Late Cenozoic volcanic activity in the Chugoku area, southwest Japan arc during back-arc basin opening and reinitiation of subduction |
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| Authors: | Jun-Ichi Kimura Tomoyuki Kunikiyo Isaku Osaka Takashi Nagao Seiki Yamauchi Susumu Kakubuchi Shomei Okada Norie Fujibayashi Ryuhei Okada Hisashi Murakami Takashi Kusano Koji Umeda Shintaro Hayashi Tsuneari Ishimaru Atusi Ninomiya Atsushi Tanase |
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| Institution: | ;Department of Geoscience, Shimane University, Matsue City, Shimane 690-8504, Japan (email: ), Center for Instrumental Analysis, Yamaguchi University, 1677-1 Yoshida-Cho, Yamaguchi 753-8512, Japan,; Faculty of Culture and Education, Saga University, 1 Hojo, Saga 840-8502, Japan,; Department of Environmental Sciences, Faculty of Education and Regional Sciences, Tottori University, Tottori City 680-8551, Japan,; Department of Geology, Faculty of Education and Human Sciences, Niigata University, 8050 Igarashi Nino-Cho, Niigata City 950-2181, Japan,; Aimi-Cho 234, Saihaku-Gun, Tottori 683-0222, Japan,; Cosmo Construction Consultant, 191 Togu, Saigo-Cho, Oki-Gun 685-0012, Japan,; Graduate School of Science and Technology, Kobe University, 1-1 Rokko-Dai, Kobe City 657-8501, Japan,; Tono Geoscience Center, Japan Nuclear Cycle Development Institute, Jorinji, Izumi-Cho, Toki City 509-5102, Japan,; Department of Earth Sciences, Faculty of Education and Human Studies, Akita University, Tegata-Gakuen-Cho, Akita City 010-8502, Japan,; Sumiko Consultants Co. Ltd, Tokyo Branch, 2-9-7 Ikenohata, Tokyo 110-0008, Japan,; Sumiko Consultants Co. Ltd, Tokyo Branch, 2-18-4 Kita-Ueno, Tokyo 110-0014, Japan |
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| Abstract: | Abstract Temporal–spatial variations in Late Cenozoic volcanic activity in the Chugoku area, southwest Japan, have been examined based on 108 newly obtained K–Ar ages. Lava samples were collected from eight Quaternary volcanic provinces (Daisen, Hiruzen, Yokota, Daikonjima, Sambe, Ooe–Takayama, Abu and Oki) and a Tertiary volcanic cluster (Kibi Province) to cover almost all geological units in the province. Including published age data, a total of 442 Cenozoic radiometric ages are now available. Across‐arc volcanic activity in an area approximately 500 km long and 150 km wide can be examined over 26 million years. The period corresponds to syn‐ and post‐back‐arc basin opening stages of the island arc. Volcanic activity began in the central part of the rear‐arc ca 26 Ma. This was followed by arc‐wide expansion at 20 Ma by eruption at two rear‐arc centers located at the eastern and western ends. Expansion to the fore‐arc occurred between 20 and 12 Ma. This Tertiary volcanic arc was maintained until 4 Ma with predominant alkali basalt centers. The foremost‐arc zone activity ceased at 4 Ma, followed by quiescence over the whole arc between 4 and 3 Ma. Volcanic activity resumed at 3 Ma, covering the entire rear‐arc area, and continued until the present to form a Quaternary volcanic arc. Adakitic dacite first occurred at 1.7 Ma in the middle of the arc, and spread out in the center part of the Quaternary volcanic arc. Alkali basalt activities ceased in the area where adakite volcanism occurred. Fore‐arc expansion of the volcanic arc could be related to the upwelling and expansion of the asthenosphere, which caused opening of the Japan Sea. Narrowing of the volcanic zone could have been caused by progressive Philippine Sea Plate subduction. Deeper penetration could have caused melting of the slab and resulted in adakites. Volcanic history in the Late Cenozoic was probably controlled by the history of evolution of the upper mantle structure, coinciding with back‐arc basin opening and subsequent reinitiation of subduction. |
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| Keywords: | arc magmatism back-arc basin opening Chugoku area K–Ar age Late Cenozoic subduction reinitiation |
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