Summary of Abstract Submission

Abstract Submission No. IO50-15-0076PresentationPoster

HYDROTHERMAL SIGNATURES IN FERROMANGANESE CRUSTS FROM THE CENTRAL AND SOUTH WEST INDIAN RIDGE

Dr Niyati Kalangutkar*1, Dr John Kurian 1

1 National Center for Antarctic and Ocean Research, India

ABSTRACT :

A number of dredging operations along, the South West Indian Ridge (SWIR) and Central Indian Ridge (CIR) areas during the recent hydrothermal expeditions carried out by National Center for Antarctic and Ocean Research (NCAOR) have recovered basalt of various types, (altered, vesicular) and also altered mafics, ultramafics and serpentinites. These rocks form substrate and have variable thickness of ferromanganese (FeMn) oxides which ranges from thin coating to maximum of 5cm layered crusts. Lumps FeMn oxides without any layers were also recovered form few stations. The oxides display rough botroidal or smooth surface textures. We studied about twenty samples to determine their mineralogical compositions and examine their microstructural features and elemental composition using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Electron Dispersive Spectroscopy (EDS) and Inductively Coupled Mass Spectrometry (ICPMS). XRD analysis shows that the dominant mineral phases of these oxyhydroxide crusts are vernadite, goethite, with minor ferrihydrite, hematite and nontronite. The SEM shows fambroids, fossil worms molds, biogenic remains of foraminifera and euhedral crystals of phillipsite on some of these FeMn crusts. The EDS results show a higher FeO wt% than MnO wt% indicating a lower Mn/Fe ratio. The Mn/Fe <1 indicates hydrothermal source for the oxide. Negative Ce anomaly is exhibited by five of the samples whereas ternary plots of MnżFeż10×(Ni+Co+Cu) also indicate characteristic geochemical signatures of mixed hydrogenous-hydrothermal origin. The studies point toward hydrothermal origin for most of the FeMn crusts along SWIR and CIR. Keywords: CIR, SWIR, ferromanganese oxides, hydrothermal.