冲绳海槽中段表层沉积物中稀土元素组成及其物源指示意义

CHARACTERISTICS OF RARE EARTH ELEMENTS IN SURFACE SEDIMENTS FROM THE MIDDLE OKINAWA TROUGH: IMPLICATIONS FOR PROVENANCE OF MIXED SEDIMENTS

冲绳海槽中段表层沉积物主要是由陆源、火山源和生物源物质按不同比例组成的混合物。研究表明 ,陆源物质 (长江和黄河沉积物 )稀土总量最高 ,轻稀土明显比重稀土富集 ;火山物质 (冲绳海槽火山玻璃 )具有较明显的正Eu异常且重稀土相对富集 ;生物源物质 (冲绳海槽有孔虫壳 )中稀土富集。 3种端员物质的稀土元素组成特征存在显著差异 ,因此 ,选择合适的稀土元素特征参数———ΣLREE/ΣHREE、Eu/Sm及MREE/ (LREE +HREE)可以分别刻画出冲绳海槽沉积物中陆源、火山源及生物源物质的组成特征。通过与前人对研究区物源定性、定量分区的结果对比 。

The geochemical behavior and characteristics of rare earth elements (REEs) have been greatly applied to the study of tracing sources of sediments. In this paper the qualitative distributions of different sources of the surface sediments from the middle Okinawa Trough were traced by utilizing the characteristic parameters of REEs. The mixed sediments from the middle Okinawa Trough are mainly composed of three end-members, known as terrigenous matter, volcaniclastic materials and biologic matter. The contribution of each end-member in mixed sediments and REEs' abundance of each end-member are the main factors that control the abundances and characteristics of REEs in the mixed sediments. Therefore, if there are remarkable differences in REEs' characteristics for different end-members, some characteristic parameters of REEs can be extracted and used as proxies for the sources of the mixed sediments. By comparison of REEs' characteristics of three end-members, it was clearly shown that terrigenous matter (fine-grained sediments obtained from the Yangtze River and Yellow River drainage basins) was characterized by highest total concentration of REEs and enriched light REEs (LREEs); Volcaniclastic material (volcanic glass) was characterized by an increase of Eu, while mid REEs (MREEs) of biologic matter (foraminifer shells) were more enriched. Accordingly, three diagnostic parameters of REEs, ΣLREE/ΣHREE,Eu/Sm and MREE/(LREE+HREE)were selected as proxies to distinguish three sources of the surface sediments. The result was consistent with the conclusion drawn by the previous researches, demonstrating that REEs’ characteristic parameters mentioned above can be used as effective proxies for the sources of the mixed sediments from the middle Okinawa Trough.