安达曼海东南部海域表层沉积物稀土元素特征及其物源指示意义

对取自安达曼海东南部海域的95个表层沉积物样品进行了稀土元素(REE)地球化学研究,揭示了区内稀土元素分布特征及其指示的物质来源。结果表明研究区沉积物REE总量变化范围为31~228 μg/g,平均值为117 μg/g。沉积物REE球粒陨石配分模式呈现轻稀土元素相对富集而重稀土元素平坦,无明显Ce异常,呈现中等程度的Eu负异常等特征,表现出明显的陆源属性。REE的富集和分布受物质来源、沉积物类型、生物碳酸盐以及重矿物含量共同制约。根据沉积物REE特征参数将研究区分为4个物源区,各区沉积物稀土元素UCC标准化模式明显不同。物源判别分析显示,研究区西北部(Ⅰ区)沉积物主要来源于伊洛瓦底江陆源物质的输入;马来半岛西部浅海内陆架区(Ⅱ区)沉积物可能主要来自马来半岛沿岸水系输入的陆源物质以及现代近岸侵蚀;研究区北部(Ⅲ区)为残留沉积区,主要为全新世海侵形成的残留砂质沉积;研究区中部和南部大部分海域(Ⅳ区)为多源混合沉积区,主要为受印度季风驱动的西南季风流所搬运的伊洛瓦底江和马来半岛河流输入的陆源物质,该区沉积物受马来半岛入海物质影响更大。

RARE EARTH ELEMENT GEOCHEMISTRY OF SURFACE SEDIMENTS IN SOUTHEASTERN ANDAMAN SEA AND IMPLICATIONS FOR PROVENANCE

In this paper, grain size and rare earth elements (REEs) of 95 surface samples taken from the southeastern Andaman Sea have been analyzed for investigation of provenance. The total REEs vary in a range from 31 to 228 μg/g, with an average of 117 μg/g. The samples are relatively enriched in light REEs, with flat HREEs patterns and moderate negative Eu anomalies, but no Ce anomalies have been found. The REE shows obvious terrigenous affinity. According to REEs characteristics, the study area could be divided into four zones, the UCC-normalized patterns of each zone are obviously different. Provenance discrimination shows that the sediments in northwestern study area (ZoneⅠ) are mainly contributed by the Irrawaddy River. The sediments of the inner continental shelf of Malay Peninsula (ZoneⅡ) are mainly from the rivers on Malay Peninsula and modern coastal erosion. The northern study area (Zone Ⅲ) is covered by relict sands, formed during the Holocene transgression. The central and southern area (Zone Ⅳ) is a mixing zone where the sediments are transported by the southwest monsoon currents from the Irrawaddy River and Malay Peninsula, dominated by the later one.