T. Kubo and E. Ohtani, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980–8578, Japan. T. Kato, Institute of Geoscience, University of Tsukuba, Tsukuba 305–0006, Japan. T. Shinmei and K. Fujino, Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Sapporo 060–0810, Japan.(1998-07-03時点)