An investigation of methods of estimating the duration of metamorphism.
| Project/Area Number |
07640641
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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 | HIROSHIMA UNIVERSITY |
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Principal Investigator |
HOSHINO Kenichi Earth and Planetary systems Science, Science, Hiroshima University Assistant, 理学部, 助手 (80190198)
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| Co-Investigator(Kenkyū-buntansha) |
HAYASAKA Yasutaka ditto, Hiroshima University Assistant, 理学部, 助手 (10198830)
WATANABE Makoto ditto, Hiroshima University Associate Professor, 理学部, 助教授 (80033900)
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| Project Period (FY) |
1995 – 1996
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| Project Status |
Completed (Fiscal Year 1996)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1996: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1995: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Keywords | duration of metamorphism / regional metamorphism / contact metamorphism / compositional zoning / grain size / CSD / Ostwald ripening |
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| Research Abstract |
The following three metamorphic phenomena have been investigated with the aim of estimating duration of metamorphism : 1) compositional zoning in metamorphic menerals, 2) grain growth of menerals caused by regional metamorphism, and 3) grain growth of minerals caused by contact metamorphism.
Compositional zoning of a metamorphic meneral has numerically been analyzed based on the assumptions of a rapid growth rate and local equilibrium throughout metamorphism. Because of the assumptions and intracrystalline diffusion, a composition showing a maximum metamorphic temperature can not remain in the mineral. The analysis has made it possible to determine the most suitable size (MSS) of crystal which shows the highest temperature in its core for a certain duration of metamorphism. Conversely, the duration of metamorphism can be estimated by measuring the MSS.Crystals smaller than the MSS may show retrograde zoning, whereas those of large grain may retain propgrade zoning.
The usefulness of this method (the MSS method) is that one may analyze only the central compositions instead of full compositional profiles needed for the method by relaxation. Moreover, the obtained equation appears to be applied to various forms of T-t path with various maximum temperatures. One can also roughly estimate the duration without an exact knowledge of the X-T relation because of its small effect on the constant of the equation.
The grain size distribution of pyrite in regionally metamorphosed massive pyrite ores shows patterns being suitable for normal grain growth during metamorphism. The mean grain size of pyrite tends to increase with an increasing degree of metamorphism. It is also confirmed that quartz in chert thermally affected by a granite intrusion shows the same grain size distribution patterns as the above, while biotite in chert shows the patterns of nucleation and growth.
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Report
(3 results)
Research Products
(11 results)
