Accurate determination of the absolute ages of the oldest Solar System objectschondrules and Ca-Al-rich inclusions (CAIs), requires knowledge of their 238 U/ 235 U ratios. This ratio was assumed to be invariant in all U-Pb dating of meteorites so far, but the recent discovery of U isotope variations in CAIs (Brennecka et al. 2010a) shows that this assumption is invalid. We present the first combined high precision U and Pb isotopic data for a CAI, and U isotopic data for chondrules and whole rock fractions of the Allende meteorite. The Pb-Pb isochron age of the CAI SJ101 is 4567.18±0.50 Ma, calculated using the measured 238 U/ 235 U=137.876±0.043 (2), reported relative to 238 U/ 235 U=137.837 of the CRM 145 standard. Our best current estimate of the average terrestrial value is: 238 U/ 235 U=137.821±0.014.The error in the age includes uncertainties in the Pb-Pb isochron intercept and in the 238 U/ 235 U ratio. Allende bulk rock and chondrules have 238 U/ 235 U=137.747±0.017 (2), distinctly lower than the CAI. The difference in the 238 U/ 235 U ratio of 0.129±0.046 (2) between the CAI and chondrules and bulk meteorite increases the 207 Pb-206 Pb age difference by ~1.4 million years, and eliminates apparent disagreement between the CAI-chondrule formation time interval determinations with the U-Pb and extinct nuclide (26 Al-26 Mg and 182 Hf-182 W) data. We discuss standardization of 238 U/ 235 U measurements for U-Pb geochronology and cosmochronology, elemental and isotopic fractionation induced by intensive acid leaching, ages of CAIs in the context of 238 U/ 235 U variability, and possible causes of U isotopic variations in CAIs and meteorites.

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Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.

Seven size‐fractionated aerosol samples were collected from Hiroshima, Japan, and were analyzed in terms of chemical composition, soluble fraction of iron (Fe), Fe species, and Fe isotope ratios. The results suggested that Fe in fine particles contained a larger fraction of anthropogenic aerosols than coarse particles did. Iron in the fine particles was more soluble in simulated seawater (up to 25%) than that in the coarse particles and was in the form of Fe (hydr)oxide species, such as ferrihydrite or hematite. The Fe isotope ratios (δ56Fe) of the coarse particles (+0.04‰ to +0.30‰) were close to the crustal mean value (0.0‰). By contrast, the δ56Fe values of fine particles were much lower and ranged from −2.01‰ to −0.56‰. δ56Fe values of the soluble Fe fraction in the fine particles were remarkably low (−3.91 to −1.87‰), suggesting that anthropogenic aerosols yield soluble Fe with low δ56Fe values. Such low values could be explained by kinetic isotope fractionation during evaporation of Fe at high temperatures, coupled with the refractory characteristics of Fe. Marine aerosols from the Northwest Pacific were also analyzed. The δ56Fe values in the fine particles were also lower than those in the coarse particles. These results may be important to quantitatively estimate the contribution of anthropogenic Fe deposited on the surface ocean on the basis of the Fe isotopes.

Using a laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS), U-Pb age and rare earth element (REE) abundances have been determined simultaneously from a single 20 µm ablation pit of zircon. The laser ablation system utilizing 193 nm wave-length ArF excimer laser produces stable and reproducible signal intensities resulted in good precisions on measurements of element concentrations and isotopic ratios. Because of the higher energy density of the deep ultra-violet laser beam, ablation fractionation between Pb and U were reduced even with the prolonged ablation, and thus accuracy of Pb-U age was improved significantly.A chicane-type ion lens system was applied to a quadrupole-based ICPMS instrument. With the chicane ion lens, higher elemental sensitivity (4 times for light mass range and 3 times for mid to heavy mass range) and lower white background (<5 cps for light to mid mass range and <2 cps for heavy mass range) were achieved. This further improved analytical precisions for low concentration elements in samples.The 238 U-206 Pb ages for Nancy standard zircon (Nancy 91500), SHRIMP calibration standard zircon (SL13) and Antarctic zircon (PMA7) obtained in this study were 1064 ± 24 Ma, 569 ± 78 Ma and 2438 ± 101 Ma (2-sigma), respectively. Relative age differences from previous reports were 0.2%, 0.4% and 3.2% respectively, demonstrative of high reliability of the method. The REE abundances in zircon samples were calibrated using a NIST 610 glass standard reference material. The resulting REE abundance data for zircons (Nancy 91500 and SL13) show good agreement with those for literature values within the analytical precision of ~20%. The matrix effect that may occur between the synthetic glass standard and zircon crystals is obviously smaller than the precision and thus negligible for this precision levels. The data presented here demonstrate clearly that the combination of ArF excimer laser and ICPMS equipped with the chicane ion lens has a potential to become a significant tool for zircon geochemistry.Keywords: zircon, ICPMS, excimer laser, U-Pb, REE for single zircon grains are superior both in precision and accuracy, it is widely recognized that the SHRIMP is also a reliable standard technique which can produces "bench mark" U-Pb age data. The rapidity of SIMS measurements together with its ability to produce spatial data indicates that much more information can be derived from zircon populations than that produced by conventional "bulk" analysis using the TIMS technique. A relatively new technique in U-Pb zircon chronology is inductively coupled plasma mass spectrometry (ICPMS) combined with laser ablation (LA) sample introduction. Zircon crystals are ablated with a finely focused laser beam under atmospheric pressure; the generated aerosols being transported via the gas flow introduced into the ICP ion source for mass spectrometry. Major advantages of the method are minimal sample preparation, low cost and high analytical throughput. Using the first generation LA-ICPMS instruments, 207 ...