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Characteristics of chlorites in seismogenic fault zones: the Taiwan Chelungpu Fault Drilling Project (TCDP) core sample

Author(s): Y. Hashimoto | 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

Journal: eEarth Discussions
ISSN 1815-3836

Volume: 2;
Issue: 2;
Start page: 85;
Date: 2007;
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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.

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