HR: 0800h
AN: T41C-0700    [Abstracts]
TI: Crustal and uppermost mantle structure suggesting the influences of arc and rifting activities at the northernmost part of Mariana Trough
AU: * Miura, S
EM: miuras@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Kodaira, S
EM: kodaira@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Takahashi, N
EM: narumi@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Fujie, G
EM: fujie@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Sato, T
EM: tsato@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Yamashita, M
EM: mikiya@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Kaiho, Y
EM: kaihoy@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: No, T
EM: not@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Takizawa, K
EM: takizawak@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: JAMSTEC, 3173-25 Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan
AB: Izu-Bonin and Mariana Arcs (IBM) are oceanic island arcs growing by the arc activity associated with the subduction of the Pacific Plate beneath the Philippine Sea Plate. The seismic studies in the IBM have been revealed the existences of andesitic middle crust, high-velocity (~7 km/s) lower crust, and low-velocity uppermost mantle beneath the arcs (e.g. Suyehiro et al., 1996; Takahashi et al., 2007). Based on the seismic structure and petrological calculation, the lower crustal volumes between the two results are different and requiring the process transforming the denser crustal materials into the mantle (Takahashi et al., 2007). Although, the results suggesting the formation of continental crust have been discovered in the IBM region as mentioned above, the influences of rifting activities to the oceanic island arcs have not been revealed yet. Therefore, we will show the results of a seismic study at the northernmost part of Mariana Trough and discuss the influences of arc and rifting activities. The seismic structure at the northernmost part of Mariana Trough shows anomalously thick crust (~25 km) and relatively lower P-wave velocity (~7.6 km/s) beneath the thick crust than normal mantle velocity. The peak of anomalously thick crust is located not beneath the volcanic front but beneath the extension of trough axis. This implies that the accretion at the base of crust is larger at the rift zone than that of volcanic front. Therefore, the crustal thickness beneath the volcanic front is not remarkable. From the seismic structure at the northernmost part of the Mariana Trough, the crustal accretions of the rifting activities seem to be larger than those of the arc activity.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935, 7294)
DE: 3075 Submarine tectonics and volcanism
DE: 8100 TECTONOPHYSICS
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting