THE GEOCHEMICAL CHARACTERISTICS OF TRACE ELEMENTS AND REES IN SURFICIAL SEDIMENTS OF THE SOUTHWESTERN SOUTH CHINA SEA AND THEIR IMPLICATIONS
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摘要: 分析了南海西南海域表层沉积物的微量元素和稀土元素组成,结果表明,这些沉积物与大陆上地壳相比,具有相对低的Zr、Sc、V、Nb、Hf、Th、REEs含量,而Co、Cu、Ni、Ta、Rb、Cs、Sr、Ba的含量稍高;深海区表层沉积物比陆坡区具有较高的Co、Zr、Sc、V、Nb、Hf、Ta、Th和REEs,陆坡区表层沉积物相对高的生物碎屑组分对这些元素起到了一定程度的稀释作用。因子分析和相关分析显示绝大部分微量元素和稀土元素主要受陆源组分的控制,Th、Cr、Co、Sc、Nb、Zr、Hf和REEs等不活动元素之间的比值特征,并没有受到风化作用、海流搬运作用和海洋自生组分稀释作用的影响,较好地保存了源岩的化学组成特征。因此,南海西南海域表层沉积物的La/Sc、Th/Sc、Th/Cr、Th/Co比值和稀土配分曲线特征,指示这些沉积物的源岩具有陆壳成分的特点,以长英质岩石为主,缺乏深源的基性和超基性岩,火山碎屑物质成分很低,其源区主要为南海西部的印支大陆。陆架区和深海区表层沉积物具有十分相近的微量元素和稀土元素组成特征,指示它们的碎屑物质来源较为相同。Abstract: This paper presents the trace elements and REEs composition of the surficial sediments from the southwestern South China Sea (SCS). The results show that the samples have relatively low Zr, Sc, V, Nb, Hf, Th, REEs contents and high Co, Cu, Ni, Ta, Rb, Cs, Sr, Ba contents, compared with the upper continental crust (UCC). The sediments from marine basins have higher Co, Zr, Sc, V, Nb, Hf, Ta, Th and REEs abundances than those from the continental slope. Factor and correlation analyses indicate that most of these elements are land-derived.The immobile elements such as Th, Cr, Co, Sc, Nb, Zr, Hf and REEs are indicators of source rocks.There shows no influences from weathering, transportation and diluting effect of biologic materials.The high La/Sc, Th/Sc, Th/Cr, Th/Co ratios and UCC-like rare earth elements distribution patterns characterized by high ΣLREE/ΣHREE ratios and low δEu values suggest that the source of the studied sediments are mainly from continental crust with felsic rocks as the majority, but the contribution of basic/ultrabasic rocks is ignorable and the volcanic clast content in the sediments is also very low. With reference to the geography of the studied areas, the geochemistry of surficial sediments from the southwestern SCS indicates that the materials are mainly from neighbour continents, probably the Indo-China block.Both the continental slope and marine basins show a common provenance according to their similarity in trace and rare earth elements compositions.
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Keywords:
- trace elements /
- rare earth elements /
- provenance /
- South China Sea
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