A procedure was developed to accurately measure the W isotopic compositions of iron meteorites with a precision of better than ±0.1 ε on ε182W and ε184W (normalized to 186W/183W). Purification of W was achieved through a two-step, ion-exchange procedure. In most cases, the yield is better than 80%, and purified W solutions are clear of matrix elements and direct isobars of W. The final W solutions were analyzed using a Micromass Isoprobe multicollector inductively coupled plasma mass spectrometer (MC-ICPMS). Tests performed on mixtures of terrestrial standards and meteorite samples demonstrate that the method is accurate and that ε182W variations as small as ∼0.1 ε can be detected. Analyses of three different aliquote of the Gibeon (IVA) iron meteorite obtained over a period of 6 months show identical ε182W values with a weighted mean of 3.38 ± 0.05, consistent with literature data for IVA iron meteorites, and indicating that the metal-silicate differentiation event in its parent body was either contemporaneous with or slightly post-dated (by up to ∼2.5 My) the formation of refractory inclusions. We demonstrate our ability to measure ε184W accurately and precisely (within ±0.1 ε), which is useful for characterizing cosmogenic and nucleosynthetic effects that may be present in iron meteorites. We also report for the first time measurements of ε180W, albeit with large error bars (<±4 ε, in most cases).
ASJC Scopus subject areas
- Analytical Chemistry