岩鉱
Online ISSN : 1881-3275
Print ISSN : 0914-9783
ジルコンをめぐる最近の話題
III. ジルコンの希土類元素地球化学
牧嶋 昭夫中村 栄三
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1994 年 89 巻 1 号 p. 1-14

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Recent topics on the rare-earth element (REE) geochemistry of zircon are reviewed in this article.
With SIMS (secondary ion mass spectrometry), we can obtain the REE composition for a spot area (<40μm) of zircon. These SIMS studies have revealed that the LREE are much more depleted in zircon crystals than was previously believed as indicated by conventional bulk zircon analysis. SIMS studies also indicate that the REE patterns of terrestrial zircon generally have Ce anomaly. The implications of the Ce anomaly for the evolution of the atomosphere are discussed.
Because zircon crystals are resistent to decomposition with HF in an open beaker, open beaker decomposition yields erroneous results in some cases. We discuss several examples in the case of analyses of sediments.
The resistence of zircons to erosion and weathering, and its high concentration of Hf constrain sediment recycling into the mantle and the evolution of continental crust. We discuss such issues in this paper, based chiefly on Lu-Hf isotope systematics.
We conclude in our “Reviews in Zirconolgy” that SIMS is the ultimate tool for U-Pb dating and the prerequisite equipment for the study of element partitioning. Therefore, we must utilize SIMS more extensively in geochemical studies in Japan in order that our ideas will not to be outdated. And furthermore, we should create new ideas.

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