单颗粒锆石LA—MC—ICP—MS原位微区U—]Pb定年

UPb Dating of LAMCICPMS in Situ of Single Zircon

摘要:

利用193nm准分子激光剥蚀系统（LA），联用多接收电感耦合等离子体质谱仪（MCICPMS），在激光频率为2Hz，束斑直径为24μm条件下，对91500、GJ1、TEMORA1、Pleovice和Qinghu等5个标准锆石进行了原位UPb年龄测定。测试结果显示206Pb/238U加权平均年龄分别为(1062.3±4.3)Ma（2σ，n=21），(604.8±3.1)Ma（2σ，n=20），(418.3±1.6)Ma（2σ，n=27），(337.3±1.3)Ma（2σ，n=28），(159.86±0.64)Ma（2σ，n=28），207Pb/206Pb、206Pb/238U、207Pb/235U比值的分析精度（2σ）2%左右，加权平均年龄的分析精度（2σ）均小于0.5%。上述结果表明，91500、GJ1、TEMORA1、Pleovice和Qinghu等5个标准锆石的加权平均年龄在误差范围内与前人报道完全一致。对产在胶东玲珑花岗岩中的实际锆石样品JD47进行测试，所获得的206Pb/238U加权平均年龄为(154.3±2.1)Ma，与SHRIMP测试结果吻合。文中建立的24μm锆石LAMCICPMS UPb年龄测试方法，与LAICPMS方法相比，测试精度高，剥蚀时间短，激光剥蚀空间分辨率提高。

Abstract:

In situ UPb age of 91500, GJ1, TEMORA1, Pleovice and Qinghu standard zircons are analyzed by using Neptune Plus multicollectorinductively coupled plasmamass spectrometry (MCICPMS) and 193nm laser ablation, with the laser frequency being 2Hz and laser ablation spot size being 24μm. It is showed that the206Pb/238U weighted average ages of standard zircons are （1062.3±4.3） Ma（2σ，n=21）, 604.8±3.1 Ma （2σ，n=20）, （418.3±1.6） Ma（2σ，n=27）, （337.3±1.3） Ma（2σ，n=28）, （159.86±0.64） Ma（2σ，n=28）. The precision of measured Pb/U ratios is about 2% (2σ), and the relative deviation (2σ) of weighted average age are all smaller than 0.5%. Five zircons 91500, GJ1, TEMORA1, Pleovice and Qinghu standard age are within the error range, and the weighted average age shows an excellent agreement with the previously reported data. The zircon sample JD47 from Linglong granite in Jiaodong is analyzed, its 206Pb/238U weighted average age(154.3±2.1 )Ma agrees with SHRIMP data reported previously. Comparing with LAICPMS, the LAMCICPMS zircon UPb dating method (24μm) in this paper has the advantages of high accuracy, short ablation time and high spatial resolution.