Fundamental study on rhenium - osmium dating for mudstones

在本项目的早期阶段，进行了铼-锇分析的开发工作。铼质谱通常受到灯丝空白的干扰，但最终获得了成功的测量。对二叠纪赤坂灰岩、丹波群晚侏罗世泥岩、岛根县中新世泥岩、现代河流和海洋沉积物等样品进行了Re-Os定年。这些数据表明两个重要方面：（1）大多数灰岩和泥岩在成岩过程中经历了严重的热事件，不适合进行Re-Os定年。在这些过程中，再循环可能会被调动起来。(2)然而，相对年轻的泥岩，没有经过热损伤，可以获得合理的年龄，因此适合进行Re-Os测年。最后，尽管Re-Os法在沉积岩中的应用可能仅限于相对年轻的岩石，但该方法在进一步的地质调查中必须值得关注。

An early stage of the present project, developmental efforts for Re-Os analyses were made. The Re mass spectrometry was usually disturbed by filament blank, but finally successful measurements were attained. However, the contribution of filament Re is still large, and our efforts must be given to reduce such effect.The Re-Os dating method were applied to several kinds of samples such as Permian Akasaka limestones, late Jurassic mudstones from Tamba group, Miocene mudstones from Shimane Prefecture, present-day river and marine sediments. Those data indicate two important aspects: (1) Most of the limestones and mudstones undergone severe thermal event during diagenetic processes are not suitable for Re-Os dating. Re might tend to be mobilized during such processes. (2) However, relatively young mudstones, which did not undergo thermal damage, can yields reasonable age, and thus are suitable for Re-Os dating.Finally, although application of Re-Os method to sedimentary rocks might be restricted to relatively young rocks, this method must deserve attention for further geological investigations.