印度洋钙质软泥和硅质软泥稀土元素组成和富集机制

Composition and enrichment of rare earth elements in calcareous and siliceous ooze in the Indian Ocean

本文针对采自印度洋深海中最常见的两类生物成因沉积物——钙质软泥和硅质软泥,开展了全岩样和不同粒级组分中常微量元素、稀土元素和Y(REY)含量的系统分析,探讨了两类沉积物中REY的组成特征、物质来源和富集机制。研究表明,钙质软泥以富含CaO和Sr为主要特征,硅质软泥则富集SiO_2、Al_2O_3、Fe_2O_3等。钙质软泥中ΣREY平均含量为40.56×10^(-6),轻稀土元素(LREE)略有富集,REY有向细粒沉积物中富集的特征,PAAS标准化后全岩样和不同粒级组分均表现为Ce负异常、Eu和Y正异常;REY以自生来源为主,继承了海水的组成特征,同时也受到了热液流体物质和洋底玄武岩风化产物的影响。硅质软泥中ΣREY的含量为248.54×10^(-6),LREE相对富集,REY在4Φ以细的沉积物中富集;研究站位沉积物中ΣREY含量处于边界品位附近,但在细粒级沉积物中重稀土元素(HREY)含量则达到了工业品位;该类沉积物细粒组分中REY主要来自陆源或火山碎屑组分中黏土矿物和铁锰氧化物吸附作用,粗粒组分中REY来源则主要与生物作用相关;硅质软泥中REY的富集与沉积物中磷灰石等矿物相关,部分不同来源的REY可能是在沉积之后的成岩过程中再次分配向磷灰石、钙十字沸石等矿物中富集。

In this paper, two kinds of biogenic sediments, calcareous ooze and siliceous ooze, which are the most common types of biogenic sediment in the Indian Ocean, were analyzed to explore the concentration distribution of the major and trace elements, rare earth elements and Y (REY) in the bulk samples and different particle size components. The composition characteristics, material sources and enrichment mechanism of REY in these two kind sediments were discussed. The results show that the siliceous ooze is riched in CaO and Sr, and the siliceous ooze is enriched with SiO2 , Al2O3 and Fe2O3 . The average content of ΣREY in calcareous ooze is 40.56×10 -6 , which is enriched in the fine sediment, and the light rare earth element (LREE) is slightly enriched in this kind sediment. When that normalized by PAAS, REY all showed negative anomalies of Ce, positive anomalies of Eu and Y in both the bulk sediment and different particle size components. REY in the calcareous ooze reserve the composition of seawater, which is dominated by autogenous origin and also influenced by hydrothermal fluid and oceanic basalt weathering materials. Meanwhile, the content of ΣREY in the siliceous ooze is 248.54×10 -6 , which is also enriched in fine sediments (>4Φ). LREE is relatively enriched too. The ΣREY content in the sediments of the study site is near the boundary grade, but the HREY content in the fine sediments reaches the industrial grade. REY in the fine-grained components of this kind sediment mainly comes from the adsorption of clay minerals and iron-manganese oxides which come from the terrestrial or pyroclastic materials, while the REY source in the coarse-grained fraction is related to the biological effects. The enrichment of REY in siliceous ooze is associated with apatite in sediments, but REY from some different sources may be redistributed into the minerals such as apatite and phillipsite during diagenetic process.