Geochemical, mineralogical, and Sr–Nd isotopic compositions of ferromanganese encrustations from Central Indian Ridge at 06°38.5′S


Mineralogical, geochemical, and isotopic (Sr and Nd) studies of 14 ferromanganese encrustations on basaltic substrates from Central Indian Ridge at 06°38.5′S indicate that except for two (NC3 and NC4), the samples are hydrogenous type. NC3 and NC4 have slightly higher growth rates, lower bulk trace metal contents, and low ∑REE. They have a lower content of high field strength (e.g., Hf, Ta, Zr, and Nb), incompatible (e.g., Pb, Th, and U), and lithophilic elements (e.g., Sr and Ba) than others. In addition, NC3 has a lower 87Sr/86Sr ratio (0.708825) than the remaining samples (range 0.709169–0.709253) but higher 143Nd/144Nd ratio (0.512296) than others (range 0.512258–0.512279). Both NC3 and NC4 have a higher radiogenic component indicated by their low εNd value (−6.67) than the remaining samples (range −7.00 to −7.41). These evidences together indicate a possible contribution of trace metals by a local mixed source of hydrothermal and hydrogenous origin during their growth history.

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