Japan Geoscience Union Meeting 2014

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Oral

Symbol S (Solid Earth Sciences) » S-EM Earth's Electromagnetism

[S-EM37_30AM1] Geomagnetism, paleomagnetism and rock magnetism

Wed. Apr 30, 2014 9:00 AM - 10:45 AM 413 (4F)

Convener:*Ataru Sakuraba(Department of Earth and Planetary Science, University of Tokyo), Nobutatsu Mochizuki(Priority Organization for Innovation and Excellence, Kumamoto University), Chair:Ataru Sakuraba(Department of Earth and Planetary Science, University of Tokyo), Yuhji Yamamoto(Center for Advanced Marine Core Research, Kochi University)

10:30 AM - 10:45 AM

[SEM37-P06_PG] Paleomagnetic direction of the Tomikusa Group in southern Nagano Prefecture and its tectonic significance

3-min talk in an oral session

*Kazuki SAKO1, Hiroyuki HOSHI1 (1.Aichi University of Education)

Keywords:paleomagnetism, Tomikusa Group, Median Tectonic Line, Miocene, rock magnetism, tectonics

We report here a new paleomagnetic direction from Early Miocene (18-17 Ma) sediments of the Tomikusa Group in southern Nagano Prefecture, and discuss the formation of curvature of the Median Tectonic Line (MTL) in central Honshu. Sedimentary rock samples collected from 24 sites were demagnetized stepwise, and site-mean directions were determined for 23. Rock magnetic experiments suggest that the main magnetic minerals are magnetite and maghemite. The site-mean directions pass a reversal test, indicating primary remanent magnetization. The overall mean direction with a northerly declination is indistinguishable from the Early Miocene reference direction derived from the Asian continent. This comparison suggests no significant rotation in the study area with respect to the continent since 17 Ma. The mean declination is deflected about 15 deg counterclockwise with respect to the strike of the nearby MTL. The same angular relationship is also found in other sedimentary basins in central Honshu (Ichishi in Mie Pref., Chita Peninsula in Aichi Pref., Shitara in Aichi Pref., and Chichibu in Saitama Pref.). Thus we conclude that the MTL was straight in the late Early Miocene (18-17 Ma).