Simultaneous Determination of Mass-dependent Isotopic Fractionation and Radiogenic Isotope Variation of Strontium in Geochemical Samples by Multiple Collector-ICP-Mass Spectrometry

摘要

We present a method to determine 88Sr/86Sr and 87Sr/86Sr simultaneously. The former variation reflects the mass-dependent isotopic fractionation through the physico-chemical processes, and the latter originates from β--decay of the parent nuclide 87Rb as well as the mass-dependent isotopic fractionation. In order to determine the mass-dependent isotopic fractionation, the mass-discrimination effect on 88Sr/86Sr was externally corrected by an exponential law using Zr. For the radiogenic growth of 87Sr/86Sr, the mass-dependent isotopic fractionation effect on 87Sr/86Sr was corrected by a conventional correction technique using the 88Sr/86Sr ratio. The reproducibility of the 88Sr/86Sr and 87Sr/86Sr measurements for a high-purity Sr chemical reagent was 0.06‰ (2SD, n = 20) and 0.07‰ (2SD, n = 20), respectively. Strontium isotopic ratios (88Sr/86Sr and 87Sr/86Sr) were measured on six geochemical reference materials (igneous rock: JB-1a and JA-2; carbonate mineral: JLs-1, JDo-1, JCp-1 and JCt-1) and one seawater sample. The resulting 87Sr/86Sr ratios obtained here were consistent with previously published data within the analytical uncertainties. The resulting 88Sr/86Sr ratios for igneous rock samples did not vary significantly within the samples, whereas the carbonate samples showed enrichments of the lighter Sr isotopes over the seawater sample. The 88Sr/86Sr ratio of geochemical samples could reflect the physico-chemical processes for the sample formation. Also, a combined discussion of 88Sr/86Sr and 87Sr/86Sr of samples will render multi-dimensional information on geochemical processes.