1. Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto, Japan
2. Research Fellow of Japan Society for the Promotion of Science, 5-3-1 Koji-machi, Chiyoda-ku, Tokyo, Japan
3. Graduate School of Environmental Studies, Tohoku University, Aramaki-Aza-Aoba, Aoba-ku, Sendai, Japan
4. Department of Geology, Faculty of Science, Niigata University, 2-8050 Ikarashi, Nishi-ku, Niigata, Japan
5. Graduate School of Environment and Information Sciences, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama, Japan
6. Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa