LA-ICP-MSS多脉冲短时间剥蚀法锆石超薄增生边定年研究

LA-ICP-MS multi-pulse short time ablation method for ultra-thin rings of zircon

锆石是一种相对稳健的定年副矿物,其颗粒常常发育增生边,然而厚度极小(一般<5μm),给获得精确年龄带来挑战。本文从制样方法、实验条件及数据算法三个方面开展了实验对比研究,以评价多脉冲短时间剥蚀法对天然锆石的超薄增生边(~1μm)LA-ICP-MS U-Pb测年的可靠性。实验结果表明:双面胶制样虽然速度快,但是样品显微观察和后续激光分析的观察效果不佳;树脂固定制样效率高,易于透射光和反射光观察,并有利于样品表面聚焦。激光分析条件下,5 Hz、2 s剥蚀相对于10 Hz、1 s剥蚀数据结果更为稳定。数据处理峰积分法优于截距法和均值法。综合上述方法,获得Plesovice和Qinghu锆石^(206)Pb/^(238)U加权平均年龄与推荐值在误差范围内一致,但是数据误差相对较大(~5%,1σ)。根据每个信号峰峰值的50%~60%来选择信号区间,监控标样Plesovice和Qinghu准确值均提高了约3%。多脉冲短时间剥蚀法、树脂固定制样与部分峰积分数据处理方法组合可以获得较好的定年结果。本方法为测定锆石增生边年龄提供了一套完整的解决方案,可为多期次的地质过程提供更有效的年代学约束。

Zircon is a robust dating accessory mineral,and often develop thin ring(generally less than 5μm),which poses challenges to obtaining accurate ages of this ring.This article conducted a series of comparative and experimental studies from three aspects:①sample preparation methods;②experimental conditions,and③data algorithms to evaluate the reliability of multi-pulse short time ablation method for LA-ICP-MS U-Pb dating of ultra-thin ring(~1μm)in natural zircons.The results showed that although the double-sided adhesive sample preparation method is fast,the sample observation under microscopic and laser system are poor.The resin-fixed preparation method has high efficiency,is easy to observe with transmitted light and reflected light,and is conducive to sample surface focusing.For laser setting parameters,data results in 5 Hz/2 s ablation are more stable than those in 10 Hz/1s ablation.The peak integration method is superior to linear regression and mean value methods for data reduction.Our results show that by using rapid erosion method for Plesovice and Qinghu zircon dating are consistent with the recommended values within the error range,but the data error is relatively large(~5%,1σ).The zircon standards Plesovice and Qinghu are improved by 3%and 2%respectively when the 50%~60%of each signal peak value peak integration method was used.The combination of resin-fixed sample preparation,peak integration data processing method and multi-pulse short time ablation method can get an acceptable age of ultra-thin zircon ring.This method can provide more age constraints for multi-age geological processes.