eEarth, 3, 1-6, 2008
www.electronic-earth.net/3/1/2008/
doi:10.5194/ee-3-1-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
 
29 Feb 2008
Characteristics of chlorites in seismogenic fault zones: the Taiwan Chelungpu Fault Drilling Project (TCDP) core sample
Y. Hashimoto1, O. Tadai2, M. Tanimizu3, W. Tanikawa3, T. Hirono4, W. Lin3, T. Mishima5, M. Sakaguchi2, W. Soh3, S. R. Song6, K. Aoike7, T. Ishikawa3, M. Murayama5, K. Fujimoto8, T. Fukuchi9, M. Ikehara5, H. Ito6, H. Kikuta3, M. Kinoshita10, K. Masuda11, T. Matsubara9, O. Matsubayashi12, K. Mizoguchi13, N. Nakamura14, K. Otsuki14, T. Shimamoto15, H. Sone16, and M. Takahashi11
1Department of Natural Environmental Science, Kochi University, Kochi, Japan
2Marine Works Japan Ltd., Nankoku, Japan
3Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan
4Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Japan
5Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan
6Department of Geosciences, National Taiwan University, Taipei, Taiwan
7Center for Deep Earth Exploration, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
8Faculty of Education, Tokyo Gakugei University, Koganei, Japan
9Department of Earth Sciences, Graduate School of Science & Engineering, Yamaguchi University, Yamaguchi, Japan
10Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan
11Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
12Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
13Earthquake Research Department, National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan
14Department of Geoenvironmental Science, Graduate School of Science, Tohoku University, Sendai, Japan
15Department of Earth and Planetary Systems Science, Hiroshima University, Japan
16Department of Geophysics, School of Earth Sciences, Stanford University, Stanford, CA, USA

Abstract. 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. Another reason for the low value of iron content is the variation in the pH of the fluid, which can be controlled by radical reactions. Therefore, on the basis of chlorite characteristics, the reactions at the seismogenic fault are due not only to the thermal decomposition resulting from the temperature rise and but also to rock-fluid interactions.

Citation: Hashimoto, Y., Tadai, O., Tanimizu, M., Tanikawa, W., Hirono, T., Lin, W., Mishima, T., Sakaguchi, M., Soh, W., Song, S. R., Aoike, K., Ishikawa, T., Murayama, M., Fujimoto, K., Fukuchi, T., Ikehara, M., Ito, H., Kikuta, H., Kinoshita, M., Masuda, K., Matsubara, T., Matsubayashi, O., Mizoguchi, K., Nakamura, N., Otsuki, K., Shimamoto, T., Sone, H., and Takahashi, M.: Characteristics of chlorites in seismogenic fault zones: the Taiwan Chelungpu Fault Drilling Project (TCDP) core sample, eEarth, 3, 1-6, doi:10.5194/ee-3-1-2008, 2008.
 
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