GEOCHEMISTRY OF RARE EARTH ELEMENTS IN A CORE FROM MARIANA TRENCH AND ITS SIGNIFICANCE

The lithology, grain-size, clay minerals and rare earth elements (REE) of sediments from the core named JL7KGC01A, collected by "JiaoLongHao" from the Pacific Ocean, south of the Mariana Trench, are analyzed for the first time. The results show that the sample is a sort of typical pelagic clay. According to its granularity, clay minerals, REE contents, δCe and δEu values, the core can be divided to lower(1.8-2.41 m) and upper sections(0.03-1.8 m). Sediments from the lower section are coarser in grain-size, with higher M/I value (montmorillonite/illite), lower REE value, slightly negative Ce and Eu anomalies compared to the upper section, indicating that the lower section hosts more volcanic materials. According to the mineralogy, REE geochemistry and chronological data in hand, we believe that the sediments were mainly from nearby volcanic eruptives earlier than 2.2 Ma. However, the terrigenous materials played an increasingly important role in the sediments later than 2.2 Ma. The change in source of the sediments may indicate frequent volcanic activities in the Mariana before 2.2 Ma.