Age and associated stress field of middle Miocene back-arc basalt magmatism in Northeast Japan |
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| Authors: | Jun Hosoi Atsushi Yamaji Hideki Iwano Tohru Danhara Takafumi Hirata |
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| Affiliation: | 1. Research Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Tsukuba, Japan;2. Division of Earth and Planetary Sciences, Kyoto University, Kyoto, Japan;3. Kyoto Fission-Track Co., Ltd., Kyoto, Japan;4. Geochemical Research Center, The University of Tokyo, Tokyo, Japan |
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| Abstract: | A large volume of middle Miocene basaltic rocks is widely distributed across the back-arc region of Northeast Japan, including around the Dewa Mountains. Petrological research has shown that basaltic rocks of the Aosawa Formation around the Dewa Mountains were generated as a result of the opening of the Sea of Japan. To determine the precise ages of the middle Miocene basaltic magmatism, we conducted U–Pb and fission-track (FT) dating of a rhyolite lava that constitutes the uppermost part of the Aosawa Formation. In addition, we estimated the paleostress field of the volcanism using data from a basaltic dike swarm in the same formation. The rhyolite lava yields a U–Pb age of 10.73 ±0.22 Ma (2σ) and a FT age of 10.6 ±1.6 Ma (2σ), and the paleostress analysis suggests a normal-faulting stress regime with a NW–SE-trending σ3-axis, a relatively high stress ratio, and a relatively high magma pressure. Our results show that the late Aosawa magmatism occurred under NW–SE extensional stress and ended at ~ 11 Ma. |
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| Keywords: | Back-arc basalt fission-track age Northeast Japan opening of the Sea of Japan paleostress U–Pb age zircon |
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