68. 海野　進・中野　俊・石塚　治・駒澤正夫, 2009. 20万分の1地質図幅「小笠原諸島《NF-53-12, NG-54-7,8,9,16,17,18,20, NG-56-18. 産業技術総合研究所地質調査総合センター．
68. Umino, S., Nakano, S., Ishizuka, O. and Komazawa, M. , 2009. Geological Map of Japan 1:200,000, Ogasawara Shot・(in Japanese). Geological Survey of Japan, AIST.

Volcanic basement of the Chichi Jima and Muko Jima Island Groups formed by submarine volcanism of mainly boninite-series magmas 48-45 Ma. Arc tholeiitic andesite and dacite lavas are interbedded in the middle of boninitic sequences and both calc-alkalic and high-Ca boninitic magmas erupted in the north of Chichi Jima and Otōtō Jima 45 Ma. Early volcanic eruptions were quiet extrusions of lava, followed by intermittent pyroclastic falls and base surges in later periods. Chichi Jima uplifted above sea level by Oligocene in age and the Oligocene reef limestone rests on the eroded lavas and dikes. Haha Jima consists of middle Eocene (about 44 Ma) arc tholeiitic and calc-alkalic volcanic rocks deposited under shallow water and partially on land. The volcanic eruptions produced mainly hyaloclastite and fall-out scoria beds, associated with one pumice fall and three pyroclastic flow deposits. Planktonic foraminiferal zonation of P 11-14 are obtained from Nummulites-bearing calcareous sandstone, conglomerate and limestone intercalated with the volcanic rocks. The uppermost fossiliferous limestone, resting on an eroded surface of the underlying volcanic rocks in Sekimon, corresponds to Planktonic foraminiferal zonation of P 15-17. Nishinoshima and the Volcano Islands (Kitaiō Tō, Iō Tō and Minamiiō Tō) lie on the summits of large submarine volcanoes and are underlain by subaerial volcanic products younger than middle Pleistocene and the Holocene talus deposits and sand and gravel beds. Both Nishinoshima and Iō Tō comprise two volcanic edifices and sand and gravel beds filling the gaps between these two. Both volcanoes are active with some historical records. Okinotori Shima is an atoll capping the summit of a seamount, which is composed of reef and foraminifer limestone. Minamitori Shima is an uplifted atoll on the summit of a seamount, which is composed of unconsolidated sand and gravel beds. The basement, consisting of corral reef situated on a volcanic edifice, is not exposed on land.

Keyword: Hahajima, Ogasawara Archipelago, Bonin Islands, 1:50,000 Geological map, Geological Survey of Japan
キーワード: 小笠原諸島，小笠原群島，20万分の1地質図幅，産総研，地質調査総合センター