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Zircon is the most useful mineral for studies in U-Pb geochronology and Hf and O isotope geochemistry. Matrix effect is a major problem of the microbeam techniques such as SIMS and LA-(MC)-ICPMS. Therefore, external standardization using well-characterized natural zircon standards is fundamental for accurate microbeam measurements. While the isotopic geochronology and geochemistry laboratories equipped with microbeam analytical facilities have been increasingly established in China during the past decade, applications of the isotopic microanalysis are still limited due to shortage of available standards. We report here the Qinghu zircon as a potential new working reference for microbeam analysis of zircon U-Pb age and O-Hf isotopes. This zircon was separated from the Qinghu quartz monzonite from the western Nanling Range, Southeast China. It is fairly homogeneous in U-Pb age and Hf and O isotopes in terms of large amounts of mircobeam measurements by LA-MC-ICPMS and SIMS at the scales of 20–60 μm. SIMS measurements yield consistent 206Pb/ 238U age within analytical uncertainties with that obtained by ID-TIMS. Precise determinations of O isotopes by IRMS and Hf isotopes by solution MC-ICPMS are in good agreement with the statistical mean of microbeam measurements. We recommend U-Pb age of = 159.5 ± 0.2 Ma (2SE), δ18O = 5.4‰± 0.2‰ (2SD) and 176Hf/ 177Hf = 0.283002 ± 0.000004 (2SD) as the best reference values for the Qinghu zircon. [ABSTRACT FROM AUTHOR]

An atmospheric pressure needle plasma is generated with a hollowneedle-plate dielectric barrier discharge, and the plasma parameters are measured by optical emission spectroscopy. The length of the needle plasma reaches 3 cm with an argon flow rate in the range from 3.5 to 6.1 ml/min when the applied voltage is 7.2 kV. The spatial distribution of oxygen-atom spectral-line intensity indicates that there is a large concentration of excited oxygen atoms in the middle of the plasma. Gas temperature is estimated by simulating the spectrum of OH radical around 309 nm. The spatial distribution of gas temperature along the plasma is uniform. Gas temperature decreases with the increase in argon flow rate. Electron density determined by the Stark broadening of H\alpha is in the range from 5.8 \times 10^14 to 6.0 \times 10^14\ \cm^-3 when the electron temperature is 1–4 eV. The application of plasma in the modification of material surface is demonstrated. [ABSTRACT FROM PUBLISHER]

- Oxygen three-isotope ratios of three anhydrous chondritic interplanetary dust particles (IDPs) were analyzed using an ion microprobe with a 2 μm small beam. The three anhydrous IDPs show Δ17O values ranging from −5‰ to +1‰, which overlap with those of ferromagnesian silicate particles from comet Wild 2 and anhydrous porous IDPs. For the first time, internal oxygen isotope heterogeneity was resolved in two IDPs at the level of a few per mil in Δ17O values. Anhydrous IDPs are loose aggregates of fine-grained silicates (≤3 μm in this study), with only a few coarse-grained silicates (2-20 μm in this study). On the other hand, Wild 2 particles analyzed so far show relatively coarse-grained (≥ few μm) igneous textures. If anhydrous IDPs represent fine-grained particles from comets, the similar Δ17O values between anhydrous IDPs and Wild 2 particles may imply that oxygen isotope ratios in cometary crystalline silicates are similar, independent of crystal sizes and their textures. The range of Δ17O values of the three anhydrous IDPs overlaps also with that of chondrules in carbonaceous chondrites, suggesting a genetic link between cometary dust particles (Wild 2 particles and most anhydrous IDPs) and carbonaceous chondrite chondrules. [ABSTRACT FROM AUTHOR]