第四紀研究におけるK-Ar法の過去・現在・未来

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Since Wasserburg and Hayden (1955) who first applied the K-Ar method to geologic samples, the method has been commonly used in geology, petrology and chronology of metamorphic and igneous rocks, and is still powerful in radiometric dating of geologic samples. In the middle of the 1960's, the method was applied to the age range of 14C method (eg. Dalrymple, 1967). This pioneering work on dating of young rocks seemed to make the method applicable well to an age range for Quaternary research. However, two years later, Dalrymple (1969) analyzed argon isotopes of historical lavas and revealed that the initial argon isotopic ratio of rocks is not always the same value as that of atmospheric argon. This strongly suggests that the conventional K-Ar method is no more valid for dating of the Pleistocene-Holocene rocks.Though it was revealed that the conventional K-Ar method was not always valid for the Quaternary Research, many geologists have used the conventional K-Ar age data in their own research projects. Some data were useful in geology but others have shown disagreement with geology, having fostered the geologist's suspicion on the validity of the radiometric dating method. In such a case, chronologist maintaining dating facility is not always in fault, and geologist, who is familar in field occurrence of rocks, also should feel the responsibility. It should be rather essential that they cooperate to find any new methods and/or techniques to give reliable age results.In the course of search for the K-Ar method (technique) applicable to the Quaternary research, we have understood that one of the most convenient and best techniques available for argon analysis of rocks with unusual primary isotopic ratios is to adopt a newly developing mass spectrometer with a three collector system by using a peak height comparison method. When the new mass spectrometer and the associated systems, which nobody has ever tried to build so far, are completed, it is possible to date ordinary volcanic rocks of ten thousands years old with a high precision and reliability. This approach makes for the K-Ar method to contribute to the Quaternary Research.
日本第四紀学会の論文
1995-08-31

第四紀研究におけるK-Ar法の過去・現在・未来

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