山西吕梁袁家村条带状铁建造沉积相与沉积环境分析  

Analysis of sedimentary facies and depositional environment of the Yuanjiacun banded iron formation in the Lüliang area,Shanxi Province

作　　者：王长乐[1,2] 张连昌[1] 兰彩云[2,3] 李红中[1] 黄华[1] 

机构地区：[1]中国科学院地质与地球物理研究所、中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院大学,北京100049 [3]中国科学院广州地球化学研究所,广州510640

出　　处：《岩石学报》2015年第6期1671-1693,共23页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划973项目(2012CB416601);中国科学院知识创新工程重要方向项目群(KZCX-2YW-Q04-07);国家自然科学基金项目(41372100)联合资助

摘　　要：山西吕梁作为华北克拉通上条带状铁建造（BIF）的重要产区之一,位于华北中央构造带中。袁家村BIF分布于吕梁岚县袁家村一带,极有可能是华北克拉通内最为典型的Superior型BIF。与华北克拉通其他大多数BIF相比,袁家村BIF具有明显的差异性,其中包括它的形成时代（2.3-2.1Ga）、铁建造类型和低级变质程度（低绿片岩相）等。因此,研究袁家村BIF具有特殊的研究意义,可为探讨大氧化事件之后古海洋氧化还原状态以及国内Superior型BIF的成因提供研究基础。袁家村BIF产于吕梁群袁家村组变沉积岩系的下部,前人根据上覆和下伏含火山岩地层的时代,推测袁家村组的形成时代为2.3-2.1Ga。BIF整体产状陡倾,沿北北东-北东东向呈L形带状分布。依据原生矿物的共生组合及产出特征,可将BIF沉积相划分为氧化物相（60%）、硅酸盐相（30%）和碳酸盐相（10%）。氧化物相是本区BIF最主要的沉积相,主要矿物为赤铁矿、磁铁矿和石英,从而可进一步划分为赤铁矿（24%）和磁铁矿（36%）亚相;硅酸盐相BIF以大量硅酸盐矿物出现为特征,散布于研究区,主要矿物组成除了石英和磁铁矿之外,还有铁黑硬绿泥石、绿泥石、铁滑石、镁铁闪石和阳起石等。在与碳酸盐相BIF构成过渡相的BIF中,还可发现大量的铁白云石。而碳酸盐相主要矿物为菱铁矿、铁白云石和石英等,主要发育于研究区的南部。依据含铁岩系构造格局特点复原获得了原始沉积相分布略图,沉积相主要呈南北向延展,自东向西显示出相变规律,西边为碳酸盐相,东边为氧化物相,其间是过渡的硅酸盐相。通过袁家村BIF的岩相学和含铁矿物化学成分的研究,可大致推测原始沉积的矿物组成为无定形硅胶、水铁矿、与铁蛇纹石和黑硬绿泥石组成类似的铁硅酸盐凝胶、富Al的粘土碎屑和含铁、镁、钙的碳酸盐软泥。这些沉积物在随The Yuanjiacun banded iron formation（ BIF）,located in the Lüliang area,is likely to be the most representative Superior-type BIF in the North China Craton（ NCC）. Comparing with characteristics of other BIFs in China,the Yuanjiacun BIF is obviously distinct from them mainly involving three aspects： the formation age（ 2. 3 - 2. 1Ga）,the genetic type（ Superior） and mild metamorphism（ lower greenschist facies）. Thus,the Yuanjiacun BIF can be used as a good probe to understand atmospheric evolution and the chemical composition and redox states of the ancient oceans after the Great Oxidation Event（ GOE） and is of great significance for relevant research on the Superior BIFs in China. The Yuanjiacun BIF is coherent with the sedimentary rock succession of the Yuanjiacun Formation in the Lower Lüliang Group,and was interpreted to be deposited at 2. 3 - 2. 1Ga,based on ages of overlying and underlying volcanic strata. The BIF is distributed in a NNE-NEE direction with a steep occurrence. Oxide（ magnetite and hematite）,carbonate,and silicate facies iron formations are recognized based on predominant iron minerals within the iron-rich layers. The widespread oxide facies is composed of magnetite,hematite and quartz; the silicate facies is characterized by presence of iron silicate minerals and their metamorphic equivalens,consisting mainly of stilpnomelane,chlorite,minnesotaite,cummingtonite and actinolite other than quartz and magnetite; whereas the carbonate facies is rare in which the most prominent carbonate minerals are siderite and ankerite. Ankerite is commonly found in the silicate-carbonate facies iron formation. The distribution of primary sedimentary facies has been recovered on the basis of structural framework for iron-bearing rock sequences. Sedimentary facies extend along the N-S direction.The eastward transition from carbonate facies into oxide facies iron formation is accompanied by a change in mineralogical composition from siderite-facies iron formation in the west through ma

关 键 词：条带状铁建造 沉积相 原始矿物组成 沉积环境 吕梁袁家村 

分 类 号：P618.31[天文地球—矿床学]