Establishment of high-accuracy dating method of tiny zircon (<10μm) : Implication for age determination of the oldest rock on the Earth

锆石原位年龄测年为我们了解复杂地质事件提供了重要信息，本研究的目的是改进Cameca ims-1270高质量分辨率离子探针的新年龄测年方法。Camaca离子探针的高空间分辨率光学显微镜是本项目的关键设备之一。作者与OLIMPUS公司联合开发了新型光学显微镜系统（PMLOpt-1），并将其安装在我们的离子探针系统中。通过离子探针原位观测，获得了小于4μm的光学分辨率。该系统获得的特殊分辨率与SEM-EDX和CL分析相当。结合新安装的光学显微镜和“视觉舞台”系统，即处理样品座上目标坐标的数据库系统，我们可以根据样品的详细描述获得非常精确的年龄数据。利用可靠的锆石标准，建立了精确的原位年龄测年方法，并得到了传统TIMS技术的验证。这些高质量的锆石标准品通过离子探针分析证实了年龄数据的准确性。对主要来自变质岩套的锆石进行了开发技术。变质岩中锆石的典型粒度小于几十微米，因此，我们开发的高空间分辨率测年技术至关重要。与其他地球化学讨论的分析结果发表和/或准备发表。

In-situ age dating of zircon provides us the important information to understand complicated geological events, and the purpose of this research is to improve the new age dating method using high mass resolution ion probe, Cameca ims-1270. One of the key devices to establish this research project was high-spatial resolution optical microscope for the Camaca ion probe. The authors developed the new optical microscope system (PMLOpt-1) jointly with OLIMPUS Co.Ltd, and installed the system in our ion probe system. As a result, the expected optical resolution, less than 4μm, has been established, on in-situ observation by ion probe analysis. The obtained special resolution by this system is comparable with that by SEM-EDX and CL analysis. Combining observation by the newly installed optical microscope and "Visual Stage" system, which is database system handling the target's coordinates on the sample mount, we could very precise age data based on the detail description of sample. The authors also had been developed the precise in-situ age dating method using the reliable zircon standards, which had been confirmed by the conventional TIMS technique. These high-quality zircon standards confirm the accuracy of age data by the ion probe analysis. The authors applied the developed technique for the zircon mainly from metamorphic rock suites. Typical grain size of zircon in metamorphic rock is less than several tens micrometer, therefore, the high-spatial resolution dating, we developed, is essential. Analytical results with other geochemical discussions are published and/or preparing for the publication.