| Project/Area Number |
61540586
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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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 | Chiba University |
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Principal Investigator |
HIROI Yoshikuni Faculty of Science, Chiba University, 理学部, 助教授 (40019427)
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| Co-Investigator(Kenkyū-buntansha) |
TSUKUI Nasashi Faculty of Science, Chiba University, 理学部, 助手 (50192191)
TAKAI Kenji Faculty of Science, Chiba University, 理学部, 講師 (10009053)
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| Project Period (FY) |
1986 – 1987
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| Project Status |
Completed (Fiscal Year 1987)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1987: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1986: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Keywords | Abukuma metamorphic rocks / Gosaisyo series / Takanuki series / P-T-t paths of rocks / Isothermal loading / Overthrusting / 衡上運動 / ジュラ記放敬虫 / 接触変成作用 / 衝上断層 / ジュラ紀の放散虫化石 / 輝石ホルンフェルス相 / ザクロ石斑状変晶 / 累帯構造 |
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| Research Abstract |
Geological and petrological studies has been carried out on the Abukuma metamorphic rocks (the Gosaisyo series and the Takanuki series), northeastern Japan, to reveal their P(pressure)-T(temperature) evolution.
Jurassic radiolarian fossils were found for the first time in a Fe-Mn-rich metachert of the Gosaisyo series and, thus, the age of original rocks of the Gosaisyo series was confirmed to be Jurassic. Consequently, the Abukuma regional metamorphism took place after Jurassic and before the emplacement of the Cretaceous intrusive complexes about 120 Ma ago.
Rocks of the Gosaisyo series have not shown any evidence of high- to mediumpressure metamorphism. On the contrary, textures and compositions of garnet and plagioclase suggest low-pressure conditions during metamorphism.
The Takanuki pelitic rocks are characterized by the occurrence of garnet porphyroblasts showing complex chemical zoning and a sector structure. Their P-T-t paths based on the compositions of garnet, plagioclase, and biotite suggest nearly isothermal loading at high-temperatures at an early stage of regional metamorphism. The high-temperature loading is also evidenced by the occurrence of sillimanite and hercynite along with staurolite within almandine and corundum in the Takanuki lareritic rocks. It may be due to the overthrusting of the Gosaisyo series on the Takanuki series.
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