HR: 0830h
AN: GP11C-0267    [PDF]
TI: Multi-component Magnetization Of The Late Pliocene Pyroclastic Flow Deposit In Central Japan, Indicating Early Early Pleistocene Fault Activity
AU: * Ueki, T
EM: gakusetsu-ueki@aist.go.jp
AF: Institute of Geoscience, Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Yamazaki, T
EM: toshi-yamazaki@aist.go.jp
AF: Institute for Marine Resources and Environment, Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Funaki, M
EM: funaki@nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga, Itabashi Ward, Tokyo, 173-8515 Japan
AU: Hoshi, H
EM: hoshi@auecc.aichi-edu.ac.jp
AF: Course of Science Education, Aichi University of Education, 1 Hirosawa, Igaya, Kariya, 448-8542 Japan
AB: The Late Pliocene Ichiuda Welded Tuff Bed in central Japan acquired three magnetization components. All of primary reverse intermediate temperature component, and secondary normal low and high temperature components show positive fold tests, indicating that fault-related folding structure postdated the Olduvai normal subchron. The northern segment of Itoigawa-Shizuoka Tectonic Line that bounds the North American and Eurasian Plates in central Japan, comprises the geological Otari-Nakayama and active Kamishiro faults. The Ichiuda Welded Tuff Bed intruded by the 2.1 Ma Taro-yama Andesite is subjected to the NE-SW trending folding structure adjacent to the Otari-Nakayama fault. PAFD and PThD were performed to the drilled samples of Taro-yama Andesite and the Ichiuda Welded Tuff Bed at three and five sites on both limbs of the syncline, respectively. Positive fold test for the tilt-corrected site-mean directions of the andesite indicates prefolding magnetization. The fresh welded tuff bed at one site yields similar reverse direction. Whereas the greenly altered beds at four sites shows normal tilt-corrected site-mean directions by PAFD, and following three temperature-dependent directional components by PThD: normal below 350 degree, reverse from 350 to 530 degree, and normal above 530 degree, all which show positive fold test. IRM acquisition, thermal demagnetization of three orthogonal IRM, thermomagnetic analysis with VSM, and low temperature magnetization measurements with MPMS indicate that the Ichiuda Welded Tuff Bed with single and three magnetization components contains titanomagnetites, and both titanomagnetites and magnetite, respectively. Magnetization of the Taro-yama Andesite is dominated by titanomagnetites under high temperature oxidation state and minor proportion of titanomaghemites. The Taro-yama Andesite and the Ichiuda Welded Tuff Bed exhibit primary reverse magnetism corresponding to the Matsuyama Chron. The Ichiuda Welded Tuff Bed additionally acquired normal magnetization components by hydrothermal alternation in the Olduvai Subchron; low and high temperature components are secondary TRM by re-heating for titanomagnetites and CRM by formation of magnetite, respectively. Positive fold test for secondary magnetization of the welded tuff bed would introduce the early Early Pleistocene activity of the Otari-Nakayama fault.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1519 Magnetic mineralogy and petrology
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1533 Remagnetization
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting