Search

Ferromanganese (FeMn) crusts with oxides ranging from a thin coating to a maximum of 5 cm thickness were recovered from the South West Indian Ridge (SWIR) and Central Indian Ridge (CIR) segments. The substrate for the oxides are altered mafic, ultramafic, and serpentinite rocks. Twenty FeMn crusts were studied to determine their mineralogical compositions, microstructures, and chemical compositions. The crusts display rough botryoidal or smooth surface textures. Todorokite, hematite, goethite, and nontronite are the major minerals followed by vernadite, magnetite, and maghemite. Electron micrographs show framboids of FeMn oxides, fossil worms, foraminifera nuclei, and euhedral mineral crystals. The oxides have higher FeO wt% (27–47; average ∼43) than MnO (13–45, average ∼30), and the average wt% of SiO2 is ∼40, Al2O3 ∼3, MgO ∼2, CaO ∼4, Na2O ∼0.4, K2O, NiO ∼0.5, CuO ∼0.3, CoO ∼0.8, and P2O5 ∼1.5. Our studies indicate a hydrothermal origin for the crusts and this fact is corroborated by low MnO/FeO ratio (≤ 1) and occurrence of framboids and hydrothermal minerals. Negative Ce anomaly and the plot of Mn–Fe–10×(Ni + Co + Cu) indicate characteristic signatures of hydrogenous-hydrothermal origin for most of the studied FeMn crusts. [ABSTRACT FROM AUTHOR]

Six sediment cores from the Carlsberg Ridge (CR) were studied for elemental concentration, magnetic susceptibility (Χ), grain size and clay mineral distribution, and sedimentation rate to decipher possible detrital and diagenetic contributions. The sediments were characterized by very low Χ, moderate total organic carbon, high CaCO3 content and high accumulation rate (3 cm/ kyr). Clay mineralogical and geochemical data suggest major continental source from the Arabian Sea, and very low Mn distribution, absence of tephra and characteristic magnetic signatures rule out volcanic or hydrothermal input. Consistent peaks around 10, 25, 45, 60 and 80 cm depth and high uranium are due to sedimentary diagenesis. [ABSTRACT FROM AUTHOR]