1. Postdoctoral Fellow, Dept. of Earth and Environmental Sciences, College of Science, Korea Univ., 1, 5ka, Anam-dong, Sungbuk-gu, Seoul 136-701, Republic of Korea.
2. Associate Professor, Dept. of Environmental Science and Engineering, Kwangju Institute of Science & Technology (K-JIST), 1 Oryong-dong, Puk-gu, Kwangju 500-712, Republic of Korea (corresponding author).
3. Professor and Director, Institute of Petrography & Geochemistry, Univ. Karlsruhe (TH), Kaiserstrasse 12, 76128 Karlsruhe, Germany.