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Success story! Digging deep into geochronology with LG-SIMS at the Swedish Museum of Natural History

Wednesday, June 16, 2021

The NordSIMS laboratory at the Swedish Museum of Natural History has been equipped with a Large Geometry SIMS since 1997, serving international research projects across disciplines from geochronology and cosmochemistry to geobiology, ecology and nuclear safeguards.

In a recent study, Prof. Martin Whitehouse and his team investigated zircon crystallites in samples from southern India for U-Th-Pb dating.  The LG SIMS’ high-precision quantification of elemental and isotopic concentrations is unmatched for studies such as zircon U-Th-Pb. Yet, the presence of tiny, anomalous patches of lead in these samples made geochronological data interpretation problematic.

The NordSIMS scientists pursued the anomalies in these challenging samples via detailed LG SIMS analyses— including spot analysis of individual grains, rare earth element measurements, and scanning ion imaging (SII).

The unique imaging and depth profiling capabilities of their CAMECA ion microprobe enabled them to “repair the geochronometer.” By stacking successive SII scans, they constructed lead depth profiles with nm-scale resolution in a new technique they termed “scanning ion tomography”. They were able to reliably determine that the Indian zircons were formed around 1,850 million years ago (Ma), with subsequent ultra-high-temperature metamorphisms taking place at 570 and 520-510 Ma.

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