南海西沙海槽XH-CL16柱状沉积物稀土元素特征及其物源

RARE EARTH ELEMENTS GEOCHEMISTRY AND PROVENANCE OF THE SEDIMENTS FROM CORE XH-CL16 IN THE XISHA TROUGH,SOUTH CHINA SEA

西沙海槽是我国南海北部重要的天然气水合物勘探远景区。然而,目前对西沙海槽区沉积物的物源分析仍然存在众多争议。对西沙海槽XH-CL16柱状沉积物的稀土元素地球化学分析,显示该柱状沉积物的ΣREE介于131~171×10-6之间,表现为轻稀土相对富集,（La/Yb）N为9.5,具有明显的Eu负异常,δEu值在0.66~0.79之间。其稀土元素配分模式显著区别于大洋玄武岩,具有明显的陆壳特征,并且该沉积物具有相似于珠江口沉积物、红河沉积物以及黄土的稀土元素配分形态,暗示西沙海槽区沉积物主要为陆源沉积,而且可能是多物源多方式传输的结果。此外,通过该柱状沉积物中CaCO3含量变化特征与同海域标准碳酸盐地层学时标的对比,显示该柱状沉积物主要为MIS3期以来的沉积。而其中MIS2期沉积物表现为较MIS1和MIS3期沉积物更高的ΣREE和Ti含量,暗示西沙海槽在MIS2期时有更多陆源组分的输入。

The Xisha Trough is an important gas hydrate exploration prospect in the northern South China Sea. The provenance of Xisha Trough sediments remains controversial. The sediment from Core XH-CL16 in the Xisha Trough are characterized by relatively high total rare earth element contents （EREE = 131-- 171 ppm）, slightly enriched light REE （[-La/Yb]N = 9.5） and clearly negative Eu anomalies （3Eu = 0.66 -0.79）. Their chondrite-normalized REE patterns are similar to the upper continental crust and the sedi- ments from Chinese loess, the Pearl River and Mekong River, but different from the normal middle oceanic ridge basalt （N-MORB） and deep-sea clay. Thus, the sediments of the Xisha Trough show terrestrial af- finity, which probably result from multi-provenance and multi-transmission. Contrasting with the standard carbonate formation in the Xisha Trough, the variations in CaCO3 contents for the sediments from Core XH-CL16 suggests that they were deposited since approximately MIS3. In addition, sediments in MIS2 have higher ZREE, CaCO3 and Ti contents than those of sediments in MIS1 and MIS3, which may indicate more continental contribution during the MIS2.