THE GEOCHEMICAL CHARACTERISTICS OF TRACE ELEMENTS AND REES IN SURFICIAL SEDIMENTS OF THE SOUTHWESTERN SOUTH CHINA SEA AND THEIR IMPLICATIONS

This paper presents the trace elements and REEs composition of the surficial sediments from the southwestern South China Sea(SCS).The results show that the samples have relatively low Zr,Sc,V,Nb,Hf,Th,REEs contents and high Co,Cu,Ni,Ta,Rb,Cs,Sr,Ba contents,compared with the upper continental crust(UCC).The sediments from marine basins have higher Co,Zr,Sc,V,Nb,Hf,Ta,Th and REEs abundances than those from the continental slope.Factor and correlation analyses indicate that most of these elements are land-derived.The immobile elements such as Th,Cr,Co,Sc,Nb,Zr,Hf and REEs are indicators of source rocks.There shows no influences from weathering,transportation and diluting effect of biologic materials.The high La/Sc,Th/Sc,Th/Cr,Th/Co ratios and UCC-like rare earth elements distribution patterns characterized by highΣLREE/ΣHREE ratios and lowδEu values suggest that the source of the studied sediments are mainly from continental crust with felsic rocks as the majority,but the contribution of basic/ultrabasic rocks is ignorable and the volcanic clast content in the sediments is also very low.With reference to the geography of the studied areas,the geochemistry of surficial sediments from the southwestern SCS indicates that the materials are mainly from neighbour continents,probably the Indo-China block.Both the continental slope and marine basins show a common provenance according to their similarity in trace and rare earth elements compositions.