| Project/Area Number |
61420014
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
地質学一般
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| Research Institution | Gunma University |
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Principal Investigator |
NOMURA Satoshi Gunma University,Professor, 教養部, 教授 (20008155)
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| Co-Investigator(Kenkyū-buntansha) |
EBIHARA Mitsuru Tokyo Metropolitan University,Assistant Professor, 理学部, 助教授 (10152000)
小坂 共栄 信州大学, 理学部, 助教授 (20020670)
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| Project Period (FY) |
1986 – 1988
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| Project Status |
Completed (Fiscal Year 1988)
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| Budget Amount *help |
¥20,000,000 (Direct Cost: ¥20,000,000)
Fiscal Year 1988: ¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 1987: ¥4,800,000 (Direct Cost: ¥4,800,000)
Fiscal Year 1986: ¥12,200,000 (Direct Cost: ¥12,200,000)
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| Keywords | Geology of western part of Gunma Prefecture / Isotope ages of Late Cenozoic volcanic rocks / Paleomagnetism of Neogene and Quaternary / グリンタフ変質と放射年代値 / 新生代末火山岩の放射年代 / 中新世以降の古池磁気 / 新第三系の放射年代 / グリンタフ変質と放射年代 / 中新世以後の火山活動 / 中新世以後の地磁気編年 / 群馬・長野県境の地質 / 群馬県南西部の地質構造発達史 / 放射年代とグリンタフ変質 / 新第三紀の火山活動 |
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| Research Abstract |
The Late Cenozoic volcanic rocks are distributed in the western part of Gunma prefecture, Central Japan. but, it had been hard to determine the geologocal ages of the volcanic rocks which are poor in fossils. In this project, the writers determined the isotopic ages and measured the magnetization of the rocks. Number of samples for K-Ar ages is 65. Since then, the lower formations of the volcanic rocks have generally been believed to be Upper Miocene in age. Main results of this studies are as follows.
1. The first volcanism in this area took place in early Upper Miocene age at the northwest end of Kanto mountains. the region of the most viloent volcanic eruptions had moved to northeast in Late Pliocene.
2. Present topography on the east side of the Usui Pass had been formed by erosion during Brunhes Normal Epoch.
3. K-Ar ages of altered rocks which were collected from same stratigraphic horizons do not indicate similar values. For instance, K-Ar ages, 6.2 - 5.6 Ma of the Do^^-zen Member of Kirizumi Formation show lerger values than those, 5.2 - 5.0 Ma of Yunosawa Member which is overlain by Do^^-zen Member.
4. Volcanic rocks of the Myogi Mountains had formed during comparatively short time in the ages of 6 - 5 Ma. The lower half of the mountains is magnetized reversed and the upper is normal.
5. Basement rocks of Haruna Volcano are exposed in areas of 910 meters above the sea. The K-Ar age of the rocks is 8.14 Ma.
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