1986 Fiscal Year Final Research Report Summary
Petrolgy and geochemistry of Cenozoic igneous rocks in Northeast Japan arc
| Project/Area Number |
59420015
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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 | TOHOKU UNIVERSITY |
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Principal Investigator |
AOKI Ken-ichiro Professor, Faculty of Science, Tohoku University, 理学部, 教授 (00004276)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Ken-ichi Research Associate, College of General Education, Tohoku University, 教養部, 助手 (20158744)
KANISAWA Satoshi Professor, College of General Education, Tohoku University, 教養部, 教授 (70005784)
FUJIMAKI Hirokazu Research Associate, Faculty of Science, Tohoku University, 理学部, 助手 (90133933)
YOSHIDA Takeyoshi Research Associate, Facultu of Science, Tohoku University, 理学部, 助手 (80004505)
ONUMA Kosuke Professor, Faculty of Science, Tohoku University, 理学部, 教授 (50000865)
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| Project Period (FY) |
1984 – 1986
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| Keywords | normalized incompatible element pattern / island arc volcanic rocks / active continental margin volcanic volcanic rocks / tholeiitic / 陸孤型 / 組成の時空分布と成因的考察 / ソレアイト / カルク・アルカリ |
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| Research Abstract |
In order to elucite the geochemical characteristics and origin of igneous rocks in Northeast Japan arc, we have determined major elements of 2,000 and trace elements of 600 rock samples. The following several important conclusions have been clarified:
There are some chemical differences between the Pliocene to Quaternary and Miocene volcanic rocks even in the same regions. Namely, the latter do not have a nature of the typical island arc, but active continental margin. It seems likely that the change of chemical nature of magmas is related to the different tectonic setting, opening of the Japan Sea.
Quaternary volcanoes distributed widely are divided into four volcanic zones from the Pacific to continental side based on geological, petrographical and geochemical evidences.
Vlocanoes along the volcanic front consist of tholeiitic and calc-alkaline suites, both of which exhibit clearly different chemical and isotopic variation with eath other. It is suggested that two types of parental magmas have been generated in the upper mantle at different depths or from the common source but under different physic-chemical conditions.
Variations of the normalized incompatible trace element pattern are different between tholeiitic and calc-alkaline suites. Accordingly, it is very difficult to produce calc-alkaline andesites by simple magma mixing of tholeiitic basalt and its salic end product.
Not only alkalies and incompatible trace elements, but other major and compatible elements in volcanic rocks show the lateral variations across the arc as well.
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