西南日本,島根半島佐波地域の中新世海底火山(<特集>水底における火山活動とその噴出物)

概要

論文の詳細を見る
In the Shimane Peninsula, lower (Koura Formation) to middle (Josoji and Ushikiri Formations) Miocene strata, consisting mainly of shale and volcanigenic materials are distributed. The middle Miocene magmatism can be divided into three stages based on the type of activity. The Sanami volcanic rocks lie stratigraphically in the middle of the Ushikiri Formation, approximately at the boundary between the effusives of Stage II (the formation of isolated submarine volcanoes) and Stage III (eruption of sheet flows). The Sanami volcanic rocks comprises, in stratigraphic order, basalt pillow lavas, andesite sheet flows, basalt volcaniclastic rocks, basalt sheet flows and dacite pyroclastic rocks. The succession is cut by northwest trending faults, along which basaltic dikes have been intruded. These faults and dikes are particularly abundant in a narrow zone around Sanami Bay, which includes much evidences of nearvent activity such as; feeders to pillow lava, high velocity pyroclastic flows containing many bombs, a crater and neck breccias. The explosive activities in Sanami district took place alternately with effusions of sheet flows in a shallow marine environment, which is corroborated by the marine shell fossils.
地学団体研究会の論文
1990-11-25