著者
山﨑 誠子 星住 英夫 松本 哲一
出版者
特定非営利活動法人日本火山学会
雑誌
火山 (ISSN:04534360)
巻号頁・発行日
vol.61, no.3, pp.519-531, 2016-09-30 (Released:2016-11-08)
参考文献数
33

Unspiked K-Ar dating procedure enables the correction for mass fractionated initial 40Ar/36Ar ratios, and has been successfully applied to young volcanic samples, especially younger than 0.5 Ma. We reconstructed the growth history of western to central part of Kuju Volcanic Group based on the unspiked K-Ar age data. The unspiked K-Ar ages for the small andesitic-dacitic volcanoes of Stage 1 (Kutsukakesan Volcano, Iozan Lava, Kuroiwasan Volcano, Narukoyama Volcano) provided with two age group of ca. 160-150 and ca. 90-80 ka, suggesting that Stage 1 may be divided into at least two sub-stages. During Stage 3 after the largest eruption associated with Handa pyroclastic flow deposit, some lava domes and stratovolcanoes in the central part (Ogigahana Volcano, Nakadake Volcano and Mimatayama Volcano) were built up from ca. 54 to 34 ka, which is older than the previous interpretation.Based on these K-Ar ages and estimated volume for each volcanic unit, we calculated the magma discharge rate during each volcanic stage and the whole period of the volcano history. The calculated magma discharge rate for Stage 1, 3 and 4 are 0.09, 0.12, 0.18 km3/ky, respectively, showing that the activity has slightly increased. The rate of 0.12 km3/ky for the whole period is similar to that for Aso and Unzen volcanoes lie to the west of this volcano.
著者
松本 哲一 中野 俊 古川 竜太 山元 孝広
出版者
国立研究開発法人 産業技術総合研究所 地質調査総合センター
雑誌
地質調査研究報告 (ISSN:13464272)
巻号頁・発行日
vol.69, no.3, pp.153-163, 2018-08-10 (Released:2018-08-29)
参考文献数
21
被引用文献数
3

山形・福島県境に位置する第四紀の大型複成火山である吾妻火山について,同位体希釈法による38溶岩試料のK–Ar年代測定を行い,火山活動の時間的空間的変遷を明らかにした.吾妻火山は安山岩の溶岩流が主体の火山であり,一部の火山体を除き,岩石学的にはほとんど区別できない.年代測定に基づき,完新世に形成された浄土平火山を含め,12の火山に区分した.最も古い活動は 1200 ka 頃に東側で開始し,徐々に西方へ移動し,700 ka 頃に西端で活動,その後,再び東側に時間をおって活動中心が移動している.従来は,吾妻火山の活動は300 ka 以降,完新世の活動までの長い休止期が存在するとされていたが,その期間にも活動は継続しており,現在まで長い休止期を挟まずにほぼ継続的に活動が続いていることが明らかになった.
著者
松本 哲一 水垣 桂子 玉生 志郎 小野 晃司 北原 哲郎 品田 正一 笹田 政克
出版者
特定非営利活動法人 日本火山学会
雑誌
火山 (ISSN:04534360)
巻号頁・発行日
vol.38, no.1, pp.1-13, 1993-04-01 (Released:2017-03-20)
参考文献数
21
被引用文献数
1

Taga Volcano, in northern part of the Izu Peninsula, central Japan, is a large Quaternary strato volcano made of andesite and basalt. The Hata Basalts underlying the Taga volcanic rocks is a pile of pyroclastics with some lava flows mainly of basalts which include the most mafic basalt in the late Tertiary to Quaternary volcanic rocks of north Izu and Hakone region. This Basalts has been treated as the late Tertiary product by previous workers. In order to clarify the volcano-stratigraphic relationship between the Hata Basalts and the Taga volcanic rocks, geologic investigations were carried out in and around the Tanna Basin, and the core and cuttings samples from three 500-600 m drill holes in the Tanna Basin were examined. The Hata Basalts is lithologically characterized by dominant pyroclastics, especially high-temperature oxidized, reddish-brown agglutinate, whereas the products of Taga Volcano are characterized by dominant lava flows. The Hata Basalts is overlain by the Taga volcanic rocks (TV4 and TV5) unconformably at the eastward of the Tanna Basin, and overlain by the Shimo-Tanna Shales and the Taga volcanic rocks unconformably at the westward. Petrography and major elements chemistry suggest that both the Hata Basalts and the Taga volcanic rocks are petrologically very similar to each other. K-Ar dating of two rock samples of the Hata Basalts and one sample of Taga Volcano revealed that they were products of almost the same age, around 600-700 ka. All the samples dated can be correlated to the Brunhes normal polarity epoch. We conclude that the Hata Basalts is the early stage products of Taga Volcano.
著者
松本 哲一 小林 武彦
出版者
特定非営利活動法人 日本火山学会
雑誌
火山 (ISSN:04534360)
巻号頁・発行日
vol.44, no.1, pp.1-12, 1999-03-05 (Released:2017-03-20)
参考文献数
12
被引用文献数
4

A systematic K-Ar age determination has been made on thirty-seven samples from the Older Ontake volcanic products, Ontake Volcano, central Japan, with analytical uncertainties mostly within ±5% (1σ level). The “Kuragoehara Lava”, which the previous researchers used as a key bed for stratigraphic correlation, gives significantly different eruption ages in each disthbution area, and some lavas classified into the same stratigraphic units among each area also show quite diffrent K-Ar ages. Hence, a revised volcano-stratigraphy is proposed based on the radiometric data obtained in the present study. The Older Ontake Volcano may be a compound volcano consisting of more than four stratovolcanoes with different vents. The first one, “;Tobu Volcano Group”, erupted at around 750-650 ka on the wide eastern side. The second one, “Tsuchiurazawa Volcano”, erupted at around 680-570 ka mainly in the western area. The third one, “Uetawarayama Volcano”, produced lavas at around 540-520 ka, and the products filled along valleys in the western area. The last one, “Mikasayama Volcano” erupted at around 440-420 ka in the southeastern area. The inactive period between the Older and Younger Ontake volcanic products continued for more than three hundred thousand years. The present study has revealed that the K-Ar age determination is effective for estimating a time gap between the Quatermary volcanic products whose stratigraphic relation can not be well defined in field.
著者
西来 邦章 竹下 欣宏 田辺 智隆 松本 哲一
出版者
一般社団法人 日本地質学会
雑誌
地質学雑誌 (ISSN:00167630)
巻号頁・発行日
vol.120, no.3, pp.89-103, 2014-03-15 (Released:2014-07-26)
参考文献数
28
被引用文献数
1

四阿火山において地質調査,K-Ar年代測定および全岩化学組成分析を行い,火山活動史の再検討を行った.本火山は噴出物の分布と地形の開析の程度差,活動年代および全岩化学組成から,3つの火山体(初期火山体,根子岳火山体,浦倉山火山体)からなる.本火山の活動は,約80万年前に開始した(初期火山体の活動).約70万年前には,根子岳周辺でデイサイトの火山活動が発生し(根子岳火山体の活動),数万年間で山体が形成された.初期火山体は約55万年前まで活動が継続したのち,5万年程度の活動休止期を挟み,約50万年前には,浦倉山周辺で安山岩の火山活動が発生した(浦倉山火山体の活動).この火山体の活動は約45万年前には終息した.そして,約30万年前には,四阿火山の北西方において小規模な火山体(鳴岩火山)が形成された.
著者
西来 邦章 高橋 康 松本 哲一
出版者
一般社団法人 日本地質学会
雑誌
地質学雑誌 (ISSN:00167630)
巻号頁・発行日
vol.119, no.7, pp.474-487, 2013-07-15 (Released:2013-11-02)
参考文献数
35
被引用文献数
2

活火山を有する浅間・烏帽子火山群において21試料のK–Ar年代測定を行い,火山活動場の時空間的変遷を明らかにした.本火山群は西北西–東南東方向に約22 kmにわたり分布し,主稜線は成層火山体で構成され,周辺域には溶岩ドームなど単成火山的な山体で広範囲に分布する.本火山群は活動地域と休止期を基に以下の4つのステージに区分される.ステージⅠ(約100万年前),西部地域のみ;ステージⅡ(85~75万年前),西部地域で南北にやや伸張した広範囲;ステージⅢ(45~24万年前),西部地域から中央部;ステージⅣ(約13万年前以降),中央部から東部地域.本火山群で認められる単成火山的な活動は,約80万年前,約30万年前,約10万年前および約2万年前の短期間に限られる.約30万年前には,西部地域のみであった活動場が東進し,現在の浅間・烏帽子火山群の配列方向である西北西–東南東方向の活動場へ移行した.
著者
松本 哲一 宇都 浩三 柴田 賢
出版者
日本質量分析学会
雑誌
Journal of the Mass Spectrometry Society of Japan (ISSN:13408097)
巻号頁・発行日
vol.37, no.6, pp.353-363, 1989 (Released:2007-05-01)
被引用文献数
11 8

Precise determination of argon isotopic ratios was made on twenty-seven historic lavas from Japan. Their isotopic ratios were mostly mass fractionated from that of the atmospheric argon toward the enrichment in lighter isotopes. This suggests that the correction for the mass fractionated initial 40Ar/36Ar ratio is very important for the K-Ar dating of volcanic rocks younger than 0.1 Ma. The limit of measurable K-Ar age is estimated to be 0.03 Ma for a normal andesitic lava having a fractionated initial argon.