DEVELOPMENT OF HIGH SENSITIVITY LASER ICP MASS SPECTROMETER FOR ZIRCON CHRONOLOGY

我们一直在发展一种新的分析方法，用于精确的U-Pb年龄测定使用电感耦合等离子体质谱与新开发的激光微探针技术相结合。为了获得锆石10 μ m光斑的精确U-Pb年龄数据，采用266 nm紫外激光烧蚀取样技术。与传统的红外激光取样技术相比，样品体积减少到原来的1/50，因此，提高质谱仪的元素灵敏度是U-Pb年龄测定的必然要求。在这项研究中，这是通过不同的三种技术实现的：（a）离子提取透镜的修改，（B）通过应用高容量旋转泵来提高第一离子提取级的真空度，以及（c）使用称为AMI（放大MOS成像器）的二维固体离子检测器进行灵敏的离子检测。这里获得的基本同位素数据清楚地表明，U-Pb年代学使用激光ICPMS有可能成为一个重要的和成本效益的工具，用于U-Pb锆石年代学。

We have been developing a new analytical method for precise U-Pb age determinations using an inductively coupled plasma mass spectrometry coupled with newly developed laser microprobe technique. In order to determine the precise U-Pb age data from 10 microns spot of the zircon samples, laser ablation sampling technique using 266nm UV laser beam was developed. Resultant sample volume for the analysis was decreased down to 1/50 level compared with conventional laser sampling technique using IR fundamental Nd-YAG laser, and therefore enhancement of elemental sensitivity of the mass spectrometer was inevitable for the U-Pb age determinations. In this study this was achieved by different three techniques ; (a) modification of ion extraction lens, (b) improving the vacuum for first ion extraction stage by applying the high capacity rotary pump, and (c) sensitive ion detection using 2 dimensional solid ion detector called AMI (Amplified MOS Imager). The basic isotopic data obtained here demonstrate clearly that U-Pb chronology using Laser-ICPMS has a potential to become a significant and cost-effective tool for use in U-Pb zircon chronology.