DEVELOPMENT OF HIGH SENSITIVITY LASER ICP MASS SPECTROMETER FOR ZIRCON CHRONOLOGY

我们一直在开发一种新的分析方法，利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，进行精确的U-Pb年龄测定。为了准确测定锆石样品10微米光斑的U-Pb年龄数据，发展了266 nm紫外光激光烧蚀取样技术。与传统的红外基频激光取样技术相比，分析所需的样品体积减少到了1/50，因此提高质谱仪的元素灵敏度是进行U-Pb年龄测定的必然要求。在这项研究中，这是通过三种不同的技术实现的：(A)离子引出透镜的改进，(B)通过应用高容量旋转泵来提高离子引出第一级的真空度，以及(C)使用被称为放大MOS成像器的二维固体离子探测器进行灵敏离子检测。这里获得的基本同位素数据清楚地表明，激光-ICPMS U-Pb年代学有可能成为一种重要的、成本效益高的锆石U-Pb年代学工具。

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.