长江主要支流与干流沉积物的REE组成

Rare Earth Element Compositions of the Sediments from the Major Tributaries and the Main Stream of the Changjiang River

系统采集了长江主要支流与干流从上游到下游不同地区的河漫滩沉积物样品,用1 M盐酸淋滤处理研究了REE在不同相态中的组成特征。研究表明,长江沉积物中REE主要赋存于酸不溶相中,约占总含量的70%。不同REE的酸提取效率不同,酸溶相明显富集REE,主要受磷灰石等磷酸盐矿物和部分Fe-Mn氧化物矿物的控制。主要赋存于粘土矿物中的不同轻稀土元素在酸溶相中百分比接近,而富重稀土元素的重矿物可以明显影响REE在不同相态中的组成和不同地区河流沉积物中REE的配分特征。长江支流沉积物的REE组成变化大于干流,流域源岩组成差异是控制REE组成的基本因素,但干流和支流沉积物全样与酸不溶相的REE配分模式基本类似,反映了各自流域风化上陆壳的平均组成。尽管一些支流对邻近干流沉积物的REE组成贡献较大,但总体上干流样品代表了不同支流水系沉积物的混合,尤其是下游近河口地区细粒级沉积物样品的酸不溶组分可以代表长江入海颗粒物的平均REE组成,用于示踪判别东部边缘海长江沉积物的源汇过程。

The floodplain sediments were systematically collected from the major tributaries and mainstream of the Changjiang River to investigate their rare earth elements（REEs） compositions.In this study,1M HCl was used to separate the acid-leachable REE from the residual REE in the bulk samples.The analytic results suggested that the residual fraction enriches REE with a proportion up to 70% of the bulk concentration.Different REEs show variable leaching proportions and the leached fraction mainly contains middle REEs,which are predominantly sourced from the dissolution of phosphate minerals such as apatite and partly from Fe-Mn oxide minerals.Light REEs primarily reside in clay minerals and exhibit similar leaching proportions;whereas heavy REEs generally concentrates in some heavy minerals demonstrate regular leaching proportions.The HREE-enriched heavy minerals significantly influence the REE compositions between two different fractions of the sediments from different tributaries.Overall,the variations of REE compositions in the tributaries sediments are larger than those in the mainstream sediments,reflecting the control of provenance rocks on REE compositions in river sediments.The UCC-normalized REE patterns in the bulk samples and the residual fractions from the major tributaries and the mainstream are similar,basically representing the average compositions of the weathered upper continental crust within different catchments.Our study suggested that the REE compositions in the residual fraction of the Changjiang mainstream sediments sampled from the lower reaches near the estuary reflect the average compositions of the fine-grained Changjiang sediments into the sea,although the REE compositions in some floodplain sediments from the upper mainstream may be altered by the nearby local tributaries.The main research result from this study will be helpful for the reconstruction of sediment source-to-sink patterns in the marginal seas.