Geochemistry of rare earth elements in oceanic phillipsites |
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Authors: | A V Dubinin |
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Affiliation: | (1) Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovskii pr. 36, 117851 Moscow, Russia |
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Abstract: | The behavior of rare earth elements (REE) was examined in oceanic phillipsites collected from four horizons of eupelagic clay
in the Southern Basin of the Pacific. The REE concentrations were determined in the >50-μm-fraction phillipsite samples by
the ICP-MS method. The composition of separate phillipsite accretions was studied using the electron microprobe and secondary
ion mass-spectrometry. Rare earth elements in phillipsite-only samples are related to the admixture of ferrocalcium hydroxophosphates.
The analysis of separate phillipsite accretions reveals low (<0.1–18.1 ppm) REE (III) concentrations. The Ce concentration
varies between 2.7 and 140 ppm. The correlation analysis shows that REE (III) are present as an admixture of iron oxyhydroxides
in separate phillipsite accretions. Based on the REE (III) concentration in iron oxyhydroxides, we can identify two generations
of phillipsite accretions. Massive rounded accretions (phillipsite I) are depleted in REE, while pseudorhombic (phillipsite
II) accretions are enriched in REE and marked by a positive Ce anomaly. Oceanic phillipsites do not accumulate REE or inherit
the REE signature of the volcaniclastic material and oceanic deep water. Hence, the REE distribution in phillipsites does
not depend on the sedimentation rate and host sediment composition. |
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