Abstract
Thermoluminescence (TL) dating of volcanic rocks and pumice flows around Onikobe-Naruko area was carried out by checking suitability of the sample for this technique. Samples for TL dating were divided into three ranks, A, B and C, on the basis of physical/petrographical characters and geological origin. Rank A sample is hard and compact rock which is chemically stable. Rank B is soft pumice flow or equivalent sample which is chemically unstable for long geologic time. Rank C is sediment deposited in water. For precise and reliable TL dating, only rank A sample must be used.
TL ages obtained from samples of rank A are 30.4 ka for Naruko dome lava, 187 ka for Takahinatayama lava, 169 ka and 170 ka for Shimoyamazato Tuff Formation, and 296 ka and 268 ka for Ikezuki Tuff Formation. Mitsuzawa Formation at western part of Naruko, pyroclastic flows at Yubama and Byobuiwa are identified as Ikezuki Tuff Formation due to their TL ages of 258 ka, 231 ka to 345 ka and 238 ka, respectively. TL ages of two sites are not well coincide to Ikezuki Tuff Formation. TL ages of the samples from Yubama Onsen and Gyojadaki are 169 ka and 362 ka, which correspond to the age of other eruption products rather than Ikezuki Tuff Formation.
TL age data for 83 samples of rank B and C are checked by comparison with those of rank A and existence age data. It could be reconciled with stratigraphic evidence and corresponding ages of rank A. Rank B and C data are selectively apply for preliminary stage or special purposes that the rough ages are still useful for research program.
