马里亚纳海沟柱状沉积物稀土地球化学特征及其指示意义

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

对我国载人潜器＂蛟龙号＂首次在马里亚纳海沟南部获取的沉积物柱状样（JL7KGC01A）进行了涂片观察、粒度、黏土矿物和稀土元素组成分析。结果表明：沉积物为典型深海黏土沉积。根据沉积物的粒度、黏土组分和稀土元素含量变化以及不同程度的δCe和δEu异常将该沉积物柱状剖面分为明显的上下两个沉积层段,即：1.8～2.41m段与0.03～1.8m两个层段。下部层段（1.8～2.41m）相比上部层段（0.03～1.8m）,沉积物平均粒径较粗,蒙脱石/伊利石比值较高,稀土元素含量低且具有弱的Ce负异常和Eu正异常,表明该段沉积物受到较多的火山物质的影响。结合年代学分析认为研究区沉积物在2.2 Ma发生明显转变,2.2 Ma之前沉积物物源以附近火山物质为主,2.2 Ma之后物源仍以火山物质为主,但陆源物质供应逐渐增加。物源的转变暗示着本区在2.2 Ma之前火山活动较为频繁。

The lithology,grain-size,clay minerals and rare earth elements（REE）of sediments from the core named JL7KGC01 A,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 andδEu 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.