广西钦州石夹剖面硅质岩稀土元素地球化学特征

REE Geochemical Characteristics of Siliceous Rocks in the Shijia Section,Qinzhou,Guangxi,China

为探讨广西钦州石夹剖面晚泥盆世—早石炭世硅质岩成因及其沉积背景,应用X荧光光谱、等离子质谱等分析方法对硅质岩稀土元素地球化学特征进行了研究。结果显示,研究区晚泥盆世—早石炭世硅质岩ΣREE平均为94.81×10-6,ΣCe/ΣY为3.66~9.28（平均5.99）,δCe为1.02~1.37（平均1.18）,δEu为0.89~1.30（平均1.04）,（La/Yb）N为1.38~3.20（平均2.02）,（La/Ce）N为0.74~1.14（平均0.87）,表明稀土元素组成与北美页岩相似,而明显有别于开阔洋盆和洋中脊的硅质岩,为古大陆边缘盆地（陆内海槽）硅质岩;在泥盆纪-石炭纪界线处δCe、（La/Yb）N降低,（La/Ce）N升高,结合（La/Ce）N对Al2O3/（Al2O3＋Fe203）判别图以及硅铝铁成分比值成因判别图,推测此时沉积盆地短暂受到热液活动的影响。

In order to discuss the genesis and sedimentation environment of Late Devonian-Early Carboniferous siliceous rocks in the Shijia section,Qinzhou,Guangxi,REE geochemical characteristics of siliceous rocks have been studied through analyzing their REE contents by using XRF,ICP-MS instruments. It is shown that the average Σ REE contents of siliceous rocks is 94. 81×10-6,with Σ Ce/Σ Y,δCe,δEu,（ La/Yb）N,and（ La/Ce）N,values ranging from 3. 66 to 9. 28（ average5. 99）,from 1. 02 to 1. 37（ average 1. 18）,from 0. 89 to 1. 30（ average 1. 04）,from 1. 38 to 3. 20（ average 2. 02）,and from0. 74 to 1. 14（ average 0. 87）,respectively. This indicates that the siliceous rocks were formed in paleocontinental marginal basin（ intracontinental geosyncline）,as their REE compositions are similar to those of the North American shale,but significantly different to those of the open ocean basin and Mid-oceanic ridge siliceous rocks. The δCe and（ La / Yb）Nvalues of siliceous rocks at the Devonian-Carboniferous boundary are lower but（ La / Ce）Nvalues are higher than those of the siliceous rocks occurred in other places in the Shijia section. Combining with the（ La / Ce）N-Al2O3/（ Al2O3＋Fe203） and Si-Al-Fe components discrimination diagrams for these siliceous rocks,it is speculated that the sedimentary basin in Shijia,Qinzhou was transitorily influenced by hydrothermal activity in Late Devonian-Early Carboniferous.