海成石灰岩と分配係数を用いた古代海水の希土類元素存在度の新しい推定法
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概要
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The seamount-type limestone formed on the top of seamount away from continents, preserves chemical features of ancient seawater. Chondrite-normalized rare earth element (REE) abundance patterns for Japanese Permian seamount-type limestones show seawater-like characteristics of convex tetrad effects and Y fractionation from Ho as well as negative Ce and Eu anomalies. Apparent REE partition coefficients between marine limestone and present-day seawater suggest that REE fractionation and enrichment occurred when seawater REEs were incorporated into limestone. Laboratory REE partition experiments between calcite and aqueous solution have been carried out in order to elucidate the incorporation process. Experimentally determined REE partitioning patterns show concave tetrad effect variations and Y fractionation from Ho. Combining REE analyses of ancient limestone samples and the experimental partition coefficients, it is possible in principle to estimate REE abundances in ancient seawater. REE abundances in Permian seawater estimated by this new method quite resemble those in the present-day seawater samples in chondrite-normalized patterns.
- 日本地球化学会の論文
- 2005-05-30