关键词: K-Ar, Ar-Ar, 精细测年, 检验

Abstract: The K-Ar and Ar-Ar dating methods are the developed methods and widely applied to various geosciences'fields. Study on the active tectonics,latter-day volcanoes and paleo-geomagnetism requires that the K-Ar and Ar-Ar methods should be developed towards the accurate dating and small time-scale. In recent years,geologists have paid much attention to dating the Tongchang volcano,Changbaishan volcano and Wadalianchi volcano in China and acquired many achievements. So it is practically significant to study and summarize the K-Ar and Ar-Ar methods and their test for accurate dating. The key to accurate dating is: (1) appropriate sample; (2) strict pretreatment; and (3) proper measurement. In detail,the appropriate sample is that the sample can stand for right geological meanings and it is examined to be fresh under microscope over rock slice. The pretreatment is a complex process and is very important. For example,the age of raw volcanic rock in eastern slop of Maanshan is 0.18?0.08Ma and 0.45?0.32Ma due to the effect of excess argon in crystal. However,by picking out the olivine and plagioclase crystal,the age is 0.025?0.004Ma,0.028?0.006Ma and 0.030?0.005Ma,showing a good consistency. The useful method to test the validity of the measurement process is the repeated measurement of standard sample and geologic specimen. At the same time,the difference between the repeatedly measured results should be less than the theoretic error. For example,the repeatedly measured results of the two samples from Maanshan are 0.028?0.006Ma and 0.030?0.005Ma,0.030?0.005Ma and 0.036?0.005Ma,and 0.046?0.004Ma and 0.050?0.003Ma,respectively. In addition,inter-lab comparison and inter-chronology comparison are valid methods,too. The result of K-Ar and Ar-Ar dating usually is the value which is measured one time from one sample. There are two factors,including sample and measurement,which affect the result. In order to improve the accuracy of measurement,the sampling and experiment process should be reasonable and stringent. In addition,it is necessary to test out the result by a series of methods,such as inter-chronology comparison,inter-lab comparison and geological feature.

Key words: K-Ar, Ar-Ar, accurate dating, test