| Project/Area Number |
02453045
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
AOKI Ken-ichirou Tohoku Univ., Fac. of Sci., Prof, 理学部, 教授 (00004276)
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| Co-Investigator(Kenkyū-buntansha) |
YOSHIODA T. Tohoku Univ., Dept. Earh Sci., Assist. Prof, 教養部, 助教授 (80004505)
TSUCHIYA N. Tohoku Univ., Fac. of Sci., Assist., 理学部, 助手 (50192646)
HASENAKA T. Tohoku Univ., Fac. of Sci., Assist., 理学部, 助手 (50202429)
FUJIMAKI H. Tohoku Univ., Fac. of Sci., Assist. Prof., 理学部, 助教授 (90133933)
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| Project Period (FY) |
1990 – 1992
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| Project Status |
Completed (Fiscal Year 1992)
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| Budget Amount *help |
¥6,400,000 (Direct Cost: ¥6,400,000)
Fiscal Year 1992: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1991: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1990: ¥4,500,000 (Direct Cost: ¥4,500,000)
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| Keywords | Kitakami mountain / Rb-Sr dating / Cretaceous Granite / Sr initial ratio / Hashigami complex / Tanohata complex / Ohtanabe complex / Kuki complex / 大田名部岩体 / 田野畑岩体 / RbーSr年代 / アイソクロン / 中生代深成岩体 / 初生87Sr / 86Sr比 / 中生代深成岩類 / SmーNd年代 / 初生同位体組成 / 等時線 / 固結年代 / 宮本複合岩体 |
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| Research Abstract |
Chronological studies have been carried out to contribute to petrological research of plutonic complex in northern Kitakami mountains, northeastern Japan. In this project, four plutonic complexes were selected, and we dated them by Rb-Sr method. Ohtanabe complex from Zone I of Kitakami is rather depleted in Rb and all the rocks from the complex made line on a isochron plot. The obtained age is 118 Ma with initial ^<87>Sr/^<86>Sr ratio of 0.7039. The results are similar to Taro complex in the same zone. In contrast, rocks from Hashigami complex in the Zone II is highly depleted in Rb but enriched in Sr, and they do not make an isochron as a whole. The complex can be divided into 3 rock types that intruded in a similar place in a similar age, and constitute the entire complex. Six samples from one of the rock types made 135 Ma isochron with 0.7036 initial ^<87>Sr/^<86>Sr ratios. A similar features were found for Tanohata complex to the south of Hashigami complex in the same zone. The rocks consisting marginal types of Tanohata complex were not plotted on any isochron. Instead, the rocks from the central area of the complex made 125 Ma isochron with 0.7038 ^<87>Sr/^<86>Sr initial ratio. Summarizing the results obtained in this project, 1) the solidification ages of the complexes in northern Kitakami are roughly 120-135 Ma, 2) initial ^<87>Sr/^<86>Sr ratios are as low as 0.7036-0.7038, 3) the magmas of the plutonic complexes in the Zone I were once homogenized before solidification, 4) the magmas of the complexes of the Zone II were not homogenized before solidification, and 5) the complexes of the Zone I are enriched in Rb, but those of the Zone II are depleted in Rb but enriched in Sr.
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