北部湾东部海域表层沉积物稀土元素组成及物源指示意义

Rare earth element compositions and provenance implication of surface sediments in the eastern Beibu Gulf

对北部湾东部海域70个表层沉积物样品的稀土元素(REE)分析结果表明,研究区沉积物REE呈现轻稀土元素(LREE)富集、重稀土元素(HREE)平坦以及中等程度的Eu异常等特征。REE组成受沉积物粒度和生物碳酸盐含量的制约,具有典型风化上陆壳REE特征,其源岩以上陆壳的长英质岩石为主。根据研究区沉积物REE分布规律,研究区可划分为4个地球化学分区,各区域上陆壳标准化曲线明显的不同。物源判别显示研究区的西部、海南岛西南侧(Ⅰ区)呈多源沉积特征,来自以下几个物源区:(1)海南岛西南侧河流沉积物和沿岸侵蚀物;(2)由南向北输入的外海沉积物(冬季);(3)夏季或冬季由北部湾西北部和西部搬运来的沉积物。研究区中部粗粒沉积区(Ⅱ区)与北部湾西部沉积物来源是相同的,主要来源于红河输砂。东北部砂质区(Ⅲ区)沉积物可能来源于雷州半岛西北部近岸基岩侵蚀。研究区东北部(Ⅳ区)沉积物主要来自北部湾北部沿岸侵蚀、琼州海峡和雷州半岛西部的沿岸侵蚀。此外,部分沉积物还可能来自珠江流域以及南海北部陆架区和北部湾西北部。

In this study, rare earth elements （REEs） of 70 surface samples have been analyzed to investigate the provenance in the eastern Beibu Gulf. The samples show relative enrichments in light REEs, with flat HREE patterns and moderate Eu anomalies. REEs compositions of sediments were constrained by grain size and carbonate content. The REEs characteristics of sediments are the same as weathered upper continental crust and the sources of sediments are mainly from continental crust with felsic rocks. The studied area can be separated into four zones based on REEs characteristics and the UCC-normalized patterns of each zone are different. Provenance discrimination indicates the west of the eastern Beibu Gulf （Zone 1） is mixing zone. The sediments mainly originate from rivers of Hainan Island and coastal bed rock erosion around, the sediments offshore transported from south to north （in winter）, and the sediments from the northwestern and western Beibu Gulf in summer orwinter. The provenance of coarse sands in the middle of the Beibu Gulf （Zone 2） is the same as that of the western sediments, mainly originated from the Red River. Sands in the northeast （Zone 3） maybe come from coastal bed rock erosion of the northwestern Leizhou Peninsula. The sediments in the northeast （Zone 4） are mainly derived from coastal erosion of northern Beibu Gulf, Qiongzhou Strait and western Leizhou Peninsula. Furthermore, several sediments may be derived from the Pearl River basin, the shelf of southern South China Sea and northwestern Beibu Gulf.