2005 Fiscal Year Final Research Report Summary
Determination of isotopic ratios, abundances and chemical species (chemical state) on platinum group elements and its application to the study of geochemical cycle and environmental change on the surface of the Earth
| Project/Area Number |
15204051
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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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, 大学院・理学研究科, 教授 (60090544)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Yoshio Hiroshima University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (10304396)
SUZUKI Katsuhiko Japan Marine Science and Technology Center, Institute for Frontier Research on Earth Evolution, Group Leader, 地球内部変動研究センター, グループリーダー (70251329)
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| Project Period (FY) |
2003 – 2005
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| Keywords | platinum group elements / Re-Os isotopic system / chemical species / XAFS / continental crust / iron meteorite / chert / mass extinction |
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| Research Abstract |
Isotopic ratios, abundances and chemical species (chemical state) on platinum group elements were determined to study geochemical cycle and environmental change on the surface of the Earth.
1. Rhenium-osmium systematics on continental crust : The first Re-Os isotopic data were reported for the Taklimakan Desert sands and glacial moraines from the Kunlun Mountains. The Taklimakan Desert sands from various regions show surprisingly homogeneous Os isotopic data. It is supported that the Taklimakan Desert sands are derived from moraines and river sediments around the desert or from Tibetan soils and are homogenized by aeolian activity in the deserts. Our Re-Os data for the Taklimakan Desert sands were compared with those of loess from the Loess Plateuau, and it was concluded that the Re-Os data for the loess can be used and as proxy for the upper continental crust.
2. Speciation of osmium in an iron meteorite and a platinum ore specimen based on X-ray absorption fine-structure spectroscopy :
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We reported the first synchrotron radiation-based X-ray absorption fine structure (XAFS) spectra for Os in geo- and cosmo-chemical materials and showed that Os in the iron meteorite and the platinum ore chiefly exist as a metallic species. It is expected that further application of the XAFS technique to the Os speciation in natural samples will be help to elucidate Re/Os fractionation processes in the Re-Os isotopic system.
3. Evolution of Os isotope ratios in the ocean (Osmium isotope ratio at P-T boundary) : Osmium isotopic compositions deduced from cherts from the outer zone in the southwest Japan show the higher contribution of mantle material to seawater from early Permian to Triassic, suggesting the mass extinction event at P-T boundary is more likely caused by large igneous province activity.
4. Removal mechanism of Re and Os from seawater to sediments : In seawater-sediment system, it was shown that Re was removed from seawater only under reducing environment and Os was readily removed from seawater to sediments under various redox conditions. Less
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