| Project/Area Number |
18540482
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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 |
Geochemistry/Astrochemistry
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| Research Institution | Hiroshima University |
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Principal Investigator |
SHIMIZU Hiroshi Hiroshima University, Graduate School of Science, Professor (60090544)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Yoshio Hiroshima University, Graduate School of Science, Associate Professor (10304396)
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| Project Period (FY) |
2006 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,550,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥450,000)
Fiscal Year 2007: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2006: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Keywords | Re-Os system / redox condition / marine sediment / XAFS / molybdenite / local atomic structure / 固相-液相反応 / 酸化還元条件 / XANES / 溶存形態 |
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| Research Abstract |
The removal behaviors of Re and Os in a seawater-sediment system and Re/Os fractionation during removal were studied by performing laboratory experiments using a multitracer technique and XAFS spectroscopy.
1. Rhenium and Os can be removed from artificial seawater to sediments with development of reducing conditions, confirming that reductive removal is an important process for Re and Os. The removal of Os from the seawater to burnt sediment and organic-free sediment under oxic conditions was also observed, while Re was not removed from the seawater to the sediments under the same conditions. The removal process of Os seems to be controlled by several factors, such as reduction, hydrolysis, and orgaic complexation.
2. Although Re is removed to sediments only under highly reducing condition in our experiments, the slow kinetics of Re reduction can inhibit the observation of Re removal under less reducing condition within the timescale of the experiments. Hence, we here conclude that reduction condition is needed for the removal of Re to sediments, while Os can be removed even under oxic condition as shown in our experiments. Thus, a high ^<187>Re/^<188>Os ratio can our in reducing sediments, such as black shale. The high ^<187>Re/^<188>Os ratio makes black shale suitable for Re-Os dating due to the large growth of high ^<187>Re/^<188>Os. In contrast, authigenic sediments (and minerals) under oxic environments can only enrich Os, which cause a much lower ^<187>Re/^<188>Os ratio than that of seawater. The osmium isotopic system of these materials can be used as a paleo-marine environmental tracer because the ^<187>Os/^<188>Os ratio cannot grow significantly due to its extremely low ^<187>Re/^<188>Os ratio.
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