| Project/Area Number |
14540454
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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 |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | National Science Museum |
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Principal Investigator |
YOKOYAMA Kazumi National Science Museum, Dept of Geology, senior curator, 地学研究部, 室長 (40126628)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2002: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | monazite / age / Japanese Islands / provenance / 年代 |
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| Research Abstract |
Paleo-current trends, the classification of species of rock fragments and, modal and chemical analyses of heavy minerals provide strong basis for analysis and interpretation of sandstone provenence. The age distribution patterns of detrital minerals such as zircon and monazite give us a powerful approach to the provenance study since the development of single grain age analyses. In this study, we analyzed detrital monazites in the sandstones from various terranes in the Japanese Islands. They were formed at the continental shelf and have been derived from regions in the East Asian continent. In addition, we collected present sands from the Asian continent to compare the age data wit h those in the sandstones in the Japanese Islands.
The comparison revealed the following conlustions :
1:Detrital minerals in most of the sandstones in the Japanese Islands were derived from the Korean Peninsual or its equivalent areas including the Shangdon Peninsual. These sandstones have bimodal age ditrib
… More
ution with peaks at 250 Ma and 1900 Ma.
2:Cretaceous to Tertiary sandstones in Hokkaido and Permian to Triassic sandstones in the Maizuru belt have age distribution similar to the sands in Amur River. Similar pattern was observed in the Tertairy sandstones in the Shimanto belt from the Shikoku to Kanto regions.
3:Contribution from the Paleo-Yangtze and Yellow rivers is restricted. The similar age pattern is observed only in the Tertiary sandstones in the Shimanto belt in Kyushu and Okinawa.
Through this age study, many problems were cleared. The most remarkable ones are dissolution and formation of heavy minerals. Garnet is one of the most resistant minerals in the sandstones. However, Ca-rich garnets are easily decomposed. As a result, the chemical compositions of garnet in the sandstones are highly restricted into Ca-free side. This shows the misleading of the provenance if we conclude only based on the chemical compositions of garnet. Monazite is one of the decomposition minerals at the low-grade metamorphic conditions. It usually decomposed into allanite. But at very low temperature conditions, detrital monazite decomposed into Th-free monazite. We should becareful about the dissolution, decomposition and formation of heavy minerals in the sandstones at the provenance study. Less
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