中元古代海绿石:前寒武纪海洋浅化变层深度的潜在指示矿物

发布时间：2018-04-11 23:01

  本文选题：海绿石 + 海水氧化还原状态　； 参考：《地学前缘》2016年06期

【摘要】：显生宙的海绿石主要形成于具低沉积速率的外陆架至上斜坡深水环境,而前寒武纪海绿石则多见于具高沉积速率的浅水环境。为揭示导致这种明显差别的主要环境控制因素,本文对华北中元古代铁岭组叠层石礁内发育的海绿石进行了包括野外观察、岩相学和XRD、SEM、EDS、ICP-MS分析在内的综合研究。据海绿石的分布位置和基质孔隙度特征,本文将铁岭组自生海绿石分为3种类型:类型Ⅰ产于孔隙最发育的叠层石柱和微晶基质交接带,类型Ⅱ位于较少孔隙的基质中,类型Ⅲ常见于致密的叠层石柱体内。这三种类型的海绿石都具有高且稳定的K_2O含量(平均8%),指示孔隙水具有高K~+离子浓度。从Ⅲ型至Ⅰ型海绿石,Fe_2O_3含量逐渐升高,而Al_2O_3含量逐渐降低,表明基质孔隙度对海绿石演化具有控制作用,海绿石的成熟度演化需要Fe的持续补充。由于叠层石碳酸盐岩明显缺乏陆源碎屑输入,因此Fe可能主要来自海水,要求存在很浅的Fe氧化还原界面,这也得到了碳酸盐岩中Ce异常证据的支持。我们认为多孔的基质、高K~+浓度以及次氧化海水条件是促进中元古代浅水海绿石沉淀和演化的重要环境因素。
[Abstract]:The Precambrian glauconite is mainly formed in the deep-water environment of the upper slope of the outer shelf with low deposition rate, while the Precambrian sea greenstone is more common in the shallow water environment with high deposition rate.In order to reveal the main environmental control factors leading to this obvious difference, a comprehensive study including field observation, petrography and the analysis of XRDSEMN EDSICP-MS has been carried out on the mesoproterozoic stromatolites in the Middle Proterozoic Tieling formation of North China.According to the distribution location and matrix porosity characteristics of glauconite, this paper classifies Tieling formation as three types of authigenic glauconite: type I occurs in the intersecting zone between the most developed stony column and microcrystalline matrix, and type 鈪，

本文编号：1738028