eEarth www.electronic-earth.net 1815-381X 1815-3828 3 1 2008 10.5194/ee-3-1-2008 http://www.electronic-earth.net/3/1/2008/ http://www.electronic-earth.net/3/1/2008/ee-3-1-2008.html http://www.electronic-earth.net/3/1/2008/ee-3-1-2008.pdf 1 6 2008-02-29 Characteristics of chlorites in seismogenic fault zones: the Taiwan Chelungpu Fault Drilling Project (TCDP) core sample Y. Hashimoto hassy@cc.kochi-u.ac.jp O. Tadai M. Tanimizu W. Tanikawa T. Hirono W. Lin T. Mishima M. Sakaguchi W. Soh S. R. Song K. Aoike T. Ishikawa M. Murayama K. Fujimoto T. Fukuchi M. Ikehara H. Ito H. Kikuta M. Kinoshita K. Masuda T. Matsubara O. Matsubayashi K. Mizoguchi N. Nakamura K. Otsuki T. Shimamoto H. Sone M. Takahashi Department of Natural Environmental Science, Kochi University, Kochi, Japan Marine Works Japan Ltd., Nankoku, Japan Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Japan Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan Department of Geosciences, National Taiwan University, Taipei, Taiwan Center for Deep Earth Exploration, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan Faculty of Education, Tokyo Gakugei University, Koganei, Japan Department of Earth Sciences, Graduate School of Science & Engineering, Yamaguchi University, Yamaguchi, Japan Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan Earthquake Research Department, National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan Department of Geoenvironmental Science, Graduate School of Science, Tohoku University, Sendai, Japan Department of Earth and Planetary Systems Science, Hiroshima University, Japan Department of Geophysics, School of Earth Sciences, Stanford University, Stanford, CA, USA The iron content and the asymmetry of iron and magnesium ions in chlorites are examined for the Chelungpu Fault in Taiwan, which is a seismogenic fault. The samples are collected from the cores drilled for the Taiwan Chelungpu Fault Drilling Project (TCDP, borehole B). Three fault zones are recognized as candidates for the source of seismogenic materials. The fault zones are composed of fractured-damaged rocks, breccia, gray gouge, black gouge, and black material. Chlorite from each type of rock was analyzed by using X-ray diffraction (XRD). The iron content and asymmetry of the iron and magnesium ions in the chlorites were estimated from the XRD peak ratios. The hydroxide and silicate layers of chlorite in the black gouge and black material have low iron contents. Many studies have suggested that a temperature rise occurred at the fault zones. In addition, the temperature rise can result in the production of iron oxides such as magnetite or maghemite, as reported by other studies. However, the temperature rise cannot explain the low value of iron content in the chlorites. 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