HR: 1340h
AN: T13A-1122    [Abstracts]
TI: Tectonic Setting of the Lyra Basin, west of the Ontong Java Plateau
AU: * Nakanishi, M
EM: nakanisi@earth.chiba-u.ac.jp
AF: Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan
AU: Sano, T
AF: Department of Geology and Paleontology, The National Science Museum, Tokyo, 3-23-1 Hyakunincho, Shinjuku-ku, Tokyo, 169-0073, Japan
AU: Shimizu, K
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan
AB: We present the preliminary results of the geophysical investigation and rock sampling in the Lyra Basin, the deep ocean basin west of the Ontong Java Plateau. The Ontong Java Plateau (OJP) is one of the most voluminous large igneous provinces. The evidences from drilling samples indicate that most of the OJP formed rapidly about 120 Ma at mid-southern latitude in the Pacific Basin. Deep ocean basins are contiguous with the OJP. For settlement of the argument about the origin of the OJP, the tectonic setting of the deep ocean basins around the OJP must be revealed. Tectonic histories of the Nauru, East Mariana, and Pigafetta basins, were revealed using the Mesozoic magnetic anomaly lineations. That of Lyra basin is, however, still unknown because of lack of magnetic anomaly lineations. The depth of the seafloor in the Lyra Basin deepens west, from 4000 to 5000 m. The Lyra Trough, crossing the Lyra Basin, is a broad and deep graben. In December 2006, we conducted the geophysical investigation and rock sampling in the Lyra Basin using R/V KAIREI, Japan Agency for Marine-Earth Science and Technology. Our bathymetric measurement revealed the topographic expression of the Lyra Trough. The depth of the trough is around 5500 m. The bottom of the trench as a whole is very smooth except for several lineated ridges. The height of the lineated ridges is about 500 m. The length of the lineated ridges is around 20 km. The strike of some ridges is N35°W and parallel to the trough strike. That of others is N50°W and oblique to the trough strike. Seamounts are located in the eastern rim of the Lyra Trough south of 1°30'N. The height of the seamounts is more than 2500 m. We obtained volcanic samples from the lineated ridge in the Lyra Trough and the seamount in the eastern rim of the trough. Most of igneous rocks are volcanic breccia, being coated by thick Mn crust. Although many volcanoclastic rocks are highly altered, some fresh samples were recovered. They are olivine-titanaugite phyric alkaline basalt or picrite. This type of volcanic rocks is different from that of the OJP's volcanic rocks.
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3038 Oceanic plateaus and microcontinents
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 9355 Pacific Ocean
DE: 9610 Cretaceous
SC: Tectonophysics [T]
MN: 2007 Fall Meeting