著者

津屋 弘達

出版者

東京帝国大学地震研究所

雑誌

東京帝国大学地震研究所彙報 (ISSN:00408972)

巻号頁・発行日

vol.16, no.1, pp.171-200, 1938-03-20

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Nii-sima, situated abjut 40 km SW. of Volcano O-sima, in 34°23'N. and 139°15'E., is a volcanic island measuring about 11 km in a N.-S. direction and 2.5 km E.-W. It consists, like Kozu-sima, of several Quaternary liparitic volcanoes, besides the ruin of a basaltic volcano, of which the Mukoyama volcano in the southern part of the island is the youngest as well as the largest. The rocks constituting the liparitic volcanoes are grouped under three main headings―hornblende-plagioliparite, hornblende-biotite-plagioliparite, and biotite-plagioliparite―in order of eruption. Thus the structural scheme of the island, together with the rock-types represented may be summarized as follows: 1. Lavas forming the lowest visible part of Nii-sima (hornblende-plagioliparite)…{Seto-yama lava. Minezi lava. Zinaka-yama lava. Daisan-yama tuff and tuff-breccia (juvenile ejecta: hornblende-plagioliparite). Simawake-zawa tuff (juvenile ejecta: hornblende-plagioliparite). 2. Akasakino-mine volcano (hornblende-plagioliparite)…{Akasakino-mine lava. Akasakino-mine ejecta bed. 3. Niisima-yama volcano (hornblende-biotite-plagioliparite)…Niisima-yama lava. Marusima-yama volcano (hornblende-biotite-plagioliparite)…Marusima-yama lava. 4. Wakago basaltic volcano (augite-oli ine-bytownite-basa't)…Wakago basaltic ejecta bed. 5. Miyatuka-yama volcano (biotite-plagioliparite)…{Habusi-ura ejecta bed. Miyatuka-yama lava. Miyatuka-yama ejecta bed. 6. Atti-yama volcano (biotite-plagioliparite)…{Awai-ura ejecta bed. Atti-yama lava. 7. Muko-yama volcano (biotite-plagioliparite)…{Siromama bed (Omine pumicecone). Muko-yama ejecta bed. Muko-yama lava.