High Spatial Resolution U-Pb Dating of Low-Uranium Calcite Using LA-MC-ICP-MS

The combination of carbonate minerals with the U-Pb isotope dating system provides direct temporal constraints for geoscientific applications. LA-MC-ICP-MS with its high sensitivity and accuracy, has been successfully applied to the high spatial resolution U-Pb dating of zircon, calcite and other minerals. The experimental parameters of LA-MC-ICP-MS were optimized in detail, and a high spatial resolution U-Pb dating method was established for low-uranium calcite minerals. The effects of cone combination, GE mode, N2 introduction and Ar carrier gas flow rate on the U and Pb signal intensity and oxide yield (UO/U) were discussed in detail. The results showed that the highest sensitivity of Pb was achieved under the conditions of Jet+X cone combination, guard electrode (GE) grounded state, 8mL/min N2 introduction and 0.9L/min Ar carrier gas flow rate, while the oxide yield (UO/U) was lower than 1%. Three low uranium (0.04−0.63μg/g), calcite U-Pb dating reference materials were used to validate the reliability of the method. Samples LD-5, PTKD-2 and TARIM yielded a lower intercept age of 73.20±0.56Ma, 152.7±2.5Ma and 206.2±1.3Ma, respectively, under the condition of 44μm beam spot, which were in agreement with the calibrated results of ID-TIMS/ID-MC-ICP-MS within the error range. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202403160057.