Compositional variation and genesis of ferromanganese crusts of the Afanasiy—Nikitin Seamount, Equatorial Indian Ocean |
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Authors: | R P Rajani V K Banakar G Parthiban A V Mudholkar A R Chodankar |
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Institution: | (1) National Institute of Oceanography, Dona Paula, 403 004 Goa, India |
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Abstract: | Eight ferromanganese crusts (Fe-Mn crusts) with igneous and sedimentary substrates collected at different water depths from
the Afanasiy-Nikitin Seamount are studied for their bulk major, minor and rare earth element composition. The Mn/Fe ratios
< 1.5 indicate the hydrogenetic accretion of the Fe-Mn hydroxides. These Fe-Mn crusts are enriched in Co (up to 0.9%, average
∼ 0.5%) and Ce. The Ce-content is the highest reported so far (up to 3763 ppm, average ∼ 2250 ppm) for global ocean seamount
Fe-Mn crusts. In spite of general similarity in the range of major, minor, and strictly trivalent rare earth element composition,
the dissimilarity between the present Fe-Mn crusts and the Pacific seamount Fe-Mn crusts in Co and Ce associations with major
mineral phases indicates inter-oceanic heterogeneity and region-specific conditions responsible for their enrichment. The
decrease in Ce-anomaly (from ∼ 8 to ∼ 1.5) with increasing water depth (from ∼ 1.7 km to ∼ 3.2 km) might suggest that the
modern intermediate depth low oxygen layer was shifted and sustained at a deeper depth for a long period in the past. |
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Keywords: | Ferromanganese crusts composition seamount Equatorial Indian Ocean |
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