CHARACTERISTICS OF RARE EARTH ELEMENTS IN SURFACE SEDIMENTS FROM THE MIDDLE OKINAWA TROUGH: IMPLICATIONS FOR PROVENANCE OF MIXED SEDIMENTS

Abstract

The geochemical behavior and characteristics of rare earth elements (REEs) have been greatly applied to the study of tracing sources of sediments. In this paper the qualitative distributions of different sources of the surface sediments from the middle Okinawa Trough were traced by utilizing the characteristic parameters of REEs. The mixed sediments from the middle Okinawa Trough are mainly composed of three end-members, known as terrigenous matter, volcaniclastic materials and biologic matter. The contribution of each end-member in mixed sediments and REEs' abundance of each end-member are the main factors that control the abundances and characteristics of REEs in the mixed sediments. Therefore, if there are remarkable differences in REEs' characteristics for different end-members, some characteristic parameters of REEs can be extracted and used as proxies for the sources of the mixed sediments. By comparison of REEs' characteristics of three end-members, it was clearly shown that terrigenous matter (fine-grained sediments obtained from the Yangtze River and Yellow River drainage basins) was characterized by highest total concentration of REEs and enriched light REEs (LREEs); Volcaniclastic material (volcanic glass) was characterized by an increase of Eu, while mid REEs (MREEs) of biologic matter (foraminifer shells) were more enriched. Accordingly, three diagnostic parameters of REEs, ΣLREE/ΣHREE,Eu/Sm and MREE/(LREE+HREE)were selected as proxies to distinguish three sources of the surface sediments. The result was consistent with the conclusion drawn by the previous researches, demonstrating that REEs’ characteristic parameters mentioned above can be used as effective proxies for the sources of the mixed sediments from the middle Okinawa Trough.