Intra-Annual Variation in the Stable Oxygen and Carbon and Trace Element Composition of Sclerosponges

This paper presents data to support the presence of (1) intra-annual signals in the chemical composition (δ18O and Sr/Ca) of the skeletons ofsclerosponges from the Bahamas and (2) variable rates of skeletal accretion. These conclusions are based on data obtained by using a microsampling method for the stable oxygen and carbon isotopes in which material was extracted at a resolution of one sample every 34 μm and a laser microprobe which obtained trace element data every 20 μm (Sr, Mg, and Pb). An age model was established using a combination of changes in the concentration of Pb, the change in the δ13C of the skeleton of the sclerosponges, and U/Th isotopic measurements. These methods yield a mean growth rate of 220 μm/yr but suggest that the growth rate in this particular sclerosponge was not constant. The calculated growth rate is within error identical to that determined by U/Th methods. The variable growth rate was confirmed through spectral analysis of the δ18O and Sr/Ca data that showed peaks corresponding to the annual cycle in these parameters as well as peaks corresponding to growth rates of approximately 128, 212, 270, and 400 μm/yr. The presence of these additional frequencies suggests a growth rate between approximately 100 and 300 μm/yr. These conclusions were supported by modeling of oxygen isotopic data measured on a scleractinian coral as well as model isotope data generated on synthetic time series. These findings have important implications for the use of sclerosponges as proxies of paleoclimate because they emphasize the need for a precise yearly chronology in order that proxy data can be compared with climatic variables. Copyright 2002 by the American Geophysical Union

Precise Sulfur Isotope Ratio Measurements in Trace Concentration of Sulfur by High Resolution Inductively Coupled Plasma Sectorfield Mass Spectrometry (HR-ICP-SMS).

Abstract not availableJRC.D-Institute for Reference Materials and Measurements (Geel

A new method integrating high-precision U-Pb geochronology with zircon trace element analysis (U-Pb TIMS-TEA)

Increased precision in isotope-dilution thermal ionization mass spectrometry (ID-TIMS) U-Pb geochronology has revealed age complexities in zircon populations that require new tools for understanding how the growth of zircon is related to geologic processes. U and Pb are routinely separated from other elements in dated minerals by ion exchange separation prior to TIMS isotope measurement. We develop a method in which trace elements in the exact same volume of zircon are redissolved and analyzed using solution nebulization inductively coupled plasma sector-field mass spectrometry with matrix-matched external liquid calibration. Using <0.5 ml solution, resulting concentrations are between <1 ppt for elements such as Ti, Nb and Ta and tens of ppb for Zr. By analyzing a series of standard solutions, zircons and procedural blanks, we show that accurate measurements are performed on Zr, Hf, Y, Sc, and the HREE while low-concentration elements can be measured accurately to <5 ppt. We performed combined U-Pb ID-TIMS geochronology with trace element analysis (here called U-Pb TIMS-TEA) on zircons from eight volcanic rocks comprising several volcanic systems and one metamorphic sample. Similar to previous in situ trace element analyses, zircon geochemistry is distinct between different samples and records petrogenetic processes such as fractional crystallization, assimilation and/or magma mixing. Unique from in situ analysis, U-Pb TIMS-TEA can trace geochemical evolution in accessory minerals with adequate age precision to resolve magmatic processes in rocks at least 200 million years old. This provides a means to identify auto-, ante- and xenocrystic zircon and lead to more robust age interpretations in ID-TIMS U-Pb geochronology. One suite of Cretaceous andesitic zircons shows correlations in geochemistry and absolute time that record evolution of a magmatic system over similar to 250 ka prior to eruption. Future work will combine U-Pb TIMS-TEA with solution isotopic analysis of Nd, Sr and Hf and will be applied to a host of datable minerals such as monazite, sphene, apatite, rutile, xenotime, and baddeleyite. These combined tools will provide access to an improved understanding of a wide range of igneous and metamorphic processes as a function of tim

Nickel isotopes in iron meteorites-nucleosynthetic anomalies in sulphides with no effects in metals and no trace of Fe-60

Iron-60 decays to 60Ni with a half-life of 1.49 Myrs such that Ni isotopic studies of iron meteorites have the potential to provide powerful new constraints on the energy budgets and time-scales of planetesimal melting, differentiation and core formation. We report high-resolution MC-ICPMS Ni isotope compositions for the Fe-Ni metal phase from 33 iron meteorites as well as for 10 coexisting sulphides. The isotopic composition of every metal sample is indistinguishable from that of the standard within uncertainties, whereas several sulphides show an excess of 61Ni correlated with a deficit in 60Ni. These latter effects are not explicable by currently known analytical artefacts. Nor can they be readily explained by spallation reactions or radioactive decay. Based on our sampling they seem more prevalent in, but not exclusive to, non-magmatic iron meteorites and could reflect admixing of less than 0.4 ppm pure s-process component into "normal" Ni on meteorite parent bodies. Sulphides do not show the excess 60Ni expected from their high Fe/Ni ratios if they formed within the first few million years of the solar system. The data provide evidence that sulphides in iron meteorites crystallized more than 10 Myrs after the start of the solar system. © 2005 Elsevier B.V. All rights reserved

Nickel isotopes in iron meteorites: Nucleosynthetic anomalies in sulphides with no effects in metals and no trace of 60Fe

International audienc

Fe-60-Ni-60 systematics in the eucrite parent body: A case study of Bouvante and Juvinas

Eucrites are basaltic meteorites that cooled rapidly but are in many instances thermally metamorphosed and impact brecciated. The exact timing of these events remains unclear. In this study, Ni isotopic compositions and Fe/Ni elemental ratios are presented for two non-cumulate eucrites, Bouvante and Juvinas, including mineral separates from the latter. The samples are characterized by variable, well-resolved 60Ni-excesses consistent with the former presence of live 60Fe (t1/2=2.62Ma) at the time of eucrite crystallization. A significant fraction of Ni with a terrestrial-like composition appears to be surface correlated. This Ni may be the product of terrestrial contamination or was introduced by a chondritic impactor during brecciation. Altogether, the data provide evidence for a complex and probably multi-stage history of Fe and/or Ni redistribution, which impedes the interpretation of the chronological data. © 2011 Elsevier Ltd

Correlated iron-60, nickel-62, and ziconium-96 in refractory inclusions and the origin of the Solar System.

International audienc

Correlated iron-60, nickel-62, and ziconium-96 in refractory inclusions and the origin of the Solar System.

International audienc