Ferromanganese nodules and their associated sediments from the Central Indian Ocean Basin: Rare earth element geochemistry

The rare earth element (REE) distribution in nine deep-sea ferromanganese n odules and their associated siliceous sediments from the Central Indian Oce an Basin (CIOB) have been studied to elucidate the REE relationship among t hem. Total REE concentration varies from 398-928 ppm in the nodules and 137 -235 ppm in the associated sediments, suggesting two- to four fold enrichme nt in the nodules compared to associated sediments. REE of nodules and thei r associated sediments show a positive correlation, suggesting REE are supp lied from a common source such as seawater. The positive correlation betwee n REE of nodules and sediments from the CIOB is contrary to the competitive scavenging of REE between nodules and sediment in the equatorial Pacific O cean. REEs in the nodules are carried by Fe, P, and Ti, whereas in the sedi ment they are carried by P and Mn phases. A similar REE fractionation patte rn with middle REE enrichment over heavy and light REE in both the nodules and their associated sediment suggest fractionation is independent of REE a bundance and their carrier phases.