DOI： 10.22541/essoar.167065816.65575976/v1

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japan Academy  

DOI： 10.2183/pjab.98.015

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union ({AGU})  

DOI： 10.1029/2021JB023328

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media {LLC}  

<jats:title>Abstract</jats:title><jats:p>C-type asteroids<jats:sup>1</jats:sup> are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing<jats:sup>2–7</jats:sup> and on-asteroid measurements<jats:sup>8,9</jats:sup> with Hayabusa2 (ref. <jats:sup>10</jats:sup>). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu<jats:sup>11</jats:sup>, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m<jats:sup>−3</jats:sup>, which is lower than that of meteorites<jats:sup>12</jats:sup>, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements<jats:sup>5,9</jats:sup>. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu<jats:sup>3,4</jats:sup> and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.</jats:p>

DOI： 10.1038/s41550-021-01550-6

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その他リンク： https://www.nature.com/articles/s41550-021-01550-6

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier {BV}  

DOI： 10.1016/j.micromeso.2019.03.050

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掲載種別：研究論文（学術雑誌）  

Subduction processes introduce crustal materials into the mantle, and mantle plumes return them to the surface. However, when and how the subducted materials were recorded in the plume-related basalts remains unclear. Here we investigate geochronology, bulk-rock composition, and Sr-Nd-Pb isotopes of Cenozoic basalts from Southeast China, occurring near the west Pacific subduction zone and the seismically detected Hainan plume. Volcanism beginning in the late Oligocene in the continental margin of SE China consistently becomes younger landward. Together with a compilation of published results on the synchronous basalts from the South China Sea seamounts and the Indochina peninsula, the volcanoes close to the Pacific subduction zone exhibit more radiogenic Pb and Sr isotopes associated with less radiogenic Nd isotopes compared with those of the inland volcanoes. Such spatiotemporal variations in radiogenic isotopes imply oceanic crusts of different ages in the source, each corresponding to a different geographical volcanic belt. Major-element features such as low CaO, high TiO2 and high Fe/Mn ratios imply that pyroxenite/eclogite could serve as a source lithology of the SE China basalts. Specific trace-element signatures reveal the important roles of recycled oceanic crust along with surface sediment, which was inconsistently dehydrated during subduction. A geologically, geochemically, and geophysically plausible scenario is proposed to illustrate the time-space-source correlation of the late Cenozoic basaltic lavas in SE Asia. The Hainan plume delivered the ancient subducted crust (1·5 Ga) from the core-mantle boundary and, subsequently, the subducted Pacific plate crustal materials from the mantle transition zone to the shallow mantle as a result of mantle convection induced by continuous subduction of the Pacific plate. Such recycled materials of different ages contributed to the geographical compositional heterogeneities of the late Cenozoic basaltic lavas in SE Asia.

DOI： 10.1093/petrology/egaa060

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：MARY ANN LIEBERT, INC  

The Hayabusa2 mission successfully collected samples from the asteroid Ryugu last year and will return these to Earth in December 2020. It is anticipated that the samples will enable the analysis of terrestrially uncontaminated organic matter and minerals. Such analyses are in turn expected to elucidate the evolution of organic matter through Solar System history, including the origination and processing of biogenically important molecules, which could have been utilized by the first organisms on Earth. In anticipation, studies have made predictions concerning the properties of Ryugu, including its composition. The spectral characteristics of Ryugu, such as albedo, have been employed to relate the asteroid to members of the carbonaceous chondrite group that have been identified on Earth. However, the recent Hayabusa2 touchdown highlights a disparity between the color of surfaces of displaced platy fragments, indicating a brightening trend for the surface exposed to space compared to that facing into the body. Here we present a mass balance calculation with reference to data from the literature, which indicates that Ryugu may contain a significantly higher abundance of organic matter (likely >50%) than the currently most accepted meteorite analogues. A high organic content may result in high levels of extractable organic matter for the second touchdown site, where the spacecraft sampled freshly exposed material. However, high abundances of insoluble aromatic/graphitic rich organic matter may be present in the first touchdown site, which sampled the surface of Ryugu that had been exposed to space. Moreover, we suggest that the potentially high organic abundance and the rubble-pile nature of Ryugu may originate from the capture of rocky debris by a comet nucleus and subsequent water-organic-mineral interactions and sublimation of water ice.

DOI： 10.1089/ast.2019.2198

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Subduction processes introduce crustal materials into the mantle, and mantle plumes return them to the surface. However, when and how the subducted materials were recorded in the plume-related basalts remains unclear. Here we investigate geochronology, bulk-rock composition, and Sr-Nd-Pb isotopes of Cenozoic basalts from Southeast China, occurring near the west Pacific subduction zone and the seismically detected Hainan plume. Volcanism beginning in the late Oligocene in the continental margin of SE China consistently becomes younger landward. Together with a compilation of published results on the synchronous basalts from the South China Sea seamounts and the Indochina peninsula, the volcanoes close to the Pacific subduction zone exhibit more radiogenic Pb and Sr isotopes associated with less radiogenic Nd isotopes compared with those of the inland volcanoes. Such spatiotemporal variations in radiogenic isotopes imply oceanic crusts of different ages in the source, each corresponding to a different geographical volcanic belt. Major-element features such as low CaO, high TiO2 and high Fe/Mn ratios imply that pyroxenite/eclogite could serve as a source lithology of the SE China basalts. Specific trace-element signatures reveal the important roles of recycled oceanic crust along with surface sediment, which was inconsistently dehydrated during subduction. A geologically, geochemically, and geophysically plausible scenario is proposed to illustrate the time-space-source correlation of the late Cenozoic basaltic lavas in SE Asia. The Hainan plume delivered the ancient subducted crust (1.5 Ga) from the core-mantle boundary and, subsequently, the subducted Pacific plate crustal materials from the mantle transition zone to the shallow mantle as a result of mantle convection induced by continuous subduction of the Pacific plate. Such recycled materials of different ages contributed to the geographical compositional heterogeneities of the late Cenozoic basaltic lavas in SE Asia.

DOI： 10.1093/petrology/egaa060

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掲載種別：研究論文（学術雑誌）  

Carbonaceous chondrites contain many abiotic organic compounds, some of which are found in life on Earth. Both the mineral and organic matter phases, of these meteorites, have been affected by aqueous alteration processes. Whilst organic matter is known to be associated with phyllosilicate phases, no such relationship has yet been identified for specific organic compound classes. Furthermore, ongoing sample return missions, Hyabusa 2 and OSIRIS-Rex, are set to return potentially organic rich C-type asteroid samples to the Earth. Consequently, strategies to investigate organic-mineral relationships are required. Here we report spatial data for free/soluble organic matter (FOM/SOM) components (akylimidazole and alkylpyridine homologues) and mineral phases. Low and intermediate molecular weight alkylimidazole homologues are more widely distributed than higher molecular weight members, likely due to their affinity for the aqueous phase. On aqueous alteration of anhydrous mineral phases, transported FOM is adsorbed onto the surface or into the interlayers of the resulting phyllosilicates and thus concentrated and protected from oxidising fluids. Therefore, aiding the delivery of biologically relevant molecules to earth, shortly preceding the origin of life.

DOI： 10.7185/geochemlet.2010

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41467-019-10832-7

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PubMed

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2183/pjab.95.013

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PubMed

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1029/2017JB015066

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.epsl.2017.12.014

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.chemgeo.2014.05.002

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jseaes.2012.04.025

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本表面科学会  

DOI： 10.1380/jsssj.33.681

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：TRANS TECH PUBLICATIONS LTD  

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 X 10(6) g for 100 hours at 150 degrees C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). Pb-206/Pb-208 and Pb-207/Pb-208 isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy Pb-208 isotope abundance increased and the light Pb-206 isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of Pb-206/Pb-208 versus Pb-207/Pb-208 proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.

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記述言語：英語   出版者・発行元：日本地質学会  

DOI： 10.14863/geosocabst.2008.0.49.0

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出版者・発行元：日本地球化学会  

沈み込み帯からマントル深部へ物質が移送される際，その化学組成は，共存する流体との間での元素分配を経て変化するが，その化学進化の過程は必ずしもよくわかっていない．本研究では，沈み込む地殻物質に特徴的であり，かつ流体が関与する過程での移動性が高い元素（ホウ素）に注目し，コクチェタフ超高圧変成岩に産する電気石のホウ素同位体組成を検討した．<BR>コクチェタフ産の電気石には，より低変成度の泥質変成岩に産するNa電気石と，最も変成度が高い含ダイアモンド岩の産地にのみ産するK電気石がある．前者のホウ素同位体組成が¹⁰Bに富んでいるのに対して，後者のそれは¹¹Bに富んでいる．地殻物質のみをホウ素の貯蔵庫とする従来のモデルでは，K電気石のホウ素同位体組成を説明できない．そこで，そのホウ素同位体組成が，沈み込んだリソスフェリックマントル中の蛇紋石に由来するという新たなモデルを提案する．

DOI： 10.14862/geochemproc.55.0.67.0

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：宇宙航空研究開発機構  

We have participated in the analytical competition related to the sample-return mission, MUSES-C of the ISAS, to be launched in May 2003 and returned in summer 2007. In this competition, we have determined major and trace element abundances and isotopes (as many as possible), both for two powdered samples provided by the ISAS and for chondrules separated from Allende meteorite as an additional demonstration of our high-spatial resolution analytical capabilities for fragment samples. 100 mg of each of the competition samples, 1C and 2C, were split into two fractions of approximately 30 and 70 mg for the determinations of elemental abundances and the isotope analyses, respectively. The bulk concentrations of 55 elements in each 30 mg sample were analyzed by quadruple-type ICP-MS and sector-type ICP-MS with analytical uncertainties better than 10 percent (1 sigma). B, Pb, Li, Rb, Sr, Sm and Nd were successively separated from the remaining 70 mg of each of the samples, using a novel integrated, multi-ion exchange column chemistry approach, and then the isotopes of these elements were successfully determined by TIMS with analytical errors similar to those for analyses of terrestrial samples. The Sr, Nd, Re and Os isotopic compositions were also analyzed using the remaining aliquots of the sample solutions for trace element analyses by ICP-MS. The results obtained in this study indicate that 1C and 2C samples are probably ordinary chondrite and the Allende meteorite, respectively. However, extreme W, Ta and Nb enrichments in the 1C were probably caused by contamination during sample preparation. Furthermore, both of the samples were extensively contaminated by B from the borosilicate glass container in which the samples were delivered. Five chondrules were separated from Allende meteorite and then sliced into three pieces using a dicing saw. The center slices were used to petrographically determine the mineral phases, compositionally map these phases by SEM-EDX, and obtain quantitative major and trace element compositions (30 elements) by SEM-EDX and ion microprobe. The two outer slices, for which sample masses were less than 1 mg, were chemically treated to obtain the bulk trace elements and isotope compositions of the chondrules. For the chondrule slices, 24 trace elements and Sr and Nd isotopic compositions were determined with extremely small analytical uncertainties by ICP-MS and TIMS (for Sr and Nd, respectively). Based on the analytical experience, including this competition, we believe that all of the analyses carried out could have been completed within 50 days if we could have concentrated on this project alone during that 50-day period. In this report, we describe the analytical techniques employed for the powdered samples and the chondrules, and we present all of the results obtained during the approximately 3-month period of the analytical competition.

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記述言語：日本語   出版者・発行元：日本地質学会  

DOI： 10.14863/geosocabst.2003.0_130_2

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記述言語：日本語   出版者・発行元：特定非営利活動法人 日本火山学会  

DOI： 10.18940/vsj.1994.2.0_156

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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

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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

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記述言語：英語  

DOI： 10.1016/j.lithos.2014.09.007

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

Oxygen isotope compositions are reported for the first time for the Himalayan metabasites of the Kaghan Valley, Pakistan in this study. The highest metamorphic grades are recorded in the north of the valley, near the India-Asia collision boundary, in the form of high-pressure (HP: Group I) and ultrahigh-pressure (UHP: Group II) eclogites. The rocks show a step-wise decrease in grade from the UHP to HP eclogites and amphibolites. The protoliths of these metabasites were the Permian Panjal Trap basalts (ca. 267 +/- 2.4 Ma), which were emplaced along the northern margin of India when it was part of Gondwana. After the break-up of Gondwana, India drifted northward, subducted beneath Asia and underwent UHP metamorphism during the Eocene (ca. 45 +/- 1.2 Ma). At the regional scale, amphibolites, Group I and II eclogites yielded delta O-18 values of +5.84 and +5.91 parts per thousand, +1.66 to +424 parts per thousand, and -2.25 to +0.76 parts per thousand, respectively, relative to VSMOW. On a more local scale, within a single eclogite body, the delta O-18 values were the lowest (-2.25 to-1.44%.) in the central, the best preserved (least retrograded) parts, and show a systematic increase outward into more retrograded rocks, reaching up to +0.12 parts per thousand. These values are significantly lower than the typical mantle values for basalts of + 5.7 +/- 0.3 parts per thousand. The unusually low or negative delta O-18 values in Group II eclogites potentially resulted from hydrothermal alteration of the protoliths by interactions with meteoric water when the Indian plate was at southern high latitudes (similar to 60 degrees S). The stepwise increase in delta O-18 values, among different eclogite bodies in general and at single outcrop-scales in particular, reflects differing degrees of resetting of the oxygen isotope compositions during exhumation-related retrogression. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2014.09.007

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

Metapelitic rocks of the Schistes Lustre's in the Cation Alps, Italy (peak metamorphic conditions of 350-500 degrees C, 1.2-2.0 GPa) and at the UHP Lago di Cignana locality (Valtournenche, Italy; similar to 550 degrees C, 2.5-3.0 GPa) preserve records of prograde devolatilization in their mineral modes and chemistry, contents of volatiles and fluid-mobile elements (elements relatively mobile in aqueous fluids), and B and N isotope compositions. This suite allows study of prograde devolatilization history, across a wide range in metamorphic grade, in metasedimentary rocks that experienced high-P/T prograde paths similar to those experienced in most modern subduction zones.
Across grade, whole-rock samples are in general uniform in their concentrations of relatively fluid-mobile elements N, B, Li, Cs, Ba, and Rb, normalized to the concentrations of the less mobile K2O and Al2O3, showing only hints of loss in several of the highest-grade samples. With increasing grade, ion microprobe analyses of phengites show subtle decrease in B concentration, uniformity in Ba and Cs concentrations, and increase in Li concentrations, the latter likely due to release from chlorite during its breakdown. In one Cignana sample, phengite inclusions in garnets are enriched in B relative to matrix phengite, consistent with either whole-rock B loss after garnet growth or, more likely, closed-system behavior and partitioning of B into paragonite or tourmaline stabilized after garnet growth. In samples with both paragonite and phengite, paragonite shows relative enrichment in B and Sr, and phengite is enriched in Cs, Ba, and presumably also N and Rb (the latter showing strong whole-rock correlations with K2O).
Whole-rock delta N-15 shows a hint of shift to higher values in the highest grade rocks (Cignana) and, accordingly, calculated prograde dehydration histories for appropriate bulk compositions, using the Perple-X database, indicate that significant (similar to 20%) dehydration would for some rocks occur over the temperature interval of 450 to 550 degrees C, largely related to the breakdown of chlorite (and to a lesser extent carpholite). Small amounts of loss of N into these fluids could have resulted in minor shift in delta N-15, with decrease in whole-rock N concentration masked by heterogeneity inherent with the sedimentary protoliths. Partitioning of Cs and Li (possibly also Rb and Ba) from white micas into H2O-rich fluids largely produced by chlorite breakdown could similarly have produced the subtle decreases in the concentrations in these elements noted in several high-grade samples. Neoblastic tourmaline in higher-grade rocks likely sequestered some fraction of the B lost from micas, resulting in a lack of obvious whole-rock B loss to accompany the up-grade trend of decreasing B concentrations in phengite. This tourmaline shows core-to-rim decrease in delta B-11 consistent with growth during small amounts of progressive B loss from phengites.
Taken together, the whole-rock and SIMS data presented here, and the whole-rock dataset of Busigny et al. (2003), demonstrate impressive retention, during prograde forearc devolatilization, of elements thought to be relatively fluid-mobile (particularly H, N, B, Li, Bo, and Cs). Retention of these elements in metasedimentary rocks subducted to depths overlapping those beneath arc volcanic fronts (similar to 90 km estimated for subsolidus, peak Cignana metamorphism) implies their availability for transfer into arc source regions, in aqueous fluids or silicate melts, or into the mantle to depths beyond subarc regions. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2013.01.009

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

Dislocation textures of olivine grains and Pb isotopic compositions (Pb-207/Pb-206 and Pb-208/Pb-206) of olivine-hosted melt inclusions in basaltic lavas from three Hawaiian volcanoes (Kilauea, Mauna Loa, and Koolau) were examined. More than 70% of the blocky olivine grains in the studied samples have a regular-shaped dislocation texture with their dislocation densities exceeding 10(6) cm(-2), and can be considered as deformed olivine. The size distribution of blocky olivine grains shows that more than 99% of blocky olivines coarser than 1.2 mm are identified as deformed olivine. These deformed olivine grains are identified as antecrysts, which originally crystallized from previous stages of magmatism in the same shield, followed by plastic deformation prior to entrainment in the erupted host magmas. This study revealed that entrainment of mantle-derived crystallization products by younger batches of magma is an important part of the evolution of magnesium-rich Hawaiian magma. Lead isotopic compositions of melt inclusions hosted in the olivine antecrysts provide information of the evolutionary history of Hawaiian volcanoes which could not have been accessed if only whole rock analyses were carried out. Antecryst-hosted melt inclusions in Kilauea and Koolau lavas demonstrate that the source components in the melting region changed during shield formation. In particular, evidence of interaction of plume-derived melts and upper mantle was observed in the earliest stage of Koolau magmatism. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2012.07.025

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記述言語：英語  

DOI： 10.1007/s00410-011-0713-5

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記述言語：英語   掲載種別：書評論文，書評，文献紹介等  

DOI： 10.1016/j.jvolgeores.2011.12.011

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記述言語：英語   出版者・発行元：NATL ACAD SCIENCES  

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 mu m, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-mu m-sized craters but also a large number of sub-mu m-to several-mu m-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-mu m-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

DOI： 10.1073/pnas.1116236109

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記述言語：英語   出版者・発行元：NATL ACAD SCIENCES  

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 mu m, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-mu m-sized craters but also a large number of sub-mu m-to several-mu m-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-mu m-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

DOI： 10.1073/pnas.1116236109

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

Measurements of (238)U-(230)Th-(226)Ra disequilibria, Sr-Nd-Pb-Hf isotopes and major-trace elements have been conducted for lavas erupted in the last quarter-millennium at Hekla volcano, Iceland. The volcanic rocks range from basalt to dacite. Most of the lavas (excluding dacitic samples) display limited compositional variations in radiogenic Sr-Nd-Pb-Hf isotopes ((87)Sr/(86)Sr = 0.70319-0.70322; (143)Nd/(144)Nd = 0.51302-0.51305; (206)Ph/(204)Pb = 19.04-19.06; (207)Pb/(204)Pb = 15.53-15.54; (208)Pb/(204)Pb = 38.61-38.65; (176)Hf/(177)Hf = 0.28311-0.28312). All the samples possess ((230)Th/(238)U) disequilibrium with (230)Th excesses, and they show systematic variations in ((230)Th/(232)Th) and ((238)U/(232)Th) ratios. The highest (226)Ra excesses occur in the basalt and most differentiated andesite lavas, while some basaltic-andesite lavas have ((226)Ra/(230)Th) ratio that are close to equilibrium. The (238)U-(230)Th-(226)Ra disequilibria variations cannot be produced by simple closed-system fractional crystallization with radioactive decay of (230)Th and (226)Ra in a magma chamber. A closed-system fractional crystallization model and assimilation and fractional crystallization (AFC) model indicate that the least differentiated basaltic andesites were derived from basalt by fractional crystallization with a differentiation age of similar to 24 +/- 11 kyr, whereas the andesites were formed by assimilation of crustal material and fractionation of the basaltic-andesites within 2 kyr. Apatite is inferred to play a key role in fractionating the parent daughter nuclides in (230)Th-(238)U and (226)Ra-(230)Th to make the observed variations. Our proposed model is that several batches of basaltic-andesite magmas that formed by fractional crystallization of a basaltic melt from a deeper reservoir, were periodically injected into the shallow crust to form individual magma pockets, and subsequently modifying the original magma compositions via simultaneous assimilation and fractional crystallization. The assimilant is the dacitic melt, which formed by partial melting of the crust. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2010.10.001

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

The mechanisms and the timescales of magmatic evolution were investigated for historical lavas from the Askja central volcano in the Dyngjufjoll volcanic massif, Iceland, using major and trace element and Sr, Nd, and Pb isotopic data, as well as U-238-Th-230-Ra-226 systematics. Lavas from the volcano show marked compositional variation from magnesian basalt through ferrobasalt to rhyolite. In the magnesian basalt-ferrobasalt suite (5-10 wt% MgO), consisting of lavas older than 1875 A.D., Sr-87/Sr-86 increases systematically with increasing SiO2 content; this suite is suggested to have evolved in a magma chamber located at similar to 600 MPa through assimilation and fractional crystallization. On the other hand, in the ferrobasalt-rhyolite suite (1-5 wt% MgO), including 1875 A.D. basalt and rhyolite and 20th century lavas, Sr-87/Sr-86 tends to decrease slightly with increasing SiO2 content. It is suggested that a relatively large magma chamber occupied by ferrobasalt magma was present at similar to 100 MPa beneath the Oskjuvatn caldera, and that icelandite and rhyolite magmas were produced by extraction of the less and more evolved interstitial melt, respectively, from the mushy boundary layer along the margin of the ferrobasalt magma chamber, followed by accumulation of the melt to form separate magma bodies. Ferrobasalt and icelandite lavas in the ferrobasalt-rhyolite suite have a significant radioactive disequilibrium in terms of (Ra-226/Th-230), and its systematic decrease with magmatic evolution is considered to reflect aging, along with assimilation and fractional crystallization processes. Using a mass-balance model in which simultaneous fractional crystallization, crustal assimilation, and radioactive decay are taken into account, the timescale for the generation of icelandite magma from ferrobasalt was constrained to be &lt;similar to 3 kyr which is largely dependent on Ra crystal-melt partition coefficients we used. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2010.10.009

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記述言語：英語   出版者・発行元：SPRINGER  

A rare composite xenolith and abundant cumulative pyroxenites obtained from the Mesozoic Fangcheng basalts on the eastern North China Craton record a complex history of melt percolation and circulation in the subcontinental lithospheric mantle. The composite xenolith has a dunite core and an olivine clinopyroxenite rim. The dunite is of cumulative origin and has a granular recrystallized texture and extremely low Mg# [100 Mg/(Mg + Fe) = 81-82] contents in olivines. The olivine clinopyroxenite contains larger clinopyroxene and/or orthopyroxene with a few fine-grained olivine and tiny phlogopite, feldspar, and/or carbonate minerals interstitial to clinopyroxene. The clinopyroxene has low Mg# (83-85). Compositional similarity between dunitic olivine and pyroxenitic one indicates a sequential crystallization of dunite and pyroxenite from a precursor melt. Pyroxenite xenoliths include olivine websterites and clinopyroxenites, both are of cumulative origin. Estimation of the melt from major oxides in olivines and REE concentrations in clinopyroxenes in these composite and pyroxenite xenoliths suggests a derivation from subducted crustal materials, consistent with the highly enriched EMII-like Sr and Nd isotopic ratios observed in the pyroxenites. Occurrence of phlogopite, feldspar and carbonate minerals in some xenoliths requires the melt rich in alkalis (K, Na), silica and volatiles (water and CO(2)) at the latest stage as well, similar to highly silicic and potassic melts. Thus, the occurrence of these composite and pyroxenite xenoliths provides an evidence for voluminous injection of recycled crustal melts into the lithosphere beneath the southeastern North China Craton at the Late Mesozoic, a reason for the rapid lithospheric enrichment in both elemental and isotopic compositions.

DOI： 10.1007/s00531-009-0467-8

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記述言語：英語   出版者・発行元：SPRINGER  

A rare composite xenolith and abundant cumulative pyroxenites obtained from the Mesozoic Fangcheng basalts on the eastern North China Craton record a complex history of melt percolation and circulation in the subcontinental lithospheric mantle. The composite xenolith has a dunite core and an olivine clinopyroxenite rim. The dunite is of cumulative origin and has a granular recrystallized texture and extremely low Mg# [100 Mg/(Mg + Fe) = 81-82] contents in olivines. The olivine clinopyroxenite contains larger clinopyroxene and/or orthopyroxene with a few fine-grained olivine and tiny phlogopite, feldspar, and/or carbonate minerals interstitial to clinopyroxene. The clinopyroxene has low Mg# (83-85). Compositional similarity between dunitic olivine and pyroxenitic one indicates a sequential crystallization of dunite and pyroxenite from a precursor melt. Pyroxenite xenoliths include olivine websterites and clinopyroxenites, both are of cumulative origin. Estimation of the melt from major oxides in olivines and REE concentrations in clinopyroxenes in these composite and pyroxenite xenoliths suggests a derivation from subducted crustal materials, consistent with the highly enriched EMII-like Sr and Nd isotopic ratios observed in the pyroxenites. Occurrence of phlogopite, feldspar and carbonate minerals in some xenoliths requires the melt rich in alkalis (K, Na), silica and volatiles (water and CO(2)) at the latest stage as well, similar to highly silicic and potassic melts. Thus, the occurrence of these composite and pyroxenite xenoliths provides an evidence for voluminous injection of recycled crustal melts into the lithosphere beneath the southeastern North China Craton at the Late Mesozoic, a reason for the rapid lithospheric enrichment in both elemental and isotopic compositions.

DOI： 10.1007/s00531-009-0467-8

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記述言語：英語   出版者・発行元：SPRINGER  

During its 1800-year-long persistent activity the Stromboli volcano has erupted a highly porphyritic (HP) volatile-poor scoriaceous magma and a low porphyritic (LP) volatile-rich pumiceous magma. The HP magma is erupted during normal Strombolian explosions and lava effusions, while the LP one is related to more energetic paroxysms. During the March-April 2003 explosive activity, Stromboli ejected two typologies of juvenile glassy ashes, namely highly vesicular LP shards and volatile-poor HP shards. Their textural and in situ chemical characteristics are used to unravel mutual relationships between HP and LP magmas, as well as magma dynamics within the shallow plumbing system. The mantle-normalized trace element patterns of both ash types show the typical arc-lava pattern; however, HP glasses possess incompatible element concentrations higher than LP glasses, along with Sr and Eu negative anomalies. HP shards are generally characterized by higher Li contents (to similar to 20 ppm) and lower delta Li-7 values (+1.2 to -3.8aEuro degrees) with respect to LP shards (Li contents of 7-14 ppm and delta Li-7 ranging between +4.6 and +0.9aEuro degrees). Fractional crystallization models based on major and trace element compositions, combined with a degassing model based on open-system Rayleigh distillation and on the assumption that D-melt/fluid(Li) &gt; 1, show that abundant (similar to 30%) plagioclase precipitation and variable degrees of degassing can lead the more primitive LP magma to evolve toward a differentiated (isotopically lighter) HP magma ponding in the upper conduit and undergoing slow continuous degassing-induced crystallization. This study also evidences that in March 2003 Stromboli volcano poured out a small early volume of LP magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending LP magma erupted during the April 5 paroxysm. The different ascent rates and cooling rates of the two LP magma batches (i.e., pre- and post-paroxysm) resulted in small, but detectable, differences in their chemical signatures. Finally, this study highlights the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic activity and of Li isotopes as tracers of degassing processes within the shallow plumbing system.

DOI： 10.1007/s00410-009-0441-2

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DOI： 10.1007/s00410-009-0441-2

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記述言語：英語   出版者・発行元：GEOLOGICAL SOC PUBL HOUSE  

Nappes in file southern sector of the Southern Brasilia Belt record suturing of the Paranapanema Block and Socorro-Guaxupe Arc with a subducted passive margin oil the western side of the Sao Francisco Craton. We report secondary ion mass spectrometry U-Pb zircon ages that for the first time constrain the age of. (1) retrograded eclogite from a block along the tectonic contact beneath the uppermost nappe in a stack of passive margin-derived nappes; (2) high-pressure granulite-facies metamorphism in the uppermost passive margin-derived nappe; (3) high-pressure granulite-facies metamorphism in the overlying arc-derived nappe. Rare zircons from a retrograded eclogite yield a (206)Pb/(238)U age of 678 +/- 29 Ma. which we interpret as most likely to (late close-to-peak-P metamorphism and to provide a minimum age for detachment of the overlying passive margin-derived nappe from the subducting plate. Zircon associated with ilmenite in samples from two structural levels in the passive margin-derived high-pressure granulite nappe yields (201)Pb/(238)U ages of 648 +/- 12 and 647 +/- 11 Ma, and Ti-in-zircon crystallization temperatures from c. 860 degrees C down to c. 785 degrees C. but skewed toward the lower part of the range. These data indicate zircon formation during cooling from around peak T to the solidus, consistent with the high-T retrograde P-T path deduced front microstructures linked to phase assemblage fields in isochemical phase diagrams. Rb-Sr multi-mineral-whole-rock isochrons from two samples from close to the bottom of this nappe date formation of a retrograde sillimanite-bearing penetrative fabric to c. 590 Ma at temperatures of c. 750 degrees C (based on Ti-in-quartz thermometry). Rare zircons from leucosome in high-pressure granulite from the overlying arc-derived nappe yield a (206)Pb/(238)U age of 622 +/- 28 Ma and Ti-in-zircon crystallization temperatures from c. 970 degrees C down to c. 820 degrees C, which we interpret to record formation of zircon during cooling from peak high-pressure granulite-facies conditions. These ages indicate that the first stage of craton amalgamation in West Gondwana may have occurred earlier than previously inferred.

DOI： 10.1144/0016-76492008-140

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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 &gt;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

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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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：ELSEVIER SCIENCE BV  

We investigated the oceanic-type Xiongdian high-pressure eclogites in the western part of the Dabie orogen with combined U-Pb, Lu-Hf, Sm-Nd and Ar-Ar geochronology. Three groups of weighted-mean (206)Pb/(238)U ages at 315 +/- 5, 373 +/- 4 and 422 +/- 7 Ma are largely consistent with previous dates. In contrast, Lu-Hf and Sm-Nd isochron dates yield identical ages of 268.9 +/- 6.9 and 271.3 +/- 5.3 Ma. Phengite and amphibole Ar-Ar total fusion analyses give Neoproterozoic apparent ages, which are geologically meaningless due to the presence of excess (40)Ar. Plagioclase inclusions in zircon cores suggest that the Silurian ages likely represent protolith ages, whereas the Carboniferous ages correspond to prograde metamorphism, based on the compositions of garnet inclusions. Despite weakly-preserved prograde major- and trace element zoning in garnet, a combined textural and compositional study reveals that the consistent Lu-Hf and Sm-Nd ages of ca. 270 Ma record a later event of garnet growth and thus mark the termination of high-pressure eclogite-facies metamorphism. The new U-Pb, Lu-Hf and Sm-Nd ages suggest a model of continuous processes from oceanic to continental subduction, pointing to the onset of prograde metamorphism prior to ca. 315 Ma for the subduction of oceanic crust, while the peak eclogite-facies metamorphic episode is constrained to between ca. 315 and 270 Ma. Thus, the initiation of continental subduction is not earlier than ca. 270 Ma. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2009.01.013

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DOI： 10.1144/0016-76492008-140

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DOI： 10.1016/j.lithos.2009.03.017

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

Multi-stage formation of tourmaline occurs in the Hnilec granite-related hydrothermal tin mineralisation system from the Western Carpathians, Slovakia. The tourmalines belong to the schorl-dravite series and have two major stages of formation: the majority crystallized during the first stage (defined as M-stage), forming zoned tourmaline crystals with the cores being generally more Fe, Al, and Mn rich than the rims. During the second stage (defined as L-stage), tourmaline formed as small veins or irregular patches along fractures and cracks in the M-stage tourmaline grains. In the contact metapelites near the granite body, the L-stage tourmalines are more Mg-rich and Fe, Al, Mn depleted than the M-stage tourmalines. in the granites, the L-stage tourmalines have generally similar compositions to those of the M-stage tourmaline rims. The boron isotopic compositions of the M-stage tourmalines vary from -10.3 parts per thousand to -15.4 parts per thousand; with no clear variation between the cores and the rims, however, some of the tourmaline grains from the contact metapelites show a slightly higher delta(11)B in the cores than in the rims. The L-stage tourmalines have lower delta(11)B value of -16.0 parts per thousand to -17.1 parts per thousand. We suggest that these trends reflect a changing fluid source from a dominant magmatic-hydrothermal fluid derived from the granites to a late-stage metamorphic fluid derived from the regional metamorphism (chlorite and biotite zone) in the metapelites. The significantly higher Fe(3+) in the L-stage than the M-stage tourmalines reflect changing redox conditions towards a more oxidising environment. This redox condition change may have important implications for the hydrothermal tin mineralisation in the area. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2008.04.004

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

The Cretaceous Okhotsk-Chukotka volcanic belt (CCVB) is one of the largest subduction-related volcanic provinces of the Earth. It is thought to be related with the subduction of paleo-Pacific plates under the collage of terranes of NE Asia accreted during Jurassic and Early Cretaceous time. The CCVB comprises a remarkably high portion of silicic rocks, up to 80-90% in some segments. Within the Central Chukotka segment of the belt, volcanic sequences reveal a rather uniform Ar-40/Ar-39 and U-Pb isotopic age of near 89-87 Ma. But the felsic volcanic unit with coeval subsurface intrusives named the 'Berlozhya magmatic assemblage' (BMA) yields much older zircon U-Pb ages (146.0+/-2.4 for rhyolitic tuff and 145.5+/-1.8 Ma for related granodiorite). The relationship of the BMA with the active boundary between the Chukotka-Arctic Alaska microcontinent and the Anyui-Angayucham oceanic basin is suggested. BMA rocks seem to be undeformed, and their age puts constraints on the timing of main compressional events in the North Chukotka area.
We present analytical data for both BMA and OCVB silicic magmatic rocks, including the first isotopic compositions of Sr, Nd, Pb, and Hf for the 1500 km long northern part of the CCVB. We infer that felsic magmas of both BMA and OCVB were produced by the melting of the continental crust, without a significant direct contribution from mantle sources. However, the crustal protolith could contain some ancient island arc complexes, which affected the chemical and isotopic composition of magmatic derivatives. The BMA exhibits a relatively uniform isotopic composition (Sr-87/Sr-86(i)=0.7057 to 0.7070, epsilon(i)(Nd)=-0.51 to -0.12, epsilon(i)(Hf)=4.41 to 4.92, Pb-206/Pb-204(i)=18.50 to 18.57, and Pb-208/Pb-204(i)=38.23 to 38.31), and its chemical diversity likely results from crystal fractionation. The protolith of CCVB rhyolites has more variable isotopic characteristics (Sr-87/Sr-86(i)=0.7032 to 0.7082, epsilon(i)(Nd)=-4.06 to -2.84, epsilon(i)(Hf)=-1.56 to 3.77, Pb-206/Pb-204(i)=18.56 to 18.81, and Pb-208/Pb-204(i)=38.21 to 38.63), and reveals at least three end-members. Each of them is distinct from the source of the Berlozhya assemblage, thus suggestive of compositional layering of the crust. Nd and Hf model ages of all studied rocks correspond to Neoproterozoic. The estimated Nd model age of the OCVB protolith is slightly older than that for the BMA, but both fall into the Neoproterozoic interval (1000 to 800 Ma). (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2008.05.005

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記述言語：英語   出版者・発行元：TAYLOR & FRANCIS LTD  

The sedimentation of isotope atoms hits been realized in monoatomic liquid and solid Se. It was observed that the concentration ratio Se-82/Se-76 increased by % level in the specimen ultracentrifuged at 0.7-0.9 million G under liquid and solid states. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion, and suggests its possible application to isotope separation by condensed matter centrifugation.

DOI： 10.1080/00223131.2008.10875988

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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

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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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

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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 &gt; 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

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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

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DOI： 10.1007/s00410-007-0228-2

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DOI： 10.1016/j.gca.2008.05.002

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DOI： 10.1016/j.lithos.2008.05.005

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DOI： 10.1016/j.lithos.2008.04.004

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DOI： 10.1080/00223131.2008.10875989

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

A strong gravitational field resulted in the sedimentation of isotope atoms in monatomic liquid. The concentration ratio (82)Se/(76)Se increased by greater than 3.5% in specimen ultracentrifuged at (0.7-0.9) x 10(6) G and at 300 degrees C. The recovered sample had a feather-shaped crystalline morphology. The concentration gradient was nearly twice that of the steady state analytical result (ideal gas system), indicating a nonideal system diffusion. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion and suggestes its possible application to isotope separation, crystalline control, and matter dynamics in massive star. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2819070

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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

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   出版者・発行元：V H WINSTON & SON INC  

A highly fertile mantle xenolith entrained in the Upper Cretaceous Daxizhuang basalt, Shandong Province, China provides petrological evidence for reaction between basaltic melt and refractory peridotite in Mesozoic lithospheric mantle beneath the eastern North China craton. The xenolith is zoned with a Iherzolite core, a sheared wehrlite mantle, and a reactant rim. The lherzolite has a medium-grained granular texture and contains olivine, orthopyroxene, clinopyroxene, and spinel with low Mg# values (87). This is the lowest Value observed globally in mantle xenoliths entrained in both kimberlites and basalts from old cratons, but is close to low-Mg# spinel lherzolites entrained in adjacent region of the eastern North China craton. The wehrlite mantle shows clear orientation and foliation of constituent olivine and clinopyroxene. The reactant rim displays a symplectite texture of fine-grained olivine, clinopyroxene, and spinel, and is characterized by LREF-enriched patterns. Orthopyroxene is lacking from the sheared mantle and reactant rim. Clear zoning and systematic core-run variations in ma jor and trace elements of the constituent minerals demonstrate the Occurrence of the refertilization through the melt-peridotite reaction in the xenolith. This reaction may have produced the low-Mg# peridotite from a high-Mg# protolith and could be an important mechanism for the change of the subcontinental lithospheric mantle from a Paleozoic refractory mantle to a Late Mesozoic fertile mantle.

DOI： 10.2747/0020-6814.49.7.658

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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

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

DOI： 10.1093/petrology/egm019

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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 (&lt; 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 (&lt; 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

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DOI： 10.1016/j.gca.2007.07.006

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DOI： 10.1063/1.2819070

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DOI： 10.1016/j.chemgeo.2006.08.009

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DOI： 10.2138/am.2007.2343

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/j.gca.2006.06.1246

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1016/j.gca.2006.06.650

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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

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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

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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

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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

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DOI： 10.1016/j.gca.2006.02.027

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DOI： 10.1016/j.jafrearsci.2006.03.004

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DOI： 10.1007/s00710-005-0093-5

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DOI： 10.1016/j.gca.2006.06.650

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DOI： 10.1016/j.gca.2006.06.1246

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記述言語：英語   出版者・発行元：V H WINSTON & SON INC  

Felsic veins several cm thick to bodies several hundreds of m wide are sporadically distributed in the Kamila amphibolites of the Kohistan are sequence. Some small dikes (less than one m thick) were deformed together with ductile deformation of wall-rock amphibolites; other small underformed dikes crosscut foliation in the amphibolites. Large granitic intrusive bodies include gneissose and massive varieties. Ion-microprobe U-Pb dating of zircon grains reveal ages as follows: three deformed dikes, 107.7 +/- 1.8 Ma, 94.0 +/- 1.9 Ma, 81.0 +/- 1.6 Ma; a single gneissose granitic body, 89.5 +/- 4.2 Ma; three underformed dikes, 82.0 +/- 2.0 Ma, 80.6 +/- 4.5 Ma, 75.8 +/- 1.7 Ma; a massive granitic body, 75.7 +/- 2.2 Ma; and a foliated amphidolite xenolith in the massive granitic body, 110.7 +/- 4.9 Ma. Ages of the deformed dikes, the gneissose granitic body, and the amphibolite xenolith indicate that ductile deformation in the lower crust of the Kohistan arc took place episodically or successively during the period from 107 to 81 Ma. Ages of the underformed dikes and the massive granitic body indicate that ductile deformation ceases prior to 80 Ma. We conclude that the ductile deformation events did not extend beyond the time of Asia-Kohistan collision.

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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

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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DOI： 10.1103/PhysRevB.72.024108

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記述言語：英語   出版者・発行元：AMER GEOPHYSICAL UNION  

We demonstrate an approach to examining the metamorphic history of subducting oceanic crust that can complement records of subduction zone chemical cycling derived from studies of igneous rocks produced at volcanic arcs. By merging methods utilizing garnet zoning to establish prograde reaction histories with in situ high-resolution trace element geochemistry, and application to coesite-bearing mafic eclogites representing subduction to depths beneath arcs, we are able to directly identify geochemical manifestations of reactions contributing to element mobility in the subducting slab that are only inferred in studies of volcanic arcs or theoretical metamorphic models. Specifically, we identify a prograde metamorphic reaction, based solely on the zoning of geochemistry and mineral inclusions within garnet, and infer that these features are a record of the breakdown of coexisting clinozoisite + titanite and probable liberation of trace element-laden fluid from the rock during prograde metamorphism. We are then able to assign a specific depth interval for the reaction through calculation of the P-T dependence of the reaction for these eclogites and comparison with a published P-T trajectory. Because of the robust preservation of records of petrologic and geochemical processes by garnet, this methodology is particularly suited for study of ultrahigh-pressure (UHP) eclogites, in which severe retrograde alteration ( generally related to exhumation) commonly obscures prograde history.

DOI： 10.1029/2004GC000746

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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 &lt;1.2%, &lt;1.6%, and &lt;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

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記述言語：英語  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.14824/jampeg.2004.0.57.0

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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

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DOI： 10.1029/2004GC000746

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DOI： 10.1016/j.chemgeo.2004.08.050

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

Pre-emption processes are investigated for magmas erupted in 1983 from Miyake-jima volcano, which is one of the most active volcanoes in Japan. The whole-rock compositional trends of the eruptive products are principally smooth and linear. Magmas erupted from some fissures have compositions that deviate from the main linear trend. Phenocryst contents of samples displaced from the linear compositional trends are significantly lower than those of samples on the main trends. Anorthite-rich plagioclase phenocrysts, present throughout the 1983 products, are too calcic to have crystallized from the erupted magma composition, and were derived from a basaltic magma through magma mixing. Although the linear whole-rock composition trends favor simple two-component magma mixing.. this cannot explain the presence of samples that deviate from the main trend. Instead, the observed composition trends were formed by mixing of a homogeneous basaltic magma with andesitic magmas exhibiting compositional diversity. The original linear composition trends of the andesitic end-member magma were rotated and shifted to the direction of the basaltic end-member magma by magma mixing. The samples out of the main trends represent magmas with less basaltic component than those on the trend. The density and viscosity of the basaltic end-member magma were comparable with those of the andesitic end-member magmas. The basaltic magma, discharged from one magma chamber at similar to2 kbar pressure, was injected into a magma chamber at lower pressure occupied by the chemically zoned andesite magma (similar to1 kbar), and possibly as a fountain. To establish the characteristic mixing trend of the 1983 magma, the basaltic component must have been distributed systematically in the zoned andesite magma. A requirement is that the basaltic magma spread laterally and mixed with the andesite magma at various levels of ascent of the fountain in the host andesite magma. Analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1 kbar magma chamber.

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

DOI： 10.1130/0091-7613(2003)031<0589:FOTSFP>2.0.CO;2

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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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：AMER GEOPHYSICAL UNION  

U-238-Th-230-Ra-226 systematics in lavas from Miyakejima volcano, Japan, are presented to estimate the timescale of magmatic processes beneath an island arc. Miyakejima volcano has four recent eruptive stages (Stages 1-4) starting &gt;7000 BP. U-238-Th-230-Ra-226 disequilibria observed in lavas with large U-238 and Ra-226 excesses imply metasomatism of depleted mantle by fluid-related processes. This metasomatism is also suggested by trace element and Sr-Nd-Pb isotopic systematics in the same lavas. In the equiline diagram, the trends for two magmatic stages (Stages 1 and 2) are regarded as two different isochrons with a common initial (Th-230/Th-232) ratio, although the trend for Stages 3 and 4 is a magma mixing line. Our model calculations show that slab-derived fluids can deliver some Th and a very rapid ascent time of the slab components in the mantle wedge (&lt;7 kyr) is inferred. This rapid ascent can be explained by nearly instantaneous material transport in the mantle wedge by a hydrofracture model for fluid and a channel flow model for melt. Such a timescale estimate is not increased even if melting processes that enhance Ra-226 are taken into account. The age difference in the equiline diagram corresponds to the interval of individual fluid-release events (13 kyr between Stages 1 and 2, and 5 kyr between Stages 2 and 3). Thus fluid release from the slab and subsequent magma generation occur as episodic events on a several-kiloyear timescale.

DOI： 10.1029/2002JB002103

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DOI： 10.1029/2002JB002103

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記述言語：英語   出版者・発行元：JAPAN ACAD  

We present U-238-Th-230-Ra-226 systematics in lavas from Miyakejima volcano, Izu arc, Japan, together with major element, trace element and Sr-Nd-Pb isotopic compositions, to estimate the timescale of magmatic processes beneath an island arc. U-238-Th-230-Ra-226 disequilibria observed in Miyakejima lavas with large excesses of U-238 and Ra-226 to Th-230 imply metasomatism of depleted mantle by fluid related processes. Our data reveal that fluid components released from the slab ascend rapidly through the mantle wedge (&gt; 50 m/yr), and that individual stages of subaerial volcanism are induced by flushing of different fluid batches to the mantle wedge with a periodicity of 1-13 kyr. This indicates that arc magmatism is controlled by pulsed release of fluid from the slab occurring on such a small timescale, which might be related to the occurrence of earthquakes in the subducting slab.

DOI： 10.2183/pjab.78.190

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記述言語：英語  

We present 238U-230Th-226Ra systematics in lavas from Miyakejima volcano, Izu arc, Japan, together with major element, trace element and Sr-Nd-Pb isotopic compositions, to estimate the timescale of magmatic processes beneath an island arc. 238U-230Th- 226Ra disequilibria observed in Miyakejima lavas with large excesses of 238U and 226Ra to 230Th imply metasomatism of depleted mantle by fluid related processes. Our data reveal that fluid components released from the slab ascend rapidly through the mantle wedge (&gt
50 m/yr), and that individual stages of subaerial volcanism are induced by flushing of different fluid batches to the mantle wedge with a periodicity of 1-13 kyr. This indicates that arc magmatism is controlled by pulsed release of fluid from the slab occurring on such a small timescale, which might be related to the occurrence of earthquakes in the subducting slab.

DOI： 10.2183/pjab.78.190

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   掲載種別：研究発表ペーパー・要旨（国際会議）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

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記述言語：英語   出版者・発行元：JAPAN ACAD  

We improved the U-Pb zircon dating method employing HR-SIMS by applying i) preparation of precise and homogeneous zircon standards by ID-TIMS, ii) simultaneous analysis of Pb isotopes by multi-collection system, and iii) use of a highly focused primary ion beam as small as 5 mum in diameter. Using the improved HR-SIMS technique, U-Pb ages of zircons in an eclogite xenolith from the Colorado Plateau were determined. Zircon occurs as small inclusions (&lt; 20 mum) in most constituent minerals. Ten zircons were measured, and the concordant analyses of these zircon data yielded a weighted mean value of 65.2 +/- 0.7 Ma for the age of crystallization Petrographic and geochemical observations suggest that this zircon age represents the age of initial subduction of basaltic oceanic crust. We conclude that the eclogite xenolith was a fragment of basaltic oceanic crust subducted to &gt; 90 km depth along a cold geotherm with a subduction rate of &gt; 2 cm/y in Tertiary.

DOI： 10.2183/pjab.78.51

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記述言語：英語   出版者・発行元：GEOSTANDARDS  

A simple and accurate method for the determination of Cr, Ni, Cu and Zn at mug g(-1) levels in milligram-sized bulk silicate materials is reported using isotope dilution high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS) with a flow injection system. Silicate samples with Cr, Ni, Cu and Zn spikes were digested with HF-HBr and Br-2, and subsequently decomposed at 518 K in a Teflon bomb. In this procedure, all sulfides and chromite, major hosts of these elements, were completely decomposed, thus allowing for isotope equilibration between the sample and spike. Magnesium and A fluorides formed after the digestion of the sample were removed by centrifugation, and the supernatant was directly aspirated into a HR-ICIP-MS at a mass resolution of 7500, where interfering oxide ions, ArO+, CaO+, TiO+, CrO+ and VO+, were separated from Cr+, Ni+, Cu+ and Zn+. No matrix effects were observed down to a dilution factor of 50. Detection limits for these elements in silicate samples were &lt; 0.04 mug g-1. The effectiveness of the technique was demonstrated by the analysis of 13 to 40 mg test portions of USGS and GSJ silicate reference materials with a major element composition ranging from andesite to peridotite, in addition to 8-23 mg of the Smithsonian reference Allende. Both the reproducibility and the deviation from the reference value for most reference materials of various rock types were ( 9%, and thus confirm that the method gives accurate analytical results for small sample sizes over a wide range of Cr, Ni, Cu and Zn contents. This method is, therefore, suitable for analysing small and/or precious bulk samples, such as meteorites, mantle peridotites and mineral separates, and for the characterisation of silicate and sulfide minerals for use as calibration samples in secondary ion mass spectrometry or laser ablation ICP-MS.

DOI： 10.1111/j.1751-908X.2002.tb00622.x

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DOI： 10.2183/pjab.78.51

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

Major and trace element, and Sr, Nd and Pb isotopic compositions were determined for whole-rock samples from the 'isotopically anomalous' Akagi volcano in the volcanic front of the NE Japan arc. Sr and Nd isotopic compositions of phenocrysts were also analyzed together with their major and trace element compositions. Compared with the other volcanoes from the volcanic front, the whole-rock isotope compositions of Akagi show highly enriched characteristics; Sr-87/Sr-86 = 0.7060-0.7088, epsilon (Nd) = -0.40 to -8.6, and Pb-208/Pb-204 = 38.4-38.8. The rare earth element (REE) patterns are characterized by heavy REE (HREE) depletions with U-shaped patterns from middle REE (MREE) to HREE, suggesting that amphibole fractionation was induced by a reaction between clinopyroxene and H2O-rich magma in the lower crust. The integrated isotope and trace elements systematics, and tectonic structure beneath Akagi volcano, suggest that lower-crustal assimilation by the H2O-rich primary magma could have been affected by the double subduction of Philippine Sea and Pacific oceanic plates. This double subduction could have supplied larger amounts of water to the magma source region in the wedge mantle than in the case of a single subduction zone. Significant differences in isotopic compositions are observed between phenocrysts and the coexisting melts. Such isotopic disequilibrium may have resulted from magma mixing between an isotopically depleted aphyric and an enriched porphyritic magma in a shallow magma chamber. The geochemical characteristics of these end-member magmas were retained in the lower crust, despite differing extents of lower-crustal assimilation by the H2O-rich magmas.

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記述言語：英語   出版者・発行元：OXFORD UNIV PRESS  

Major and trace element, and Sr, Nd and Pb isotopic compositions were determined for whole-rock samples from the 'isotopically anomalous' Akagi volcano in the volcanic front of the NE Japan arc. Sr and Nd isotopic compositions of phenocrysts were also analyzed together with their major and trace element compositions. Compared with the other volcanoes from the volcanic front, the whole-rock isotope compositions of Akagi show highly enriched characteristics; Sr-87/Sr-86 = 0.7060-0.7088, epsilon (Nd) = -0.40 to -8.6, and Pb-208/Pb-204 = 38.4-38.8. The rare earth element (REE) patterns are characterized by heavy REE (HREE) depletions with U-shaped patterns from middle REE (MREE) to HREE, suggesting that amphibole fractionation was induced by a reaction between clinopyroxene and H2O-rich magma in the lower crust. The integrated isotope and trace elements systematics, and tectonic structure beneath Akagi volcano, suggest that lower-crustal assimilation by the H2O-rich primary magma could have been affected by the double subduction of Philippine Sea and Pacific oceanic plates. This double subduction could have supplied larger amounts of water to the magma source region in the wedge mantle than in the case of a single subduction zone. Significant differences in isotopic compositions are observed between phenocrysts and the coexisting melts. Such isotopic disequilibrium may have resulted from magma mixing between an isotopically depleted aphyric and an enriched porphyritic magma in a shallow magma chamber. The geochemical characteristics of these end-member magmas were retained in the lower crust, despite differing extents of lower-crustal assimilation by the H2O-rich magmas.

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記述言語：英語   出版者・発行元：JAPAN ACAD  

Isotopic compositions of Sr, Nd and Pb and REE concentrations have been determined for samples from ''isotopically anomalous'' Akagi volcano locating on the Volcanic front of Northeast Japan Are. The Sr isotopic compositions show a large variation with highly enriched isotope character (Sr-87/Sr-86=0.7060 to 0.7088) compared to those from other volcanoes on the front. The Nd isotopic compositions, ranging from epsilon(Nd) = -0.40 to -8.6, have a negative correlation with the Sr isotopic compositions. The Pb isotopic data along with Sr and Nd isotope systematics clearly indicate that the isotopic variations of Akagi volcano were caused by a two-component mixing between an end member isotopically similar to the primary magma on the volcanic front of Northeast Japan Are and a lower crustal component. Chondrite-normalized REE patterns of Akagi samples show U-shaped, HREE-depleted pattern with positive Eu anomaly. Such REE features may have been developed by fractionation of amphibole formed by the reaction between a fluid-rich magma and clinopyroxene in granulitic lower crust. The fluid-rich magma could be originated from a highly metasomatized mantle wedge caused by the dehydration of oceanic slabs of the Pacific plate and the overlapping Philippine Sea Plate. Such a unique tectonic setting could result in higher water supply to the source region of magma than normal circumstances and thereby generating fluid-rich magma which could enhance assimilation of lower crust beneath Akagi volcano.

DOI： 10.2183/pjab.73.69

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記述言語：英語   出版者・発行元：JAPAN ACAD  

Isotopic compositions of Sr, Nd and Pb and REE concentrations have been determined for samples from ''isotopically anomalous'' Akagi volcano locating on the Volcanic front of Northeast Japan Are. The Sr isotopic compositions show a large variation with highly enriched isotope character (Sr-87/Sr-86=0.7060 to 0.7088) compared to those from other volcanoes on the front. The Nd isotopic compositions, ranging from epsilon(Nd) = -0.40 to -8.6, have a negative correlation with the Sr isotopic compositions. The Pb isotopic data along with Sr and Nd isotope systematics clearly indicate that the isotopic variations of Akagi volcano were caused by a two-component mixing between an end member isotopically similar to the primary magma on the volcanic front of Northeast Japan Are and a lower crustal component. Chondrite-normalized REE patterns of Akagi samples show U-shaped, HREE-depleted pattern with positive Eu anomaly. Such REE features may have been developed by fractionation of amphibole formed by the reaction between a fluid-rich magma and clinopyroxene in granulitic lower crust. The fluid-rich magma could be originated from a highly metasomatized mantle wedge caused by the dehydration of oceanic slabs of the Pacific plate and the overlapping Philippine Sea Plate. Such a unique tectonic setting could result in higher water supply to the source region of magma than normal circumstances and thereby generating fluid-rich magma which could enhance assimilation of lower crust beneath Akagi volcano.

DOI： 10.2183/pjab.73.69

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DOI： 10.2183/pjab.73.69

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