ANALYTICAL PROCEDURES FOR STRONTIUMSr isotopic compositions were measured at UBC on a 60° sector, 30.5-cm radius, solid-source mass spectrometer of a modified U.S. National Bureau of Standards design. Data produced by this system have one sigma 87 Sr/ 86 Sr errors of less than 0.0001. All values reported are normalized and adjusted so that the Eimer and Amend Standard gives 0.70800 and the NBS standard SrCOa (SRM 987) gives 0.71024. Samples were prepared for mass spectrometry by dissolution in HF and HCIOΛ and separation of Sr in one pass through an ion exchange column (Dowex AG 5OW-X8 200-400 mesh) using 2.5 JV HC1 (redistilled in silica glass). The blank for the chemical procedure is less than 0.01 µg. This is a negligible amount (<0.1%) in the case of most igneous rocks, including ocean floor basalts. For ultramafic rocks containing only a few ppm of Sr, the blank, with a β7 Sr/ 86 Sr ratio of ~0.704, may amount to 2% to 5% of the analyzed sample but the correction to the observed 87 Sr/ 86 Sr ratio would be less than 0.0001. Rb and Sr concentrations were determined by X-ray fluorescence on pressed powder pellets. One sigma errors for concentration are 5% or 1 ppm.
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