离子探针多接收技术在锆石U-Pb定年中的应用

Zircon U-Pb dating using conventional Secondary Ion Mass Spectrometry (SIMS) is one of the most important in-situ geochronology methods. The uncertainty of U-Pb zircon age could be achieved at ~ 1% level with spatial resolution of 10-30 µm. However, the method has begun to stagnate after an evolution of several decades. The studies on many aspects, like mechanism of U-Pb fractionation, spatial resolution and analytic content, seem to have reached their limits. This proposal summarized three trends of SIMS U-Pb dating technique: higher precision, better resolution and more information. With the most advanced MC-SIMS platform, IMS-1280HR, multi-collector technique will be applied to the routine SIMS U-Pb dating analysis. Primary beam density can be improved by studying on material and geometry of the ion source cathode systematically; a data processing program will be developed by studying on the relationships between U-Pb fractionation behaver and depth of crater, under the conditions of different beam density; more information will be acquired during the analysis by using multi-collector; the precision of relative yield calibration and the analytical accuracy will be improved by studying on the non-linear corrections of EM dead-time. The limit of precision and spatial resolution of the U-Pb dating technique will be explored in this study. More information like REE pattern will be acquired during the U-Pb analysis, simultaneously. The improvements of the SIMS U-Pb dating technique will provide high quality data support in solving complex geological problems.

离子探针锆石U-Pb定年技术是原位微区年代学中最重要的方法之一。可在10-30µm尺度上实现~1%精度的U-Pb年龄测定。然而，该技术经过半世纪的发展已进入瓶颈期，包括对U-Pb分馏规律的认知、空间分辨率的提高及分析内容的开发等方面似乎已达到极限。本申请总结了该领域“更精、更细、更多元”的发展趋势，将最先进的IMS-1280HR离子探针多接收技术应用到U-Pb定年中。通过研究该仪器离子源阴极材料及形状，提高离子束密度；通过研究不同离子束密度下U-Pb分馏及剥蚀深度间关系，提出新的数据处理方式；通过使用多接收器提高分析效率，在不显著延长分析时间的前提下增加分析内容；通过研究电子倍增器死时间非线性校正方法，提高多接收器分析的准确度。进而探索离子探针锆石U-Pb定年精确度、空间分辨率的极限，实现U-Pb年龄与REE等多元信息的同步测定。为解决更复杂的地质问题提供技术支持。

大型离子探针具有高精度、高空间分辨率的优点，其微区、原位的分析能力使其成为现代地球化学分析的重要手段。在众多应用中，锆石U-Pb定年无疑是离子探针应用范围最广的领域，根据其“更精、更细、更多元”的发展趋势，本项目基于IMS-1280HR多接收离子探针，通过离子源改进提高离子束密度，从而在不明显损失精度的前提下获取更高的空间分辨率，在原有5微米定年技术的基础上进一步突破，获得了2-3微米的空间分辨率；通过研究集中选点的条件下U-Pb年龄的偏差与分析参数的关系，提出新的数据校正方式，使得年龄偏差控制在正常的1%水平，显著提高了复杂锆石年龄的准确性；通过结合高质量分辨率的单接收器和动态多接收技术，提高分析效率，在不显著延长分析时间的前提下，在10微米尺度上同时获取高精度的U-Pb年龄（～1%）和REE含量信息。为解决珍贵样品的精确定年提供了新的技术支持。