Advances in in-situ Re-Os isotope ratio measurements by LA-MC-ICP-MS

Developments in in-situ high precision isotope ratio measurements are revolutionising our understanding of the geodynamic Earth at all scales. Laser ablation (LA) multi-collector (MC-) ICP-MS provides spatially resolved data for geochemistry and geochronology that can be interpreted in a microstructural context. One example of the application of the in-situ method is to study the Re-Os isotope systematics of individual sulfide grains and Os-Ir alloys in mantle peridotites. Mantle sulfides are time capsules and they provide a record of multiple events in the lithospheric mantle. Although instrumentation and analytical protocols have advanced significantly in the past decade there is an on-going challenge to optimize accuracy and precision while improving spatial resolution in order to constrain the timing of these events. Further improvements in the in-situ methodologies using LA-MC-ICP-MS require a more rigorous treatment of measurement uncer tainties and error budgets. Many factors contribute to the internal and external precision of in-situ measurements: sample composition, laser characteristics and operating conditions, and processes in the ICP and mass spectrometer. Analyses of a suite of synthetic NiS beads with different Re/Os ratios are used to demonstrate how accuracy and precision are affected by the total beam intensities of Re and Os, the Re/Os ratio, detector calibration and linearity, and the degree of Re/Os fractionation during ablation.