1993 Fiscal Year Final Research Report Summary
CHARACTERISTICS OF CRETACEOUS IGNEOUS ACTIVITY IN JAPAN ARC
| Project/Area Number |
03452067
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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 |
地質学一般
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
KANISAWA Satoshi TOHOKU UNIV., FACULTY OF SCIENCE, PROF., 理学部, 教授 (70005784)
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| Co-Investigator(Kenkyū-buntansha) |
TSUCHIYA Nobutaka TOHOKU UNIV., FACULTY OF SCIENCE, RESEARCH ASSOC., 理学部, 助手 (50192646)
ISHIKAWA Ken'ichi TOHOKU UNIV., FACULTY OF SCIENCE, RESEARCH ASSOC., 理学部, 助手 (20158744)
YOSHIDA Takeyoshi TOHOKU UNIV., FACULTY OF SCIENCE, ASSOC.PROF., 理学部, 助教授 (80004505)
EHIRO Masayuki TOHOKU UNIV., FACULTY OF SCIENCE, ASSOC.PROF., 理学部, 助教授 (10124554)
AOKI Ken'ichiro TOHOKU UNIV., FACULTY OF SCIENCE, PROF., 理学部, 教授 (00004276)
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| Project Period (FY) |
1991 – 1993
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| Keywords | Cretaceous / igneous activity / plutonism / shoshonite / slab-melting / origin of magma / tectonics |
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| Research Abstract |
1) The pre-Cretaceous lithology, stratigraphy, age and geolgic structures were investigated to clarify the background of the Cretaceous igneous activity in Japan.
2) Petrographic description, compositional zonation and measurements of Sr-isotopic ratios of some plutons were carried out for the basic data.
3) Some dyke rocks in Zone IV plutons are shoshonite and high-K andesite having higher Nb content than those in island-arc tholeiites, and have different mineral compositions, therefore, the occurrence of those rocks has a important significance for the tectonic setting of the Kitakami Mountains during the Cretaceous age.
4) The high-Sr series rocks of Zone II plutons in the Kitakami Mountains are characterized by high SiO_2 greater than 61 wt. %, higher Na_2O and lower K_2O, slightly higher Al_2O_3 and lower FeO* and MgO.They are richer in Sr and Ga, and poorer in Rb, Pb and Y.These characteristics are similar in composition to those of the high-Al_2O_3 trondhjemite, tonalite and dacite (high-TTD). Slab-melting was playda greater role for the origin of high-Sr series rocks.
5) On the characteristics of the Southwest Japan-are from thecretaceous to Miocene age, it is clarified that the products of the Shimanto-autochthonous activity is those of the bimodal ones at the outer-uprifted zone developed at the fore-arc in the active continental margin.
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