In situ micro-beam U–Pb dating of apatite using CAMECA 1300HR3 LG-SIMS

Abstract

Apatite is a U-bearing mineral commonly present in planetary materials and has been widely used for geochronological studies. However, precise in situ U–Pb dating of tiny apatite (grain size <15 μm) remains challenging due to its low abundance of uranium (U) and radiogenic lead (Pb). To address this issue, we have developed two micro-beam analytical methods (i.e., 5 nA and 500 pA primary beams) using three apatite reference materials (BR5, AFG2, and Otter lake) and a CAMECA IMS 1300HR3 large-geometry secondary ion mass spectrometry (LG-SIMS). The 5 nA method (mono) produces a larger sputter crater (12.5 × 12.5 × 4.1 μm) and achieves higher dating precision, with age errors (n = 20) of <0.5% (1σ) for BR5, <2.5% (1σ) for AFG2, and <0.7% (1σ) for Otter lake. In contrast, the 500 pA method (multi) produces a smaller sputter crater (5.3 × 5.3 × 1.4 μm) that results in lower dating precision, with age errors (n = 25) of <1.3% (1σ) for BR5, <4.1% (1σ) for AFG2, and <1.8% (1σ) for Otter lake. Both methods yield accurate ages within the uncertainties and are applicable for apatite U–Pb dating. For data reduction, we recommend the use of the Pb/U vs. UO2/U calibration protocol, because it introduces less age bias compared to those of Pb/U vs. UO/U and Pb/UO vs. UO2/UO protocols. The methodological approaches of this study enable high-precision in situ U–Pb dating of tiny apatite and they will expand the application of LG-SIMS in geochronological studies of (extra-) terrestrial apatite samples.

Graphical abstract: In situ micro-beam U–Pb dating of apatite using CAMECA 1300HR3 LG-SIMS

Supplementary files

Article information

Article type
Paper
Submitted
08 Jul 2025
Accepted
11 Aug 2025
First published
15 Aug 2025

J. Anal. At. Spectrom., 2025, Advance Article

In situ micro-beam U–Pb dating of apatite using CAMECA 1300HR3 LG-SIMS

Y. Guan, J. Li, A. K. Kennedy, D. Du, L. Tian, W. Xie and X. Wang, J. Anal. At. Spectrom., 2025, Advance Article , DOI: 10.1039/D5JA00266D

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