西南日本,岡山県柵原地域北東部のペルム系舞鶴層群と夜久野オフィオライト

A Permian convergent margin rock suite is discussed on the basis of the results of precise mappmg at the junction area of the Maizuru and the Kozuki-Tatsuno Belts. Middle to Late Permian radiolarians have been discovered from both the Kozuki unit (argillite-meta volcanicsbeded chert) and the Maizuru Group (predominantly mudstones). The newly proposed Tonoshiki Formation is composed of sedimentary breccias interpreted as being derived mostly from the Yakuno Ophiolitic rocks. Lower Permian radiolarians have been discovered from mudstone intercalated in the Tonoshiki breccias. The fomation is regarded to have been deposited on the ophiolite. The Yakuno Ophiolitic rocks together with the Tonoshiki Formation may have constituted a volcanic arc system, separating the Maizuru and Kozuki basins in Middle Permian time. The Tonoshiki Formation can be compared with the Upper Permian Upukerora Formation of the Maitai Group from the South Island of New Zealand, which was derived predominantly from the underlying Dun Mountain Ophiolite.