Evolution of Mount Fuji,Japan: Inference from drilling into the subaerial oldest volcano,pre‐Komitake |
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| Authors: | Mitsuhiro Yoshimoto Toshitsugu Fujii Takayuki Kaneko Atsushi Yasuda Setsuya Nakada Akikazu Matsumoto |
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| Institution: | 1. Department of Natural History Sciences, Faculty of Science, Hokkaido University, N10 W8, Kita‐ku, Sapporo, 060‐0810, Japan (email: m‐yoshi@mail.sci.hokudai.ac.jp);2. Earthquake Research Institute, University of Tokyo, 1‐1‐1 Yayoi, Bunkyo‐ku, Tokyo 113‐0032, Japan;3. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 7, 1‐1, Higashi 1‐Chome, Tsukuba, Ibaraki 305‐8567, Japan |
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| Abstract: | A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km3/ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO2, differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO2. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven. |
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| Keywords: | basalt drilling core eruptive history Fuji Volcano hornblende dacite Komitake Volcano pre‐Komitake Volcano |
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