地質年代学に関する技術的進歩と日本における年代学的研究  [in Japanese] Technical development in geochronology and research in Japan  [in Japanese]

Owing to the development in electronics and ultra-high vacuum technique, K-Ar, Rb-Sr and U-Th-Pb methods of radiometric dating made great advances during the 1970's, and moreover new methods, such as Sm-Nd, Lu-Hf and La-Ce, have been established. Geochronological laboratories in Japan quickly followed the development. K-Ar method is becoming more important in dating young rocks. Problems on K-Ar dating, particularly on error, argon loss and excess argon, are discussed in some detail. In Japan only few laboratories are engaged in this method, therefore they cannot meet all the needs of the Japanese geologists. Rb-Sr dating in Japan is focused on the whole-rock isochron method. A few laboratories acquired high-precision mass spectrometers and now produce high-quality data on age and initial ^<87>Sr/^<86>Sr ratio. U-Th-Pb method is known to be bery useful for dating rocks subjected to complex igneous or metamorphic history. The technique has developed to a level where even a single zircon grain can be dated. However, U-Th-Pb dating has not been carried out yet in Japan. Fission-track dating is most widely used in Japan; more than 10 laboratories are now engaged in this method. There remain, however, some technical problems to be solved. Common use of decay constants in geochronology was quickly achieved after the recommendation by the IUGS Subcommission on Geochronology in 1977. New Phanerozoic time scales were proposed by ARMSTRONG and McDOWALL (1974) and HARLAND and others (1982) during this period. Important contributions to the geochronology on the Japanese Islands are briefly reviewed.