Study of low-relief surfaces development using volcanic products, Japan

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The purpose of this study is to estimate the ages of low-relief surfaces using volcanic products in Japan, and to reconstruct the paleogeography in and around mountain area. It aims to promote the chronological study of mountain buildings. For this study, tephrochronological method, radiometric ages and basal landforms of Cenozoic volcanic products were used in Abukuma, Kanto, Hida Mountains. The results are as follows. First, pyroclastic flow deposit covering the northwest part of Abukuma Mountains, correlated to the Shirakawa Pyroclastic Flow Deposit Group by previous study, was identified as older one than expected using paleomagnetic survey and K-Ar dating. One the other hand, two pyroclastic flow deposits belonging to the Shirakawa Pyroclastic Flow Deposit Group were found in Koriyama Basin and along the boundary of Koriyama Basin and Abukuma Mountains. The model of development of low-relief surfaces and geomorphic development around the Abukuma Mountains were established. Second, stratigraphy of tephra layers in several hills along the west margin of the Kanto Plain and underground of the west part of the Kanto Plain were revised. Third, characteristic properties of pyroclastic flow deposits providing several data for reconstruction of paleogeography around the Hida Mountains were clarified.