Radiogenic Nd in bioapatite from rare earth elements rich deep sea sediments from Central Indian Oceanic Basin and its implication in material sources

Abstract

Rare Earth Element and Yttrium (REY)-rich deep sea sediments have been estimated to be a highly important potential resource. However, the main material sources that supply the huge amount of REY resources, as well as geochemical procedure determines the distinct REY patterns of these sediments, remain unclear. To fill this research gap, in this study, three sediment cores (GC02, GC04, and GC11) collected from the Central Indian Ocean Basin (CIOB) and a core (GC03) from eastern of the 90° E Ridge (NER) were sampled for mineral identification and elemental (major, trace, and rare earth elements) analyses. Fish teeth and detrital minerals were isolated from the sediments, and their 87Sr/86Sr and 143Nd/144Nd ratios were measured. Accumulation of REY is revealed in three cores of GC02, GC04, and GC11 from CIOB with mean value of 511.93 μg/g, 614.79 μg/g, and 1036.14 μg/g, respectively. Most REY rich sediment exhibit obvious to slight negative Ce abnormal, slight positive Eu and Y abnormal. The detrital fraction of the REY rich sediments exhibit less radioactive εNd values of − 8.36295 and more radioactive 87Sr/86Sr of of 0.71651. On the contrary, the fish teeth exhibit less radiogenic 87Sr/86Sr ratio of 0.70915 but more radiogenic εNd values of − 5.13511 than those of the sea water of the Indian Ocean. The results reveal that the REY-rich sediments in the CIOB are characterized by multiple material sources including weathering continental products, alteration of volcanogenic glasses, hydrothermal and marine authigenic materials. Distinct volcanogenic materials input are obvious in the CIOB evidenced with radiogenic 143Nd/144Nd ratios of the fish teeth, the wide occurrence of clinoptilolite and high Te contents contained. The volcanogenic related hydrothermal materials are then indicated to provide most part of REY for the fish teeth, which contribute the most amount of REY of the sediments. However, the terrestrial input of REY cannot be neglected, which indicates the REY-rich deep sediments were formed under multi-source supply system. The study indicated that continuous exchange of Sr between fish teeth and ambient pore water after deposition, and ambient pore water was concluded to contain an abundance of released radiogenic terrestrial Sr. However, the exchange of Nd between fish teeth and bottom sea water ceased after buried in depth. Nd ratios on the fish teeth recorded the more radioactive hydrothermal material carried by bottom seawater at the early stage of precipitation.