Isotope imaging of ultra-traces by LA-fs HR-ICP-MS for U-series dating (U/Th) of archaeological biominerals: how far can we go?

Abstract

Abstract To overcome the problems associated with the traditional U-series dating protocol (large amount of sample required, possible contamination during preparation and consideration of sample contamination in the past), we present a new approach using isotope mapping of radioelements produced by femtosecond laser ablation coupled with high resolution mass spectrometry (LA-fs HR-ICP-MS). This protocol, developed and validated on different carbonate supports, has been applied to a series of archaeological biominerals (shells, teeth, calcitic crusts). A high resolution of a few micrometres has been achieved, as well as a significant improvement of the sensitivity. This allows to obtain U/Th ages with minimal sampling (< 1mg), even though only ultra-traces of uranium (sub-ppb) are present. The isotope mapping approach also allows a real study of the material, highlighting areas potentially contaminated with detrital thorium, but also areas that have experienced leaching. The potential of this method and its limitations are discussed.