新疆巴音沟蛇绿混杂岩带中硅质岩及硅质泥岩的元素地球化学特征及其形成环境

Geochemical Characteristics and Sedimentary Environments of Siliceous Rocks and Siliceous Mudstone——Case Study of Bayingou Ophiolitic Mélange in Xianjiang

摘要: 巴音沟蛇绿混杂岩带中成薄层状产出的硅质岩、硅质泥岩的SiO₂=55.37%～91.19%,Al₂O₃含量较高,变化在3.07～17.66,TiO₂=0.12～0.8,Al₂O₃与TiO₂具有较好的正相关关系,表明它们含有较高比例的陆源泥质沉积物质。样品经北美页岩标准化的稀土模式呈现无Ce负异常(Ce/Ce^*=1.03～1.45)的平坦稀土谱型,球粒陨石标准化稀土模式为轻稀土富集,Eu具明显负异常的右倾谱型,均显示与大陆边缘沉积硅质岩、硅质泥岩相似的稀土配分模式。它们的(La/Ce)N=0.62～0.92,V/Y=0.32～8.87,Th/U=2.99～6.45,表明这些硅质岩、硅质泥岩形成于与陆源物质输入密切相关的大陆边缘环境,综合大地构造背景、蛇绿岩带中超基性、基性岩元素地球化学以及年代学分析认为,蛇绿岩就位于早石炭世晚期,形成在大陆裂谷向大洋裂谷转换并形成小洋盆的环境。

Abstract: The flaggy cherts and argillite in the ophiolitic mélange of Bayingou have a SiO₂ content of 55.37%-91.19%,a high Al₂O₃ content between 3.07%-17.66%,and a TiO₂ content of 0.12%-0.8%,having a good positive correlation between Al₂O₃ and TiO₂,suggesting that they have a relatively high percentage of terrigenous muddy sediments Moreover,they have typical NASC-normalized flat REE patterns without any visible Cenegative anomaly;and the Eu has an obvious right-hand dipping pattern.