HR: 0800h
AN: V51A-1461    [Abstracts]
TI: New type volcanism along fractures on the flexural Cretaceous Pacific Plate
AU: * Hirano, N
EM: nhirano@geo.titech.ac.jp
AF: Department of Earth & Plametary Science, Tokyo Institute fo Technology, 1-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Takahashi, E
EM: etakahas@geo.titech.ac.jp
AF: Department of Earth & Plametary Science, Tokyo Institute fo Technology, 1-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Hirata, T
EM: hrt1@geo.titech.ac.jp
AF: Department of Earth & Plametary Science, Tokyo Institute fo Technology, 1-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Yamamoto, J
EM: jyama@bep.vgs.kyoto-u.ac.jp
AF: Institute for Geothermal Sciences, Kyoto University, Noguchibaru, Beppu, 874-0903 Japan
AU: Machida, S
EM: machida@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo, 164-8639 Japan
AU: Ishii, T
EM: ishii@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo, 164-8639 Japan
AU: Abe, N
EM: abenatsu@jamstec.go.jp
AF: Institute for Research Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, 237-0061 Japan
AB: No present-day volcanic activity had been documented on a Cretaceous lithosphere so far. However, Hirano et al. (2001) reported a young basalt (6 Ma) on the 130 Ma Pacific Plate in the Japan Trench. Through our expedition for the young volcanoes in the NW Pacific conducted during the KR04-08 cruise of JAMSTEC R/V KAIREI in June 2004, apparently quite young lavas were dredged from a knoll. The site is located on the eastern edge of the outer-rise, and at the inferred eruption site for the 6 Ma lavas found in the Japan Trench. Young (<1 Ma) volcanoes of strongly alkaline magma was discovered on the Early Cretaceous (135 Ma) Pacific Plate. Major and trace element compositions of lavas suggest the magma from asthenosphere. Noble gas isotopes of bubbles in the quenched glasses clearly show that the source of magma is similar to MORB rather than that of OIB. The WNW-ESE alignments of knolls are perpendicular to hinge lines on the flexural outer-rise. The eruption occurred along the maximum horizontal compression due to the down-warping of the Pacific Plate for sub-crustal magma injection. An old lithosphere may be deformed or flexed due to seamount-loading, and due to bending related to the plate subduction. Large curvatures of the lithosphere might cause brittle fractures. The location of this study coincides with the concave part of the outer-rise. Some workers have supposed that the highly alkaline magma leaks on the flexural part of lithosphere such as the flexural arch and rejuvenated stages, which are far from the active shield volcanoes at the Hawaiian and the Samoan islands. Hence, the asthenospheric melt may be able to escape to the surface wherever the lithosphere is flexed and fractured, and this young volcano might be such an example.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3075 Submarine tectonics and volcanism
DE: 3615 Intra-plate processes (1033, 8415)
DE: 8138 Lithospheric flexure
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005