Hydrothermal Genesis of Fe–Mn Crust in the Southernmost Segment of the Mohns Ridge, Norwegian Sea: REE Geochemistry and Sr and Nd Isotopic Composition.

Mineralogical, geochemical, and isotopic studies of the Fe–Mn crust collected in the Jan Mayen vent field area have been carried out for the first time. The crust (about 3 cm thick) has a distinct microstratified structure, sharp contact with the underlying volcanic substrate, and colloform Fe and Mn oxyhydroxides at its bottom. The crust is composed mainly of Mn oxyhydroxides: birnessite and buserite with an impurity of volcanic glass. As follows from the layer-by-layer study of the crust, the Mn content increases by 3–10 times from bottom to top, whereas Fe and REE decrease in the same direction. The samples are marked by a positive Eu anomaly (Eu/EuNASC 1.08–1.41). Ce/CeNASC is 0.89 ± 0.05. 87Sr/86Sr in the crust's lower and middle layers is within 0.70621–0.70713, while εNd reaches 5.6–6.2. These parameters are 0.70740 and –0.1, respectively, in the uppermost layer of the crust. The REE composition, positive Eu anomaly, high εNd values, and low 87Sr/86Sr ratios in the crust are indicative of the fact that the ore material mainly originated from hydrothermal solutions. Changes in the Sr and Nd isotope characteristics and REE composition in the crust layers are due to a decrease in the hydrothermal material contribution as the crust grew at a high crust deposition velocity in the Jan Mayen vent field area. [ABSTRACT FROM AUTHOR]