High precision Mg isotope measurements of meteoritic samples by secondary ion mass spectrometry

Tu-Han Luu*, Marc Chaussidon, Ritesh Kumar Mishra, Claire Rollion-Bard, Johan Villeneuve, Gopalan Srinivasan, Jean-Louis Birck

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

19 Citations (Scopus)

Abstract

The possibility of establishing an accurate relative chronology of the early solar system events based on the decay of short-lived Al-26 to Mg-26 (half-life of 0.72 Myr) depends on the level of homogeneity (or heterogeneity) of Al-26 and Mg isotopes. However, this level is difficult. to constrain precisely because of the very high precision needed for the determination of isotopic ratios, typically of +/- 5 ppm. In this study, we report for the first time a detailed analytical protocol developed for high precision in situ Mg isotopic measurements ((25)mg/(24)mg and (26)mg/Mg-24 ratios, as well as Mg-26 excess) by MC-SIMS. As the data reduction process is critical for both accuracy and precision of the final isotopic results, factors such as the Faraday cup (FC) background drift and matrix effects on instrumental fractionation have been investigated. Indeed these instrumental effects impacting the measured Mg-isotope ratios can be as large or larger than the variations we are looking for to constrain the initial distribution of Al-26 and Mg isotopes in the early solar system. Our results show that they definitely are limiting factors regarding the precision of Mg isotopic compositions, and that an under- or over-correction of both FC background instabilities and instrumental isotopic fractionation leads to important bias on delta Mg-25, delta(26)mg and Delta Mg-26 values (for example, olivines not corrected for FC background drifts display Delta Mg-26 values that can differ by as much as 10 ppm from the truly corrected value). The new data reduction process described here can then be applied to meteoritic samples (components of chondritic meteorites for instance) to accurately establish their relative chronology of formation.

Original languageEnglish
Pages (from-to)67-76
Number of pages10
JournalJournal of Analytical Atomic Spectrometry
Volume28
Issue number1
DOIs
Publication statusPublished - Jan 2013

Keywords

  • EARLY SOLAR-SYSTEM
  • MAGNESIAN CHONDRULES
  • RICH INCLUSIONS
  • ALLENDE
  • ORIGIN
  • FRACTIONATION
  • AL-26-MG-26
  • CHONDRITES
  • MICROPROBE
  • ELEMENTS

Cite this