长江与黄河沉积物稀土元素随粒度变化对比研究

依据Stoke定律将长江小于63μm的沉积物分成4个粒级.将黄河小于63μm的沉积物分成6个粒级.采用ICP-MS法分别测试了分粒级沉积物的REE含量,结果显示:相同粒级中长江沉积物的∑REE均高于黄河沉积物.长江沉积物REE的丰度遵循元素的"粒度控制律",即随粒度变细∑REE含量依次增高;黄河沉积物∑REE呈"高—低—高"的不对称马鞍型分布;北美页岩标准化分布曲线均呈右倾状,轻重稀土分馏明显,相对富集LREE,具弱Ce亏损,明显的Eu正异常.长江与黄河沉积物REE组成特征差异与两条河流流域的风化作用及沉积物的矿物组成密切相关,黄河∑REE的马鞍型分布是细粒级中黏土矿物吸附及粗粒级中相对高含量的重矿物富集作用的结果,而长江沉积物随粒级增大∑REE的衰减趋势主要是随粒级增大逐步增加的石英和长石含量的稀释作用所造成.

COMPARISON OF REE VARIATIONS WITH GRAIN SIZES IN SEDIMENTS BETWEEN THE YANGTZE RIVER AND THE YELLOW RIVER

According to the Stoke＇s Law,the grain sizes of sediments from the Yangtze River and the Yellow River are classified into four and six grades,separately.The REE contents in the sediments of various sizes are tested with ICP-MS.The results show differences between the two rivers.For the same grain size,the content of REE in the samples form Yangtze River is higher than that from Yellow River.The contents of REE form the Yangtze River reduce with the increasing of grain sizes of sediments.However,with the increasing of grain sizes,the REE contents in samples from the Yellow River present an unsymmetrical high-low-high distribution pattern.The North America Shale-normalized patterns show that the fractionation patterns are similar for different grain-sized sediments,and also for the two rivers.The differences of REE contents between the Yangtze River and the Yellow River are closely related to the weathering and mineral compositions in the sediments of the two river basins.The reducing trend of REE contents with grain size increasing for the Yangtze River is resulted from the dilution of quartz and feldspar contents which increase with the grain size.The REE distribution pattern of sediments from Yellow River is the result of the absorption of clay minerals in fine-grained sediment and the enrichment of heavy minerals in coarse-grained sediment.