Jacob Mulder, Graham Hagen-Peter, Teresa Ubide , Rasmus Andreasen, Ellen Kooijman, Melanie Schmitt, Yu-Xing Feng, Bence Paul, Andreas Karlsson, Christian Tegner, Charles Lesher, Fidel Costa

Laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA-MC-ICP-MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr-baseline subtraction, Rb-peakstripping using βRb derived from a bracketing glass standard, and a CaCa/CaAr correction for plagioclase and CaCa/CaAr + REE2+ correction for rock glasses, yields the most accurate and precise 87Sr/86Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50—65 μm diameter beam can readily achieve <100 ppm 2SE internal precision for 87Sr/86Sr measurements for materials with <1000 ppm Sr.