A DISCUSSION ON PRECAMBRIAN GEOCHRONOLOGY

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.