2004 Fiscal Year Final Research Report Summary
Role of tectonic erosion in formation of accretionary prism - examples from the Southern Chichibu Belt and the Shimanto Belt
| Project/Area Number |
14540428
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Yamaguchi University |
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Principal Investigator |
KIMINAMI Kazuo Yamaguchi Univ., Fac.of Science, Professor, 理学部, 教授 (20127757)
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| Co-Investigator(Kenkyū-buntansha) |
MIYASHITA Sumio Niigata Univ., Fac.of Science, Professor, 理学部, 教授 (60200169)
KAMATA Yoshihito Yamaguchi Univ., Research Institute for Time Studies, Assoc.Professor, 時間学研究所, 助教授 (30294622)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Chichibu Belt / Shimanto Belt / seamount / collision / greenstone / volcaniclastics / tectonic erosion / accretionary prism |
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| Research Abstract |
The followings have been performed to clarify geologic consequences of subduction of topographic high and implication of chronological absence in accretionary prism which may have close association with tectonic erosion : age of limestone pebble from the Kuzuu Complex of the Ashio Belt, petrography of greenstones from the Yukagi Formation in the Southern Chichibu Belt, geology and radiolarian ages of the boundary area of the Northern and Southern Shimanto belts in western Shikoku, and occurrence and petrography of volcaniclastic rocks from the southern Shimanto Belt of western Shikoku. The main results are as follows.
1.Early Toarcian ammonite was found from limestone conglomerate in the Kuzuu Complex, and its implication was discussed.
2.Petrography of basaltic rocks and radiolarian age of the Yukagi Formation are indicative of a collision of seamount during the late Jurassic-Early Cretaceous at the convergent margin of Kyushu.
3.The Shimanto Supergroup, western Shikoku, can be divided into twelve tectonostratigraphic units on the basis of lithofacies and depositional ages, and ranges in age from the Santonian to the late Oligocene-Early Miocene. Pebbly shales with large rubbles of sandstone and shale of slope-failure origin begin to increace after the Late Campanian. The sandstones from the Upper Paleocene were mainly derived from the Sanbagawa Metamorphic Belt.
4.Volcaniclastic rocks such as volcanic breccia, volcanic conglomerate, volcanic sandstone and mudstone with volcanic rock gravels are found in small bodies sporadically scattered in the Shimanto Supergroup in east coast area of the Hata Peninsura, western Shikoku. Most volcanic rocks have a geochemical affinity of within-plate alkaline basalts of seamount origin on some discrimination diagrams using some alteration-resistant elements. The data are suggestive of a collision of seamount during the Late Oligocene-Early Miocene at the convergent margin of western Shikoku
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