1996 Fiscal Year Final Research Report Summary
Temporal and spacial geochemical variation in the Neogene volcanic rocks and the dource mantle in NE Honshu arc
| Project/Area Number |
07454129
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Tohoku University |
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Principal Investigator |
YOSHIDA Takeyoshi Tohoku Univ., Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (80004505)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Ken-ichi Tohoku Univ., Graduate School of Science, Research Associate, 大学院・理学研究科, 助手 (20158744)
EHIRO Masayuki Tohoku Univ., Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (10124554)
KANISAWA Satoshi Tohoku Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (70005784)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Cenozoic volcanic rocks / Northeast Honshu arc / Magmatic distribution / Magmatic source material / Mantle isotherm / Segregation depth / Process identification |
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| Research Abstract |
The NE Honshu arc has the most completely studied Cenozoic section. In this section, there are three volcanic periods ; continental margin volcanic period, back-arc basin volcanic period, and issland arc volcanic period. The 1320ﾟC iotherm in the mantle wedge is monotonously deep to the back-arc side at the continental margin volcanic period and the island arc volcanic period. The inclination of the isotherm in the continental margin volcanic period is more gentle than in the island arc volcanic period. The magma segregation depth at the volcanic front was much deeper in the continental margin volcanic period than in the island arc volcanic period. On the other hand, the mantle temperature was the highest at the back-arc side in the back-arc basin volcanic period.
The presence of mantle heterogeneity between the volcanic front side and the back-arc side was clearly shown in the process identification diagrams for the volcanic rocks of the island arc volcanic period. The two source mantles can be mineralogically heterogeneous, and vertically layred. The heterogeneity and across-arc profile of magmatic temperatures are closely related to the seismic velocity structure with the localized low-velocity regions.
The Quaternary volcanism shows short-term and long-term spreading to back arc side. This eruption arrays in a temporal-spatial plot have usually commenced at the volcanic front, and propagated to the back-arc sequentially. Simultaneous magma transfer from the deeper reservoirs by tectonic pulse could be a cause of the synchronized volcanic activity. Through the Quaternary age in the southern part of the NE Honshu arc, the periodic magma eruption episodes at intervals of 50 to 100 thousand years synchronized with tectonic movements exists. The climactic eruptions seems to match the timing of the eccentricity-maximums of the Earth's orbit around the Sun. The tidal forces could work supplementary to the compressive stress from subducting plate.
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[Publications] Ohguchi, T., Hayashi, S., Kobayashi, N., Itaya, T.and Yoshida, T.: "K-Ar dating unravels the volcanic history of the Kuguriiwa lava and Kamo lava members, Oligocene Monzen formation, Oga Peninsula, NE Japan. (in Japanese)" Mem.Geol.Soc.Japan. 44. 39-54 (1995)
Description
「研究成果報告書概要(欧文)」より
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[Publications] Kanisawa, S., Yoshida, T., Ishikawa, K., Kuroda, Y., Yamada, T., Yamaguchi, Y., Morikiyo, T.and Maruyama, T.: "Comparative studies of chemical composition of granitic rocks in the Japanese island arc and the Baltic shield (IGCP-315)." Japan Contribution to the IGCP. 19-25 (1996)
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