单颗粒锆石LA-MC-ICP-MS原位微区UPb定年

U-Pb Dating of LA-MC-ICP-MS in Situ of Single Zircon

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(MC-ICP-MS),在激光频率为2Hz,束斑直径为24μm条件下,对91500、GJ-1、TEMORA-1、Plesovice和Qinghu等5个标准锆石进行了原位U-Pb年龄测定。测试结果显示^(206)Pb/^(238)U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),^(207)Pb/^(206)Pb、^(206)Pb/^(238)U、^(207)Pb/^(235)U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、GJ-1、TEMORA-1、Plesovice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JD-47进行测试,所获得的^(206)Pb/^(238)U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LA-MC-ICP-MS U-Pb年龄测试方法,与LA-ICP-MS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。

In situ U-Pb age of 91500,GJ-1,TEMORA-1,Plesovice and Qinghu standard zircons are analyzed by using Neptune Plus multicollector-inductively coupled plasma-mass spectrometry(MC-ICP-MS)and 193nm laser ablation,with the laser frequency being 2Hz and laser ablation spot size being 24μm.It is showed that the^(206)Pb/^(238)U 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,GJ-1,TEMORA-1,Plesovice 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 JD-47 from Linglong granite in Jiaodong is analyzed,its ^(206)Pb/^(238)U weighted average age(154.3±2.1)Ma agrees with SHRIMP data reported previously.Comparing with LA-ICP-MS,the LA-MC-ICP-MS zircon U-Pb dating method(24μm)in this paper has the advantages of high accuracy,short ablation time and high spatial resolution.