| Summary: | Routine generation of large Rb-Sr age datasets has been limited by the time-consuming requirement of chromatographic isolation of Sr from Rb to avoid the isobaric interference of 87Rb+ on 87Sr+. Recently, direct measurement of interference-free 87Sr/86Sr has become possible with the advent of tandem quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). Here, we describe a method that uses ICP-MS/MS to measure 87Sr/86Sr combined with a standard addition calibration for precise determination of Rb/Sr, allowing efficient generation of Rb-Sr ages. The method is demonstrated on a suite of ~50 to 90 Myrs (million years) old celadonite samples that are dated with age uncertainties typically of ±2 to 5 Myrs provided the sample Rb/Sr is >2. A method to separate the phyllosilicate fraction from the bulk sample, because it commonly has a higher Rb/Sr more suitable for dating, using differential settling is also described. • Differential settling allows high Rb/Sr phyllosilicates to be separated from other phases • ICP-MS/MS allows 87Sr/86Sr measurement without chromatographic isolation of Sr+ from Rb+ • Single-spike standard addition ICP-MS was used for Rb/Sr measurement
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