Abstract:Building on previous research, we employed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating method to maximize sensitivity and minimize elemental fractionation effects. This was achieved by improving the testing process, optimizing the instrument parameters, and incorporating auxiliary gas sensitization equipment, such as nitrogen. In this study, three standard zircons—Qinghu, Plešovice, and Tanz—were dated using beam spot diameters of 32, 24, and 16 μm, respectively. The experimental results reveal that with a 32 μm beam spot, standard zircon Qinghu 206Pb/238U age range is 162~157 Ma, weighted average 206Pb/238U age is 159.5±0.8 Ma (2σ, n= 6, MSWD=0.36); Standard zircon Plešovice 206Pb/238U age range is 340~334 Ma, weighted average 206Pb/238U age is 337.1±1.5 Ma (2σ, n=27, MSWD=0.085); Standard zircon Tanz 206Pb/238U age range is between 574~562 Ma, weighted average 206Pb/238U age 566.6±2.9 Ma (2σ, n=29, MSWD=0.070). With a 24 μm beam spot, standard zircon Qinghu 206Pb/238U age range is 162~157 Ma, weighted average 206Pb/238U age is 159.3±0.7 Ma (2σ, n=30, MSWD=0.22); Standard zircon Plešovice 206Pb/238U age range is 341~334 Ma, weighted average 206Pb/238U age is 337.2±1.5 Ma (2σ, n=29, MSWD=0.13); Standard zircon Tanz 206Pb/238U age range is 568~561 Ma, weighted average 206Pb/238U age is 566.5±2.9 Ma (2σ, n=30, MSWD=0.054). With a 16 μm beam spot, standard zircon Qinghu 206Pb/238U age range is 163~154 Ma, weighted average 206Pb/238U age is 159.5±1.4 Ma (2σ, n=25, MSWD=0.45); Standard zircon Plešovice 206Pb/238U age range is 340~334 Ma, weighted average 206Pb/238U age is 337.3±2.0 Ma (2σ, n=30, MSWD=0.063); Standard zircon Tanz 206Pb/238U age range is 575~563 Ma, weighted average 206Pb/238U age is 567.0 ±4.3 Ma (2σ, n=30, MSWD=0.028). The weighted average ages of the three standard zircons (Qinghu, Plešovice, and Tanz) are consistent with their recommended values within the margin of error. These findings demonstrate the feasibility of using small beam spot sizes (24 μm and 16 μm) for zircon LA-ICP-MS U-Pb dating. This refined method extends the applicability of LA-ICP-MS zircon U-Pb dating, making it suitable for small zircon grains with complex structures. This model has significant theoretical research implications and economic value.
