四川盆地西南部中二叠世栖霞组白云岩稀土元素地球化学特征及流体来源

REE geochemical characteristics and origin within fluid of Middle Permian Qixia Formation dolomites,SW Sichuan Basin

以四川盆地西南部出露的中二叠世栖霞组张村剖面为例,基于岩相学基础,首先利用X射线衍射法(XRD)确定白云岩的副矿物含量,再利用电感耦合等离子体质谱法(ICP-MS)分析白云岩的稀土元素,研究白云岩储层地球化学特征和流体来源。结果表明:白云岩副矿物为石英和长石类矿物,含量均较低,范围为0~4.5%。白云岩稀土元素含量偏低,范围为1.64~3.24μg/g,呈现轻稀土亏损,重稀土富集的分馏特征。分别用后太古代以来澳大利亚平均页岩和海水标准化方式,鞍形白云岩均呈明显的铕正异常,显示热液流体的参与。

Based on REE geochemical characteristics of the dolomites in Zhangcun profile,Middle Permian Qixia Formation,SW Sichuan Basin were studied by combined application of X-ray diffraction(XRD)and inductively coupled plasma-mass spectrometry(ICP-MS).The results show that the dolomites have low non-carbonate minerals including quartzs and feldspar minerals ranging from 0 to 4.5%.The total REE content of dolomites are low,ranging from 1.64 to 3.24μg/g with the depletion of LREEs and the enrichment of HREEs.The REE patterns of saddle-shape dolomites normalized by post-Archean Australian shale and seawater,respectively,show obvious positive Eu anomaly,indicating the involvement of hydrothermal fluid.