著者

角縁 進 永尾 隆志 長尾 敬介

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.29, no.5, pp.191-198, 2000 (Released:2008-08-30)

参考文献数

41

被引用文献数

15 16

---

More than 40 monogenetic volcanoes are distributed over an area of 400 km2 in the Abu Monogenetic Volcanic Field, southwest Japan. The eruptive products consist of alkaline basalt and calc-alkaline andesite to dacite lavas and pyroclastics, which are collectively known as the Abu Monogenetic Volcano Group. We have examined the eruption history of the Abu Monogenetic Volcano Group based on 33 new K-Ar ages. Most samples were dated by normal K-Ar method, and yielded ages between 1.9 and 0.1 Ma. The ages of two very young samples were determined using an unspiked method incorporating a mass-fractionation correction procedure. This gave an averaged age of about 40 ka. K-Ar ages from the Abu Monogenetic Volcano Group are concentrated at around 1.7 Ma and 0.2 Ma, and the activity is therefore classified into early and late periods, respectively. The early activity had a duration of about 0.4 mys, during which time 0.3 km3 of alkaline basalt alone was erupted. The late activity produced 0.8 km3 of alkaline basalt and 2.1 km3 calc-alkaline andesite to dacite, and lasted about 0.8 mys. Alkaline basalt was mostly produced in the first half of the late period, with maximum eruption rate at about 0.4 Ma. This activity was followed by more voluminous calc-alkaline andesite-dacite eruptions which climaxed at 0.2 Ma. Although associated alkaline basalt activity continued in this period, eruption volumes steadily decreased. Periodic alkaline basalt activity in southwest Japan is thought to have originated from small mantle diapirs, with intermediate calc-alkaline magmas being produced by mixing between alkaline basalt and felsic crustal melts. Coincidence of alkalic and calc-alkaline magmas and the eruption history in the later period in the Abu Monogenetic Volcano Group suggest that heating induced by repeated intrusion of alkaline basalt resulted in partial melting of the lower crust, thus producing intermediate to felsic calc-alkaline magmas. These crustal melts may then have mixed with alkaline basalt and produced the relatively voluminous intermediate calc-alkaline magmas erupted in the latest stage.

著者

佐藤 彰 永尾 隆志 堀川 義之 堀江 智敬

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 (ISSN:24335320)

巻号頁・発行日

vol.2008, 2008

著者

小阪 哲也 永尾 隆志

出版者

日本地質学会

雑誌

地質学論集 (ISSN:03858545)

巻号頁・発行日

no.44, pp.139-154, 1995-11-30

---

五島列島最北端に位置する宇久島には, 新第三紀鮮新世に活動した玄武岩〜デイサイトまでの火山岩類が分布している。層序区分にもとづくと, 下位から玄武岩〜デイサイト(ステージ1)と玄武岩〜安山岩(ステージ2)の2回の火山活動があったことが明らかになった。これらの火山岩類はソレアイト的な特徴を持っている。両ステージの火山活動は, 主成分および微量成分変化図, Sr同位体比のデータから, ある程度の地殻物質との混成作用の影響を受けているものの, 火山岩類の組成変化に大きな役割を果たしたのは分別結晶作用であることがわかった。さらに, 火山層序に基づいた化学組成変化およびSr同位体比の検討から, ステージ1は一連のマグマの活動で形成され, ステージ2は異なる化学的な特徴を持つ3回のマグマの活動で形成されたことを示唆している。また, 宇久島火山岩類の親マグマは, 2Nb-Zr/4-Y区分図およびスパイダーグラムのパターンから判断すると, プレート内ソレアイトである。

著者

角縁 進 永尾 隆志 長尾 敬介

出版者

日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.29, no.5, pp.191-198, 2000-11-30

被引用文献数

3 16

---

More than 40 monogenetic volcanoes are distributed over an area of 400 km² in the Abu Monogenetic Volcanic Field, southwest Japan. The eruptive products consist of alkaline basalt and calc-alkaline andesite to dacite lavas and pyroclastics, which are collectively known as the Abu Monogenetic Volcano Group. We have examined the eruption history of the Abu Monogenetic Volcano Group based on 33 new K-Ar ages. Most samples were dated by normal K-Ar method, and yielded ages between 1.9 and 0.1 Ma. The ages of two very young samples were determined using an unspiked method incorporating a mass-fractionation correction procedure. This gave an averaged age of about 40 ka.<br> K-Ar ages from the Abu Monogenetic Volcano Group are concentrated at around 1.7 Ma and 0.2 Ma, and the activity is therefore classified into early and late periods, respectively. The early activity had a duration of about 0.4 mys, during which time 0.3 km³ of alkaline basalt alone was erupted. The late activity produced 0.8 km³ of alkaline basalt and 2.1 km³ calc-alkaline andesite to dacite, and lasted about 0.8 mys. Alkaline basalt was mostly produced in the first half of the late period, with maximum eruption rate at about 0.4 Ma. This activity was followed by more voluminous calc-alkaline andesite-dacite eruptions which climaxed at 0.2 Ma. Although associated alkaline basalt activity continued in this period, eruption volumes steadily decreased.<br> Periodic alkaline basalt activity in southwest Japan is thought to have originated from small mantle diapirs, with intermediate calc-alkaline magmas being produced by mixing between alkaline basalt and felsic crustal melts. Coincidence of alkalic and calc-alkaline magmas and the eruption history in the later period in the Abu Monogenetic Volcano Group suggest that heating induced by repeated intrusion of alkaline basalt resulted in partial melting of the lower crust, thus producing intermediate to felsic calc-alkaline magmas. These crustal melts may then have mixed with alkaline basalt and produced the relatively voluminous intermediate calc-alkaline magmas erupted in the latest stage.

著者

山元 正継 永尾 隆志 本多 朔郎 高島 勲 マノプラクサスクロン

出版者

日本地質学会

雑誌

日本地質学会学術大会講演要旨

巻号頁・発行日

vol.95, 1988-04-02

著者

永尾 隆志

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

vol.30, no.2, pp.110-121, 1976-03-20

---

In the Chugoku and Shikoku provinces, are extensively distributed various kinds of the late Cenozoic volcanic rocks as follows. (1) Calc-alkaline volcanic rocks derived by the volcanism associated with the "Gree Tuff Crustal Movement" in the San'in and Setouchi districts (middle to late Miocene). (2) Alkaline volcanic rocks mainly composed of basalts in the San'in district (the so called "Circum Japan Sea Alkaline Petrographic Province") and the Chugoku mountainland (late Miocence to Recent). (3) Calc-alkaline volcanic rocks which formed the volcanoes beloging to the so called Daisen Volcanic Zone in the San'in district (Quaternary). The middle to late Miocene volcanic activity might have been controlled by the structure in the direction of the Honshu arc. On the other hand, in the Pliocene to Recent time (especially middle Pleistocene to Recent) the volcanic activity has occurred mainly in relation to the structure of north-south trend, which crosses the Honshu arc direction. These evidences may suggest that the volcanisms of the above two periods have occurred in relation to the different crustal movement, respectively. Considering from many published chemical analyses, it is possible to point out the following chemical differences among the late Cenozoic volcanic rocks in these provinces. (1) There is a clear distinction of the chemical features between the middle to late Miocenct calc-alkaline volcanic rocks occurring in the San'ir and Setouchi districts. The latter have highei contents of alkalies, especially K2O, than those from the former. (2) Similar chemical difference is also observed in the alkaline volcanic rocks from the Pliocene to Recent in the Chugoku province. In this case alkaline volcanic rocks from the Sanyo district are richer in alkali contents than those from the San'in district. (3) It may be noticed, moreover, that the Pliocene to Recent calc-alkaline volcanic rocks in the San'in district have higher alkali contents than those of the middle to late Miocene in the same district. The above first two evidences may conflict with the general tendency in the chemical character of the island arc volcanic rocks, and seem to be inconsistent with the genetical interpretation based on plate tectionics held by JAKES-WHITE (1968,1972) and many others.