Institution: | Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro, Tokyo 152, Japan, E-mail: ,;Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305, Japan,;Geology Department, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK,;Department of Earth Sciences, University of Sheffield, Sheffield S3 7HF, UK |