Clay Minerals and Sr-Nd Isotope Compositions of Core CG 1601 in the Northwest Pacific: Implications for Material Source and Rare Earth Elements Enrichments

Abstract

Deep-sea sediments generally refer to the sediments distributed on the seafloor with a depth of more than 2000 m. Many rare earth elements and yttrium (REY)-rich sediments were recently discovered in the sea area of Minamitorishima Island, Northwest Pacific. To understand the material source and REY enrichments of sediments in this area, here, we performed clay minerals and Sr-Nd isotopes analyses on gravity core GC1601 gained in the Southeast Sea area of Minamitorishima Island. The clay mineral composition of the core is very similar to that of terrigenous materials, and its montmorillonite/illite (M/I) ratio ranges from 0.09 to 0.20 with an average of 0.15, indicating that the sediments in the study area should be mainly dominated by terrestrial sources, consistent with the results of Sr-Nd isotope study. Considering that the study area is far away from the mainland and in the downwind direction of the East Asian monsoon, we propose that the terrigenous material of the sediments in the study area is likely East Asian dust. The εNd values of GC1601 show a positive correlation with P2O5, Co, Ni, and Cu, and have an increasing trend with increasing depth, approaching that of the seawater, indicating that the sedimentary environment in the area is relatively stable. Although the total REY content (ΣREY) of the core increases with depth, due to the large supply of terrigenous materials for the sediments, it is difficult for the study area to form high-grade REY-rich muds.