摘要
对南海表层沉积物中稀土元素、微量元素丰度和分布特征的研究结果表明,在空间分布上,∑REE与Nb、Th、Ta、Rb、Ti、Zr、Hf、Cs、Ga、Li等相似,呈显著正相关,反映出这些元素在风化、搬运和沉积过程中地球化学行为非常相似;元素Sr几乎与所有元素都呈负相关,指示其来源或存在形式不同于其他元素,主要来源于生物作用,而在粗粒级的钙质生物贝壳和碎屑中富集。∑REE与Nb、Th、Ta、Rb、Ti、Zr、Hf、Cs、Ga、Li在陆架区具有沿陆分带特点,北部陆架区、中南半岛中东部和加里曼丹岛西北部沿大陆区域富集,与该区陆源河流物质输入及海流的分选作用,造成某些富含稀土和微量元素的重砂矿的富集有关;西南部巽他陆架和东南部岛礁区以及中、西沙附近区域含量较低,与该区域的生源碳酸盐的稀释作用,使粘土矿物相对减少和火山物质对其产生的"稀释"作用有关。南海各海区沉积物和全海区表层沉积物平均值的球粒陨石标准化稀土元素分布模式,总体上与中国大陆沉积物和浅海沉积物相似,而与大洋玄武岩完全不同,反映了南海沉积物与中国浅海沉积物及中国大陆沉积物的物源大致相同,主要来自陆源。南海各海区沉积物稀土元素的球粒陨石标准化配分曲线仍表现出了一定差异,陆架区轻稀土比重稀土明显富集,存在比较明显的Eu负异常,与陆架区相比较,陆坡区和海盆区则轻稀土含量相对降低,重稀土含量有所上升。LREE/HREE从陆架区、陆坡区到海盆区逐渐降低,显示陆架区主要为陆源,而陆坡和海盆沉积物中则有幔源物质加入。稀土元素的大陆壳标准化配分模式大部分较为平坦,少数样品呈轻稀土弱富集型或重稀土弱富集型,说明南海海表层沉积物主要来源于周边大陆。从各海区沉积物稀土元素的大陆壳标准化配分曲线对比来看,陆架区表现为轻稀土富集、重稀土亏损,具一定的铕负异常,深部海盆区则出现明显的中稀土和重稀土的富集,铕异常变弱,与深部海盆区有基性火山物质的加入的地质事实相吻合。南海表层沉积物稀土元素和微量元素总体上呈现出以陆源沉积为主的特征,其元素平均丰度和各参数值都比较接近陆源河流和中国浅海沉积物,而与深海沉积物和大洋玄武岩差别显著,显示南海沉积物虽然受到火山沉积和生物沉积的混合作用的影响,但其物质源仍然主要来自于周缘大陆。
The content and distribution of Sigma REE and trace element such as Nb, Th, Ta, Rb, Ti, Zr, Hf, Cs, Ga, Li etc from surficial sediment in the South China Sea are very similar, having notably positive corelation, which show they have similar geochemical behavior during weathering, transposition and sedimentation. Sr having negative corelation with these element show its source and existing form are different with the these elements, enriching in coarse calcium organism and mostly coming from the biogenic process. Sigma REE, Nb, Th, Ta, Rb, Ti, Zr, Hf, Cs, Ga and Li have the characteristic of along land zoning in shelf area. They are concentration along north shelf area, and eastern area of the mid- south peninsula and the northwest area of Kalimantan island, corresponding to continental source of river matter input and ocean current sorting function, which make some heavy sand mineral containing REE and trace element rich. The low content of these element in southwest Sunda shelf, southeast reef section and vicinity of Zhongsha and Xisha islands are made by carbonate diluting effect of biologic source result in clay mineral lessen relatively and volcanic giving them 'diluting' effect. The REE chondrite normalization distribution pattern of average surficial sediment in the each sea area and whole sea area of South China Sea are wholly similar to Chinese mainland sediments and shallow sea sediment, but deeply different from ocean basalt, reflect the main source of surficial sediment of South China Sea is mainland substance. Chondrite-normalized REE distribution pattern of surficial sediment in the each sea area and whole sea area of South China Sea still have some difference, LREE are richer than HREE at shelf area, and Eu negative anomaly is obvious relatively. Comparing with the shelf area, LREE content is low in continental slope area and basin area, HREE content increase, and LREE/HREE reduce gradually from shelf area, continental slope area to basin area, displaying that shelf area are mainly continental source, however, continental slope area and marine basin area sediments also have some mantle source input. The most of crust-normalized REE distribution patterns are flat, the few sample show slight enrichment of LREE or HREE, indicate the surficial sediment of south china sea mostly come from neighbour continents. Seen from the crust-normalized REE distribution patterns of sediments from each sea area, the shelf area show the LREE enrichment, HREE depletion and definite Eu negative anomaly, while deep marine basin area show remarkable MREE, HREE enrichment and less Eu anomaly, which fit with the geology events of basic volcanics input in deep marine basin area. REE and trace element of surficial sediment in South China Sea wholly show main characteristic of the terrigenous sediment. The element average abundance and each parameter approach to terrigenous river and Chinese shallow sea sediments, remarkably distinct with ocean marine sediments and basalt, indicate that their material also mainly come from neighbour continent.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第11期2963-2980,共18页
Acta Petrologica Sinica
基金
国家自然科学基金项目(No.40234041
No.40060005)及西北大学科研启动项目。
关键词
南海
表层沉积物
元素地球化学
South China Sea
surficial sediments
element geochemistry
