1989 Fiscal Year Final Research Report Summary
Geological Correlation between the Inner and the Outer Zones of Southwest Japan since the Cretaceous by Fission-track Dating
| Project/Area Number |
62460053
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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 | Osaka City University |
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Principal Investigator |
WADATSUMI Kiyoshi Osaka City Univ., Facult. of Science, Professor, 理学部, 教授 (90047572)
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| Co-Investigator(Kenkyū-buntansha) |
MASUMOTO Shinji Osaka City Univ., Facult. of Science, Research Associate, 理学部, 助手 (40173760)
SHIONO Kiyoji Osaka City Univ., Facult. of Science, Associate Professor, 理学部, 助教授 (40047387)
YAO Akira Osaka City Univ., Facult. of Science, Associate Professor, 理学部, 助教授 (40047353)
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| Project Period (FY) |
1987 – 1989
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| Keywords | Fission-track dating / Cretaceous / Southwest Japan / Image processing / Geothermal / Inner zone / Outer zone / Zircon |
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| Research Abstract |
(1) Zircon fission-track dating are carried out with the computerized image processing system installed an optical disk using the world age standard (Fish Canyon Tuff) zircon by means of the external detector method.
(2) As the results, the volcanic rocks in the inner zone at the Kinki-Chugoku district (Ikuno, Aioi, Arima, Yadagawa groups) and sedimentary rocks (Izumi group) have a series of geological ages from Cretaceous to Paleogene (l2O-6OMa). The younger ages drift apart from the ages expected can be measured from the rocks of hornfels and ore mineralization in the Aioi and the Ikuno groups, and from the bottom of the thickest part of Izumi group. From the outer zone, the younger ages are always measured more than that of Radiolaria fossil ages.
(3) Fission tracks in the zircon are usually shortened by the geothermal effect (158-224ﾟC) and disappeared more than 224ﾟC. Therefore, it is necessary to correct the age data by the ratio of track lengths of spontaneous and induced tracks to get the accurate ages of rock generation. On the other hand, the ratio values teach us geothermal conditions of the samples at the natural environments by the magmatic activities, sedimentary basin development and metamorphic effects by tectonics.
(4) We are discussing on these data from the views of tectonic differences between the inner and the outer zones of Southwest Japan, so that the results will be published at near future.
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