Language：Japanese  

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Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.64.0_243

CiNii Article

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The Accessible Silicate Earth (ASE) has a higher Nd-142/Nd-144 ratio than most chondrites. Thus, if the Earth is assumed to have formed from these chondrites, a complement low-Nd-142/Nd-144 reservoir is needed. Such a low-Nd-142/Nd-144 reservoir is believed to have been derived from a melt in the early Earth and is called the Early Enriched Reservoir (EER). Although the major element composition of the EER is crucial for estimating its chemical and physical properties (e.g., density) and is also essential for understanding the origin and fate of the EER, which are both major factors that determine the present composition of the Earth, it has not yet been robustly established. In order to determine the major element composition of the EER, we estimated the age and pressure-temperature conditions to form the EER that would best explain its Nd isotopic characteristics, based on Sm-Nd partitioning and its dependence on pressure, temperature, and melting phase relations. Our estimate indicates that the EER formed within 33.5 Myr of Solar System formation and at near-solidus temperatures and shallow upper-mantle pressures. We then performed high-pressure melting experiments on primitive peridotite to determine the major element composition of the EER at estimated temperature at 7 GPa and calculated the density of the EER. The result of our experiments indicates that the near-solidus melt is iron-rich komatiite. The estimated density of the near-solidus melt is lower than that of the primitive peridotite, suggesting that the EER melt would have ascended in the mantle to form an early crust. Given that high mantle potential temperatures are assumed to have existed in the Hadean, it follows that the EER melt was generated at high pressure and, therefore, its composition would have been picritic to komatiitic. As the formation age of the EER estimated in our study precedes the last giant, lunar-forming impact, the picritic to komatiitic crust (EER) would most likely have been ejected from the Earth by the last giant impact or preceding impacts. Thus, the EER has been lost, leaving the Earth more depleted than its original composition.

DOI： 10.1186/s40645-016-0099-0

Web of Science

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Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

The difference in ¹⁴²Nd/¹⁴⁴Nd between present Bulk Silicate Earth and chondrites has been reported and this difference indicates a reservoir enriched in incompatible elements. Kondo & Kogiso (2014) discussed that the reservoir could be the solidus melt of peridotite at 7GPa. So in this study we determined the composition of the solidus melt from Modified Iterative Sandwich Experiment proposed by Hirschmann and Dasgupta (2007). Determined melt composition was komatiitic and conformable to the composition extrapolated from Walter (1998). The concentration of K and P in the solidus melt, however, was lower than in the expected melt and the reservoir would not have KREEPy composition.

DOI： 10.14862/geochemproc.61.0_154

CiNii Article

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Event date： 2016.6.26 - 2016.7.1

Language：English   Presentation type：Poster presentation  

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Event date： 2015.8.16 - 2015.8.21

Language：English   Presentation type：Poster presentation  

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Event date： 2014.6.8 - 2014.6.13

Language：English   Presentation type：Poster presentation  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Poster presentation  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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