eEarth Discussions www.electronic-earth-discuss.net 1815-3836 1815-3844 2 2 2007 10.5194/eed-2-85-2007 http://www.electronic-earth-discuss.net/2/85/2007/ http://www.electronic-earth-discuss.net/2/85/2007/eed-2-85-2007.html http://www.electronic-earth-discuss.net/2/85/2007/eed-2-85-2007.pdf 85 98 2007-07-02 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 K. Aoike T. Ishikawa M. Murayama W. Soh S. R. Song K. Fujimoto T. Fukuchi M. Ikehara H. Ito H. Kikuta M. Kinoshita W. Lin K. Masuda T. Matsubara O. Matsubayashi T. Mishima K. Mizoguchi N. Nakamura K. Otsuki M. Sakaguchi 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 Deep Earth Exploration, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan Department of Geosciences, National Taiwan University, Taipei, Taiwan 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). 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 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, the reactions at the seismogenic fault are due to not only the thermal decomposition resulting from the temperature rise and but also rock-fluid interactions based on the chlorite characteristics. Hirono, T. Ikehara, M., Otsuki, K., Mishima, T., Sakaguchi, M., Soh, W., Omori, M., Lin,W., Yeh, E. C., Tanikawa, W., and Wang, C. Y.: Evidence of frictional melting from disk-shaped black material, discovered within the Taiwan Chelungpu fault system, Geophys. Res. Lett., 33, L19311, doi:10.1029/2006GL027329, 2006a. Hirono, T., Lin, W., Yeh, E. C., Soh, W., Hashimoto, Y., Sone, H., Matsubayashi, O., Aoike, K., Ito, H., Kinoshita, M., Murayama, M., Song, S. R., Ma, K. F., Hung, J. H., Wang, C. Y., and Tsai, Y. B.: High magnetic susceptibility of fault gouge within Taiwan Chelungpu fault: Nondestructive continuous measurements of physical and chemical properties in fault rocks recovered from Hole B, TCDP, Geophys. Res. Lett., 33, L15303, doi:10.1029/2006GL026133, 2006b. Kameda, J., Saruwatari, K., and Tanaka, H.: H₂ generation in wet grinding of granite and single-crystal powders and implications for H₂ concentration on active faults, Geophys. Res. Lett., 30, SDE 10-1-5, 2003. Kano, Y., Mori, J., Fujio, R., Ito, H., Yanagidani, T., Nakao, S., and Ma, K.: Heat signature on the Chelungpu fault associated with the 1999 Chi-Chi, Taiwan earthquake, Geophys. Res. Lett., 33, L14306, doi:10.1029/2006GL026733, 2006. Ma, K. F., Brodsky, E. E., Mori, J., Ji, C., Song, T. R. A., and Kanamori, H.: Evidence for fault lubrication during the 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6), Geophys. Res. Lett., 30, 48-1-4, 2000. Malmstrom, M., Banwart, S., Lewenhagen, J., Duro, L., and Bruno, J.: The dissolution of biotite and chlorite at 25°C in the near-neutral pH region, J. Contam. Hydrol., 21, 201–213, 1996. Mishima, T., Hirono, T., Soh, W., and Song, S. R.: Thermal history estimation of the Taiwan Chelungpu fault using rock-magnetic methods, Geophys. Res. Lett., 33, L23311, doi:10.1029/2006GL028088, 2006. Moore, D. M. and Reynolds, R. C.: X-ray diffraction and the identification and analysis of clay minerals, Oxford University Press, Wellington, 348, 1989. Ohta, E. and Yajima, J.: Magnesium to iron ratio of chlorite as indicator of type of hydrothermal ore deposit, Mining Geology Special Issue, 12, 17–22, 1988. Özdemir, Ö. and Dunlop, D. J.: Chemical remanent magnetization during $\gamma $FeOOH phase transformations, J. Geophys. Res., 98, 4191–4198, 1993. Pan, Y. X., Zhu, R. X., Banerjee, S. K., Gill, J., and Williams, Q.: Rock magnetic properties related to thermal treatment of siderite: Behavior and interpretation, J. Geophys. Res., 105, 783–794, 2000. Ross, F. J.: Acid dissolution of chlorites: Release of magnesium, iron, and aluminum and mode of acid attack, Clay. Clay Miner., 17, 347–354, 1969. Saruwatari, K., Kameda, J., and Tanaka, H.: Generation of hydrogen ions and hydrogen gas in quartz-water crushing experiments: An example of chemical processes in active faults, Phys. Chem. Miner., 31, 176–182, 2004. Shibson, R. H.: Fault rocks and fault mechanisms, J. Geolog. Soc. London, 133, 190–213, 1977. Snowball, I. and Torii, M.: Incidence and significance of magnetic iron sulphides in Quaternary sediments and soils, in: Quaternary Climates, Environments, and Magnetism, edited by: Maher, B. A. and Thompson, R., pp. 199–230, Cambridge Univ. Press, New York, 1999. Vrolijik, P. and van der Pluijm, B. A.: Clay gouge, J. Struct. Geol., 21, 1039–1048, 1999.