Fujiokia, K., H. Wada, K. Okino et al.

Izu-Bonin transect dive program –cross section of oceanic crust, serpentinite seamount, manganese pavement-

JAMSTEC Deep Sea Res., 10, 1-35, 1994 (Japanese with English abstract)

Abstract.

Izu-Bonin arc-trench transect dives were successfully performed and the following new evidences arose. Highly in situ deformed mudstone in the new fissures were found at the seaward slope. On the Mariana seaward slope, Cretaceous pillow lavas and chert, oceanic crust assemblage, were observed and collected by submersible for the first time. Forearc basement was dolerite and boninitic volcanics. Precise overview of the TOWBAC was made clear and sediments under the community, ear bone were obtained. Along the steep cliff of the Torishima Rift, 1.7 km continuous cross section of the arc volcanics were observed and it was comparable with deep sea drilling. Manganese pavements similar to those found at the seaward slope of the Ryukyu trench was found together with rop and pillow lavas at the Kinan escarpment, eastern Shikoku basin. Sepentinites were collected at Conical, Pacman seamounts as well as Coni-Pac triangle in the Mariana forearc. Peridotite which constitutes the upper mantle were contained in serpentine flows. Gid sea anemone which was found during Alvin dive, 1987 still alive on tone of the carbonate chimneys. These results offer new evidences that the oceanic type Izu-Bonin and Mariana arc-trench system has quite different nature with the continental type Northeast Japan arc-trench system, specially morphology and stratigraphy at seaward slope, structure and chemistry of the wedge mantle, formation of rift and crustal structure and backarc crust and history.

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