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      Permanent link:
      https://www.ias.ac.in/article/fulltext/jess/114/01/0051-0061

    • Keywords

       

      Ferromanganese crusts; composition; seamount; Equatorial Indian Ocean

    • 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.

    • Author Affiliations

       

      R P Rajani1 V K Banakar1 G Parthiban1 A V Mudholkar1 A R Chodankar1

      1. National Institute of Oceanography, Dona Paula, Goa - 403 004, India

    • Dates

       
      Published
      February 2005
      Manuscript received
      7 May 2004
      Accepted
      12 August 2004

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