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Shifting of the volcanic fronts during Early to Late Miocene in the Northeast Japan arc |
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| Authors: | Jun'ichi Ohki Naoki Watanabe Kenji Shuto Tetsumaru Itaya |
| Institution: | Graduate School of Science and Technology, Niigata University, Igarashi, Niigata 950-21, Japan;Department of Geology and Mineralogy, Faculty of Science, Niigata University, Igarashi, Niigata 950-21, Japan;Hiruzen Research Institute, Okayama University of Science, Ridai-cho, Okayama 700, Japan |
| Abstract: | Abstract Recent advanced chronological studies for the Tertiary volcanic rocks from the Northeast (NE) Japan arc revealed three volcanic fronts which differed in temporal and spatial distribution. These fronts were (i) the Matsumae-Shizukuishi-Shiogama line of 22–25 Ma which is obliquely across the Quaternary volcanic front (QVF); (ii) the Tomari-Shiogama line of 13–16 Ma which exists 30–50 km east of the QVF and (iii) a line of 0–8 Ma which is the same as the QVF. The first shifting of the 22–25 Ma line to the 13–16 Ma one was due to the counterclockwise rotation of the NE Japan arc during 20–12 Ma as proposed by Otofuji et al . (1985), and the second shifting of the 13–16 Ma line to the 0–8 Ma line could have contributed to a decrease in the dip of the slab of the Pacific plate which subducted beneath the NE Japan arc during 13–8 Ma. |
| Keywords: | counter-clockwise rotation Northeast Japan arc shifting of volcanic front subduction dip angle |