Fundamental study on rhenium - osmium dating for mudstones

在本项目的早期阶段，开展了Re-Os分析。Re-MS通常会受到灯丝空白的干扰，但最终获得了成功的测量结果。然而，细丝Re的贡献仍然很大，必须努力减少这种影响。对二叠纪赤坂灰岩、坦巴群晚侏罗世泥岩、岛根县中新世泥岩、现代河流和海洋沉积物进行了Re-Os测年。这些数据表明了两个重要方面：(1)大多数在成岩过程中经历了强烈热事件的灰岩和泥岩不适合Re-Os测年。在这样的过程中，RE可能倾向于被动员。(2)相对年轻的泥岩没有遭受热损伤，具有合理的年龄，适合于Re-Os测年。最后，虽然Re-Os方法在沉积岩中的应用可能仅限于相对年轻的岩石，但该方法必须在进一步的地质调查中得到重视。

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.