Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.v41e..07p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #V41E-07
Physics
8410 Geochemical Modeling (1009, 3610), 8494 Instruments And Techniques
Scientific paper
Strontium isotope systematics consist of the stable 88Sr/86Sr ratio, the radiogenic 87Sr/86Sr ratio and the 84Sr/86Sr ratio which is stable in terrestrial materials and may vary due to nuclear- synthetic processes in some meteorites [1]. Growing interest in natural mass dependent 88Sr/86Sr variations indicate that terrestrial samples vary by ~500 ppm and have been measured to a precision of 50-70 ppm by MC-ICP-MS [2, 3]. However, the precision is large relative to the likely variation in many terrestrial systems. Furthermore, 84Sr/86Sr ratios are poorly determined due to spectral interferences and therefore MC-ICP-MS techniques are not appropriate for high-precision analyses of all the Sr isotope ratios. Recent advances in TIMS allow 87Sr/86Sr and 84Sr/86Sr ratios to be measured to an external precision of ~5 and 60 ppm respectively with instrumental fractionation being corrected by internal normalisation to a constant 88Sr/86Sr ratio. Following on from the pioneering work of [4] we use an 84Sr- 87Sr double-spike coupled with TIMS analyses. Optimal spiking, extended ion collection times and a 25-fold improvement in the determination of the spike composition compared to [4] allow us to measure 87Sr/86Sr and 88Sr/86Sr ratios to better than 10 ppm external precision. The double-spike determination consists of an un-spiked and spiked measurement, with spiking prior to chemical separation because column separation produces a consistent and resolvable light fractionation effect of 21 to 93 ppm. The un-spiked run allows us to assess any non-mass dependent fractionation effects. Double-spike deconvolution is performed in 87Sr denominator space. Our preliminary high-precision data allows us to resolve small (25 ppm) mass-dependent shifts in seawater 88Sr/86Sr, which may reflect short-timescale Sr fluxes in the oceans. References [1] D.A. Papanastassiou, G.J. Wasserburg, Geophys. Res. Lett. 5 (1978) 361-376. [2] J. Fietzke, A. Eisenhauer, Geochem. Geophys. Geosyst., 7, (2006) Q08009, doi:10.1029/2006GC001243. [3] G.M. Nowell, et al., Geochim. Cosmochim. Acta. 71 (2007) A725. [4] P.J. Patchett, Nature, 283 (1980b) 438-441.
Burton Kevin W.
Charlier Baudouin Le
Mokadem Fatima
Parkinson Ian J.
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