HR: 0800h
AN: T11C-0402    [Abstracts]
TI: Hahajima Seamount: an enigmatic tectonic block at the junction between Izu-Bonin and Mariana Trench
AU: Tokunaga, W
EM: tokunagaw@jamstec.go.jp
AF: Global Ocean Development Inc, 1-13-8, Kamioooka-Nishi, Konan-ku, Yokohama, 233-0001 Japan
AU: * Fujioka, K
EM: fujiokak@jamstec.go.jp
AF: Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Yokose, H
EM: Yokose yokose@sci.kumamoto-u.ac.jp
AF: Department of Earth Sciences, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555 Japan
AB: The Hahajima Seamount located at the junction between Izu-Bonin and Mariana forearc slopes, represents a notable rectangular shape and consists of various kinds of rocks. An elaborated bathymetric swath mapping with geophysical measurements and dredge hauls showed the Hahajima Seamount is cut by two predominating lineaments, NE-SW and NW-SE. These lineaments are of faults based on the topographic cross sections and three-dimensional view (Whale's-eye view). The former lineament is parallel to the transform faults of the Parece Vela Basin in the Philippine Sea whereas the latter is to the nearby transform fault on the subducting Pacific Plate underneath the Izu-Bonin arc-trench system. The rocks obtained from the Hahajima Seamount are ultramafic rocks mostly harzburgite, boninite, basalt, andesite, gabbro breccia and sedimentary rocks, which characterize an island arc and an ocean basin affinities. The gravity measurement and seismic reflection survey offer neither definite gravity anomaly at the seamount nor definite internal structures beneath the seamount. The NW-SE trending fault and small scale serpentine flows were observed during the JAMSTEC submersible Shinkai 2000 dives at the Hahajima Seamount. The rectangular shape, size of seamount, various kinds of rocks and all the geophysical measurements strongly support that the Hahajima Seamount is not a simple serpentine seamount but a tectonic block unlike previously believed that was controlled by various tectonic movements.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8140 Ophiolites (3042)
DE: 8178 Tectonics and magmatism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: Fall Meeting 2005