太平洋西部富稀土深海沉积物的地球化学特征及其指示意义

Geochemistry characteristics of REY-rich sediment from deep sea in Western Pacific,and their indicative significance

深海富稀土沉积物已成为潜在的战略资源。为探讨富稀土粘土的地球化学特征及其来源和富集机制,对太平洋西部深海区域进行底层水和深层沉积物的系统采样,分析了样品的主、微量元素和稀土元素地球化学特征,并采用氧化还原环境、稀土元素的迁移和分馏以及海洋稀土循环的分析方法对富稀土沉积物的成因进行探讨。结果显示:沉积物的∑REY与Ce/Ce*表现出负相关关系,并与生物成因的P和Ca关系密切。样品Th/U、V/Sc、(La/Yb)_N、(La/Sm)_N和(Sm/Yb)_N值呈系统的变化,沉积物均处于氧化或次氧化环境。底层海水具重稀土富集的特征,海水-沉积物界面轻、中稀土含量上升,下覆的较深层沉积物表现出中、重稀土富集。初步推断沉积物的稀土元素来源于海水,与生物相关的物质是其REY富集和Ce负异常的主要控制因素。宽的氧化或次氧化环境和生物相关氧化物的强吸附能力导致稀土元素未扩散至海水而引起了沉积物稀土元素的富集。

The REY-rich sediment from deep sea is a strategic resource. In order to determine geochemistry characteristic, origins and enrichment mechanism of REY-rich sediment, seawater and sediment samples were systematically collected from Western Pacific. We analyzed the major element, trace element and REY in sediment, as well as, REY in seawater. The redox condition, transfer and fractionation of REY and REY cycle of marine are used to analysis the origin of rare earth elements. The results indicated that, ∑REY and Ce/Ce＊ show a negative correlation, and, biogenic P and Ca play a key role in REY-rich sediment. Systematic variations of Th/U, V/Sc, （La/Yb）N, （La/Sm）N and （Sm/Yb）N values indicated oxic/dyoxic condition in sediment. The REE pattern showed HREE enrichment in bottom seawater, LREE and MREE enrichment in water-sediment interface, as well as, MREE and HREE enrichment in lower layer sediment. We suggested that, REY in sediment might come from seawater, and REY enrichment and negative anomalies of Ce was closely related with biological matter. The extensive oxic/dyoxic condition and biogenic oxide with relatively strong adsorption capacity resulted in few diffusion of sediment flux and enrichment of REY.