HR: 13:40h
AN: T43C-01    [Abstracts]
TI: Seismic structure and crustal evolution in the Izu-Bonin arc - results from active source seismic studies along the volcanic front and the rear arc -
AU: * Kodaira, S
EM: kodaira@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Sato, T
EM: tsato@jamstc.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Takahashi, N
EM: narumi@jamstec.gojp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Yamashita, M
EM: mikiya@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Miura, S
EM: miuras@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Kaneda, Y
EM: kaneda@jamstec.go.jp
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Showa-machi 3173-25, Kanazawa-ku, Yokohama, 236-0001, Japan
AB: JAMSTEC has conduced intensive active source seismic surveys, which have been widely covered in the Izu- Bonin arc, since 2004. All of those data have been acquired with equal data acquisition parameters (e.g., 200L air-gun, 5km-spacing OBSs, 204 ch streamer cable, a profile length of 500km). This makes it possible to quantitatively compare structural variations obtained along those profiles. In this study, we show seismological constraints of evolution of the arc crust on the basis of the seismic image along the present-day volcanic front: i.e., 1) crust of continental composition having Vp of 6 – 6.8 km/s has been predominantly generated beneath basaltic volcanic centers along the volcanic front, 2) the bulk compositions of the crust does not changed during evolution from the thin Bonin arc crust to the thick Izu arc crust, but represent more mafic (basaltic) than an average composition of typical continental crusts, 3) a process to return mafic to ultramafic lower crustal components to the mantle is required for an arc crust to evolve into a continental crust. In addition, we newly discovered a seismological evidence of a paleo-Izu arc (presumably Oligocene arc) based on recently acquired seismic data in the rear arc. Along arc structural variation in the rear arc is similar to that we found in the present- day volcanic front; i.e., a volume of the 6-6.8 km/s crustal component (continental composition) shows 50-80 km scale variation, which corresponds to the distribution of the basalt volcanoes. Another important finding is that the along arc structural variation in the rear arc is not correlated with the rear arc seamount chains. A remarkable difference between the two arcs is observed in the thinner parts of the 6-6.8 km/s crustal component. A volume ratio of a cruatal component having over 7 km/s (mafic to ultra-mafic composition) between the basalt volcanoes in the present-day arc shows significantly larger than that in the Oligocene arc. A process to predominantly increase such a high velocity crustal component between the basalt volcanoes may be required during the evolution process from the Oligocene arc to the present-day arc.
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7205 Continental crust (1219)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting