Review of High-Precision Sr Isotope Analyses of Low-Sr Geological Samples

Isotope plays an important role in both tracing and dating in earth science, especially 87Rb-86Sr system. With the development of earth science, whole-rock analysis can’t sufficiently meet the requirements for scientific research and the micro-analysis becomes more and more significant. Laser ablation multi-collector inductively-coupled plasma mass-spectrometry (LA-MC-ICP-MS) has been extensively applied in micro-zone analysis due to its low sample-consumption, high accuracy, in situ and low requirements on matrix, but it is still difficult to accurately measure Sr isotope compositions especially for the samples with high Rb/Sr ratios and low Sr contents as it is restricted by severe quality discrimination and various types of mass spectrum interferences. Consequently, thermal ionization mass-spectrometry (TIMS), as the most accurate and precise method to analyze isotopic ratios, is still the most popular method of analyzing Sr ratios, especially for the samples with low Sr contents. This paper makes a systematic review on the high-precision Sr isotope analyses of low-Sr geological samples, including the micro-sampling technique, ultra-low procedural blank chemical method and TIMS measurement technique. The combination of ultra-low procedural blank and TIMS can be used to perform high-precision micro-analysis of the samples with ng magnitude, which will be undoubtedly an important direction for Rb-Sr geochronology, geochemistry and environmental studies.