Abstract: Two microbeam techniques, synchrotron radiation X-ray fluorescence micro-analysis (μ-SR... more Abstract: Two microbeam techniques, synchrotron radiation X-ray fluorescence micro-analysis (μ-SRXRF) and secondary ion mass spectrometry (SIMS) are compared for analyzing diffusion profiles of trace elements in two hydrous rhyolitic glasses (1.87 and ...
Geostandards Newsletter-the Journal of Geostandards and Geoanalysis, 1999
Isotope dilution calibration has been applied to the determination of Zr and Hf in whole rocks by... more Isotope dilution calibration has been applied to the determination of Zr and Hf in whole rocks by laser ablation (LA)-ICP-MS. Enriched isotopes were added during the preparation of flux-free, synthetic whole rock glasses and homogenised through a combination of grinding and fusion. This method avoids problems, such as solution instability and the chemical resistance of minerals such as zircon, inherent in acid digestion sample preparation. The use of isotope dilution removes the need for external calibration using certified reference material glasses such as NIST SRM 612 for which certified Zr and Hf values are not available. The precision of Zr and Hf determinations were found to be < 1% and 3.5% respectively, limited by Poisson counting statistics which contributed to 50% of the final precision of analysis. Measured values correlate closely with compiled literature values.La méthode de dilution isotopique a été appliquée à la détermination de Zr et Hf en roche totale par ablation laser (LA)-ICP-MS. Des isotopes enrichis ont été ajoutés au cours de la préparation des verres synthétiques de roche totale, verre sans fondant et homogénéisés par une procédure combinant broyage et fusion. Cette méthode évite les problèmes comme l'instabilité de la solution ou la résistance chimique de minéraux tels que le zircon, inhérents à toute préparation d'échantillon par attaque acide. L'emploi de la dilution isotopique supprime la nécessité d'une calibration externe par rapport à des verres de référence certifiés, tel que NIST SRM 612 pour lequel les valeurs certifiées en Zr et Hf ne sont pas connues. La précision des mesures de Zr et Hf est respectivement < 1% et 3.5%. Elle est limitée par le comptage statistique de Poisson qui contribue pour plus de 50%à la précision finale de l'analyse. Les valeurs mesurées sont très proches des données compilées dans la littérature.
Primary carbonates in peridotite xenoliths from the East African Rift in northeastern Tanzania oc... more Primary carbonates in peridotite xenoliths from the East African Rift in northeastern Tanzania occur as intergranular patches with accessory minerals (olivine and spinel), as patches with accessory magmatic minerals (nepheline), and as round monomineralic inclusions in primary olivine grains. All are characterized by calcitic compositions (Ca/Ca + Mg + Fe from 0.83 to 0.99), extremely low SiO2 + Al2O3 + Na2O + K2O, low trace element abundance [total rare-earth element (REE) abundance <25 ppm], uniform extinction, and lack of reaction textures with the host xenolith. Calculated Fe–Mg exchange coefficients between carbonate and primary olivine indicate disequilibrium in most samples. Combined with the lack of significant reaction textures, this suggests that the carbonates were introduced shortly before or during eruption of the host magma. A global compilation of electron microprobe analyses of mantle-derived carbonates (in xenoliths, xenocrysts, and megacrysts) reveals compositional clusters near end member calcite, end member magnesite, and stoichiometric dolomite. Eutectic liquid compositions are less common, suggesting that many carbonate inclusions reported worldwide may be crystalline precipitates. Likewise, the calcites in this study are not interpreted to represent quenched carbonatitic melts, but are interpreted instead to be crystalline cumulates from such melts. These inferences are consistent with recent experiments, which show that carbonatitic melts cannot become more calcitic than CaCO3∼80 wt%. Low trace element abundance may be a diagnostic feature of cumulate carbonate, and in combination with petrography and major element composition, serve to distinguish it from quenched carbonated liquid.
Geostandards Newsletter-the Journal of Geostandards and Geoanalysis, 1997
The microanalytical capability of laser ablation microprobe-inductively coupled plasma-mass spect... more The microanalytical capability of laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) to determine ultra trace elemental concentrations has been demonstrated by the analysis of two low concentration glass standard reference materials, NIST SRM 614 and 616. Results for fifty two elements at concentrations in the low ng g-1 range are compared with those determined using secondary ion mass spectrometry (SIMS). Both techniques provide results at these concentrations that generally agree within 95% confidence limits, demonstrating the accuracy for ultra-trace level of in situ determinations by the two techniques. At concentrations of less than 20 ng g-1 in NIST SRM 616, an accuracy and precision of better than 10% has been obtained for most mono-isotopic rare earth elements, when a spot size of 50 μm is used. Limits of detection for selected elements were as low as 0.5 ng g-1.Les potentialités de l'ablation laser couplée à un ICP-MS (LAM-ICP-MS) dans le domaine de la microanalyse de concentrations en ultra-traces ont été démontrées par l'analyse de deux verres standards de référence à faibles teneurs, NIST SRM 614 et 616. Les résultats obtenus pour cinquantedeux éléments à des concentrations inférieures à quelques ng g-1 sont comparés avec ceux déterminés par spectrométrie de masse àémission d'ions secondaires (SIMS). Les deux techniques donnent des résultats situés dans l'intervalle de confiance de 95%, démontrant l'exactitude des deux méthodes pour l'analyse in situ d'ultra-traces. Dans l'échantillon NIST SRM 616, dont les concentrations sont inférieures à 20 ng g-1, une exactitude et une justesse meilleures que 10% ont été obtenues pour la plupart des terres rares mono-isotopiques en choisissant un cratère d'impact de 50 micromètre. Les limites de détection pour certains éléments particuliers étaient inférieures a 0,5 ng g-1
Abstract: Two microbeam techniques, synchrotron radiation X-ray fluorescence micro-analysis (μ-SR... more Abstract: Two microbeam techniques, synchrotron radiation X-ray fluorescence micro-analysis (μ-SRXRF) and secondary ion mass spectrometry (SIMS) are compared for analyzing diffusion profiles of trace elements in two hydrous rhyolitic glasses (1.87 and ...
Geostandards Newsletter-the Journal of Geostandards and Geoanalysis, 1999
Isotope dilution calibration has been applied to the determination of Zr and Hf in whole rocks by... more Isotope dilution calibration has been applied to the determination of Zr and Hf in whole rocks by laser ablation (LA)-ICP-MS. Enriched isotopes were added during the preparation of flux-free, synthetic whole rock glasses and homogenised through a combination of grinding and fusion. This method avoids problems, such as solution instability and the chemical resistance of minerals such as zircon, inherent in acid digestion sample preparation. The use of isotope dilution removes the need for external calibration using certified reference material glasses such as NIST SRM 612 for which certified Zr and Hf values are not available. The precision of Zr and Hf determinations were found to be < 1% and 3.5% respectively, limited by Poisson counting statistics which contributed to 50% of the final precision of analysis. Measured values correlate closely with compiled literature values.La méthode de dilution isotopique a été appliquée à la détermination de Zr et Hf en roche totale par ablation laser (LA)-ICP-MS. Des isotopes enrichis ont été ajoutés au cours de la préparation des verres synthétiques de roche totale, verre sans fondant et homogénéisés par une procédure combinant broyage et fusion. Cette méthode évite les problèmes comme l'instabilité de la solution ou la résistance chimique de minéraux tels que le zircon, inhérents à toute préparation d'échantillon par attaque acide. L'emploi de la dilution isotopique supprime la nécessité d'une calibration externe par rapport à des verres de référence certifiés, tel que NIST SRM 612 pour lequel les valeurs certifiées en Zr et Hf ne sont pas connues. La précision des mesures de Zr et Hf est respectivement < 1% et 3.5%. Elle est limitée par le comptage statistique de Poisson qui contribue pour plus de 50%à la précision finale de l'analyse. Les valeurs mesurées sont très proches des données compilées dans la littérature.
Primary carbonates in peridotite xenoliths from the East African Rift in northeastern Tanzania oc... more Primary carbonates in peridotite xenoliths from the East African Rift in northeastern Tanzania occur as intergranular patches with accessory minerals (olivine and spinel), as patches with accessory magmatic minerals (nepheline), and as round monomineralic inclusions in primary olivine grains. All are characterized by calcitic compositions (Ca/Ca + Mg + Fe from 0.83 to 0.99), extremely low SiO2 + Al2O3 + Na2O + K2O, low trace element abundance [total rare-earth element (REE) abundance <25 ppm], uniform extinction, and lack of reaction textures with the host xenolith. Calculated Fe–Mg exchange coefficients between carbonate and primary olivine indicate disequilibrium in most samples. Combined with the lack of significant reaction textures, this suggests that the carbonates were introduced shortly before or during eruption of the host magma. A global compilation of electron microprobe analyses of mantle-derived carbonates (in xenoliths, xenocrysts, and megacrysts) reveals compositional clusters near end member calcite, end member magnesite, and stoichiometric dolomite. Eutectic liquid compositions are less common, suggesting that many carbonate inclusions reported worldwide may be crystalline precipitates. Likewise, the calcites in this study are not interpreted to represent quenched carbonatitic melts, but are interpreted instead to be crystalline cumulates from such melts. These inferences are consistent with recent experiments, which show that carbonatitic melts cannot become more calcitic than CaCO3∼80 wt%. Low trace element abundance may be a diagnostic feature of cumulate carbonate, and in combination with petrography and major element composition, serve to distinguish it from quenched carbonated liquid.
Geostandards Newsletter-the Journal of Geostandards and Geoanalysis, 1997
The microanalytical capability of laser ablation microprobe-inductively coupled plasma-mass spect... more The microanalytical capability of laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) to determine ultra trace elemental concentrations has been demonstrated by the analysis of two low concentration glass standard reference materials, NIST SRM 614 and 616. Results for fifty two elements at concentrations in the low ng g-1 range are compared with those determined using secondary ion mass spectrometry (SIMS). Both techniques provide results at these concentrations that generally agree within 95% confidence limits, demonstrating the accuracy for ultra-trace level of in situ determinations by the two techniques. At concentrations of less than 20 ng g-1 in NIST SRM 616, an accuracy and precision of better than 10% has been obtained for most mono-isotopic rare earth elements, when a spot size of 50 μm is used. Limits of detection for selected elements were as low as 0.5 ng g-1.Les potentialités de l'ablation laser couplée à un ICP-MS (LAM-ICP-MS) dans le domaine de la microanalyse de concentrations en ultra-traces ont été démontrées par l'analyse de deux verres standards de référence à faibles teneurs, NIST SRM 614 et 616. Les résultats obtenus pour cinquantedeux éléments à des concentrations inférieures à quelques ng g-1 sont comparés avec ceux déterminés par spectrométrie de masse àémission d'ions secondaires (SIMS). Les deux techniques donnent des résultats situés dans l'intervalle de confiance de 95%, démontrant l'exactitude des deux méthodes pour l'analyse in situ d'ultra-traces. Dans l'échantillon NIST SRM 616, dont les concentrations sont inférieures à 20 ng g-1, une exactitude et une justesse meilleures que 10% ont été obtenues pour la plupart des terres rares mono-isotopiques en choisissant un cratère d'impact de 50 micromètre. Les limites de détection pour certains éléments particuliers étaient inférieures a 0,5 ng g-1
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