| Abstract |
Electron spin resonance (ESR) dating has been tried on quartz from hydrothermally altered rocks in the Unzen geothermal field, Western Kyushu, Japan. The Un zen field is roughly separated into two parts (north-eastern and south-western) by a national road running across the center of the field. The north-eastern part is very active with fumaroles and hot springs. The southwestern part will be old only with altered rocks. ESR ages were obtained from six samples: three (UJ-8,16,17) from the north-eastern part and other three (UJ-2l,22,22') from the south-western part. It is examined that ESR dating will apply to geothermal area by the comparison of these ESR ages to present geothermal manifestation. ESR method is one of microwave spectroscopy which can detect lone electrons. ESR age is obtained from the density of lone electrons produced by natural radiation. The density of lone electrons is in proportion to the total radiation dose (TD). ESR age is calculated by TD(Gy) / Dose(Gy/y). TD can be obtained by comparing ESR intensity of unirradiated samples with that of samples irradiated artificial gamma ray. Dose (D) is calculated by concentrations of U, Th and K analyzed chemically or radiometrically. ESR signals are from some lattice defects in quartz (e.g. E',Ge centers and OHC) which holds lone electrons. Dating can be made on each lattice defect individually. Usually three ages can be obtained from one sample due to different thermo-stability of each signal. |