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Tanase, Atsushi*; Oikawa, Teruki*; Ninomiya, Atsushi; Hayashi, Shintaro*; Umeda, Koji
Kazan, 52(1), p.39 - 61, 2007/02
Temporal and spatial variations on Plio-Pleistocene volcanism in the Ryohaku Mountains, central Japan, have been investigated by newly obtained K-Ar ages on 38 groundmass samples separated from volcanic rocks. The volcanoes in the Ryohaku Mountains form two volcanic rows of the Kuzuryu and hakusan Volcanic Chains which have ESE-WNW and N-S alignments, respectively. Early volcanic activity occurred intermittently from 3.6 Ma to 1.5 Ma, and the volcanoes near the junction of the two volcanic chains were active. The volcanic activity in the ESE-WNW trending Kuzuryu Volcanic Chain was restricted in the age range from 1.2 Ma to 0.7 Ma with migration from Eboshi-Washigatake Volcano (ESE end) to Hoonji Volcano (WNW end). The N-S trending Hakusan Volcanic Chain was active from 0.4 Ma to the present.
Oikawa, Teruki; Nishiki, Kuniaki*
Kazan, 50(2), p.143 - 148, 2005/05
The authors will report two K-Ar ages of volcanic rocks from the Kirigamine Volcano, which composes the uppermost part of the Enrei Formation. Based on the newly obtained ages, previously reported radiometric ages, and volcanostratigraphic data, we identify activity periods of 1.3 to 0.75Ma for Kirigamine Volcano. And, we estimate that the Oiwake Volcanic Graben field by Kirigamine Volcano formed rapidly at ca 0.85Ma. Judging from the previous studies and this study, the duration of the activity of the Enrei Formation is mainly ca.1.5 to 0.75 Ma.
Umeda, Koji; Uehara, Daijiro; Ogawa, Yasuo*; Kudo, Takeshi; Kakuta, Chifumi
Kazan, 48(6), p.461 - 470, 2003/12
None
Umeda, Koji; Yusa, Yasuhisa; *; Kobayashi, Tetsuo*; Koyama, Masato*
Kazan, 44(6), p.285 - 289, 2000/00
None
Umeda, Koji; Kusanagi, Megumi*; Furusawa, Akira*; Ui, Tadahide*
Kazan, 41(2), p.61 - 71, 1996/00
None
