Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous chondrites

Audrey Bouvier, Meenakshi Wadhwa, Steven B. Simon, Lawrence Grossman

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

We present high-precision measurements of the Mg isotopic compositions of a suite of types I and II chondrules separated from the Murchison and Murray CM2 carbonaceous chondrites. These chondrules are olivine- and pyroxene-rich and have low 27Al/24Mg ratios (0.012-0.316). The Mg isotopic compositions of Murray chondrules are on average lighter (δ26Mg ranging from -0.95‰ to -0.15‰ relative to the DSM-3 standard) than those of Murchison (δ26Mg ranging from -1.27‰ to +0.77‰). Taken together, the CM2 chondrules exhibit a narrower range of Mg isotopic compositions than those from CV and CB chondrites studied previously. The least-altered CM2 chondrules are on average lighter (average δ26Mg = -0.39 ± 0.30‰, 2SE) than the moderately to heavily altered CM2 chondrules (average δ26Mg = -0.11 ± 0.21‰, 2SE). The compositions of CM2 chondrules are consistent with isotopic fractionation toward heavy Mg being associated with the formation of secondary silicate phases on the CM2 parent body, but were also probably affected by volatilization and recondensation processes involved in their original formation. The low-Al CM2 chondrules analyzed here do not exhibit any mass-independent variations in 26Mg from the decay of 26Al, with the exception of two chondrules that show only small variations just outside of the analytical error. In the case of the chondrule with the highest Al/Mg ratio (a type IAB chondrule from Murchison), the lack of resolvable 26Mg excess suggests that it either formed >1 Ma after calcium-aluminum-rich inclusions, or that its Al-Mg isotope systematics were reset by secondary alteration processes on the CM2 chondrite parent body after the decay of 26Al.

Original languageEnglish (US)
Pages (from-to)339-353
Number of pages15
JournalMeteoritics and Planetary Science
Volume48
Issue number3
DOIs
StatePublished - Mar 2013

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chondrule
carbonaceous chondrites
carbonaceous chondrite
isotopic fractionation
fractionation
magnesium
isotopic composition
chondrites
parent body
chondrite
vaporizing
decay
volatilization
olivine
pyroxene
calcium
silicates
silicate
isotopes
aluminum

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Cite this

Magnesium isotopic fractionation in chondrules from the Murchison and Murray CM2 carbonaceous chondrites. / Bouvier, Audrey; Wadhwa, Meenakshi; Simon, Steven B.; Grossman, Lawrence.

In: Meteoritics and Planetary Science, Vol. 48, No. 3, 03.2013, p. 339-353.

Research output: Contribution to journalArticle

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