HR: 1340h
AN: T13A-1127    [Abstracts]
TI: A discovery of another petit spot volcanic field in the Cretaceous Pacific Plate
AU: * ABE, N
EM: abenatsu@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AU: Fujimoto, H
EM: fujimoto@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6, Aoba, Aoba-ku, Sendai, 980-8578, Japan
AU: Hirano, N
EM: nhirano@eqchem.s.u-tokyo.ac.jp
AF: Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113- 0033, Japan
AU: Kirby, S
EM: skirby@usgs.gov
AF: US Geological Survey, MS977 375Middlefield, Mennlo Park, CA94061, United States
AU: Kido, M
EM: kido@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6, Aoba, Aoba-ku, Sendai, 980-8578, Japan
AU: Osada, Y
EM: osada@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6, Aoba, Aoba-ku, Sendai, 980-8578, Japan
AU: Hino, R
EM: hino@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6, Aoba, Aoba-ku, Sendai, 980-8578, Japan
AU: Tsushima, H
EM: tsushima@aob.geophys.tohoku.ac.jp
AF: Graduate School of Science, Tohoku University, 6-6, Aoba, Aoba-ku, Sendai, 980-8578, Japan
AU: Koike, Y
EM: koikey@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan
AB: Petit spot is a volcanic micro-knolls recently discovered in the NW Pacific (Hirano et al., 2006). According to Hirano et al. (2006), this new kind of intra-plate volcanism is explained by reaking of small fraction of upper mantle melt from asthenosphere through flexure-induced fractures in the subducting oceanic plate. Thus, they suggest it is a non-plume related intra-plate. Two volcanic fields of petit spot volcanoes have discovered in the NW Pacific on a single flow line of the current plate motion since a JAMSTEC R/V Kairei cruise (KR04-08) in June 2004. They erupted at 0.1~1.0 Ma on one site and 4.2-8.5 Ma on the other site. Petit spot volcanism is still enigmatic phenomenon. We do not know the eruption mechanism, the melt formation in the upper mantle, nor their uniqueness. On the other hand, another possible volcanic field of petit spot volcanoes was previously shown by multi-narrow beam survey (Hirano et al., 2006). This field is also in the Cretaceous Pacific Plate, but about 200km away from the same flow line with the previously discovered petit spot volcanic field. If it is also petit spot volcanic field, it will imply that this kind of melt leaking volcanism is not unique, but occurs anywhere in the similar tectonic settings of the oceanic plates. During R/V Kairei cruise in June 2007 (KR07-07), three dives by JAMSTEC ROV KAIKO 7000II took place the field, called -Chocochip knolls-. We sampled petitspot-like young alkaline basalt from two knolls of them, and the other one knoll has a large volcanic caldera with fresh outcrops of mid-ocean ridge basalt and dolerite. Their eruption ages have not measured yet, but they are certainly unaltered recent erupted basalt in the Cretaceous Pacific Plate as it was expected. Furthermore, these knolls are overlapped with an aftershock distribution of one large outer rise earthquake (M7.1) in 2005. That is sub-parallel to the trench axis, and horst & graben structure on the Pacific Plate. The relationships between the petit spot volcanism and the outer rise earthquake is not clear, but the petit spot activity certainly disturbs the oceanic plate strutigraphy and may change its physical property.
DE: 7218 Lithosphere (1236)
DE: 7220 Oceanic crust
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8415 Intra-plate processes (1033, 3615)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting