沾化凹陷新近系沉积岩地球化学特征及其物源指示意义  

Geochemical Characteristics of Neogene Sedimentary Rocks from Zhanhua Sag and Its Implication for Provenance

作　　者：蔡观强[1] 郭峰[1] 刘显太[2] 隋淑玲[2] 李超文[1] 高晓峰[1] 赵亮[1] 

机构地区：[1]中国科学院广州地球化学研究所边缘海地质重点实验室 [2]中国石油化工股份有限公司胜利油田分公司地质科学研究院,山东东营257015

出　　处：《地质科技情报》2007年第6期17-24,共8页Geological Science and Technology Information

基　　金：中国石油化工股份有限公司胜利油田分公司地质科学研究院资助项目

摘　　要：采用ICP-MS详细研究了沾化凹陷新近系馆陶组（Ng）和明化镇组（Nm）沉积岩的微量元素地球化学特征。结果显示：样品稀土元素（REE）质量分数相对较高,w（ΣREE）介于106.4×10^-6-390.9×10^-6间,馆陶组和明化镇组的平均值分别为198.83×10^-6,203.18×10^-6,高于大陆上地壳（UCC）和后太古宙页岩（PAAS）的平均值;稀土元素配分曲线显示LREE富集、HREE平坦和中等负Eu异常[δ（Eu）介于0.66-0.83,平均值为0.75]的典型后太古宙沉积岩特征。样品过渡族元素Cr、Co、Ni质量分数较低,与UCC相近,稍低于PAAS;高场强元素Zr、Hf、Nb、Ta、Th质量分数则相对比它们在UCC和PAAS中的质量分数高。泥岩样品的REE、Nb、Ta、Th质量分数明显高于粉砂岩和细砂岩,表明黏土矿物的吸附作用对这些元素的富集有重要的控制作用;但稀土元素的配分模式和特征参数,以及不活动元素之间的比值[如w（La）/w（Co）,w（Co）/w（Th）,w（Cr）/w（Th）,w（Zr）/w（Hf）]并不受粒度效应的影响。微量元素地球化学特征指示沾化凹陷新近系馆陶组和明化镇组沉积岩的源岩以中酸性的长英质岩石为主,可能主要来自盆地东部的胶东隆起区,而南部鲁西隆起区广泛出露的太古宇岩石对盆地供应的碎屑量较小;物源供应的变化表明馆陶组上段沉积时期,东营水系和车沾水系开始衰退,而垦青水系仍较发育。This study presents the REE geochemical characteristics of sedimentary rocks from Neogene Guantao Formation （Ng） and Minghuazhen Formation （Nrn） in Zhanhua Sag. The results show that the samples have higher REE concentrations relative to UCC and PAAS, ranging from 106. 4 μg/g to 390.9 μg/g, and the averages of the Ng and Nrn formations are 198.83 μg/g, 203.18 μg/g, respectively. The chondrite-normalized REE patterns are similar to those of UCC and PAAS, with LREE enrichment （averaging ∑LREE/∑HREE 11. 22）, flatted HREE and moderate negative Eu anomaly （from 0. 66 to 0.83）. Compared with UCC and PAAS, the samples are also rich in Zr, Hf, Nb, Ta, and Th, but relatively lower in Cr, Co, Ni. The mudstones have higher REE, Nb, Ta, and Th than siltstones and sandstones, indicating that the absorption of clay minerals plays an important role in the enrichment of these elements. However, the ratios of the immobile elements （e. g. La/Co, Co/Th, Cr/Th, Zr/Hf） and REE distribution patterns do not show significant changes in different grain size sediments, thus they quantitatively record the information of the source rocks. The analysis of geochemical characteristics of the trace elements in samples reveals that the source rock of the Ng and Nrn formations are dominantly intermediate-acidic rocks, possibly from the Jiaodong Rise to the east, whilst the Archean rocks widely cropped out the Luxi Rise to the south did not supply much detritus to the basin during Neogene. This suggests that the palaeodrainage system to the east of the basin is still well developed, however, the other two palaeodrainage systems have declined, to the east and north of the basin, respectively.

关 键 词：沾化凹陷 馆陶组 明化镇组 物源 稀土元素 

分 类 号：P588.20[天文地球—岩石学]