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Isotopic imaging using fsLA single-collector ICP-SFMS for direct U/Th dating of small archaeological carbonates

Abstract : We present a new methodology for the U/Th dating of carbonate materials using femtosecond laser ablation single-collector inductively coupled plasma sector field mass spectrometry (fsLA single-collector ICP-SFMS), isotopic mappings, and image processing. This approach allows working on samples at very low U levels (ng·g$^{–1}$). One of the major advantages of this imaging method is that it allows us to exploit deteriorated samples that could not be analyzed by conventional bulk U/Th dating methods, thanks to the identification of contaminated or leached areas at the scale of a few tens of microns and the subsequent correction for detrital 230Th incorporation. Only a few milligrams of material are required for measurement, which allows us to work on small samples such as shell fragments. The parameters of the fsLA single-collector ICP-SFMS coupling have been carefully optimized to ensure very high sensitivity detection and ultralow background while preserving good plasma robustness and a spatial resolution of 30 × 50 μm$^2$. The accuracy was evaluated from low-level U speleothems previously dated by a conventional U/Th dating technique involving digestion, resin purification, double spike, and detection by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). U/Th ages of two archaeological samples with U at low ng·g$^{–1}$ levels, a giant terrestrial snail shell and a burned ostrich eggshell, were determined. The measured U/Th ages are consistent with the expected ages determined by luminescence dating methods.
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https://hal.archives-ouvertes.fr/hal-03550046
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Submitted on : Monday, January 31, 2022 - 6:40:43 PM
Last modification on : Tuesday, November 8, 2022 - 3:28:22 PM

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Loïc Martin, Asmodée Galy, Gaëlle Barbotin, Fanny Claverie, Edwige Pons-Branchu, et al.. Isotopic imaging using fsLA single-collector ICP-SFMS for direct U/Th dating of small archaeological carbonates. Analytical Chemistry, 2022, 94 (7), pp.3046-3055. ⟨10.1021/acs.analchem.1c02241⟩. ⟨hal-03550046⟩

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