Showing papers by "Eizo Nakamura published in 2010"

Chromium isotope systematics of achondrites: chronology and isotopic heterogeneity of the inner solar system bodies

Abstract: The standard planetary formation models assume that primitive materials, such as carbonaceous chondrites, are the precursor materials of evolved planetesimals. Past chronological studies have revealed that planetesimals of several hundred kilometers in size, such as the Howardite-Eucrite-Diogenite (HED) parent body (Vesta) and angrite parent body, began their differentiation as early as ~3 million years of the solar system formation, and continued for at least several million years. However, the timescale of planetesimal formation in distinct regions of the inner solar system, as well as the isotopic characteristics of the reservoirs from which they evolved, remains unclear. Here we present the first report for the precise 53Mn-53Cr ages of monomict ureilites. Chemically separated phases from one monomict ureilite (NWA 766) yielded the Mn-Cr age of 4564.60 ± 0.67 Ma, identical within error to the oldest age preserved in other achondrites, such as angrites and eucrites. The 54Cr isotopic data for this and seven additional bulk ureilites show homogeneous e54Cr of ~–0.9, a value distinct from other achondrites and chondrites. Using the e54Cr signatures of Earth, Mars, and Vesta (HED), we noticed a linear decrease in the e54Cr value with the heliocentric distance in the inner region of the solar system. If this trend can be extrapolated into the outer asteroid belt, the e54Cr signatures of monomict ureilites will place the position of the ureilite parent body at ~2.8 AU. These observations imply that the differentiation of achondrite parent bodies began nearly simultaneously at ~4565 Ma in different regions of the inner solar system. The distinct e54Cr value between ureilite and carbonaceous chondrite also implies that a genetic link commonly proposed between the two is unlikely.

53Mn-53Cr CHRONOMETRY OF CB CHONDRITE: EVIDENCE FOR UNIFORM DISTRIBUTION OF 53Mn IN THE EARLY SOLAR SYSTEM

Abstract: High-precision Cr isotope ratios for chondrules and metal grain separated from CB chondrite Gujba were determined. The e54Cr values (eiCr = [(iCr/52Cr)sample/(iCr/52Cr)standard – 1] × 104) for all samples were identical within the analytical uncertainty, with a mean value of +1.29 ± 0.02. Uniform e54Cr signatures of both chondrules and metal grains imply that the Cr isotope systematics of the meteorite was once completely equilibrated. The e53Cr values of the chondrules and metal grain, on the other hand, display a strong correlation with the 55Mn/52Cr ratio. The 53Mn/55Mn calculated from the slope of the isochron is (3.18 ± 0.52) × 10–6. This corresponds to absolute ages of 4563.7 ± 1.2 Ma and 4563.5 ± 1.1 Ma using angrites D'Orbigny and LEW 86010, respectively, as time anchors. These ages are consistent with the ages obtained using other short- and long-lived radio nuclides, supporting the uniform distribution of 53Mn in the early solar nebula.

Protracted oceanic subduction prior to continental subduction: New Lu-Hf and Sm-Nd geochronology of oceanic-type high-pressure eclogite in the western Dabie orogen

Abstract: Oceanic-type high-pressure eclogite from the Huwan melange in the western part of the Dabie orogen, north of the classic ultrahigh-pressure terrane, has been investigated with combined Lu-Hf and Sm-Nd geochronology. The eclogites are thought to have formed during the subduction of oceanic crust prior to the subduction of the Yangtze craton beneath the North China block. Garnet Lu-Hf and Sm-Nd garnet-whole rock dates yield similar ages of 257.4 ± 1.4 and 252.5 ± 2.7 Ma, the youngest ages reported thus far from this melange. Despite the partially preserved prograde major- and trace-element zoning in garnets, the Lu-Hf and Sm-Nd ages mostly reflect the high-pressure eclogite-facies metamorphism instead of the early phase of garnet growth. The data define a new high-pressure age population for the Dabie orogen, which provides a more detailed insight into the subduction history of the Yangtze craton before continental collision. The new Lu-Hf and Sm-Nd dates for these oceanic-type eclogites, combined with existing geochronological information, range from 315 to 253 Ma. This broad interval suggests that the overall subduction of oceanic crust occurred over a period of ~60 Ma and that different slices with distinct pressure-temperature histories underwent HP metamorphism at distinct times. A model of a continuous evolution from oceanic to continental subduction is favored, and the onset of the deeply continental subduction occurred probably not before ca. 257 Ma.

Degassing, crystallization and eruption dynamics at Stromboli: trace element and lithium isotopic evidence from 2003 ashes

Abstract: 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 ~20 ppm) and lower δ7Li values (+1.2 to −3.8‰) with respect to LP shards (Li contents of 7–14 ppm and δ7Li ranging between +4.6 and +0.9‰). 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 melt/fluidDLi > 1, show that abundant (~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.

Precise isotopic determination of Hf and Pb at sub-nano gram levels by MC-ICP-MS employing a newly designed sample cone and a pre-amplifier with a 1012 ohm register

Abstract: Precise isotopic determination methods for Hf and Pb at sub-nano gram levels have been undertaken for this contribution utilizing the Neptune multiple collector ICP-MS (MC-ICP-MS) with a newly designed sample cone (the Jet cone) and a new pre-amplifier with a highly-resistive register of 1012 ohm. The Jet cone enhanced sensitivities 1.6 and 3 times for Hf and Pb, respectively. The Jet cone showed no significant improvements in reproducibility of Hf isotope analysis at >1 ng compared to the normal cone, but the reproducibility improved considerably by half when Hf concentration of <1 ng was measured. Thus, 0.3 and 0.8 ng of Hf can yield reproducibility (2SD in e-unit) of 3 and 1.7, respectively. Reproducibility (RSD) of 207Pb/206Pb, 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb were 0.026, 0.28, 0.33 and 0.36% using total Pb of 0.025 ng, and 0.02, 0.10, 0.10 and 0.08% using 0.05 ng, respectively. Thus, the Jet cone with the new pre-amplifier showed the best performance compared to the normal cone and pre-amplifier and are similar or even better than those obtained by the 202Pb-205Pb double-spike TIMS or multi-ion counting ICP-MS techniques.

Determination of Fluorine and Chlorine by Pyrohydrolysis and Ion Chromatography: Comparison with Alkaline Fusion Digestion and Ion Chromatography

Abstract: Une methode de determination des teneurs en F et cl des materiaux silicates par pyrohydrolyse et chromatographie ionique (CI) est decrite. La pyrohydrolyse implique le melange entre un echantillon pulverise (~ 40 mg) et du V 2 O 5 (~ 160 mg) et un chauffage a 1 100 °C sous un flux d'oxygene humide dans un tube de quartz. Les rendements du F et du Cl ont ete d'environ 97% en utilisant une solution standard de NaF + NaCl. Les limites de detection de la methode Cl-pyrohydrolyse pour les echantillons silicates ont ete respectivement de 0.36 et 0.69 μg g -1 pour F et Cl. Les concentrations en F et Cl ont ete determinees dans les materiaux de reference JB-2, JB-3 et JA-1 du GSJ; BCR-2, BHVO-1, BHVO-2, AGV-1 et AGV-2 de l'USGS et dans les verres de reference NIST SRM 610, 612 et 614. Les precisions (RSD) pour les determinations du F ont variees entre 1 et 13% (sauf pour le NIST SRM 614) et entre 2 et 19% dans le cas de celles du Cl. Elles dependent de la concentration et de la correction du blanc. La plupart des resultats obtenus dans cette etude sont en bon accord avec ceux des etudes precedentes. En comparaison, la methode de fusion utilisant le couple Na 2 CO 3 + ZnO a 900 °C montre que les rendements de F et Cl par fusion alcaline diminuent systematiquement avec la duree de fusion. Les rendements ont ete respectivement de 84 et 83% pour JB-3, ce qui sous entend une perte de F et de Cl durant cette fusion alcaline.

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

Abstract: 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 CO2) 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.

Diagnostic system for carcinogenicity and diagnostic method for carcinogencity

Abstract: A diagnostic system for carcinogenicity diagnoses a risk of developing cancer due to a radioactive material deposited in a human body. The system includes a detecting apparatus that detects radiations emitted from the radioactive material; and a determining apparatus that obtains a dose of the radiations detected by the detecting apparatus and determines the risk based on the dose.

Filter and air cleaner

Abstract: There is provided a filter for filtering gas or liquid, wherein a constituent material of the filter contains a protein that absorbs iron, radium, or heavy metal (except iron), the constituent material is an iron-containing fiber body 4, the iron-containing fiber body 4 is a fiber body including iron or a fiber body 41 on which iron is supported, and the protein is ferritin or hemosiderin and bound to iron of the iron-containing fiber body 4.

Metal recovery device

Abstract: There is provided a metal recovery device 10 for removing and recovering predetermined metal, from a liquid to be processed, by passing the liquid to be processed through a filter 41, wherein a constituent material of the filter 41 contains a protein that absorbs iron, radium, or heavy metal (except iron).