@article{oai:u-fukui.repo.nii.ac.jp:00027143,
 author = {藤井, 純子 and 中島, 正志 and FUJII, Junko and NAKAJIMA, Tadashi},
 journal = {福井大学教育地域科学部紀要 第II部 自然科学 (地学編)},
 month = {Dec},
 note = {Paleomagnetic studies of widespread late Pleistocene tephras have been carried out in order to construct geomagnetic charts for Japan in prehistoric times. Magnetic minerals contained in the welded tuff specimens are likely to be titanomagnetite and magnetite on the basis of the thermal demagnetization (ThD) results. Since ThD experiments were not performed on the ash samples, it is not certain what magnetic minerals are in the ash samples. Progressive acquisition of isothermal remanent magnetization (IRM) and ThD of a three-component IRM, therefore, were investigated to identify the ferromagnetic mineral content in the ash samples. For the IRM experiments, one sample from each site was arbitrarily chosen after the paleomagnetic measurements. Because they are unconsolidated and readily disintegrate, the ash samples were held in plastic cubes, which melt at about 160 ℃. Synthetic specimens were prepared using the ash samples and plaster of Paris for ThD of the induced IRM. The IRM acquisition experiments were carried out using a pulse magnetizer in magnetic fields with intensities up to 3000 mT. A three-component IRM was produced by applying a different DC field (3000, 400, and 120 mT) to each of the three perpendicular axes of the specimen with the pulse magnetizer. The acquisition and ThD curves of the IRM components for almost all the specimens show similar features (A-type). The smooth IRM acquisition curves rise steeply up to 100 mT, and reach saturation by 500 mT. The ThD of each IRM component is plotted separately in the demagnetization diagram. The ThD curves show that the soft (<120 mT) coercivity fraction is the largest, and that the medium (120 to 400 mT) and hard (400 to 3000 mT) fractions are minor. The soft coercivity fraction was demagnetized smoothly to zero by 580 ℃, indicating that the specimens'magnetic mineralogy is also dominated by titanomagnetite and magnetite. The IRM acquisition curves for other some samples rise steeply at first but does not reach saturation even in 3000 mT. The ThD curves show that the medium and hard fractions exhibit evidences for unblocking of hematite at 680 ℃ (B-type), or unblocking of goethite at 100 ℃ (C-type).},
 pages = {47--55},
 title = {第四紀火山灰についての段階的 I RM獲得実験と三成分 I RMの熱消磁実験  Progressive acquisition of IRM and thermal demagnetization of a three-component IRM for the Quaternary volcanic ashes},
 volume = {54},
 year = {2002}
}