1990 Fiscal Year Final Research Report Summary
The Chronology and Correlation of the Tephra in the Chugoku Mts. During the Middle and Late Pleisocene
| Project/Area Number |
01580246
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
自然地理学
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| Research Institution | Kobe University College of Liberal Arts |
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Principal Investigator |
NOMURA Ryotaro Kobe University, Liberal arts. Assistant Professor, 教養部, 助教授 (50164744)
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| Project Period (FY) |
1989 – 1990
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| Keywords | temperature valuable method / refractive index of the volcanic glass / Daisen Volcano / Sanbe Volcano / tephra |
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| Research Abstract |
The distribution of the glassy volcanic ash in the Chugoku Mountains is well Known. They are usually wide spread tephra. The tephras composed of pumice which are distributed in a small area are little known.
They are maninly pumicous tephra and derived form Daisen Volcano. Some group of tephras are derived form Sanbe Volcano. Both of these volcanoes situated in the Chugoku Mountains.
These pumicous tephras can be distinguished by examining the refractive indices of volcanic glass and examine the mineral composition. The differences of these indices are very small, so the accurate measurements are needed for this purpose.
In this study, I took accurate measurements of the refractive indices for the purpose of tephrochronology. For the purpose of this study, I made a microscope stage which is temperature valuable and the temperature of the stage are measured directly by thermocouple. The thermocouple is so fine that it is observable the volcanic glass and thermocouple in the same microscope field.
By this equipment, the refractive index of volcanic glass which are distributed in the Chugoku Mountains are measured grain by grains. As a results, it is found that high accuracy measurement is very useful for discernment of the tephra.
Using this method, I revealed that some tephra derived from Daisen and others derived from Sanbe volcano, respectively. And some tephras are newly found in this area.
These tephras are important as time markers of late quarterly period. Studies of these tephra will reveal the timing of the environmental change. It is neccessary farther investigations of these tephra in a wide area.
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