Genesis and Nd Isotope Composition of Ferromanganese Deposits of the Sea of Okhotsk and the Kuril Island Arc

摘要

The Nd isotope composition of ferromanganese deposits (FMD) from the central part of the Sea of Okhotsk and the Kuril island arc has been studied. The results showed that diagenetic samples from the Dayugin Basin have a heterogeneous Nd isotope composition. The positive epsilon(Nd) values here might be both due to the input of a terrigenous impurity and due to diffuse endogenetic element supply. The FMD samples from the Sonne underwater ridge show a epsilon(Nd) value specific to seawater (-3.2). The epsilon(Nd )value of hydrogenetic FMD from Volcano 7.14 is -3.4, which corresponds to the epsilon(Nd )value of the Pacific water. The FMD samples from Volcano 5.5 are characterized by epsilon(Nd) = -2.0. The higher epsilon(Nd )value might be due to a moderate dilution of the hydrothermal fluid by seawater and might also indicate the presence of volcanic fragments in the FMD samples. The highest epsilon(Nd )value (+4.4) has been established for volcaniclastic sandstone saturated with Fe and Mn hydroxides. It points to a mixing of volcanomictic and hydrothermal materials.