湛江湾沉积物稀土元素特征及其地质意义

    Characteristics and Provenance of Rare Earth Elements in the Sediments of Zhanjiang Bay

    • 摘要: 本文对湛江湾33个沉积物样品的稀土元素进行了系统对比,以揭示其组成特征、影响因素及物质来源。结果表明:湛江湾沉积物平均粒径为21.21 μm,以粉砂和砂质粉砂为主;稀土元素总量(ΣREE)为114.06~286.83 μg/g,平均含量为208.83 μg/g,呈轻稀土(LREE)富集、重稀土(HREE)均一、Eu负异常明显和Ce无明显异常的特征。进一步分析表明,研究区ΣREE受沉积物粒度、化学蚀变指数(CIA)及物源共同制约。球粒陨石标准化配分模式显示,湛江湾与广东沿海花岗岩、中国陆壳等物质具有明显相似特征,表现出较强的亲陆源性。采用(Gd/Yb)N-(La/Yb)N和δEu-(La/Yb)N图解进行物源判别,结果显示,湛江湾沉积物主要来源于花岗岩(或花岗质陆壳)、环湛江湾玄武岩及第四纪沉积物的混合多元供给,且物源贡献的比例呈现一定的变化趋势。

       

      Abstract: A systematic comparative analysis of rare earth elements (REEs) in 33 sediment samples collected in 2022 from Zhanjiang Bay was conducted to reveal their distribution characteristics, influencing factors, main material sources, and transport mechanisms. Results show that the average size of the sediment particles was 21.21μm. Most of them were made up of silt and sandy silt. The total REE content (ΣREE) ranged from 114.06 to 286.83 μg/g, with an average of 208.83 μg/g. The sediments featured light REEs (LREE) enrichment, flat heavy REEs (HREE) pattern, pronounced negative Eu anomaly, and absence of significant cerium (Ce) anomaly. Correlation analysis between ΣREE with grain size, chemical index of alteration (CIA), and major mineral elements revealed that the REE distribution of this study area is closely related to grain size, CIA, and provenance. The chondrite-normalized REE patterns of Zhanjiang Bay sediments are similar to those of coastal granites in Guangdong and the upper continental crust of China, indicating strong terrigenous influence. Provenance discrimination by means of δEu-(La/Yb)N and (Gd/Yb)N-(La/Yb)N diagrams that were calculated from chondrite-normalized values, suggested that the sediments of Zhanjiang Bay are mainly derived from a mixture of granite or granitic continental crust, the surrounding basaltic rocks of Zhanjiang Bay, and the Quaternary sediments. In addition, our preliminary finding indicates that the relative contributions to REE enrichment in the sediments of Zhanjiang Bay are likely changing gradually.

       

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