesites from the Yanji area, NE China

Feng Guo, Eizo Nakamura, Weiming Fan, Katsura Kobayashi, Chaowen Li, Xiaofeng Gao

LITHOS 112 ( 3-4 ) 321 - 341 2009年10月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

Paleocene (55-58 Ma) adakitic andesites from the Yanji area of NE China are subdivided into clinopyroxene andesites and amphibole andesites. Relative to the clinopyroxene andesites, the amphibole andesites contain higher SiO(2), K(2)O and lower MgO, FeGr, Al(2)O(3), CaO, TiO(2), Cr, Ni, Sr, Y and Nb, and have evolved Sr-Nd-Pb isotope compositions. Compositional variation between the clinopyroxene andesites and amphibole andesites involves systematic decreases in MgO, Sr/Nd and epsilon(Nd)(t) accompanied by increases in (87)Sr/(86)Sr(i) and (206)Pb/(204)Pb(i), and suggests a role for crustal contamination. The compositional variations recorded in clinopyroxene and amphibole phenocrysts indicate that the primary mantle-derived adakitic magma experienced complex crustal-level processes, including magma mixing, fractional crystallization and crustal contamination or assimilation. The low Na(2)O contents and adakitic trace element features (high Sr/Y and Nd/Yb) in Mg-rich parts of clinopyroxene phenocrysts, and negative Sr and Eu anomalies in the Fe-rich clinopyroxene cores, suggest that all clinopyroxenes crystallized in equilibrium with little or no garnet, and argues against magmatic evolution involving differentiation of basaltic magmas. Combined mineralogical and geochemical data indicate that the clinopyroxene andesites were generated by magma mixing, clinopyroxene fractionation and limited degrees of crustal assimilation; whereas the amphibole andesites underwent magma mixing, fractionation of clinopyroxene + amphibole +/- plagioclase and higher degree of crustal assimilation. The difference in mineralogical assemblage between the two rock types was influenced by magma temperature, i.e., 900-950 degrees C for the amphibole andesites and >950 degrees C for the clinopyroxene andesites. Our results provide the following important constraints on high-MgO adakitic magma (or low-SiO(2) adakite) petrogenesis: (1) the primary magma of such adakites is probably produced through melting of slab melt-modified mantle rather than being a slab melt variably hybridized by peridotite: (2) The complex magmatic evolution recorded in the Yanji adakitic andesites suggests that such adakitic rocks are far from melts in equilibrium with mantle, and magmatic process needs to be carefully examined before the petrogenetic or geodynamic significance can be assessed: (3) The perquisites for creating high-MgO or low-SiO(2) adakites include slab melt-mantle interaction during oceanic slab subduction and melting of this metasomatized mantle, but this melting event need not necessarily be related in time to the subduction event. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2009.03.017

Accumulation of radium in ferruginous protein bodies formed in lung tissue: association of resulting radiation hotspots with malignant mesothelioma and other malignancies

Eizo Nakamura, Akio Makishima, Kyoko Hagino, Kazunori Okabe

PROCEEDINGS OF THE JAPAN ACADEMY SERIES B-PHYSICAL AND BIOLOGICAL SCIENCES 85 ( 7 ) 229 - 239 2009年7月

記述言語：英語出版者・発行元：JAPAN ACAD

While exposure to fibers and particles has been proposed to be associated with several different lung malignancies including mesothelioma, the mechanism for the carcinogenesis is not fully understood. Along with mineralogical observation, we have analyzed forty-four major and trace elements in extracted asbestos bodies (fibers and proteins attached to them) with coexisting fiber-free ferruginous protein bodies from extirpative lungs of individuals with malignant mesothelioma,. These observations together with patients' characteristics suggest that inhaled iron-rich asbestos fibers and dust particles, and excess iron deposited by continuous cigarette smoking would induce ferruginous protein body formation resulting in ferritin aggregates in lung tissue. Chemical analysis of ferruginous protein bodies extracted from lung tissues reveals anomalously high concentrations of radioactive radium, reaching millions of dines higher concentration than that of seawater. Continuous and prolonged internal exposure to hotspot ionizing radiation from radium and its daughter nuclides could cause strong and frequent DNA damage in lung tissue, initiate different types of tumour cells, including malignant mesothelioma cells, and may cause cancers.

DOI： 10.2183/pjab.85.229

Transitional time of oceanic to continental subduction in the Dabie orogen: Constraints from UPb, LuHf, SmNd and ArAr multichronometric dating

Cheng, H, King, R. L, Nakamura, E, Vervoort, J. D, Zheng, Y.-F, Ota, T, Wu, Y.-B, Kobayashi, K, Zhou, Z.-Y

Lithos, 110, 327-342, 2009. 110 ( 1-4 ) 327 - 342 2009年6月

Elemental and isotopic abundances of lithium in chondrule constituents in the Allende meteorite

Seiji Maruyama, Masaki Watanabe, Tak Kunihiro, Eizo Nakamura

GEOCHIMICA ET COSMOCHIMICA ACTA 73 ( 3 ) 778 - 793 2009年2月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Elemental and isotopic abundances of lithium in chondrule constituents in the Allende CV3 meteorite were determined using secondary ion mass spectrometry. Olivines and mesostasis dominated by a feldspathic phase are depleted in Li (< 1 mu g g(-1) and 0.1-0.6 mu g g(-1), respectively). In contrast, low-Ca pyroxenes and mesostasis dominated by a Na-rich phase are enriched in Li (similar to 1-8 mu g g(-1) and 0.4-3.5 mu g g(-1), respectively) and the interchondrule matrix is generally enriched in Li (similar to 2.0 mu g g(-1) on average). The Li isotopic abundance of olivine ranges from delta(7)Li similar to -32 to 21. The spatial distributions of elemental and isotopic abundances of Li in olivines within individual chondrules exhibit no systematic pattern. This suggests that the distribution of Li in olivine was not disturbed during aqueous alteration or thermal metamorphism on the Allende meteorite parent body. Although mesostasis is the last crystallizing phase from a chondrule melt and is expected to be enriched in Li, in the Allende meteorite it is generally depleted in Li. We suggest that during aqueous alteration on the CV asteroid, Li in mesostasis was leached out by aqueous fluids. The Li-enriched Na-rich mesostasis was probably produced later by infiltration of Na-rich fluids. It seems likely that aqueous fluids sequestered alkali elements from the Allende-chondrite region in the CV parent asteroid, although significant amounts of Li are preserved in ferrous olivine in the interchondrule matrix. (C) 2008 Elsevier Ltd. All rights reserved,

DOI： 10.1016/j.gca.2008.10.039

Determination of Ge, As, Se and Te in Silicate Samples Using lsotope Dilution-Internal Standardisation Octopole Reaction Cell ICP-QMS by Normal Sample Nebulisation, Geostand.

Makishima, A, Nakamura, E

Geoanal. Res. ( 33 ) 369 - 384 2009年

Comprehensive analysis for major, minor and trace element contents and Sr-Nd-Pb-Hf isotope ratios in sediment reference materials, JSd-1 and MAG-1

Nagender Nath, B, Makishima, A, Noordmann, J, Tanaka, R, Nakamura, E

, Geochem. J. ( 43 ) 207 - 216 2009年

Recycled crustal melt injection into lithospheric mantle: implication from cumulative composite and pyroxenite xenoliths,

Zhang, H.-F, Nakamura, E, Kobayashi, K, Ying J.-F, Tang, Y.-J

Int. J. Earth. Sci., ( 98 ) 2009年

Coupled Lu-Hf and Sm-Nd geochronology constrains garnet growth in ultra-high-pressure eclogites from the Dabie orogen

H. Cheng, R. L. King, E. Nakamura, J. D. Vervoort, Z. Zhou

JOURNAL OF METAMORPHIC GEOLOGY 26 ( 7 ) 741 - 758 2008年9月

記述言語：英語出版者・発行元：WILEY-BLACKWELL

Ultra-high-pressure eclogites from the Dabie orogen that formed over a range in temperatures (similar to 600 to > 700 degrees C) have been investigated with combined Lu-Hf and Sm-Nd geochronology. Three eclogites, sampled from Zhujiachong, Huangzhen and Shima, yield Lu-Hf ages of 240.0 +/- 5.0, 224.4 +/- 1.9 and 230.8 +/- 5.0 Ma and corresponding Sm-Nd ages of 222.5 +/- 5.0, 217.6 +/- 6.1 and 224.2 +/- 2.1 Ma respectively. Well-preserved prograde major- and trace-element zoning in garnet in the Zhujiachong eclogite suggests that the Lu-Hf age mostly reflects an early phase of garnet growth that continued over a time interval of c. 17.5 Myr. For the Huangzhen eclogite, despite preserved elemental growth zoning in garnet, textural study reveals that the Lu-Hf age is biased towards a later garnet growth episode rather than representing early growth. The narrow time interval of < 6.6 Myr defined by the difference between Lu-Hf and Sm-Nd ages indicates a short final garnet growth episode and suggests a rapid cooling stage. By contrast, the rather flat element zoning in garnet in the Shima eclogite suggests that Lu-Hf and Sm-Nd ages for this sample have been reset by diffusion and are cooling ages. The new Lu-Hf ages point to an initiation of prograde metamorphism prior to c. 240 Ma for the Dabie orogen, while the exact peak metamorphic timing experienced by specific samples ranges between c. 230 to c. 220 Ma.

DOI： 10.1111/j.1525-1314.2008.00785.x

Metamorphic history and tectonic evolution of the Himalayan UHP eclogites in Kaghan valley, Pakistan

Hafiz Ur Rehman, Hiroshi Yamamoto, M. Ayub Khan Khalil, Eizo Nakamura, Muhammad Zafar, Tahseenullah Khan

JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES 103 ( 4 ) 242 - 254 2008年8月

記述言語：英語出版者・発行元：JAPAN ASSOC MINERALOGICAL SCIENCES

Eclogites of the Kaghan valley, Pakistan Himalaya were investigated petrographically and geochemically. Based on petrography, geochemistry and mineral compositions, metamorphic history and a reasonable tectonic model are proposed. Eclogites exposed in the Kaghan valley are classified into two groups. Group I eclogites appear as massive and Group II are lens-type. Group I eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, quartz, symplectite with rare epidote and phengite. Accessory minerals include abundent zircon, rutile. ilmenite, and rare apatite. Group II eclogites have a mineral assemblage of garnet, omphacitic clinopyroxene, phengite, quartz/coestie, epidote, and symplectite. In accessory minerals rutile and ilmenite are common while zircon and apatite are rare. Different types of protolith are proposed for these eclogites. Group I eclogitcs have higher FeO and TiO2 contents and trace element contents. and seem to be derived from gabbroic protolith. Group II eclogites have lower FeO and TiO2 and trace element contents and were derived From basalts. Pressure-temperature-time path was constructed for the Kaghan valley eclogites using various mineral assemblages along with textural relationship and inclusions Study. At least three distinct metamorphic stages were identified. The first stage is the prograde garnet growth stage deduced from the inclusion paragenesis in garnet core. The second stage records the ultrahigh-pressure metamorphic stage deduced from the pressence Of coesite inclusions in omphacitic clinopyroxene. The third stage is the decompression stage and is deduced from the quartz-albite-amphibole symplectite portions. These petrological and geochemical results combined with isotopic ages reported elsewhere indicate that basalts and associated gabbroic dikes were emplaced at about 267 Ma when the Indian plate was moving northward and passing above an unknown hot spot. The Closure of the Tethys and initiation of collision of the Indian plate with the Kohistan-Ladakh Island Arc is reported from 65-50 Ma. After that the leading-edge of the Indian plate underwent eclogite facies metamorphism at 49 Ma and when it reached to depths of about 100 kin, the Ultrahigh-pressure metamorphic event took place at 46 Ma.

DOI： 10.2465/jmps.080222

Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

Tsutomu Ota, Katsura Kobayashi, Takuya Kunihiro, Eizo Nakamura

GEOCHIMICA ET COSMOCHIMICA ACTA 72 ( 14 ) 3531 - 3541 2008年7月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in B-11 relative to B-10 (delta B-11 = -1.2 to +7.7) and Li-7 relative to Li-6 (delta Li-7 = -1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (delta B-11 = -16.6 to -2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle. (c) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2008.05.002

Multiple pulses of the mantle plume: Evidence from Tertiary Icelandic lavas

Hiroshi Kitagawa, Katsura Kobayashi, Akio Makishima, Eizo Nakamura

JOURNAL OF PETROLOGY 49 ( 7 ) 1365 - 1396 2008年7月

記述言語：英語掲載種別：書評論文，書評，文献紹介等出版者・発行元：OXFORD UNIV PRESS

We present major and trace element concentrations and Sr-Nd-Hf-Pb isotope data for the c. 13-2 Ma Tertiary lavas from eastern Iceland. Our new geochemical results, together with published geological, geochronological, geochemical and geophysical data, are used to evaluate temporal changes in mantle sources contributing to the Tertiary Icelandic magmatism and the relative roles of these sources in magma productivity. The trace element and radiogenic isotopic compositions clearly distinguish three distinct end-member components in the Tertiary magmatism. Temporal variations in lava geochemistry can be attributed to changes in the relative contributions of these three end-member components to the erupted magmas and correlated with temporal variations in magma productivity. The extrusion of lavas with geochemically and isotopically enriched compositions was particularly pronounced at similar to 13-12 and 8-7 Ma, coincident in time with higher magma productivity. However, the geochemical characteristics of the lavas are different during these two periods: the 13-12 Ma lavas have more radiogenic Hf-176/Hf-177 and less radiogenic Pb-206/Pb-204 than those erupted from 8 to 7 Ma. The eruption of relatively depleted lavas, at around 10 Ma and younger than 6.5 Ma, is coincident with lower magma productivity. The correlation between the composition and productivity of the Tertiary lavas from eastern Iceland is probably due to periodic changes in the involvement of the enriched end-member component, followed by a gradation to periods dominated by the signature of the depleted end-member component and lower magma productivity, at an approximate frequency of 5 Myr.

DOI： 10.1093/petrology/egn029

Gravity-induced diffusion of isotope atoms in monoatomic solid Se

T. Mashimo, M. Ono, X. S. Huang, Y. Iguchi, S. Okayasu, K. Kobayashi, E. Nakamura

EPL 81 ( 5 ) 56002 - 56002 2008年3月

記述言語：英語出版者・発行元：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY

A strong gravitational field resulted in the gravity-induced diffusion (sedimentation) of isotope atoms in monoatomic solid Se. The layer crystalline morphology consisting of three zones of the fine-grained crystals, the long crystals and feather-shaped crystals grown parallel to gravity direction appeared in the specimen ultracentrifuged at (0.8-1) x 10(6) G and at 190 degrees C. Change in the concentration ratio (82)Se/(76) Se of > 0.8% was observed in the grown crystalline region. These results show an evidence for the sedimentation of substitutional atoms in solids via self-diffusion, and suggest the possibility of application to the control of impurity and crystalline states as well as to isotope separation. Copyright (c) EPLA, 2008.

DOI： 10.1209/0295-5075/81/56002

Crystal-size distribution and composition of garnets in eclogites from the Dabie orogen, central China

Hao Cheng, Zuyi Zhou, Eizo Nakamura

AMERICAN MINERALOGIST 93 ( 1 ) 124 - 133 2008年1月

記述言語：英語出版者・発行元：MINERALOGICAL SOC AMER

Crystal-size and spatial distributions of minerals in metamorphic rocks provide insight into their nucleation, growth environment, and the metamorphic evolution of their host rocks. Episodic nucleation and growth histories for garnets in eclogites from the Dabie orogen arc revealed by variations in crystal size, geochemical zoning, and mineralogy of inclusions in garnets. The studied garnets show pseudo-lognormal crystal-size distributions (CSDs), prograde chemical zoning patterns indexed by mineral inclusions, and are mainly distributed at random. Constant growth rate for each episode is proposed based on the mineralogy of inclusions in garnets and the chemical zoning patterns. The CSD shapes were evaluated in terms of a size-dependent proportionate growth model and a thermally accelerated, diffusion-controlled model but neither is consistent with the geochemical data and the concordant occurrence of mineral inclusions in garnet. Initial increasing nucleation rate followed by a subsequent, medial stage of nearly constant growth and finally declining nucleation rate is inferred from the CSD data. This study suggests that linking chemical analysis with textural analysis is crucial to avoid misleading interpretation solely through CSD shapes of minerals in metamorphic rocks.

DOI： 10.2138/am.2008.2556

Hawaiian double volcanic chain triggered by an episodic involvement of recycled material: Constraints from temporal Sr－Nd－Hf－Pb isotopic trend of the Loa-type volcanoes

Tanaka, R, Makishima, A, Nakamura, E

Earth Planet. Sci. Lett. 265 ( 3-4 ) 450 - 465 2008年1月

Tourmaline breakdown in a pelitic system: implications for boron cycling through subduction zones

Tsutomu Ota, Katsura Kobayashi, Tomoo Katsura, Eizo Nakamura

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY 155 ( 1 ) 19 - 32 2008年1月

記述言語：英語出版者・発行元：SPRINGER

Pressure-temperature conditions of tourmaline breakdown in a metapelite were determined by high-pressure experiments at 700-900 degrees C and 4-6 GPa. These experiments produced an eclogite-facies assemblage of garnet, clinopyroxene, phengite, coesite, kyanite and rare rutile. The modal proportions of tourmaline clearly decreased between 4.5 and 5 GPa at 700 degrees C, between 4 and 4.5 GPa at 800 degrees C, and between 800 and 850 degrees C at 4 GPa, with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable. Decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite, and increasing that of clinopyroxene, garnet and kyanite; the boron content of phengite increases significantly. These changes suggest that, with increasing pressure and temperature, tourmaline reacts with coesite to produce clinopyroxene, garnet, kyanite, and boron-bearing phengite and fluid. Our results suggest that: (1) tourmaline breakdown occurs at lower pressures and temperatures in SiO(2)-saturated systems than in SiO(2)-undersaturated systems. (2) In even cold subduction zones, subducting sediments should release boron-rich fluids by tourmaline breakdown before reaching depths of 150 km, and (3) even after tourmaline breakdown, a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments.

DOI： 10.1007/s00410-007-0228-2

New sequential separation procedure for Sr, Nd and Pb isotope ratio measurement in geological material using MC-ICP-MS and TIMS

Akio Makishima, B. Nagender Nath, Eizo Nakamura

GEOCHEMICAL JOURNAL 42 ( 3 ) 237 - 246 2008年

記述言語：英語出版者・発行元：GEOCHEMICAL SOC JAPAN

A new 3-step sequential separation chemistry for Sr, Nd and Pb from silicate samples, which is suitable for isotope analysis by MC-ICP-MS as well as TIMS, has been developed. The chemistry is designed to minimize the number of evaporation steps, enabling high throughput especially when MC-ICP-MS is employed. The sample solution in 0.5 mol 1(-1) HNO3 after digestion with HF-HCIO4, which is prepared for trace element analysis, can be directly used in the new chemistry. In the first column using Sr resin, Sr and Pb are collected. The recovered solution for Sr can be directly aspirated into MC-ICP-MS. The Pb solution is dried, re-dissolved, separated into two aliquots and measured by double spike MC-ICP-MS. Subsequently, LREEs are collected by the second column packed with cation exchange resin. Finally, Nd was purified from Sm using Ln resin in the third column. The recovered Nd solution can also be directly nebulized into MC-ICP-MS. The Sr and Nd isotope ratios for the standard material JB-3 (basalt) from the Geological Survey of Japan by MC-ICP-MS and TIMS were reported to verify the chemistry and mass spectrometry developed in this study.

DOI： 10.2343/geochemj.42.237

Generation of Rear-arc Magmas Induced by Influx of Slab-derived Supercritical Liquids: Implications from Alkali Basalt Lavas from Rishiri Volcano, Kurile Arc

Kuritani, T, Yokoyama, T, Nakamura, E

J. Petrol. ( 49 ) 1319 - 1342 2008年

New preconcentration technique of Zr, Nb, Mo, Hf, Ta and W employing coprecipitation with Ti compounds: Its application to Lu-Hf system and sequential Pb-Sr-Nd-Sm separation

Akio Makishima, Eizo Nakamura

GEOCHEMICAL JOURNAL 42 ( 2 ) 199 - 206 2008年

記述言語：英語出版者・発行元：GEOCHEMICAL SOC JAPAN

A new preconcentration technique of Zr, Nb, Mo, Hf, Ta and W has been invented employing coprecipiation with Ti compounds. Silicate samples were digested by HF with addition of Ti. Subsequent drying with HClO4 resulting in complete elimination of fluorine produces Ti compounds (oxide/hydroxides). The sample was then dissolved with dilute nitric acid and centrifuged, and the residual Ti compounds were collected. The Ti compounds forming from 2 mg of Ti without matrix elements concentrate 84-98% of Zr, Nb, Mo, Hf, Ta and W. In 20 mg basaltic and 50 mg peridotitic matrices, the addition of I nig of Ti was appropriate and gave yields of 46-69 and 54-79%, respectively, for Zr, Nb, Mo, Hf, Ta and W. Exploiting this preconcentration, sequential separation protocols of Hf, Pb, Sr, Lu, Nd and Sm for isotope analysis are developed with total blanks of 16, 11, 60, 2.4, 3 and 0.4 pg, respectively. The method is suitable for Lu-Hf system studies with capability of simultaneous separation of Pb, Sr, Nd and Sm from the same sample digest as well as isotopic anomaly studies of Zr, Mo and W. As application examples, accurate Lu-Hf data and Pb isotope ratios were obtained for basalt (JB-3) and peridotite (JP-1) by MC-ICP-MS.

DOI： 10.2343/geochemj.42.199

Isotope Fluctuation in Indium-Lead alloy induced by Solid Centrifugation

Ono, M, Iguchi, Y, Okayasu, S, Esaka, F, Kobayashi, K, Hao, T, Bagum, R, Osawa, T, Fujii, K, Nakamura, E, Mashimo, T

J. Nuclear Sci. & Tech. in Press 2008年

Direct measurements of impact devolatillization of calcite using a laser gun.

Ohno, S, Kadono, T, Ishibashi, K, Kawaragi, K, Sugita, S, Nakamura, E, Matsui, T

Geophys. Res. Lett. ( 35 ) 2008年

Precise measurement of (228)Ra/(226)Ra for (226)Ra determination employing total integration and simultaneous (228)Th correction by multicollector ICP-MS using multiple ion counters

Akio Makishima, Takele A. Chekol, Eizo Nakamura

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 23 ( 8 ) 1102 - 1107 2008年

記述言語：英語出版者・発行元：ROYAL SOC CHEMISTRY

A precise method of measuring (228)Ra/(226)Ra for (226)Ra determination used in U-series disequilibrium studies has been developed using the total integration method with simultaneous 228Th isobaric interference correction by multicollector ICP- MS with multiple ion counters (MIC). A sample solution of 0.2 ml was separately taken into a test tube, and all (226)Ra(+) and (228)Ra(+) signals as well as (229)Th(+) and (228)Th(16)O(+) from beginning to end were integrated simultaneously using four channeltrons, IC1, IC3, IC4 and IC5, respectively. Gains between IC1 and IC3 and the mass discrimination factor for (228)Ra/ (226) Ra determination were canceled out by measurement of a Ra spike solution with an accurately known Ra isotope ratio determined by TIMS, with which samples were bracketed. The isobaric interferences of (228)Th(+) were simultaneously corrected from the signal of (228)Th(16)O(+) and the oxide forming ratio of (228)Th, which was separately determined by simultaneous measurements of (229)Th(+) and 2(29)Th(16)O(+) by IC3 and IC5. The gains between IC3 and IC5 for the Th correction were also canceled out. The ion yield of Ra in MIC- ICP- MS was similar to 1.5%. The intermediate precision using 6.6, 3.3, 1.7, 0.83 and 0.41 fg of (226)Ra with (228)Ra/(226)Ra similar to 5 was 0.33, 0.93, 0.76, 1.6 and 1.5%, respectively. The (228)Ra/(226)Ra ratio showed no systematic change dependent on (228)Th/(228)Ra up to 0.25, indicating the validity of the (228)Th correction. At similar amounts of Ra, our method gives intermediate precision values similar to or better than previous MC-ICP-MS and TIMS studies. The precision of the method was verified using another Ra spike with (228)Ra/ (226)Ra = similar to 1 determined by TIMS. The analytical performance of the method was further investigated using the silicate samples JB-2 and JB-3 basalts issued by GSJ.

DOI： 10.1039/b807431c

Sedimentation of isotope atoms in monoatomic solid Se

Mashimo, t, Ono, M, Huang, X. S, Iguchi, Y, Okayasu S, Kobayashi, K, Nakamura, E

Europhys. Lett., in press. 2008年

Lithium isotopic systematics of peridotite xenoliths from Hannuoba, North China Craton: Implications for melt-rock interaction in the considerably thinned lithospheric mantle

Yan-Jie Tang, Hong-Fu Zhang, Eizo Nakamura, Takuya Moriguti, Katsura Kobayashi, Ji-Feng Ying

GEOCHIMICA ET COSMOCHIMICA ACTA 71 ( 17 ) 4327 - 4341 2007年9月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Li concentrations and isotopic compositions of coexisting minerals (ol, opx, and cpx) from peridotite xenoliths entrained in the Hannuoba Tertiary basalts, North China Craton, provide insight into Li isotopic fractionation between mantle minerals during melt-rock interaction in the considerably thinned lithospheric mantle. Bulk analyses of mineral separates show significant enrichment of Li in cpx (2.4-3.6 ppm) relative to olivine (1.2-1.8 ppm), indicating that these peridotites have been affected by mantle metasomatism with mafic silicate melts. Bulk olivine separates (delta Li-7 similar to +3.3 parts per thousand to +6.4 parts per thousand) are isotopically heavier than coexisting pyroxenes (delta Li-7 similar to -3.3 parts per thousand to -8.2 parts per thousand in cpx, and -4.0 parts per thousand to -6.7 parts per thousand in opx). Such large variation suggests Li elemental and isotopic disequilibrium. This conclusion is supported by results from in situ SIMS analyses of mineral grains where significant Li elemental and isotopic zonations exist. The olivine and opx have lower Li concentrations and heavier Li isotopes in the rims than in the cores. This reverse correlation of delta Li-7 with Li concentrations indicates diffusive fractionation of Li isotopes. However, the zoning patterns in coexisting cpx show isotopically heavier rims with higher Li abundances. This positive correlation between delta Li-7 and Li concentrations suggests a melt mixing trend. We attribute Li concentration and isotope zonation in minerals to the effects of two-stage diffusive fractionation coupled with melt-rock interaction. The earliest melts may have been derived from the subducted oceanic slab with low delta Li-7 values produced by isotopic fractionation during the dehydration of the seawater-altered slab. Melts at later stages were derived from the astheno-sphere and interacted with the peridotites, producing the Li elemental and isotopic zoning in mineral grains. These data thus provide evidence for multiple-stage peridotite-melt interaction in the lithospheric mantle beneath the northern North China Craton. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2007.07.006

Rates of thermal and chemical evolution of magmas in a cooling magma chamber: a chronological and theoretical study on basaltic and andesitic lavas from Rishiri Volcano, Japan

Takeshi Kuritani, Tetsuya Yokoyama, Eizo Nakamura

JOURNAL OF PETROLOGY 48 ( 7 ) 1295 - 1319 2007年7月

記述言語：英語出版者・発行元：OXFORD UNIV PRESS

Rates of magmatic processes in a cooling magma chamber were investigated for alkali basalt and trachytic andesite lavas erupted sequentially from Rishiri Volcano, northern Japan, by dating of these lavas using U-238-Th-230 radioactive disequilibrium and C-14 dating methods, in combination with theoretical analyses. We obtained the eruption age of the basaltic lavas to be 29.3 +/- 0.6 ka by C-14 dating of charcoals. The eruption age of the andesitic lavas was estimated to be 20.2 +/- 3.1 ka, utilizing a whole-rock isochron formed by U-Th fractionation as a result of degassing after lava emplacement. Because these two lavas represent a series of magmas produced by assimilation and fractional crystallization in the same magma chamber, the difference of the ages (i.e. similar to 9 kyr) is a timescale of magmatic evolution. The thermal and chemical evolution of the Rishiri magma chamber was modeled using mass and energy balance constraints, as well as quantitative information obtained from petrological and geochemical observations on the lavas. Using the timescale of similar to 9 kyr, the thickness of the magma chamber is estimated to have been about 1.7 km. The model calculations show that, in the early stage of the evolution, the magma cooled at a relatively high rate (>0.1 degrees C/year), and the cooling rate decreased with time. Convective heat flux from the main magma body exceeded 2W/m(2) when the magma was basaltic, and the intensity diminished exponentially with magmatic evolution. Volume flux of crustal materials to the magma chamber and rate of convective melt exchange (compositional convection) between the main magma and mush melt also decreased with time, from similar to 0.1m/year to similar to 10(-3) m/year, and from similar to 1m/year to similar to 10(-2) m/year, respectively, as the magmas evolved from basaltic to andesitic compositions. Although the mechanism of the cooling (i. e. thermal convection and/or compositional convection) of the main magma could not be constrained uniquely by the model, it is suggested that compositional convection was not effective in cooling the main magma, and the magma chamber is considered to have been cooled by thermal convection, in addition to heat conduction.

DOI： 10.1093/petrology/egm018

Origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone

Hao Cheng, Eizo Nakamura, Katsura Kobayashi, Zuyi Zhou

AMERICAN MINERALOGIST 92 ( 7 ) 1119 - 1129 2007年7月

記述言語：英語出版者・発行元：MINERALOGICAL SOC AMER

Detailed electron- and ion-microprobe analyses were carried out on atoll-shaped and normal garnets in ultrahigh-pressure (UHP) metamorphic eclogite from Dabie, east-central China. Compositional profiles of both normal garnets and rings of atoll garnets show well-preserved growth zoning with a decrease in Mn, Ca, and heavy rare earth elements (HREEs), and an increase in Mg toward rims. Manganese and middle rare earth element (MREE) enrichments are observed near garnet rims. Island- and peninsula-shaped garnet inside atolls are homogeneous in major elements and show the same composition as garnet rims, whereas the HREE concentrations are similar to those of the normal garnet cores. Electron back-scatter diffraction (EBSD) analyses show that the island- and peninsula-shaped garnet fractions inside atolls have crystallographic orientations identical to that of the atoll rings. These observations suggest that the atoll garnets were formed by the consumption of earlier-formed cores by fluid released from both hydroxyl exsolution from the nominally anhydrous minerals (NAMs) and lawsonite decomposition at the onset of exhumation, (i.e., garnet breakdown was from the inside and re-growth from outside to inside). Though somewhat restricted, this study reveals that because garnet and zircon act as sinks for HREEs and Zr, respectively, the majority of released HREEs and Zr were likely re-incorporated into newly grown garnet and zircon during the Dabie UHP metamorphic slab exhumation.

DOI： 10.2138/am.2007.2343

Ancient recycled crust beneath the ontong Java plateau: Isotopic evidence from the garnet clinopyroxenite xenoliths, Malaita, Solomon Islands

Akira Ishikawa, Takeshi Kuritani, Akio Makishima, Eizo Nakamura

EARTH AND PLANETARY SCIENCE LETTERS 259 ( 1-2 ) 134 - 148 2007年7月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

We present a Sr, Nd, Hf and Pb isotope investigation of a set of garnet clinopyroxenite xenoliths from Malaita, Solomon Islands in order to constrain crustal recycling in the Pacific mantle. Geological, thermobarometric and petrochemical evidence from previous studies strongly support an origin as a series of high-pressure (> 3 GPa) melting residues of basaltic material incorporated in peridotite, which was derived from Pacific convective mantle related to the Ontong Java Plateau magmatism. The present study reveals isotopic variations in the pyroxenites that are best explained by different extents of chemical reaction with ambient peridotite in the context of a melting of composite source mantle. Isotopic compositions of bimineralic gamet clinopyroxenites affected by ambient peridotite fall within the oceanic basalt array, similar to those of Ontong Java Plateau lavas. In contrast, a quartz-gaenet clinopyroxenite, whose major element compositions remain intact, has lower Pb-206/(204) Pb-Nd-143/(144) Nd and higher (87)sr/Sr-86-Pb-207/(204) Pb ratios than most oceanic basalts. These isotopic signatures show some affinity with proposed recycled sources such as the so-called EM-1 or DUPAL types. Constraints from major and trace element characteristics of the quartz-garnet clinopyroxenite, the large extent of Hf-Nd isotopic decoupling and the good coincidence of Ph isotopes to the Stacey-Kramers curve, all indicate that pollution of southern Pacific mantle occurred by the subduction or delamination of Neoproterozoic granulitic lower crust (0.5-1 Ga). This crustal recycling could have taken place around the suture of Rodinia supercontinent, a part of which resurfaced during mantle upwelling responsible for creating the Cretaceous Ontong Java Plateau. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.04.034

Boron and lead isotope signatures of subduction－zone me´lange formation: Hybridization and fractionation along the slab-mantle interface beneath volcanic arcs.

King, R. L, Bebout, G. E, Grove, M, Moriguti, T, Nakamura, E

Chem. Geol. 239 ( 3-4 ) 305 - 322 2007年4月

Plume-litho sphere interaction beneath Mt. Cameroon volcano, West Africa: Constraints from U-238-Th-230-Ra-226 and Sr-Nd-Pb isotope systematics

Tetsuya Yokoyama, Festus T. Aka, Minoru Kusakabe, Eizo Nakamura

GEOCHIMICA ET COSMOCHIMICA ACTA 71 ( 7 ) 1835 - 1854 2007年4月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Precise measurements of U-238-Th-230-Ra-226 disequilibria in lavas erupted within the last 100 yr on Mt. Cameroon are presented, together with major and trace elements, and Sr-Nd-Pb isotope ratios, to unravel the source and processes of basaltic magmatism at intraplate tectonic settings. All samples possess U-238-Th-230-Ra-226 disequilibria with Th-230 (18-24%) and Ra-226 (9-21%) excesses, and there exists a positive correlation in a (Ra-226/Th-230)-(Th-230/U-238) diagram. The extent of U-238-Th-230-Ra-226 disequilibria is markedly different in lavas of individual eruption ages, although the (Th-230/Th-232) ratio is constant irrespective of eruption age. When U-series results are combined with Pb isotope ratios, negative correlations are observed in the (Th-230/U-238)-(Pb-206/Pb-204) and (Ra-226/Th-230)-(Pb-206/Pb-204) diagrams. Shallow magma chamber processes like magma mixing, fractional crystallization and wall rock assimilation do not account for the correlations. Crustal contamination is not the cause of the observed isotopic variations because continental crust is considered to have extremely different Pb isotope compositions and U/Th ratios. Melting of a chemically heterogeneous mantle might explain the Mt. Cameroon data, but dynamic melting under conditions of high Du and D-U/D-Th, long magma ascent time, or disequilibrium mineral/melt partitioning, is required. The most plausible scenario to produce the geochemical characteristics of Mt. Cameroon samples is the interaction of melt derived from the asthenospheric mantle with overlying sub-continental lithospheric mantle which has elevated U/Pb (> 0.75) and Pb isotope ratios (Pb-206/Pb-204 > 20.47) due to late Mesozoic metasomatism.

DOI： 10.1016/j.gca.2007.01.010

Trace element fractionation in deep subduction zones inferred from a lawsonite-eclogite xenolith from the Colorado Plateau

Tomohiro Usui, Katsura Kobayashi, Eizo Nakamura, Herwart Helmstaedt

CHEMICAL GEOLOGY 239 ( 3-4 ) 336 - 351 2007年4月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

A coesite-bearing, lawsonite-eclogite xenolith from the Colorado Plateau, interpreted as a fragment of the subducted Farallon plate, is used to characterize trace element behavior in subducted oceanic crust. The xenolith consists of almandine-rich garnet, omphacite, lawsonite, phengite, rutile, pyrite and zircon as the primary mineral assemblage. Garnet crystals are extremely zoned with respect to their Mn contents, with core to rim variation from similar to 1.4 to similar to 0.2 wt.%. The euhedral zoning feature of garnet crystals and its included mineral assemblages suggest that the garnet continued to grow in the coesite stability field during prograde lawsonite eclogite facies metamorphism. In the lawsonite-eclogite xenoliths, garnet dominates the heavy rare earth elements (HREE), and lawsonite dominates both light rare earth elements (LREE) and Sr inventories. Combining the mineralogical and petrographic observations with precise spatial resolution ion microprobe analyses (< 15 mu m) of zoned garnet as well as lawsonite inclusions in garnet, we investigated trace element fractionation in coesite stability field during lawsonite eclogite facies metamorphism. Garnet shows progressive HREE depletion from core to rim, suggesting that HREE, which once partitioned into garnet crystal, would not be involved in postdated metamorphic reactions due to the high partition coefficients of HREE into garnet. Lawsonite inclusions in garnet, which represent lower metamorphic condition relative to lawsonite in the matrix, have LREE concentrations similar to 10 times lower than those of matrix lawsonite. On the contrary, the concentration of Sr in the included lawsonite is (< 20 relative %) lower than that of the matrix lawsonite. Based on constraints from metamorphic history recorded in the prograde-zoned garnet and mass balance among all constituent minerals in the lawsonite-eclogite xenolith, this contrasting feature for Sr and LREE of lawsonite is most plausibly explained by the hypothesis that allanite coexisting with included lawsonite might have decomposed during prograde metamorphism. The LREE released from the decomposing allanite would have been incorporated into lawsonite crystals. Consequently, REE and Sr could be retained in subducting oceanic crust even in the coesite stability field, if the slab is sufficiently cold enough to pass though the lawsonite eclogite facies. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2006.08.009

Coprecipitation of Ti, Mo, Sn and Sb with fluorides and application to detennination of B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by ICP-MS

Yinghuai Lu, Akio Makishima, Eizo Nakamura

CHEMICAL GEOLOGY 236 ( 1-2 ) 13 - 26 2007年1月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca-Al-Mg fluorides under two different fluoride forming conditions: at < 70 degrees C in an ultrasonic bath (denoted as the ultrasonic method) and at 245 degrees C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca-Al-Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9-50 mg of samples with Zr-Mo-Sn-Sb-Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol FI HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and TAW ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of <= 340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0-4.6% for basalts and andesites, and 6.7-11% for peridotites except for TiO2. (c) 2006 Elsevier B.V All rights reserved.

DOI： 10.1016/j.chemgeo.2006.08.007

Precise determination of Pb isotope ratios by simple double spike MC-ICP-MS technique without Tl addition

Akio Makishima, B. Nagender Nath, Eizo Nakamura

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 22 ( 4 ) 407 - 410 2007年

記述言語：英語出版者・発行元：ROYAL SOC CHEMISTRY

A double-spike multicollector ICP-MS ( DS-MC-ICP-MS) technique for Pb isotope analysis without T1 addition is established and its analytical performance is examined in detail. This simple DS-MC-ICP-MS technique using 20 ng ml(-1) gave averages of 16.9417, 15.4988 and 36.7196 with reproducibilities of 0.007, 0.008 and 0.009% ( RSD, n = 35), respectively, for Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 in NIST 981 solution, corresponding to consumption of 4 ng of Pb in a pair of spiked and non-spiked measurements. The average is consistent with those obtained by previous studies by DS-TIMS and DS-MC-ICP-MS with T1 addition. The reproducibility ( RSD %) of Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 improves from 0.26, 0.54 and 0.69% to 0.0022, 0.0030 and 0.0029% as the Pb consumption during analysis increases from 20 pg to 11 ng. The reproducibility with 11 ng is similar to or even better than those by DS-TIMS, MC-ICP-MS with T1 addition, or with DS-T1 addition. The accuracy of the simple DS-MC-ICP-MS technique for Pb, including the column chemistry, is further confirmed by analysis of actual silicate sample, JB-3.

DOI： 10.1039/b616021b

Li C. Generation of Palaeocene Adakitic Andesites by Magma Mixing, Yanji area, NE China.

Guo, F, Nakamura ,E, Fan, W, Kobayashi, K

J. Petrol. 48, 661 - 692 2007年

Purification of Hf in silicate materials using extraction chromatographic resin, and its application to precise determination of Hf-176/Hf-177 by MC-ICP-MS with Hf-179 spike

Yinghuai Lu, Akio Makishima, Eizo Nakamura

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 22 ( 1 ) 69 - 76 2007年

記述言語：英語出版者・発行元：ROYAL SOC CHEMISTRY

A two-stage column purification method for Hf from Zr and other elements in silicate samples using the extraction chromatographic resin, UTEVA has been developed. In the first column, using an anion-exchange resin, AG 1X8, Hf, Zr and Ti were collected. In the second, using UTEVA, and after eliminating F- by evaporation with HClO4 and re-dissolution with H2O2 HNO3, Hf was purified from Ti and Zr, based on characteristic of the UTEVA resin that Hf distribution coefficient (K-d) decreases from 770 to 40, while Kd of Zr decreases less from 890 to 200, in 9 and 6 mol l(-1) HNO3, respectively. The recovery yield of Hf was B88% and total blank was similar to 4 pg. A MC-ICP-MS Hf isotope ratio determination method was also developed, which uses 179 Hf spike for simultaneous determination of the Hf concentration and Hf-176/Hf-177 ratio. Combining the chemistry and ICP-MS techniques, Hf-176/Hf-177 ratios in silicate reference materials were determined with and without the spike, which gave identical results, showing the applicability of this method.

DOI： 10.1039/b610197f

Ion microprobe zircon U-Pb dating of the late Archaean metavolcanics and associated granites of the Musoma-Mara Greenstone Belt, Northeast Tanzania: Implications for the geological evolution of the Tanzania Craton

Shukrani Manya, Katsura Kobayashi, Makenya A. H. Maboko, Eizo Nakamura

JOURNAL OF AFRICAN EARTH SCIENCES 45 ( 3 ) 355 - 366 2006年7月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Ion microprobe zircon U-Pb ages from metavolcanic and associated granitic rocks of the late Archaean Musoma-Mara Greenstone Belt (MMGB) of northeast Tanzania reveal that the oldest mafic volcanism in the belt occurred at 2676-2669 Ma followed by felsic volcanism at similar to 2668 Ma. The felsic volcanism was coeval with the emplacement of the oldest pulse of massive granitoids that is dated at 2668 Ma. The youngest volcanic episode, represented by a volcanic horizon in the largely sedimentary Kavirondian Supergroup that overlies the greenstone sequence with a marked unconformity, occurred at similar to 2667 Ma. A younger phase of post-orogenic granites concluded the magmatic evolution of the MMGB at similar to 2649 Ma.
Our age data suggests that the entire volcano-sedimentary sequence in MMGB was emplaced in a relatively short time interval between similar to 2676 and similar to 2667 Ma. It also shows that contrary to arguments based on the degree of deformation, the foliated granites and some amphibolite rafts enclosed in them do not constitute the basement to the greenstone sequence. The data further shows that volcanism in the MMGB was younger than the similar to 2820 Ma age of volcanism in the Sukumaland Greenstorie Belt (SGB) to the far southwest and the similar to 2720 Ma age of volcanism in the nearby Kilimafedha Greenstone Belt (KGB) to the south. The age of granitic magmatism (ca. 2.69-2.55 Ga) in the three belts was, however, largely coeval. Granitic magmatism of this age has also been reported in different parts of the Tanzania Craton suggesting that it was responsible for the late Archaean crustal growth and marks the beginning of a period of stability (or of cratonization). (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jafrearsci.2006.03.004

Elemental mixing systematics and Sr-Nd isotope geochemistry of melange formation: Obstacles to identification of fluid sources to arc volcanics

Robert L. King, Gray E. Bebout, Takuya Moriguti, Eizo Nakamura

EARTH AND PLANETARY SCIENCE LETTERS 246 ( 3-4 ) 288 - 304 2006年6月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

We present major and trace element concentrations in conjunction with Sr-Nd isotope ratios to investigate the geochemical characteristics of melange formation along the subduction zone slab-mantle interface. Melange matrix of the Catalina Schist formed within an active subduction zone of the southern California borderland in Cretaceous time. Melange formed through the synergistic effects of deformation and metasomatic fluid flow affecting peridotite, basaltic, and sedimentary protoliths to form hybridized bulk compositions not typical of seafloor "input" lithologies. In general, all elemental concentrations primarily reflect mechanical mixing processes, while fluid flow mediates all elemental systematios to a varying extent that is largely a function of inferred "mobility" for a particular element or the stability of suitable mineral hosts. Elemental data reveal that mineral stabilities defined by the evolution of bulk composition within melange zones are probably the most important control of solid, liquid, or fluid geochemistry within the subduction system. Sr-Nd isotope ratios are highly variable and reflect contributions of melange protoliths to varying extents. A weak mechanical mixing array present in Sr isotope data is strongly overprinted by a fluid signal that dominates melange Sr systematics. Nd isotope data suggest that Nd is more conservative during metamorphism and is largely controlled by mechanical mixing. We argue that melange formation is an intrinsic process to all subduction zones and that the geochemistry of melange will impart the strongest control on the geochemistry of metasomatic agents (hydrous fluids, silicate melts, or miscible supercritical liquids) progressing to arc magmatic source regions in the mantle wedge. Melange formation processes suggest that comparisons of subduction "inputs" to arc volcanic "outputs" as a means to infer recycling at subduction zones dangerously over-simplify the physics of the mass transfer in subduction zones, as subducted mass is consistently redistributed into novel bulk compositions. Such melange zones along the slab-mantle interface simultaneously bear characteristic elemental or isotopic signals of several distinct input lithologies, while experiencing phase equilibria not typical of any input. We recommend that future studies explore the phase equilibria of hybridized systems and mineral trace element residency, as these processes provide for a physical baseline from which it will be possible to follow the path of subducted mass through the system. (c) 2006 Elsevier B.V All rights reserved.

DOI： 10.1016/j.epsl.2006.03.053

Geochemical evolution of a shallow magma plumbing system during the last 500 years, Miyakejima volcano, Japan: Constraints from U-238-Th-230-Ra-226 systematics

T Yokoyama, T Kuritani, K Kobayashi, E Nakamura

GEOCHIMICA ET COSMOCHIMICA ACTA 70 ( 11 ) 2885 - 2901 2006年6月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

In order to unravel magma processes and the geochemical evolution of shallow plumbing systems beneath active volcanoes, we investigated U-series disequilibria of rocks erupted over the past 500 years (1469-2000 AD) from Miyakejima volcano, Izu arc, Japan. Miyakejima volcanic rocks show U-238-Th-230-Ra-226 disequilibria with excess 238 U and Ra-226, due to the addition of slab-derived fluids to the mantle wedge. Basaltic bombs of the 2000 AD eruption have the lowest (Th-230/Th-232) ratio compared to older Miyakejima eruptives, yielding the youngest U-238-Th-230 model age of 2 kyr. This reinforces our previous model that fluid release from the slab and subsequent magma generation in the mantle wedge beneath Miyakejima occur episodically on a several-kyr timescale. In the last 500 years, Miyakejima eruptives show: (1) a vertical trend in a (Th-230/Th-232)-(U-238/Th-232) diagram and (2) a positive linear correlation in a (Ra-226/Th-230)(0)-1/Th-230 diagram, which is also observed in lavas from some of the single eruptions (e.g., 1940, 1962, and 1983 AD). The variations cannot be produced by simple fractional crystallization in a magma chamber with radioactive decay of Th-230 and Ra-226, but it is possibly produced by synchronous generation of melts in the mantle wedge with different upwelling rate or addition of multiple slab-derived fluids. A much more favorable scenario is that some basaltic magmas were intermittently supplied from deep in the mantle and injected into the crust, subsequently modifying the original magma composition and producing variations in (Th-230/Th-232) and (Ra-226/Th-230)(0) ratios via assimilation and fractional crystallization (AFC). The assimilant of the AFC process would be a volcanic edifice of previous Miyakejima magmatism. Due to the relatively short timescales involved, the interaction between the assimilant and recent Miyakejima magmatism has not been recorded by the Sr-Nd-Pb isotopic systems. In such cases, Th isotopes and (Ra-226/Th-230) ratio are excellent geochemical tracers of magmatic evolution. (c) 2006 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.gca.2006.02.027

Determination of Os and Re isotope ratios at subpicogram levels using MC-ICPMS with solution nebulization and multiple ion counting

A Makishima, E Nakamura

ANALYTICAL CHEMISTRY 78 ( 11 ) 3794 - 3799 2006年6月

記述言語：英語出版者・発行元：AMER CHEMICAL SOC

A precise and accurate determination method of Os-187/ Os-188, Os-189/Os-188, and Re-185/Re-187 ratios of down to 0.2 pg of Os and 0.08 pg of Re using multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) with multiple ion counting has been developed. Os and Re were introduced into MC-ICPMS as 0.5 mol L-1 HF solutions through the desolvator, and Re-185, Os-187, Os-188, and Os-189 ions were detected simultaneously by four channeltrons. The Os and Re ratios were determined by the standard bracketing method, in which channeltron yields and mass discrimination factors are corrected together. Os and Re memories after 800-s wash were < 0.1% and negligible, typically 0.02 and 0.03%, respectively. Isotope ratios of Os-187/ Os-188, Os-189/Os-188, and Re-185/Re-187 were constant within error in the concentration ranges of 1-100, 1-40, and 0.4-5 pg mL(-1) with reproducibility (1 sigma) of 2.7-0.14, 0.33-0.10, and 0.41-0.19%, respectively. For analysis of larger amounts of Os and Re, the Faraday cup measurement was employed. The precision and reproducibility obtained in this study are comparable to those of N-TIMS and better than MC-ICPMS achieved so far with a capability of higher sample throughput with simpler sample preparation.

DOI： 10.1021/ac060183t

Petrology and geochemistry of eclogite xenoliths from the Colorado Plateau: Implications for the evolution of subducted oceanic crust

T Usui, E Nakamura, H Helmstaedt

JOURNAL OF PETROLOGY 47 ( 5 ) 929 - 964 2006年5月

記述言語：英語掲載種別：書評論文，書評，文献紹介等出版者・発行元：OXFORD UNIV PRESS

Eclogite xenoliths from the Colorado Plateau, interpreted as fragments of the subducted Farallon plate, are used to constrain the trace element and Sr-Nd-Pb isotopic compositions of oceanic crust subducted into the upper mantle. The xenoliths consist of almandine-rich garnet, Na-clinopyroxene, lawsonite and zoisite with minor amounts of phengite, rutile, pyrite and zircon. They have essentially basaltic bulk-rock major element compositions; their Na2O contents are significantly elevated, but K2O contents are similar to those of unaltered mid-ocean ridge basalt (MORB). These alkali element characteristics are explained by spilitization or albitization processes on the sea floor and during subduction-zone metasomatism in the fore-arc region. The whole-rock trace element abundances of the xenoliths are variable relative to sea-floor-altered MORB, except for the restricted Zr/Hf ratios (36.9-37.6). Whole-rock mass balances for two Colorado Plateau eclogite xenoliths are examined for 22 trace elements, Rb, Cs, Sr, Ba, Y, rare earth elements, Pb, Th and U. Mass balance considerations and mineralogical observations indicate that the whole-rock chemistries of the xenoliths were modified by near-surface processes after emplacement and limited interaction with their host rock, a serpentinized ultramafic microbreccia. To avoid these secondary effects, the Sr, Nd and Pb isotopic compositions of minerals separated from the xenoliths were measured, yielding 0.70453-0.70590 for Sr-87/Sr-86, -3.1 to 0.5 for epsilon Nd and 18.928-19.063 for Pb-206/Pb-204. These isotopic compositions are distinctly more radiogenic for Sr and Pb and less radiogenic for Nd than those of altered MORB. Our results suggest that the MORB-like protolith of the xenoliths was metasomatized by a fluid equilibrated with sediment in the fore-arc region of a subduction zone and that this metasomatic fluid produced continental crust-like isotopic compositions of the xenoliths.

DOI： 10.1093/petrology/egi101

In-situ U-PbSIMS dating and trace element (EMPA) composition of zircon from a granodiorite porphyry in the Wushan copper deposit, China

Ding, X, SY Jiang, KD Zhao, E Nakamura, K Kobayashi, P Ni, LX Gu, YH Jiang

MINERALOGY AND PETROLOGY 86 ( 1-2 ) 29 - 44 2006年1月

記述言語：英語出版者・発行元：SPRINGER WIEN

Zircons from a granodiorite porphyry at the Wushan copper deposit in the Lower Changjiang Metallogenic Belt, east central China, were dated using a Cameca IMS 1270 secondary ion mass spectrometer (SIMS); their chemical compositions and Hf isotopes were analyzed using a JEOL JX A8800 electron microprobe (EMPA) and a Neptune LA-MC-ICP-MS, respectively. The U-Pb dating of zircon reveals two age groups for the granodiorite porphyry; i.e. 144.6 +/- 3.9 Ma and 121.0 +/- 2.5 Ma. Zircons of the two age populations display distinct chemical compositional characteristics with respect to UO2/HfO2 ratios, and show a negative correlation of (UO2 + Y2O3 + ThO2) and HfO2. The older age group of similar to 145 Ma, defined by the majority of the zircons, is interpreted as the magmatic emplacement age, whereas the younger age group of similar to 121 Ma is interpreted as rejuvenation due to subsequent thermal or hydrothermal events. Other interpretations such as presence of two distinct magmatic crystallization stages or inheritance of the older zircons are also discussed in the paper. The similar to 145 Ma magmatism at Wushan is consistent with the ages of most of the granitods in the Lower Changjiang Metallogenic Belt. The Hf isotope composition of zircons (epsilon(Hf) = -2.1 and -7.0; T-DM(Hf) ages = 0.87 and 1.05 Ga), together with other available geochemical and Sr-Nd isotope data suggest that the granodioritic magma was derived from mixing of juvenile mantle with older crustal material. Due to the close spatial and temporal relationship of the granodiorite porphyry and the skarn mineralization at Wushan, the magamatic hydrothermal mineralization likely took place between 145 Ma and 121 Ma, likely around 121 Ma.

DOI： 10.1007/s00710-005-0093-5

Elemental fractionation in lavas during post-eruptive degassing: Evidence from trachytic lavas, Rishiri Volcano, Japan

T Kuritani, E Nakamura

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH 149 ( 1-2 ) 124 - 138 2006年1月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

Trachytic lavas of Rishiri Volcano, northern Japan, show a peculiar geochemical variation across lava flow units. Samples collected systematically in a vertical cross section from a lava flow unit with a thickness of about 20 in are nearly homogeneous in major element compositions. However, some trace elements, including Li, B and Cs, are considerably depleted in samples collected from the main part of the flow unit, compared to those obtained from the surface of the lava flow (clinker layer). In particular, Cs content of the main flow unit is as low as similar to 30% of the clinker layer. Br-11.B-10 ratios of samples from the main flow unit are also slightly lower than those of the clinker samples, and the isotope compositions positively correlate with boron concentrations. These geochemical variations cannot be explained by magmatic processes in magma chambers, post-eruptive weathering, or alteration process. Rather, we infer these systematics resulted from escape of these elements from the lava flow unit during post-eruptive degassing. Vapor phases in which Li, B and Cs dissolved ire suggested to have been transported through veins formed in the main flow unit as fractures due to slight,,hearing along the flow planes after lava emplacement. In the Tanetomi lava, only rocks of the clinker layer preserve original composition of magmas, although they are porous and brownish due to extensive oxidization. On the other hand, rocks of the main flow unit do not retain original magma compositions, although they are dense and grayish, and seem to tic much fresher compared to the clinkers, A similar geochemical modification of lavas can occur in other volcanic systems, especially for lavas consisting of relatively thick flow units. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jvolgeores.2005.06.008

Determination of major, minor and trace elements in silicate samples by ICP-QMS and ICP-SFMS applying isotope dilution-internal standardization (ID-IS) and multi-stage internal standardization.

Makishima, A, Nakamura, E

Geostandards and Geoanalytical Research 2006年

Carbon self-diffusion in a natural diamond

KT Koga, MJ Walter, E Nakamura, K Kobayashi

PHYSICAL REVIEW B 72 ( 2 ) 2005年7月

記述言語：英語出版者・発行元：AMER PHYSICAL SOC

We report experimentally determined self-diffusion coefficients for carbon in a type-IaA diamond at pressure and temperature conditions within diamond stability field at 10 GPa and 2075-2375 K. The activation energy of diffusion is 6.8 +/- 1.6 eV and a preexponent constant is of 4.1 x 10(-5) m(2)/s [ln(-10.1 +/- 2.0) m(2)/s]. The activation energy is approximately 30% lower than results predicted previously from ab initio calculations.

DOI： 10.1103/PhysRevB.72.024108

Assimilation and fractional crystallization controlled by transport process of crustal melt: Implications from an alkali basalt-dacite suite from Rishiri Volcano, Japan

T Kuritani, H Kitagawa, E Nakamura

JOURNAL OF PETROLOGY 46 ( 7 ) 1421 - 1442 2005年7月

記述言語：英語出版者・発行元：OXFORD UNIV PRESS

Mechanisms of fractional crystallization with simultaneous crustal assimilation (AFC) are examined for the Kutsagata and Tanetomi lavas, an alkali basalt-dacite suite erupted sequentially from Rishiri Volcano, northern Japan. The major element variations within the suite can be explained by boundary layer fractionation; that is, mixing of a magma in the main part of the magma body with a fractionated interstitial melt transported from the mushy boundary layer at the floor. Systematic variations in SiO2 correlate with variations in the Pb, Sr and Nd isotopic compositions of the lavas. The geochemical variations of the lavas are explained by a constant and relatively low ratio of assimilated mass to crystallized mass ('r value). In the magma chamber in which the Kutsogata and Tanetomi magmas evolved, a strong thermal gradient was present and it is suggested that the marginal part of the reservoir was completely solidified. The assimilant was transported by crack flow from the partially fused floor crust to the partially crystallized floor mush zone through fractures in the solidified margin, formed a ny by thermal stresses resultingfrom cooling of the solidified margin and heating of the crust. The crustal melt was then mixed with the fractionated interstitial melt in the mushy zone, and the mixed melt was further transported by compositional convection to the main magma, causing its geochemical evolution to be characteristic of AFC. ne volume flux of the assimilant from the crust to the magma chamber is suggested to have decreased progressively with time (proportional to t(-1/2)), and was about 3 x 10(-2) m/year at t = 10years and I x 10(-2) m/year at t = 100years. It has been commonly considered that the heat balance between magmas and the surrounding crust controls the coupling of assimilation and fractional crystallization processes (i.e. absolute value of r). However, it is inferred from this study that the ratio of assimilated mass to crystallized mass can be controlled by the transport Process of the assimilant from the crust to magma chambers.

DOI： 10.1093/petrology/egi021

Boron isotopic constraints on the source of Hawaiian shield lavas

R Tanaka, E Nakamura

GEOCHIMICA ET COSMOCHIMICA ACTA 69 ( 13 ) 3385 - 3399 2005年7月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Boron isotopic compositions of lavas from three representative Hawaiian shield volcanoes (Kilauea, Mauna Loa, and Koolau) were analyzed by thermal ionization mass spectrometry. The boron isotopic composition of each sample was analyzed twice, once with and once without acid leaching to evaluate the effect of posteruptive boron contamination. Our acid-leaching procedure dissolved glass, olivine, secondary zeolite, and adsorbed boron; this dissolved boron was completely removed from the residue, which was comprised of plagioclase, pyroxenes, and newly formed amorphous silica. We confirmed that an appropriate acid-leaching process can eliminate adsorbed and incorporated boron contamination from all submarine samples without modifying the original B-11/B-10 ratio. On the other hand, when the sample was weathered, i.e., the olivine had an iddingsite rim, B-11/B-10 of the acid-resistant minerals are also modified, thus it is impossible to get the preeruptive B-11/B-10 value from the weathered samples. Through this elimination and evaluation procedure of posteruptive contamination, preeruptive delta(11)B values for the shield lavas are -4.5 to -5.4 parts per thousand for Koolau (N = 8), -3.6 to -4.6 parts per thousand, for Kilauea (N = 11), and -3.0 to -3.8 parts per thousand for Mauna Loa (N = 6).
Historical Kilauea lavas show a systematic temporal trend for B content and Nb/B coupled with other radiogenic isotopic ratios and trace element ratios, at constant delta(11)B, indicating little or no assimilation of crustal materials in these lavas. Uncorrelated B content and delta(11)B in Koolau and Mauna Loa lavas may also indicate little or no effect of crustal assimilation in these lavas. The source of KEA-component (identical to the so-called Kea end member in Hawaiian lavas) of the Hawaiian source mantle, represented by Kilauea, should be derived from lower part of subducted oceanic crust or refractory peridotite in the recycled subducted stab. The systematic trend from Kilauea to Koolau-decreasing delta(11)B coupled with decreasing epsilon Nd as well as increasing Sr-87/Sr-86 and Pb-206/Pb-204-is consistent with involvement of subducted sediment components in the EMK(enriched Makapuu)-component, represented by Makapuu-stage of Koolau lavas. Copyright (C) 2005 Elsevier Ltd.

DOI： 10.1016/j.gca.2005.03.009

Jurassic oceanic lithosphere beneath the southern Ontong Java Plateau: Evidence from xenoliths in alnoite, Malaita, Solomon Islands

A Ishikawa, E Nakamura, JJ Mahoney

GEOLOGY 33 ( 5 ) 393 - 396 2005年5月

記述言語：英語出版者・発行元：GEOLOGICAL SOC AMERICA, INC

The least metasomatized xenoliths of spinel lherzolite and gabbro recovered from ainoite intruding crust of the southern Ontong Java Plateau on the island of Malaita yield an Sm-Nd age of ca. 160 Ma and an initial epsilon(Nd) value of similar to+8. In contrast, the plateau basement is ca. 120 Ma with initial epsilon(Nd) between +3.7 and +6.5. The xenoliths appear to represent normal Pacific oceanic lithosphere (uppermost mantle and lower crust) formed similar to 40 m.y. before the plateau, indicating that the southern part of the plateau was emplaced off axis on mature seafloor. The closest 160 Ma seafloor to Malaita is > 1800 km to the north, off the northeastern margin of the plateau, implying the presence of either an intervening large-offset fracture zone or a triple junction. The presence of significantly older oceanic lithosphere beneath the plateau places restrictions on proposed origins for the plateau.

DOI： 10.1130/G21205.1

U-Pb zircon dating of regional deformation in the lower crust of the Kohistan arc

Yamamoto, H, Kobayashi, K, Nakamura, E, Kaneko, Y, Kausar, A

INTERNATIONAL GEOLOGY REVIEW 2005年

Lithium, boron, and lead isotope systematics of glass inclusions in olivines from Hawaiian lavas: evidence for recycled components in the Hawaiian plume

K Kobayashi, R Tanaka, T Moriguti, K Shimizu, E Nakamura

CHEMICAL GEOLOGY 212 ( 1-2 ) 143 - 161 2004年11月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

Lithium (Li), boron (B), and lead (Pb) isotopic compositions of glass inclusions in olivine phenocrysts from Hawaiian lavas, (Kilauea Iki, Mauna Loa, and Koolau volcano) were measured by high mass resolution ion probe to search for possible signatures of recycled materials in the Hawaiian plume. In order to measure the isotopic compositions, a set of synthetic glass standards with matrices similar to those of the target glass inclusions was prepared. Isotopic variations among these synthetic standards were produced by additions of spikes, and their isotopic compositions were determined by TIMS. Using this set of standards, correction factors for instrumental mass fractionation for Li, B, and Pb isotope measurement were determined with internal precisions of <1.2%, <1.6%, and <0.8% (2sigma) uncertainties for Li, B, and Pb, respectively.
Twenty-eight glass inclusions were measured after homogenization to eliminate dendritic crystals. These glass inclusions showed isotopic variations from -10.2% to +8.4% for delta(7)Li, from -10.5% to +5.2% for delta(11)B, from 0.7994 to 0.8909 for (207) Pb/Ph-206, and from 1.989 to 2.139 for Pb-208/Pb-206, which are considerably larger than those for whole rocks. This suggests that the Hawaiian lavas are mixtures of melts derived from isotopically distinct sources, and that glass inclusions better preserve information regarding source heterogeneity than do whole rocks. In particular, significantly low delta(7)Li and delta(11)B values for the Mauna Loa and Koolau samples indicate an isotopically "light" Li and B source, perhaps containing recycled materials that experienced dehydration during subduction. The extremely low Pb isotope signature, which corresponds to HIMU, also suggests some contribution from recycled materials to the generation of the Hawaiian magma. Our results suggest that recycled materials, which experienced near-surface alteration and then dehydration during subduction, played an important role in creating geochemical heterogeneity in the Hawaiian lavas. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2004.08.050

Preface to "Lithium isotope geochemistry"

RL Rudnick, E Nakamura

CHEMICAL GEOLOGY 212 ( 1-2 ) 1 - 4 2004年11月

Experimental constraints on crystallization differentiation in a deep magma ocean

MJ Walter, E Nakamura, RG Tronnes, DJ Frost

GEOCHIMICA ET COSMOCHIMICA ACTA 68 ( 20 ) 4267 - 4284 2004年10月

記述言語：英語出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

Major and trace element mineral/melt partition coefficients are presented for phases on the liquidus of fertile peridotite at 23-23.5 GPa and 2300degreesC. Partitioning models, based on lattice-strain theory, are developed for cations in the '8-fold' sites of majorite and Mg-perovskite. Composition-dependant partitioning models are made for cations in the 12-fold site of Ca-perovskite based on previously published data. D(min/melt) is extremely variable for many elements in Ca-perovskite and highly correlated with certain melt compositional parameters (e.g. CaO and Al(2)O(3) contents). The 8-fold sites in Mg-perovskite and majorite generally have ideal site radii between 0.8 and 0.9 Angstrom for trivalent cations, such that among rare-earth-elements (REE) D(min/melt) is maximum for Lu. Lighter REE become increasingly incompatible with increasing ionic radii. The 12-fold site in Ca-perovskite is larger and has an ideal trivalent site radius of similar to1.05 Angstrom, such that the middle REE has the maximum D(min/melt). Trivalent cations are generally compatible to highly compatible in Ca-perovskite giving it considerable leverage in crystallization models. Geochemical models based on these phase relations and partitioning results are used to test for evidence in mantle peridotite of preserved signals of crystal differentiation in a deep, Hadean magma ocean.
Model compositions for bulk silicate Earth and convecting mantle are constructed and evaluated. The model compositions for primitive convecting mantle yield superchondritic Mg/Si and Ca/Al ratios, although many refractory lithophile element ratios are near chondritic. Major element mass balance calculations effectively preclude a CI-chondritic bulk silicate Earth composition, and the super-chondritic Mg/Si ratio of the mantle is apparently a primary feature. Mass balance calculations indicate that 10-15% crystal fractionation of an assemblage dominated by Mg-perovskite, but with minor amounts of Ca-perovskite and ferropericlase, from a magma ocean with model peridotite-based bulk silicate Earth composition produces a residual magma that resembles closely the convectine mantle.
Partition coefficient based crystal fractionation models are developed that track changes in refractory lithophile major and trace element ratios in the residual magma (e.g. convecting mantle). Monomineralic crystallization of majorite or Mg-perovskite is limited to less than 5% before certain ratios fractionate beyond convecting mantle values. Only trace amounts of Ca-perovskite can be tolerated in isolation due to its remarkable ability to fractionate lithophile elements. Indeed, Ca-perovskite is limited to only a few percent in a deep mantle crystal assemblage. Removal from a magma ocean of approximately 13% of a deep mantle assemblage comprised of Mg-perovskite, Ca-perovskite and ferropericlase in the proportions 93:3:4 produces a residual magma with a superchondritic Ca/Al ratio matching that of the model convecting mantle. This amount of crystal separation generates fractionations in other refractory lithophile elements ratios that generally mimic those observed in the convecting mantle. Further, the residual magma is expected to have subchondritic Sm/Nd and Lu/Hf ratios. Modeling shows that up to 15% crystal separation of the deep mantle assemblage froth an early magma ocean could have yielded a convecting mantle reservoir with (143)Nd/(144)Nd and (176)Hf/(177)Hf isotopic compositions that remain internal to the array observed for modern oceanic volcanic rocks. If kept in isolation, the residual magma and deep crystal piles would grow model isotopic compositions that are akin to enriched mantle 1 (EM1) and HIMU reservoirs, respectively, in Nd-Hf isotopic space. Copyright (C) 2004 Elsevier Ltd.

DOI： 10.1016/j.gca.2004.03.014

Discovery of Archean continental and mantle fragments inferred from xenocrysts in komatiites, the Belingwe greenstone belt, Zimbabwe

K Shimizu, E Nakamura, K Kobayashi, S Maruyama

GEOLOGY 32 ( 4 ) 285 - 288 2004年4月

記述言語：英語出版者・発行元：GEOLOGICAL SOC AMERICA, INC

Controversy exists as to whether the 2.7 Ga Belingwe greenstone belt, Zimbabwe, is autochthonous or allochthonous. In this study we report direct evidence for an autochthonous continental setting for the Bellingwe greenstone belt. Garnet and clinopyroxene xenocrysts were discovered in the fresh ultramafic komatiites. Major and trace element compositions of these xenocrysts suggest that they originated from malic lower crust, presumably garnet granulite in composition, at a low temperature of similar to600 or similar to700 degreesC. Furthermore, in a komatiitic basalt sample, we have discovered orthopyroxene and clinopyroxene xenocrysts that may have originated from lithospheric mantle beneath the continental margin. Discoveries of these xenocrysts indicate that the komatiite magma was transported to the surface and quenched rapidly enough to prevent the complete melting of continental fragments.

DOI： 10.1130/G20162.1

Precise analysis of the Ra-228/Ra-226 isotope ratio for short-lived U-series disequilibria in natural samples by total evaporation thermal ionization mass spectrometry (TE-TIMS)

T Yokoyama, E Nakamura

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 19 ( 6 ) 717 - 727 2004年

記述言語：英語出版者・発行元：ROYAL SOC CHEMISTRY

We report a new analytical technique for precise and accurate determination of the Ra-228/Ra-226 ratio by total evaporation thermal ionization mass spectrometry (TE-TIMS). An improved chromatographic separation method employing a new tandem column technique that enables high yield and high purity of Ra is also described. Repeated analysis of Ra standard solution (Ra-228/Ra-226 = 1.1) yielded an analytical reproducibility for Ra-228/Ra-226 ranging from 0.2% to 0.9% (2sigma) for 170 to 2 fg of Ra. Reproducibility was strongly controlled by counting statistics of Ra-226(+) and Ra-228(+) ion beam intensities collected by an ion counting detector, implying that in-run precision for Ra isotope analysis of our method can be evaluated using a counting statistics law. Determination of Ra-226 abundances in silicate rock samples were examined by isotope dilution TE-TIMS, and reproducibility was 0.3% (2sigma) for JR-2 (Ra-226 = 3700 fg g(-1)) and 0.6% (2sigma) for JB-2 (Ra-226 = 81 fg g(-1)); the reproducibility of these measurements are 2 - 3 times better than previously published conventional TIMS procedures. The Ra-226/Ra-228 ratio in natural samples can be also measured with an analytical uncertainty of similar to1% (2sigma). The accuracy of our method was confirmed by measuring (Ra-226/Th-230) and (Ra-228/Th-232) ratios for JR-2, a sample old enough (1 Ma) to be in Th-230 -Ra-226 and Th-232 - Ra-228 radioactive equilibria. Our method is especially effective for samples with a very low abundance of Ra.

DOI： 10.1039/b400829d

Determination for lithium contents in silicates by isotope dilution ICP-MS and its evaluation by isotope dilution TIMS

Moriguti, T, Makishima, A, Nakamura, E

Geostandards Newsletter 2004年

Lithium, boron and lead isotope and trace element systematics of Quaternary basaltic volcanic rocks in northeastern Japan: Implications for variation of slab-derived fluid composition due to mineralogical reactions in the subducting slab

Moriguti, T, Shibata, T, Nakamura, E

Chemical Geology 2004年

Ultrahigh-pressure metabasaltic garnets as probes into deep subduction-zone cycling

King, R.L, Bebout, G.E, Kobayashi, K, Nakamura, E, van der Klauw, S.N.G.C

Geochemistry, Geophysics, Geosystems 2004年

Suppression of Zr, Nb, Hf and Ta coprecipitation in fluoride compounds for determination in Ca-rich materials

R Tanaka, A Makishima, H Kitagawa, E Nakamura

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 18 ( 12 ) 1458 - 1463 2003年12月

記述言語：英語出版者・発行元：ROYAL SOC CHEMISTRY

We have evaluated recovery yields of Zr, Nb, Hf and Ta, which are called high field strength elements (HFSE), in the synthetic Ca-Al-Mg-HF solution system using two different methods: at <70&DEG;C in an ultrasonic-bath (denoted as the ultrasonic method) and at 205&DEG;C using a TFE Teflon(R) bomb (denoted as the bomb method). Full recovery of HFSE into the supernatant HF solution was not achieved in cases where fluorite (CaF2) forms in the precipitate in both methods and sellaite (MgF2) forms in the ultrasonic method. In order to suppress fluorite precipitation, an 'Al-addition method' was developed in which Al solution is added to the sample before decomposition to change the matrix solution to a composition in which no fluorite forms. Using the Al-addition method, HFSE concentrations of Ca-rich materials were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) by an isotope dilution method for Zr and Hf and by a calibration curve method for Nb and Ta. Furthermore, we found isotopic disequilibria of Zr and Hf between sample and spike without Al-addition for Ca-rich samples, and that the Al-addition method was very effective in achieving isotopic equilibria and full recovery of HFSE, resulting in high accuracy in their determination.

DOI： 10.1039/b309948b

Highly precise and accurate isotopic analysis of small amounts of Pb using Pb-205-Pb-204 and Pb-207-Pb-204, two double spikes

T Kuritani, E Nakamura

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 18 ( 12 ) 1464 - 1470 2003年12月

記述言語：英語出版者・発行元：ROYAL SOC CHEMISTRY

A new, simple, and practical method has been developed for the accurate and precise isotopic analysis of extremely small amounts of Pb (<&SIM;3 ng) by thermal ionization mass spectrometry. Two different types of double spikes, one consisting of Pb-205 and Pb-204 and another enriched in Pb-207 and Pb-204, are used to reduce "Pb-204 error" and to correct mass fractionation during mass spectrometry. Using this technique, replicate analyses of 1.5 ng of Pb from NBS981 were performed, and an external, precision of 0.02% (2σ) was attained for the Pb-208/Pb-204 ratio. Compared with results for 1.5 ng of Pb by the normal double spike method using a single Pb-207-Pb-204 double spike, the external precision for the isotopic ratios involving Pb-204 is reduced by about 60-70%, simply by addition of the Pb-205-Pb-204 double spike. The two double spikes method was also applied to isotopic analyses of natural rock samples, and we obtained an external precision of 0.06% (2σ) for Pb-208/Ph-204 in &SIM;1.5 ng of Pb separated from fresh peridotite; in which the Pb concentration is as low as. 3.2 ppb. This new technique is superior to any previous method for precise and accurate isotopic analyses of extremely small amounts of Pb, and will be a highly powerful tool in the future of earth science and environmental science.

DOI： 10.1039/b310294g

Shift and Rotation of Composition Trends by Magma Mixing: 1983 Eruption at Miyake-jima Volcano, Japan

Takeshi Kuritani, Tetsuya Yokoyama, Katsura Kobayashi, Eizo Nakamura

Journal of Petrology 2003年

Record in metamorphic tourmalines of subduction-zone devolatilization and boron cycling

Bebout, G.E, Nakamura, E

Geology 2003年

Fate of the subduted Farallon plate inferred from eclogite xenoliths in the Colorado Plateau

Usui, T, Nakamura, E, Kobayashi, K, Maruyama,S, Helmstaedt, H

Geology 2003年

Comprehensive geochemical analyses of small amounts(<100mg) of extraterrestrial samples for the analytical competition related to the sample return missiion MUSES-C

Eizo Nakamura, Akio Makishima, Takuya Moriguti, Katsura Kobayashi, Chie Sakaguchi, Tetsuya Yokoyama, Ryoji Tanaka, Takeshi Kuritani, Hiroyuki Takei

The Institute of Space and Astronautical Science Report 2003年

Mantle metasomatism and rapid ascent of slab components beneath island arcs: Evidence from 238U-230Th-226Ra disequilibria of Miyakejima volcano, Izu arc, Japan

Tetsuya Yokoyama, Katsura Kobayashi, Takeshi Kuritani, Eizo Nakamura

Journal of Geophysical Research 2003年

Isotope dating of Neoproterozoic crustal growth in the Usambara Mountains of Northeastern Tanzania: evidence for coeval crust formation in the Mozanbique Belt and the Arabian-Nubian Shield

Maboko, M.A.H, Nakamura, E

Precambrian Research 2002年

U-Pb isotope systematics of micro-zircon inclusions: Implications for the age and origin of eclogite xenolith from the Corolado Plateau

Usui, T, Kobayashi, K, Nakamura, E

Proceedings of Japan Academy 2002年

U-Pb isotope systematics of micro-zircon inclusions: Implications for the age and origin of eclogite xenolith from the Colorado Plateau

Usui, T, Kobayashi, K, Nakamura, E

Proceedings of Japan Academy 78, Ser.B, 51-56 2002年

Precise determination of ferrous iron in silicate rocks

Yokoyama, T, Nakamura, E

Geoshim. Cosmosim. Acta 2002年

Determination of Cr, Ni, Cu and Zn in milligram samples of geological materials using isotope dilution high resolution ICP-MS

Makishima, A. Kobayashi, K, Nakamura, E

Geostandards Newsletter 2002年

Precise isotope analysis of nanogram-level Pb for natural rock ssamples without use of double spikes

Kuritani, T, Nakamura, E

Chemical Geology 2002年

Sm-Nd mineral ages of pegmatite veins and their host rocks from Swat area, Chilas complex, northern Pakistan

A.Ali, E.Nakamura, H.Yamamoto

Journal of Asian Earth Sciences 2002年

Timing and trigger of arc volcanism by flushing from subducting slab

Yokoyama, T, Nakamura, E, Kobayashi, K, Kuritani, T

Proceedings of Japan Academy 2002年

Timing and trigger of arc volcanism controlled by fluid flushing from subducting slab

Yokoyama, T, Nakamura, E, Kobayashi, K, Kuritani, T

Proceedings of Japan Academy 78, Ser.B, 190-195 2002年

Geochemical Evolution of Koolau Volcano, Hawaii. AGU Monograph "Evolution of Hawaiian Volcanoes",pp.? ,311-332, 2002.

Tanaka, R, Nakamura, E, Takahashi, E

AGU Monograph of "Evolution of Hawaiian Volcanoes" 2002年

Geochemical Evolution of Akagi Volcano, Northeast Japan: Implications for Interaction between Island Arc Magma and Lower Crust, and Generation of Isotopically various Magmas

Kobayashi, K, Nakamura, E

J. Petrol. 2001年

Formation and suppression of AlF3 during HF digestion of rock samples in Teflon bomb for precise trace element analyses by ICP-MS and ID-TIMS

Takei, H, Yokoyama, T, Makishima, A, Nakamura, E

Proc. Japan Acad. 2001年

Precise analysis of 234U/238U ratio using UO2+ ion with thermal ionization mass spectrometry for natural samples

Yokoyama, T, Makishima, A, Nakamura, E

Chem. Geol. 2001年

Boron isotope geochemistry of metasedimentary rocks and tourmalines in the subduction-zone metamorphism

Nakano, T, Nakamura, E

Phys. Earth Planet. Interiors 2001年

A new group separation method of ruthenium, palladium, rhenium, osmium, iridium and platinum using their bromocomplexes and novel anion exchange resin

Makishima, A. Nakanishi, M, Nakamura, E

Anal. Chem. 2001年

Determination of total sulfer at mg g-1 levels in geological materials by oxdation of sulfer into sulfate with in situ generation of bromine using isotope dilution high resolution ICPMS

Anal. Chem. 2001年

Partitioning of major elements between garnet-structured minerals and silicate melt at pressure of 3-15 GPa

Toshihiro Suzuki, Masaki Akaogi, Eizo Nakamura

Physics of the Earth and Planetary Interiors 120 ( 1 ) 79 - 92 2000年6月

記述言語：英語

High-pressure melting experiments on primitive mantle composition material (PM1) and thoreiitic basalt (JB2) were performed from 3 to 15 GPa, and garnet (majorite)/silicate melt partition coefficients, D, were measured for major elements. In the case of PM1, garnet was the liquidus phase only at around 15 GPa, where the partitioning experiments were performed. Although experimental time of PM1 was changed from 10 to 120 min, no obvious change was found in the observed D values of major elements. The liquidus phase of JB2 was garnet under the present experimental conditions. With increase in pressure, an obvious increase in D(Na) and decrease in D(Ti) were found in JB2, but D values of the other elements showed no significant pressure dependence. The observed D values of PM1 and JB2 were compared in partition coefficient (PC)-ionic results (IR) diagram. Although the absolute D values were different, D profiles of PM1 and JB2 at 15 GPa resembled each other. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0031-9201(00)00144-8

Constraints on HIMU and EM by Sr and Nd isotopes re-examined

Takeshi Hanyu, Eizo Nakamura

Earth, Planets and Space 52 ( 1 ) 61 - 70 2000年

記述言語：英語出版者・発行元：Springer Berlin

Sr and Nd isotopes together with trace elements for ocean island basalts in the Polynesian region have been analyzed in order to investigate the origin of the HIMU and EM sources. Both whole rocks and cpx phenocrysts were analyzed for isotopic composition. Cpx samples from HIMU islands show quite uniform 87Sr/86Sr ratios (~0.70274), while leached and unleached whole rock samples show variable and higher 87Sr/86Sr than those of cpx samples. These results suggest that even leached whole rock samples have been affected by secondary contaminations of sea water. On the other hand, cpx preserves a pristine isotopic signature with minimal secondary effects. Using only the cpx analyses, HIMU form a vertical linear trend in the Sr-Nd isotope diagram with small variation in ε(Nd) (+3.3~+5.5) and constant 87Sr/86Sr. This trend is explained by a mixing of the HIMU end-member and the MORB source. Since ε(Nd) of the HIMU end-member is constrained to be less than +3.3, the HIMU source should include former sediment added to oceanic crust. To explain the vertical nature of the mixing trend, the HIMU end-member should have similar Rb/Sr to the MORB source, or much lower Sr/Nd ratio than the MORB source, which favors a mixing model between extensively dehydrated oceanic crust and sediment as the HIMU source. The correlation between ε(Nd) and trace element ratios such as Pb/Ta also supports the model.

DOI： 10.1186/BF03351614

Constraints on HIMU and EM by Sr and Nd isotopes re-examined

Hanyu, T, Nakamura, E

Earth, Planets and Space 2000年

Comprehensive geochemical analyses of small amounts (<100mg) of extraterrestrial samples for the analytical competition related to the sample-return mission, MUSES-C. .

Nakamura, E, Makishima, A, Moriguti, T, Kobayashi, K, Sakaguchi, C, Yokoyama, T, Tanaka, R, Kuritani, T, Takei, H

Report for the Analytical Competition for Extraterrestrial Materials required by Institute for Space and Astronautical Science 2000年

Determination of titanium at μg g-1 levels in milligram amounts of silicate materials by isotope dilution high resolution inductively coupled plasma mass spectrometry with flow injection

Akio Makishima, Eizo Nakamura

Journal of analytical atomic spectrometry 15 ( 3 ) 263 - 267 2000年

記述言語：英語出版者・発行元：Royal Soc of Chemistry

An accurate method for the determination of Ti at μg g-1 levels in milligram amounts of silicate materials with isotope dilution high-resolution inductively coupled plasma mass spectrometry equipped with flow injection system (ID-FI-HR-ICP-MS) is presented. The chemical procedure requires HF digestion of the sample with the Ti spike, subsequent evaporation and dissolution of Ti with HF in order to separate from Mg and Ca fluorides formed after the digestion of the sample. A 10 mg silicate sample containing 0.002% TiO2 was measured with a blank correction of &lt
5%. To demonstrate the applicability of this method, peridotite reference materials, PCC-1 and DTS-1, from the US Geological Survey (USGS) and JP-1 from the Geological Survey of Japan (GSJ) were analyzed (12-33 mg), to determine TiO2 content. The reproducibility was 3% for these peridotites with TiO2 contents of 0.003-0.004%. This method also gave TiO2 contents in BCR-1, BHVO-1 and AGV-1 from USGS and JB-1, -2, -3, JA-1, -2, and -3 from GSJ with reproducibility of 1-5% using test portions of 6-18 mg.

DOI： 10.1039/a909020g

Geochemical evolution of the Horoman peridotite complex: Implications for melt extraction, metasomatism and compositional layering in the mantle

Yoshikawa, M, Nakamura, E

J. Geophys. Res. 2000年

Timing of magmatic and metamorphic events in the Jijal complex of the Kohistan arc deduce from Sm-Nd dating on mafic granulites

Yamamoto, H, Nakamura, E

J. Geol. Soc. London 2000年

Determination of titanium at micro-g/g levels in few milligram silicate materials by Isotope dilution high resolution inductively coupled plasma mass spectrometry with flow injection (ID-FI-HR-ICP-MS)

Makishima, A, Nakamura, E

J. Anal. Atomic Spectrom. 2000年

Partitioning of major elements between garnet-structured minerals and silicate melt at pressure of 3-15 GPa

Suzuki, T, Akaogi, M, Nakamura, E

Phys. Earth Planet. Interiors 2000年

Evaluation of the coprecipitation of incompatible trace elements with fluoride during silicate rock dissolution by acid digestion

Tetsuya Yokoyama, Akio Makishima, Eizo Nakamura

Chemical Geology 157 ( 3-4 ) 175 - 187 1999年5月

記述言語：英語

Insoluble fluoride precipitates which form during HF digestion of mafic silicate rocks coprecipitate in their structures the trace elements such as Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U, thus hindering their accurate determination. We have estimated quantitatively the coprecipitation of trace elements into such fluorides, and suggest an effective method of digestion that can suppress completely fluoride precipitation. Conventional acid digestion of three samples of mafic and ultramafic silicate rocks resulted in the precipitation of sticky material and very poor yields of certain trace element in the resultant solution. XRD analysis indicated that the precipitates were composed of fluorides such as CaAlF5, CaMg2Al2F12, Na0.88Mg0.88Al1.12(F,OH)6 · H2O and MgF2, the formation of which depended on the major element composition of the rock sample. Coprecipitation of trace elements appeared to be strongly controlled by both ionic radius and valency of the elements as well as the species of the host fluoride precipitate, resulting in selective losses of the elements into these fluorides. On the other hand, almost 100% of the trace elements were recovered using larger amounts of HCIO4 than is conventionally used and evaporating the sample to dryness in a step-wise fashion. Using this method, white precipitates were formed as oxides of high field strength elements after decomposition of the sample. Coprecipitation of trace elements of interest in this study with the oxides is negligible except for Th for which 0.5-3.2% by weight was coprecipitated probably as the insoluble oxide. As our method also results in negligible blank values, it can be used for both the accurate determination of trace element using ICP-MS as well as isotope analysis using TIMS.

DOI： 10.1016/S0009-2541(98)00206-X

Determination of molybdenum, antimony and tungsten at sub micro-g /g levels in geological materials by ID-FI-ICP-MS

Makishima, A, Nakamura, E

Geostand. Newslett. 1999年

Evaluation of the coprecipitation of incompatible trace elements with fluoride during silicate rock dissolution by acid digestion

Yokoyama, T, Makishima, A, Nakamura, E

Chemical Geology 1999年

Separation of thorium and uranium from silicate rock samples using two commercial extraction chromatographic resins

Tetsuya Yokoyama, Akio Makishima, Eizo Nakamura

Analytical Chemistry 71 ( 1 ) 135 - 141 1999年

記述言語：英語出版者・発行元：American Chemical Society

A new chemical separation technique to isolate Th and U from silicate rocks was established by using two kinds of commercial extraction Chromatographic resins. In the first column procedure, with U/TEVA·spec resin, almost all elements except Th and U were eluted by 4 M HNO3. Th was then separated by using 5 M HC1, and U was finally isolated by successive addition of 0.1 M HNO3. A significant amount of Zr still remained in the Th fraction, which was then further purified in the second column stage using TEVA·spec resin. In the second procedure, Zr was eluted first by using 2 M HNO3, and then Th was collected by 0.1 M HNO3. Both the Th and U fractions obtained by these procedures were sufficiently pure for thermal ionization mass spectrometric (TIMS) analysis. Recovery yields of Th and U exceeded 90%, and total blanks were &lt
19 pg for Th and &lt
10 pg for U. Our method has advantages over previous methods in terms of matrix effects, tailing problems, and degree of isolation. Since Th and U are effectively separated without suffering any matrix interference from coexisting cations and anions, this technique can be used not only for the analysis of igneous rock samples but also for the analysis of soils, marine sediments, carbonates, phosphates and seawater, groundwater, and surface water. © 1998 American Chemical Society.

DOI： 10.1021/ac9805807

Separation of thorium and uranium from silicate rock samples using two commercial extraction chromatographic resins

Yokoyama, T, Makishima, A, Nakamura, E

Analytical Chemistry 1999年

Determination of zirconium, niobium, hafnium and tantalum at ng/g levels in geological materials by direct nebulization of samples HF solution into FI-ICP-MS

Makishima, A, Nakamura, E, Nakano, T

Geostand. Newslett. 1999年

Across-arc variation of Li isotopes in lavas and implications for crust/mantle recycling at subduction zones

Takuya Moriguti, Eizo Nakamura

Earth and Planetary Science Letters 163 ( 1-4 ) 167 - 174 1998年11月

Trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication

Eizo Nakamura, Ikuo Kushiro

Geochimica et Cosmochimica Acta 62 ( 18 ) 3151 - 3160 1998年9月

記述言語：英語

Diffusivities of geochemically important trace elements (eleven rare earth elements (REE), Rb, Sr, Ba, and Y) in jadeite and diopside melts and those of Zr, Nb, Th, and U in jadeite melt have been measured at pressures between 7.5 and 20 kbar and at temperatures 50-200°above the liquids, using diffusion couples and ion microprobe analysis. The concentrations of these elements in the experimental charges are close to those in natural igneous rocks. In the jadeite melt which is nearly fully polymerized (NBO/T ~ 0), (1) diffusivities of REE increase with increasing ionic radii, (2) diffusivities of tri- and tetravalent elements increase with increasing pressure at constant temperature, whereas those of mono- and divalent elements do not change significantly with pressure, and (3) diffusivities of these elements decrease with increasing their ionic charge at constant pressure and temperature. In the diopside melt which is considerably less polymerized (NBO/T ~ 2), (1) diffusivities of these trace elements depend mainly on their ionic radii rather than ionic charges
the diffusivities of mono- and divalent ions decrease with increasing ionic radii at constant pressure and temperature, and (2) diffusivities of REE are nearly the same as that of Ca and decrease with increasing pressure at constant temperature. The behavior of these trace elements is correlated with that of major elements
in the jadeite melt, tri- and tetravalent elements behave similarly to network-forming cations Al and Si, whereas mono- and divalent elements behave as network-modifying cations similarly to Na. In the diopside melt, the diffusion behavior of all these trace elements is similar to that of network-modifying cations Ca and Mg. The results of the present experiments suggest that the abundance of some trace elements in igneous rocks may have been affected by diffusion process at the magmatic stage. In the case of REE, for example, if two different magmas with high and low REE concentrations become in contact one another by multiple intrusion, and a zoned magma chamber is formed, diffusion begins to take place between them, and near the interface, the REE-enriched magma will become more light REE-depleted, whereas REE-depleted magma will become more light REE-enriched, and in addition, if magmas are reduced, the former will show a negative Eu anomaly, whereas the latter will show a positive Eu anomaly.

DOI： 10.1016/S0016-7037(98)00223-3

High-yield lithium separation and the precise isotopic analysis for natural rock and aqueous samples

Takuya Moriguti, Eizo Nakamura

Chemical Geology 145 ( 1-2 ) 91 - 104 1998年3月

記述言語：英語出版者・発行元：Elsevier B.V.

A high-yield lithium separation technique for rock and aqueous samples has been established together with precise Li isotope analysis by thermal ionization mass spectrometry. Four separate stages of ion-exchange chromatography were carried out using organic ion-exchange resin. An ethanol-HCl solution was used for complete separation of Li from Na at the third column stage. Total reagent volume for the entire chemical process was reduced to 42 ml and 33.3 ml for rock samples and seawater, respectively. The recovery yield and total procedural blank are 99.2-99.3% and 11 pg, respectively. Li3PO4 was used as an ion-source material in the mass spectrometric analysis. The in-run precision and reproducibility of measured 7Li/6Li ratios were ±0.04-0.07‰ (2σmean) and 0.37‰ (relative standard deviation
RSD) for rock and ±0.05-0.08‰ (2σmean) and 0.35‰ (RSD) for seawater. In this method, Rb, Sr, Sm, Nd, La and Ce can be collected after Li elution in the first column chromatography, then separated by the following specific procedures for these elements. Therefore, this method makes possible multi-isotope analysis for Li-poor and restricted small amounts of samples such as meteorites and mantle materials, extending to Li isotope geochemistry and cosmochemistry. © 1998 Elsevier Science B.V.

DOI： 10.1016/S0009-2541(97)00163-0

High-yield lithium separation and precise isotopic analysis for natural and aqueous samples

Moriguti, T, Nakamura, E

Chemical Geology 1998年

Trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication

Nakamura, E, Kushiro, I

Geochim. Cosmochim. Acta 1998年

Across-arc variation of Li isotopes in arc lavas and implications for crust/mantle recycling at subduction zones

Moriguti, T, Nakamura, E

Earth Planet. Sci. Lett. 1998年

Static multicollection of Cs2BO2+ ions for precise boron isotope analysis with positive thermal ionization mass spectrometry

Nakano, T, Nakamura, E

Int. J. Mass Spectrom. Ion Processes 1998年

Inherited Paleozoic and Mesozoic Rb-Sr isotopic signatures in Neogene calc-alkaline volcanics, Alboran volcanic province, SE Spain

Zeck, H.P, Kristensen, A.B, Nakamura, E

J. Petrology 1998年

Diffusivities of rare earth elements and Ba in magmatic silicate melts at high pressures

Eizo Nakamura, Ikuo Kushiro

Proceedings of the Japan Academy Series B: Physical and Biological Sciences 73 ( 3 ) 44 - 47 1997年

記述言語：英語出版者・発行元：Japan Academy

Diffusivities of 11 rare earth elements (REE) and Ba in jadeite (NaAlSi2O6) and diopside (CaMgSi2O6) melts have been measured at pressures between 10 and 20 kbar. In jadeite melt, diffusivities of REE increase regularly with increasing their ionic radii, light REE (e.g., La and Ce) diffuse faster than heavy REE (e.g., Yb and Lu) by about 30%, Eu diffuses faster by factor of 8 to 12 than other REE under reducing conditions, and diffusivities of REE increase with increasing pressure at constant temperature. In diopside melt, diffusivities of REE are nearly the same as that of Ca and decrease with increasing pressure. The present study demonstrates that diffusion process in magma should change the relative abundances of REE and also generate Eu anomalies without involvement of plagioclase feldspar. This diffusion-induced process is a newly recognized mechanism of changing the relative REE abundances in magmas and generating Eu anomalies, and it must be taken into account in interpreting the REE abundance patterns of igneous rocks.

DOI： 10.2183/pjab.73.44

Suppression of matrix effect in ICP-MS by high power operation of ICP: Application to precise determination of Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U at ng /g level in a few milligram silicate sample

Makishima, A, Nakamura, E

Geostandard Newsletter 1997年

Across-arc variations of isotope and trace element compositions from Quaternary basaltic rocks in northeastern Japan: Implications for interaction between subducted oceanic slab and mantle wedge

Shibata, T, Nakamura, E

Jornal of Geophysical Research 1997年

Mantle process as inferred from trace element and radiogenic isotopic geochemistry of peridotite complexes

Yoshikawa, M, Nakamura, E

Mem. Geol. Soc. Japan 1997年

Diffusivities of rare earth elements and Ba in magmatic melts at high pressure

Nakamura, E, Kushiro I

Proceedings of Japan Academy 1997年

Determination of boron in silicate samples by direct aspiration of sample HF solutions into ICPMS

Makishima, A, Nakamura, E, Nakano T

Analytical Chemistry 1997年

Possible eastward extension of Chinese collision belt in South Korea: The Imjingang belt

Jin-Han Ree, Moonsup Cho, Sung-Tack Kwon, Eizo Nakamura

Geology 24 ( 12 ) 1071 - 1074 1996年12月

記述言語：英語

Structural, petrological, and geochronological data from the middle Korean peninsula indicate that the Qinling-Dabie-Sulu cullisional belt of east-central China crosses the Yellow Sea and extends into the Imjingang belt. The Yeoncheon complex, first identified as the western Imjingang belt, comprises primarily north-dipping metamorphic sequences: (1) the northern Jingok unit, consisting of Harrovian-type metapelites, and (2) the southern Samgot unit, consisting of calc-silicate and amphibolitic rocks. South-vergent structures with reverse-sense shearing are dominant in the Jingok unit, whereas late normal-sense shearing is pervasive in the Samgot unit and the deformed granitoid to the south. These structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt. Pressure-temperature (P-T) estimates from the amphibolites suggest a high-P amphibolite-facies metamorphism (8-13 kbar and 630-790°C), possibly evolving from eclogite facies conditions along a clockwise P-T path. Sm-Nd and Rb-Sr geochronological data suggest that the amphibolites emplaced in Late Proterozoic time were metamorphosed during Permian-Triassic time.

DOI： 10.1130/0091-7613(1996)024<1071:PEEOCC>2.3.CO;2

Boron isotope ratios in meteorites and lunar rocks

Mingzhe Zhai, Eizo Nakamura, Denis M. Shaw, Toshio Nakano

Geochimica et Cosmochimica Acta 60 ( 23 ) 4877 - 4881 1996年12月

記述言語：英語

The 11B/10B ratios of thirty-two meteorite falls and nine lunar rocks were measured as Cs2BO+2 using thermal ionization mass-spectrometry. The 11B/10B ratios of meteorites vary from 4.011 to 4.098, i.e., their δ11B values (relative to NIST SRM 951) range from -10.5 to +19.2‰
however, excluding two outliers, Mokoia and Norton County, the range of most meteorites is smaller (-10.5 to +7.5). The average of two CI1 meteorites, Ivuna and Orgueil, is -3.3, in the middle of the range. The δ11B values of the lunar rocks vary less than those of meteorites, from -6.0 to -3.9. The average δ11B of CI1 chondrites is -3.3, similar to that of terrestrial fresh mid-ocean ridge basalts (-6.5 to -1.2) and to the estimated mantle value of +0.2 (Ishikawa and Nakamura, 1992), which is the best representative of the whole Earth. The similarity of δ11B values in meteorites, lunar rocks, and those parts of the Earth unaffected by water implies that the boron isotopic composition of the Solar System is rather homogeneous. Recently, Chaussidon and Robert (1995) reported larger variation of δ11B values in chondrules of three chondrites, from -50 to +40. This degree of heterogeneity is absent from bulk meteorites.

DOI： 10.1016/S0016-7037(96)00338-9

Sm-Nd dating of garnet granulites from the Kohistan complex, northern Pakistan

Hiroshi Yamamoto, Eizo Nakamura

Journal of the Geological Society 153 ( 6 ) 965 - 969 1996年11月

記述言語：英語

Sm-Nd mineral-isochron ages of garnet granulites in the southern part of the Kohistan complex are determined. The 91.0±6.3 Ma age is obtained from a granulite body of the Jijal complex at Pattan and the 69.5±9.3 Ma age is obtained from a granulite body of the Chilas complex at Zambil. These ages indicate that the granulite bodies at Pattan and at Zambil had cooled to below upper amphibolite facies by about 90 Ma and about 70 Ma respectively. The time of cooling of the granulite of the Jijal complex is comparable to the time-lapse of the Asia-Kohistan collision (102-75 Ma), although that of the Chilas complex is probably younger than the Asia-Kohistan collision and certainly older than the Asia-India collision (c. 50 Ma).

DOI： 10.1144/gsjgs.153.6.0965

The arc lavas of the Shirahama Group, Japan: Sr and Nd isotopic data indicate mantle-derived bimodal magmatism

Y. Tamura, E. Nakamura

Journal of Petrology 37 ( 6 ) 1307 - 1319 1996年

記述言語：英語出版者・発行元：Oxford University Press

New Sr and Nd isotopic data are presented and integrated with previous data for the Shirahama Group Mio-Pliocene medium-K volcanic arc suite of south-central Honshu, Japan. Main results are: (1) The Shirahama lavas range in 87Sr/86Sr from 0·70315 to 0·70337 and in 143Nd/144Nd from 0·51298 to 0·51306
the Sr and Nd isotopic data cluster tightly within the mantle array, and all lie within an overlapping field of midocean ridge basalt and ocean island basalt
(2) small differences exist among the Shirahama tholeiitic series, calc-alkaline series and mixed lavas. The present isotopic data are consistent with a previously published model, which proposes that chemical variations in magmas of coexisting tholeiitic and calc-alkaline series are produced through crystal fractionation from mantle-derived magmas of basalt and magnesian andesite, respectively. Moreover, the tholeiitic series and the calc-alkaline series are isotopically identical. Thus, both magma series can be derived from a source mantle with the same isotopic composition, supporting the hypothesis of simultaneous generation of basalt and magnesian andesite magmas from a single diapir rising through the mantle wedge above the subduction zone. The differences of water content and temperature within the diapir are again thought to have been produced through dehydration and heating of an isotopically homogeneous hydrous diapir. The isotopic data show that the high-SiO2 lavas have the same isotopic compositions as more mafic lavas. These data and liquid lines of descent of the Shirahama magmas suggest that even rhyolites can be produced by differentiation from mantle-derived magmas without crustal contamination. Analyses from 38 other arc volcanoes have been compiled to investigate the intravolcano variability of 87Sr/86Sr. Twelve of these display no intravolcano strontium isotopic variability, as is the case with the Shirahama Group, but others show greater variation of 87Sr/86Sr from individual volcanic centers, presumably reflecting crustal contamination. Most of the latter volcanoes are underlain by thick continental crust. It is noteworthy, however, that the greater variations of 87Sr/86Sr correlate with SiO2 content
andesites or dacites, not basalts, from the same volcano have the lowest 87Sr/86Sr, and these rocks are calc-alkaline in terms of FeO*/MgO and SiO2. Theoretically, assimilation of continental crust by the isotopically uniform Shirahama magmas could produce these relationships. Given that mantle-derived basalt and magnesian andesite both encounter continental crust on their ascent to the surface, the hotter basalt magma would assimilate more crustal wallrocks than the cooler andesite, resulting in the basalt being more radiogenic. Fractional crystallization, magma mixing, and/or assimilation-fractional crystallization of these magmas in crustal magma chambers could produce large compositional variations, but the derivatives of the hotter basaltic magmas (tholeiitic series in the broad sense) would display greater contamination than those derived from the cooler andesitic magmas (calc-alkaline series).

DOI： 10.1093/petrology/37.6.1307

Experimental Study of the Slab-mantle Interaction and Implications for the Formation of Titanoclinohumite at Deep Subduction Zone

Yoshiyuki Iizuka, Eizo Nakamura

Proceedings of the Japan Academy, Series B 71 ( 6 ) 159 - 164 1995年

記述言語：英語

In order to examine the behavior of elements under the control of aqueous fluid through slab-mantle interactions, a series of high-pressure and high-temperature experiments was carried out at subsolidus temperature, 850°C. The starting materials consist of two portions: metabasite from blueschist as a slab material and olivine as a mantle material. The metabasite was directly placed on the olivine and sealed within an Au tube. At 3 and 6 GPa corresponding to 100 and 200 km in depth, respectively, the slab material was changed from blueschist to rutile-bearing eclogite. Observed phases in the mantle side were primary olivine and enstatite formed by the reaction between olivine and Si02-rich aqueous fluid from the slab side. At 8 GPa, the slab material was further transformed to rutile-free eclogite, and phases occurred in the mantle side were titanoclinohumite in addition to olivine and enstatite. The titanoclinohumite was formed by the reaction between olivine and Ti-bearing aqueous fluid which was supplied from the slab side. The titanoclinohumite is essentially identical in chemical composition to those principally occurring in kimberlite xenoliths. Because the Ti-phase is a host reservoir of HFSE, the formation of titanoclinohumite at 8 GPa corresponding to 250 km in depth suggests that the aqueous fluid can be a carrier of HFSE from the subducting slab to the upper mantle, and thus the source region of kimberlite magma could be impregnated by the interaction between mantle peridotite and the HFSE-bearing aqueous fluid from the subducting slab. © 1995, The Japan Academy. All rights reserved.

DOI： 10.2183/pjab.71.159

SmNd garnet ages from the Uluguru granulite complex of Eastern Tanzania: further evidence for post-metamorphic slow cooling in the Mozambique belt

M. A.H. Maboko, E. Nakamura

Precambrian Research 74 ( 4 ) 195 - 202 1995年

記述言語：英語

Two samples from the Uluguru granulite complex yield garnet SmNd ages of 633 ± 7 and 618 ± 16 Ma, similar to previously published hornblende 40Ar39Ar and KAr ages. The similarity of the SmNd to the KAr age suggests that the closure temperature of garnet to Nd diffusion is similar to that of hornblende to Ar diffusion. Assuming that published zircon UPb ages of about 700 Ma date peak granulite-facies metamorphism, a mean post-metamorphic cooling rate of 2-3°C/Ma can be calculated for the time interval 700 to 630 Ma. Such slow cooling rates imply thermal relaxation with a thickness length-scale greater than the thickness of average continental crust. This, in turn, implies that the thermal perturbation responsible for metamorphism was preceded by regional crustal thickening probably in a collisional orogen. © 1995.

DOI： 10.1016/0301-9268(95)00008-S

GEOCHRONOLOGY OF ALKALI VOLCANISM IN OKI-DOGO ISLAND, SOUTHWEST JAPAN - GEOCHEMICAL EVOLUTION OF BASALTS RELATED TO THE OPENING OF THE JAPAN SEA

K UTO, E TAKAHASHI, E NAKAMURA, KANEOKA, I

GEOCHEMICAL JOURNAL 28 ( 6 ) 431 - 449 1994年

記述言語：英語出版者・発行元：GEOCHEMICAL SOC JAPAN

Geochronological and geochemical studies were performed on alkali volcanic rocks from Oki-Dogo Island, locating about 60 km off the coast of Southwest Japan inside the Japan Sea. There are big differences both in age and in geochemistry between the oldest alkali rocks and the younger rocks; the former having significant Nb- and Ta-deletion and Ba- and K2O-enrichment erupted at 19-18 Ma when the opening of the Japan Sea was ongoing, while the latter with no Ta-depletion were active between 5.5-0.6 Ma considerably after the cessation of the rifting activity. Syn-extensional rocks should not have erupted in the active subduction zone but are probably originated from or at least contaminated by the lithosphere beneath the early Proterozoic crust. The lithosphere is considered to have suffered mantle metasomatism to form phlogopite selectively enriched in Ba and K2O by fluids, which had been released from previous subductions at the Asian continental margin. Partial meting of such lithospheric mantle during the active rifting was essential for the generation of Ba- and K2O-enriched alkali basalt magmas. The younger basaltic rocks are probably originated either from the asthenosphere or the deeper plume mantle. A suite of volcanic rocks from mugearite through trachyte to alkali rhyolite gave concordant ages of 5.5-5.4 Ma. These ages suggest that a previously reported Rb-Sr whole rock age of 6.8 +/- 0.3 Ma does not represent the age of eruption and is probably disturbed by magma mixing between basic and acidic end members.

DOI： 10.2343/geochemj.28.431

Geochronology of alkali volcanism in Oki-Dogo Island, Southwest Japan: Geochemical evolution of basalts related to the opening of the Japan Sea

Kozo Uto, Eiichi Takahashi, Eizo Nakamura, Ichiro Kaneoka

GEOCHEMICAL JOURNAL 28 ( 6 ) 431 - 449 1994年

記述言語：英語

Geochronological and geochemical studies were performed on alkali volcanic rocks from Oki-Dogo Island, locating about 60 km off the coast of Southwest Japan inside the Japan Sea. There are big differences both in age and in geochemistry between the oldest alkali rocks and the younger rocks
the former having significant Nb- and Ta-deletion and Ba- and K2O-enrichment erupted at 19–18 Ma when the opening of the Japan Sea was ongoing, while the latter with no Ta-depletion were active between 5.5-0.6 Ma considerably after the cessation of the rifting activity. Syn-extensional rocks should not have erupted in the active subduction zone but are probably originated from or at least contaminated by the lithosphere beneath the early Proterozoic crust, The lithosphere is considered to have suffered mantle metasomatism to form phlogopite selectively enriched in Ba and K2O by fluids, which had been released from previous subduc-tions at the Asian continental margin. Partial meting of such lithospheric mantle during the active rifting was essential for the generation of Ba- and K2O-enriched alkali basalt magmas. The younger basaltic rocks are probably originated either from the asthenosphere or the deeper plume mantle. A suite of volcanic rocks from mugearite through trachyte to alkali rhyolite gave concordant ages of 5.5-5.4 Ma. These ages suggest that a previously reported Rb-Sr whole rock age of 6.8 ± 0.3 Ma does not represent the age of eruption and is probably disturbed by magma mixing between basic and acidic end members. © 1994, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.2343/geochemj.28.431

Origin of the slab component in arc lavas from across-arc variation of B and Pb isotopes

Tsuyoshi Ishikawa, Eizo Nakamura

Nature 370 ( 6486 ) 205 - 208 1994年

記述言語：英語

At convergent margins, the subducting oceanic slab is thought to dehydrate, producing fluids which metasomatize the overlying mantle wedge where island-arc magma forms. However, the nature and origin of the metasomatizing fluid, its source composition and its relation to the genesis of the chemical characteristics of arc magmas are largely controversial. Across-arc variation in the chemistry of arc lavas provides a useful key to this problem, because it may reflect the changes in the physical conditions of the subducting slab that control mass transfer from slab to mantle wedge as a function of depth. Here we report clear across-arc variations in the concentrations and isotopic compositions of boronand lead observed in lavas from the Izu arc (Japan). Our data suggest that a homogeneous slab fluid contributes to all Izu volcan-oes, but that the amount of this fluid decreases continuously with increasing depth of the subducting slab. Whereas the Izu slab fluid conies primarily from altered oceanic crust, our data for high-Mg andesites from the Setouchi volcanic belt (a nearby fore-arc) indicate a significant involvement of sediment in the fluid source. © 1994 Nature Publishing Group.

DOI： 10.1038/370205a0

Boron isotope systematics of marine sediments

Tsuyoshi Ishikawa, Eizo Nakamura

Earth and Planetary Science Letters 117 ( 3-4 ) 567 - 580 1993年

記述言語：英語

Boron contents and boron isotopic compositions were determined for modern and ancient (Permian to Miocene) marine sediments, including pelagic clay, calcareous ooze, siliceous ooze and neritic clay sediments. δ11B values of modern marine sediments range from -6.6 to +4.8‰. Isotopic variation is controlled by the simple mixing of four major constituents, detritus of continental origin, marine smectite, biogenic carbonates and biogenic silica. Detritus of continental origin, with an average δ11B value of -13 to -8‰, is the low-δ11B end-member constituent of marine sediments and its boron is largely controlled by the concentration of illite which originates from wind or fluvial transport. Marine smectite, biogenic carbonate and biogenic silica, on the other hand, represent the high-δ11B end members, with δ11B values of +2.3 to +9.2‰, +8.0 to +26.2‰ and +2.1 to +4.5‰, respectively. These high δ11B values are the result of the equilibrium uptake of boron from seawater. Spatial variations in boron isotopes in the Pacific sediments are essentially due to the distribution of the above four constituents. Although ancient argillaceous sediments (shale and slate) have boron contents that are identical with those of modern equivalents, boron contents of limestone and chert are distinctly lower than those of modern calcareous and siliceous oozes. Ancient marine sediments have systematically lower δ11B values (-17.0 to -5.6‰) than those of the modern sediments. The lower δ11B values can be caused by diagenesis, which induces (1) preferential removal of high-δ11B boron in calcium carbonate and silica during recrystallization and (2) boron isotopic exchange in the course of the smectite/illite transition. The observed boron isotopic compositions of ancient argillaceous sediments are distinctly different from those of fresh and altered MORB. Therefore, boron isotope systematics will be useful in identifying components from the descending oceanic slab involved in the formation of island arc magma and in investigating mantle-crust recycling through subduction processes. © 1993.

DOI： 10.1016/0012-821X(93)90103-G

Precise lithium isotopic analysis by thermal ionization mass spectrometry using lithium phosphate as an ion source material

Takuya Moriguti, Eizo Nakamura

Proceedings of the Japan Academy, Series B 69 ( 6 ) 123 - 128 1993年

記述言語：英語

: A high-precision Li isotope analysis was developed for determining the Li+ ion emitted from lithium phosphate as an ion source material by a Re double-filament ionization method in the thermal ionization mass spectrometry. In this method, Li isotopic fractionation is distinctly less sensitive to the filament temperature than those in the previous methods, and stable and high ion beam intensity of more than 8 × 10-11 A for 7Li is obtained. These advantages in determining the 7Li/6Li ratio result in the analytical reproducibility of 0.26%o (1σ). Furthermore, the sample preparation is simple and the low temperature (850°C) required by this method ensures the analysis of the isotopic composition of small amounts of Li with less influence of Li contamination to the sample, compared with the previous methods. © 1993, The Japan Academy. All rights reserved.

DOI： 10.2183/pjab.69.123

Precise isotope determination of trace amounts of Sr in Magnesium-rich samples.

芳川雅子, 中村栄三

岩鉱 88,KJ,-KLU ( 12 ) 548 - 561 1993年

記述言語：英語出版者・発行元：Japan Association of Mineralogical Sciences

H⁺型とピリジン型陽イオン交換クロマトグラフィによる化学分離法を用いることで,超苦鉄質岩やその構成鉱物といったMgに富む試料の,ナノグラム単位のSrの単離を可能にした。総溶離液量はわずか24mlで,この結果,化学分離時のブランクはSrが32pg,Rbが25pgにまで減少した。タンタル酸イオン化活性材を用いた静的マルチコレクター質量分析法で,超苦鉄質岩標準岩石試料PCC-1から単離した10-20 ngのSr試料が,分析精度<0.005%,再現性<0.006%で測定可能にした。同位体希釈法を用いて得られたPCC-1のSr同位体比は,スパイクを加えずに得た値と分析誤差範囲内で一致し,分析精度や再現性もほぼ同じであった。また,ナノグラム単位のRb/Sr比の再現性は2%であった。以上の方法は,Mgに富み微量のSr・Rb試料しか得られない試料のSr同位体比,Rb・Sr濃度を求めるのに有効であり,10 ngという微量Sr試料で従来(>1μg)と同程度の信頼性ある結果を得ることが可能となった。

DOI： 10.2465/ganko.88.548

Precise isotope determination of trace amounts of Sr in magnesium-rich Samples

芳川雅子, 中村栄三

Journal of Mineralogy, Petrology and Economic Geology 88,KJ,-KLU ( 12 ) 548 - 561 1993年

記述言語：英語出版者・発行元：Japan Association of Mineralogical Sciences

H⁺型とピリジン型陽イオン交換クロマトグラフィによる化学分離法を用いることで,超苦鉄質岩やその構成鉱物といったMgに富む試料の,ナノグラム単位のSrの単離を可能にした。総溶離液量はわずか24mlで,この結果,化学分離時のブランクはSrが32pg,Rbが25pgにまで減少した。タンタル酸イオン化活性材を用いた静的マルチコレクター質量分析法で,超苦鉄質岩標準岩石試料PCC-1から単離した10-20 ngのSr試料が,分析精度<0.005%,再現性<0.006%で測定可能にした。同位体希釈法を用いて得られたPCC-1のSr同位体比は,スパイクを加えずに得た値と分析誤差範囲内で一致し,分析精度や再現性もほぼ同じであった。また,ナノグラム単位のRb/Sr比の再現性は2%であった。以上の方法は,Mgに富み微量のSr・Rb試料しか得られない試料のSr同位体比,Rb・Sr濃度を求めるのに有効であり,10 ngという微量Sr試料で従来(>1μg)と同程度の信頼性ある結果を得ることが可能となった。

DOI： 10.2465/ganko.88.548

Boron isotope geochemistry of the oceanic crust from DSDP/ODP Hole 504B

Tsuyoshi Ishikawa, Eizo Nakamura

Geochimica et Cosmochimica Acta 56 ( 4 ) 1633 - 1639 1992年

記述言語：英語

Boron contents and boron isotopic compositions were determined for the uppermost 1.3 km section of typical 6.2 Ma oceanic crust from DSDP/ODP Hole 504B, Costa Rica Rift, Galapagos Spreading Center. Both the boron content and the δ11B value in the oceanic crust are controlled by two types of alteration: 1. (1) low-temperature alteration (0 to 60°C
Zones I and II) and 2. (2) high-temperature hydrothermal alteration (200 to 400°C
Zones III and IV). Basalts subjected to the low-temperature alteration are characterized by their relatively high boron contents (0.69 to 19.3 ppm) and high δ11B values (+2.2 to +10.6%.), indicating uptake of boron into secondary phases in equilibrium with seawater or evolved seawater. Hydrothermally altered basalts contain less abundant boron (0.17 to 0.52 ppm) and relatively constant δ11B values (-0.1 to +1.0%.). Although basalts from the upper part of these hydrothermal zones (&lt
1300 mbsf) show equilibrated boron content and δ11B value with aqueous fluid, effective leaching of boron from basalt is predominant in the lower part (&gt
1300 mbsf). Original boron content and δ11B value of the Hole 504B MORB were 0.35 ppm and +0.2%., respectively. The present data provide fundamental information in understanding of the distribution of boron and boron isotopes in the oceanic crust. © 1992.

DOI： 10.1016/0016-7037(92)90230-G

22. Interaction between Subducted Oceanic Slab and Wedge Mantle Inferred from Across-arc Variations of Pb, Sr and Nd Isotopic Compositions in Northeastern Japan

Tomovuki Shibata, Eizo Nakamura

Proceedings of the Japan Academy Series B: Physical and Biological Sciences 67 ( 7 ) 115 - 120 1991年

記述言語：英語

Isotopic compositions of Pb, Sr and Nd have been determined for island arc basalts from northeastern Japan. The Sr and Pb isotopic ratios decrease, and Nd isotopic ratios increase from the volcanic front towards the back-arc side. The isotopic compositions at the most back-arc side are nearly identical to those of MORB, indicating that the across-arc isotopic variations were caused by a two-component mixing between MORB-type wedge mantle and oceanic sediments with different degrees of sediment involvement which depend on the depth of subducting oceanic slab. The abundance ratios among Pb, Sr and Nd in the subducted oceanic sediment were estimated from the mixing relationships in the isotope compositions. The estimated Sr/Pb ratio of subducted sediments does not change during subduction, while the Nd/Sr and Nd/Pb increase towards the back-arc side. These observations suggest that the subduction component was added to the wedge mantle as a fluid through the dehydration of subducted oceanic sediment and the degree of dehydration decreases with increase in the depth of slab, and that the subducting oceanic slab does not melt beneath northeastern Japan. © 1991, The Japan Academy. All rights reserved.

DOI： 10.2183/pjab.67.115

Suppression of Boron Volatilization from a Hydrofluoric Acid Solution Using a Boron-Mannitol Complex

Tsuyoshi Ishikawa, Eizo Nakamura

Analytical Chemistry 62 ( 23 ) 2612 - 2616 1990年12月

記述言語：英語

Volatilization and mass fractionation of boron during evaporation of the hydrofluoric and hydrochloric acid solutions were investigated with varying mannitol/boron ratios. The degree of volatilization and mass fractionation decreases with increasing mannitol/boron mole ratio, and the boron volatilization is completely suppressed when the ratio is more than unity. These results indicate that the final stable compound is an equimolar complex of boron and mannitol. The formation of this complex in the acid solutions allows the use of hydrofluoric and hydrochloric acids for the dissolution of silicate rock samples and for the subsequent chemical separation of boron from the samples adopting anion-exchange chromatography in F− form. © 1990, American Chemical Society. All rights reserved.

DOI： 10.1021/ac00222a017

Lead isotope analyses of standard rock samples

Koide Yoshiyuki, Nakamura Eizo

Mass Spectroscopy 38 ( 5 ) 241 - 252 1990年

記述言語：英語出版者・発行元：The Mass Spectrometry Society of Japan

New results on lead isotope compositions of standard rock samples and their analytical procedures are reported. Bromide form anion exchange chromatography technique was adopted for the chemical separation of lead from rock samples. The lead contamination during whole analytical procedure was low enough to determine lead isotope composition of common natural rocks. Silica-gel activator method was applied for emission of lead ions in the mass spectrometer. Using the data reduction of "unfractionated ratios", we obtained good reproducibility, precision and accuracy on lead isotope compositions of NBS SRM. Here we present new reliable lead isotope compositions of GSJ standard rock samples and USGS standard rock, BCR-1.

DOI： 10.5702/massspec.38.241

その他リンク： https://jlc.jst.go.jp/DN/JALC/00005568604?from=CiNii

Lead isotope analyses of standard rock samples.

Koide Yoshiyuki, Nakamura Eizo

Journal of the Mass Spectrometry Society of Japan 38 ( 5 ) 241 - 252 1990年

記述言語：英語出版者・発行元：The Mass Spectrometry Society of Japan

New results on lead isotope compositions of standard rock samples and their analytical procedures are reported. Bromide form anion exchange chromatography technique was adopted for the chemical separation of lead from rock samples. The lead contamination during whole analytical procedure was low enough to determine lead isotope composition of common natural rocks. Silica-gel activator method was applied for emission of lead ions in the mass spectrometer. Using the data reduction of "unfractionated ratios", we obtained good reproducibility, precision and accuracy on lead isotope compositions of NBS SRM. Here we present new reliable lead isotope compositions of GSJ standard rock samples and USGS standard rock, BCR-1.

DOI： 10.5702/massspec.38.241

その他リンク： https://jlc.jst.go.jp/DN/JALC/00005568604?from=CiNii

K-Ar ages of basalts from the Higashi-Matsuura district, northwestern Kyushu, Japan and regional geochronology of the Cenozoic alkaline volcanic rocks in eastern Asia.

Nakamura Eizo, McDougall Ian, Campbell Ian H.

GEOCHEMICAL JOURNAL 20,91-99 ( 2 ) 91 - 99 1986年

記述言語：英語出版者・発行元：GEOCHEMICAL SOCIETY OF JAPAN

Seven new K-Ar age determinations are presented on whole rock samples from alkaline and tholeiitic basalts of the Higashi-Matsuura district, northwestern Kyushu, Japan. Ages obtained range from 2.92 ± 0.03Ma to 3.01 ± 0.04Ma; these ages are essentially identical within analytical errors and yield an average age of 2.98 ± 0.03Ma (Late Pliocene). When combined on an isochron type diagram the six Higashi-Matsuura samples give an age of 3.00 ± 0.03 Ma with the composition of nonradiogenic ⁴⁰Ar/³⁶Ar = 294.2 ± 2.0. The excellent age agreement of samples with different K contents and petrographic characteristics provides strong evidence that the tholeiitic and alkaline basalts were erupted for an extremely short period in the Higashi-Matsuura district. A basalt from Ogawashima Island yields a K-Ar age of 3.58 ± 0.04Ma. This study and previously reported data support the hypothesis that alkaline volcanic activity in southwestern Japan commenced some 10Ma ago and continued intermittently until Recent times. Systematic variations of age and distribution of Cenozoic alkaline basalts are recognized in northeastern China, Korea and southwestern Japan. It is suggested that these variations are related to the initiation of "mantle plumes" resulting from convection in the mantle wedge caused or controlled by subduction of the Kula and Pacific plates.

DOI： 10.2343/geochemj.20.91

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