前寒武纪地质年代学问题的探讨

    A DISCUSSION ON PRECAMBRIAN GEOCHRONOLOGY

    • 摘要: 从测年元素的地球化学研究看到,各种测年方法都有其局限性。在一定的地质条件下选择合适的方法将可以得出正确的结论,也可能区分出岩浆的和变质的年龄。单颗粒锆石和斜锆石U—Pb方法以及有限度地使用Rb—Sr等时方法在高级区是适宜的选择。在低级区除了单颗粒锆石和斜锆石U—Pb法外,40Ar-89Ar法和矿物Sm-Nd等时线方法是适用的。对未变质的火成岩来说,许多方法都是可用的。对沉积岩定年的可靠方法目前还没有研究出来。

       

      Abstract: Based on the studies of geochemical characteristics of dating elements, it is thought that each of the dating methods is rather limited. Selection of appropriate methods in the light of specific geological conditions may lead to a correct conclusion and make it possibte to distinguish between magmatic and metamorphic ages. The single-grain zircon and baddeleyite U-Pb method and the Rb-Sr isochron method used in a proper way are of appropiate Choice for high-grade metamorphic terrains. Besides the single-grain zircon and baddeleyite U-Pb method, the 40Ar-39Ar and mineral Sm-Nd isochron methods are applicable to low-grade terrains. Many dating methods are suitable for unmetamorphic igneouts rocks. Unfortunately, so far reliable methods of dating sedimentary rocks have not been found yet.

       

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