2014 Fiscal Year Annual Research Report
| Project/Area Number |
26287105
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| Research Institution | Ehime University |
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Principal Investigator |
GREAUX Steeve 愛媛大学, 地球深部ダイナミクス研究センター, WPI 研究員 (90543166)
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| Co-Investigator(Kenkyū-buntansha) |
西 真之 愛媛大学, 地球深部ダイナミクス研究センター, 助教 (10584120)
河合 研志 東京大学, 総合文化研究科, 助教 (20432007)
市川 浩樹 愛媛大学, 地球深部ダイナミクス研究センター, WPI 研究員 (50570503)
丹下 慶範 公益財団法人高輝度光科学研究センター, 利用研究促進部門, 研究員 (70543164)
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| Project Period (FY) |
2014-04-01 – 2018-03-31
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| Keywords | chondrite / melting temperature / high pressure / magma ocean / planetary accretion / mantle composition |
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| Outline of Annual Research Achievements |
The aim of this project is to specify the bulk composition of the primary mantle and core of terrestrial proto-planets by high-pressure melting experiments of chondrites and apply them to models of accretion and differentiation, as well as mantle convection.
During FY26 we investigated the melting phase relation of a carbonaceous chondrite (origin: Tagish Lake, TL hereafter) up to 50 GPa and 2300 K. Experiments were carried out in a multi-anvil press apparatus equipped with tungsten carbide anvils up to 25 GPa while we used sintered diamond anvils to reach ultra high pressures up to 50 GPa. After melting, samples are quenched to room T and recovered to room P and then embedded in epoxy for chemical analyses.Chemical composition of samples were analysed by FE-SEM at GRC (Ehime Univ.) and by SIMS (Hokkaido Univ.).
At mantle transition region pressures, we observed coexistence of silicate melt, Fe-Ni-S metal liquid and solid phases. We found that SiO2 stishovite is the first phase to crystallized at 20 GPa whereas pyropic majorite is the liquidus phase at P higher than 25 GPa. At lower mantle conditions, Although the Fe-bearing bridgmannite seems to be the liquidus phase, we found some occurrences of diamonds in the silicate melt and FeO in the FeS. In this experiments we could not melt completely the chondrite samples at 50 GPa and 2300 K and therefore we expect to clarify the higher pressure melting relation by future experiments at higher temperature.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Carbonaceous chondrite was successfully molten up to 25 GPa and 2000 K using tungsten carbide anvils and rhenium heaters. However at T higher than 2000 K, heater stopped to function due to rhenium hydrogenated with the release of volatiles from the chondrites. Therefore our cell design was changed to accomodate a ceramic heater (LaCrO3) for which we could reach T up to ~3000 K. This development was anyway necessary for the next step of this project which consist of melting of enstatite and ordinary chondrites, which melting temperature is expected to be higher than carbonaceous chondrites due to their lesser volatile contents.
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| Strategy for Future Research Activity |
In FY27, additional experiments will be carried out on the carbonaceous chondrite (CC) in order to clarify its melting temperature at ~50 GPa; thus strenghtening the constrain on its phase relation at high pressure. The current FE-SEM analysis gave a rough understanding of the element partitioning in between metal/silicate, silicate/melt and silicate/silicate in the solid portion of the samples. Although this results are meaningful for establishing phase relations, we plan to conduct further chemical analysis of volatiles and minor elements using SIMS and FE-EPMA techniques. We conducted preliminary measurements of hydrogen in CC samples, which showed that H may not be completely released during melting stage and could be partially retained in the melt fraction of the sample. This results need to be further confirmed.
The systematics of the CC will be carried to the study of enstatite (EC) and ordinary (OC) chondrites. The enstatite chondrite specimen (origin: Sahara) was purchased while the ordinary one is yet to be decided.
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