HR: 0830h
AN: GP11D-0287    [PDF]
TI: Magnetic Anisotropy and Paleomagnetic Studies in Relation to the Tectonic Evolution of the Miocene-Pleistocene Accretionary Sequence in the_@Boso and Miura Peninsulas, Central Japan
AU: Kanamatsu, T
EM: toshiyak@jamstec.go.jp
AF: Japan Marine Science And Technology Center, 2-15 Natsushima -cho, Yokosuka, 237-0061 Japan
AU: * Herrero-Bervera, E
EM: herrero@akolea.soest.hawaii.edu
AF: SOEST-HIGP, University of Hawaii, 1680 EAST WEST ROAD, Honolulu, HI 96822 United States
AB: In order to distinguish the invisible deformation sense as well as the intensity of deformation of sediments, anisotropy of magnetic susceptibility (AMS) and paleomagnetic methods have been applied on the middle Miocene-Pleistocene accretionary sequence in the Boso and Miura Peninsulas of central Japan. These peninsulas were formed in an arc-arc tectonic collision with subdivisions of two contrasting tectonic provinces: the southern province, which is a highly deformed accretionary prism and slope basin, and the northern province, which is a gently deformed forearc basin. The sequence in the southern province is associated with abundant synsedimentary deformation structures of folding and faulting generated in accretionary tectonics. Results of the AMS experiment of the sequence show the developing of a strong magnetic lineation. It is conceivable that such lineation had to be generated during the process of deformation, and in a direction perpendicular to the shortening of the fabric of the rock still in an unconsolidated state. Such magnetic lineations reconstructed by the paleomagnetic declinations reveal a more complicated localized rotation at the accretionary prism and slope basin area. These lineations show a consistent pattern in the east-west direction in each region. It also suggests that the sedimentary sequence was subjected to a north-south compression, although the compressive direction since 3 Ma ago has been in the northwest direction caused by the subduction of the Philippine Sea Plate. Our results indicate a northward subduction system of the Philippine Sea plate during the middle Miocene-Pliocene, and also a change in the subduction direction at about 3 Ma.
DE: 1518 Magnetic fabrics and anisotropy
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 8005 Folds and folding
DE: 8100 TECTONOPHYSICS
DE: 8123 Dynamics, seismotectonics
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting