Zambardi, T.; Poitrasson, F.; Quitte, G. and Anand, M.
(2009).
Silicon isotope variations in the Earth and meteorites.
In: Challenges to Our Volatile Planet : Goldschmidt 2009, 21-26 June 2009, Davos, Switzerland.
Abstract
A fluorhydric acid-free sample preparation method derived from Georg et al. [1] has been used to measure the natural variations of silicon isotope compositions in terrestrial
(including 12 geological standard materials) and meteoritic
bulk-rock samples.
All measurements were done using a Neptune MC-ICPMS
in medium resolution mode (m/Δm = 7000, peak-edge
definition). Magnesium was used as internal standard for
mass-bias drift correction. The δ30Si values are expressed relative to the NBS-28 silica standard.
IRMM-17 reference material yields a δ30Si of -1.4‰ ±
0.05‰ (2SD, n=11) in agreement with previous data [2-3].
Long-term reproducibilities were obtained for BHVO-2 (δ30Si
= -0.27‰ ± 0.08‰ (2SD, n=30)) and a in-house Si standard
(δ30Si = -0.01‰ ± 0.07‰ (2SD, n=20)) on a 7 months time scale.
Total variation of δ30Si in natural samples ranges from -
0.5‰ to -0.1‰. Comparison with δ29Si values shows that this
isotopic fractionation is mass-dependent. A 0.2‰ isotopic
variation occurs among terrestrial samples suggesting an
enrichment in the heavier silicon isotopes as a function of
magma differentiation, as initially hinted by Douthitt [4].
Terrestrial samples mean value (δ30SiEarth= -0.23‰) is heavier by about 0.24‰ in δ30Si compared to chondrites. This may be explained by silicon isotope fractionation during planetary accretion and/or differentiation.
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