2015 年 49 巻 1 号 p. 19-35
We carried out an optimization of analytical parameters for U–Pb zircon dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using a NIST SRM 610 glass. As a result, we obtained the following optimum analytical parameters: laser energy: 11.7 J/cm2, repetition rate: 10 Hz, pre-ablation time: 8 sec, integration time: 10 sec and crater diameter: 25 μm. The average 206Pb/238U ratio of the NIST SRM 610 glass normalized by a 91500 zircon standard under the conditions mentioned above was 0.2236±0.0044 (1σ, N : 87). The median value of this result matches with that of the literature value within range of the analytical precision. Furthermore, the 206Pb/238U weighted mean ages of the Plešovice, OD-3 and Fish Canyon Tuff zircons, having the proposed 206Pb/238U ages of 335.48±0.95 Ma (95% conf., N : 38, MSWD : 1.1), 33.25±0.38 Ma (95% conf., N : 23, MSWD : 1.5), 28.56±0.49 Ma (95% conf., N : 34, MSWD : 5.1), respectively, were measured, normalized by the NIST SRM 610 glass standard. The results were consistent within 1% error range of the recommended values. These results suggest that the matrix effect can be reduced to less than analytical precision on materials with different physical properties under well-optimized analytical conditions.