北西太平洋海盆の堆積物中の火山灰層・軽石層の岩石記載的及び磁気的特徴

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Fifteen volcanic ash and pumice layers were found in a deep-sea sediment core sampled at Northwest Pacific Basin during the cruise of the R. V. Hakuho-Maru. In the KH 69-2-4 (St.4) core the tephra-beds are very thin and their thicknesses are too small for detailed study, although some evidences are confirmed. Methods of this study consist of the examination of heavy mineral assemlage, refractive index of volcanic glass shards and some mafic minerals, Curie temperature, lattice constant and Ti/Fe mol ratio (%) of titanomagnetite in tephras. Excepting only two samples No.4 and 13a, others contain hornblende, and five contain biotite, zircon and apatite. Refractive indices of glass shards range mainly from 1.497 to 1.521, and individual range is very limited and their modes are also pretty concentrated. Therefore, it seems that these glass shards were erupted from acidic island arc volcanoes. Palaeomagnetic study shows that this core did not reach to the sediments of the Matuyama Reversed Epoch. This fact and paleontological studies of some adjacent cores may indicate that the rate of sedimentation exceeds 15 mm/1, 000 years. A correlation of the tephras to some already known activities of volcanoes of North Kanto and Tohoku districts in Japan is to be tried based on the present studies, but more data from additional nearby cores are needed for the reliable conclusions.
特定非営利活動法人日本火山学会の論文
1973-08-01