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| Titel |
Determination of U-isotope composition of silicate and carbonate reference materials for in-situ LA-ICPMS analysis by high precision MC-ICPMS |
| VerfasserIn |
Denis Scholz, Joachim Krause, Klaus Peter Jochum, Yvonne Kocot, Jan Tolzmann, Meinrat Andreae |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050307
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| Zusammenfassung |
| U-series isotope analyses are frequently used in order to constrain the timing and duration of
climatic, environmental and geological processes during the past 600Â ka. In addition to the
commonly applied TIMS and MC-ICPMS techniques, in-situ methods such as
LA-ICPMS have recently been developed in order to resolve spatial variability in the
U-isotope composition of carbonate and silicate materials (e.g., Mertz-Kraus et al.,
2010).
A prerequisite for the application of LA-ICPMS for U-isotope measurements is the
availability of matrix matched, homogeneous reference materials with precisely established
U-isotope composition. These are, for instance, required in order to control instrumental and
matrix induced biases occurring during analysis. Here we report high-precision
MC-ICPMS U-isotope ratios for various solid reference materials, especially produced for
in-situ microanalysis (KL2-G, BCR-2G, ATHO-G, ML3B-G, GSD-1G, BHVO-2G,
MACS-3).
The analyses were performed with the NU plasma MC-ICPMS at the Max Planck
Institute for Chemistry, Mainz. Samples were dissolved in an HCl-HF mixture, and U was
separated following traditional chemical separation and purification procedures. The
analytical protocol for MC-ICPMS analysis utilizes a common standard-bracketing procedure
in order to derive correction factors for mass fractionation and Faraday cup-SEM
gain.
Analyses of four splits of GSD1-G yielded 238U/235U and 234U/238U ratios in agreement
within uncertainty demonstrating the homogeneity of the material (mean values:
271.39 ±Â 0.3 and 0.000017982 ±Â 49, respectively). The 238U/235U and 234U/238U ratios
of the naturally sourced KL2-G (140.96 ±Â 0.28 and 0.00005322 ±Â 51, respectively)
are significantly different from the ratios determined for the original KL2 rock
powder (137.45 ±Â 0.28 and 0.00005493 ±Â 18, respectively), which is assumed to
be caused by U contamination during glass preparation. BCR-2G and ATHO-G
have natural 238U/235U within error. Whereas the 234U/238U ratio of BCR-2G is
slightly higher than the value expected for secular equilibrium, the 234U/238U ratio
of ATHO-G agrees with the secular equilibrium value. The 234U/238U ratios for
ATHO-G and BHVO-2G are in agreement with the TIMS values determined by
Matthews et al. (2010). Preliminary analyses of ML3B-G and BHVO-2G and the
corresponding rock powders suggest 238U/235U ratios in the range of the natural
ratio and 234U/238U in the range of secular equilibrium. The synthetic carbonate
reference material MACS-3 has a non-natural U-isotope composition (238U/235U =
373.42 ±Â 0.43; 234U/238U = 0.00001350 ±Â 87). The available 234U/238U data
indicate a potential inhomogeneity of MACS-3. This will be investigated by further
analyses.
Precise determination of U-isotope ratios in widely distributed geologic reference
materials will facilitate the application of in-situ methods such as LA-ICPMS for analysis of
U-series isotopes in a wide range of geologic materials.
References
Matthews et al. (2010) Geostandards and Geoanalytical Research DOI:
10.1111/j.1751-908X.2010.00080.x
Mertz-Kraus et al. (2010) JAAS, 25, 1895-1904. |
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