鄂西地区寒武系底部层状硅质岩成因及其地质意义  

Genesis and Geological Significance of Layered Siliceous Rocks at the Bottom of Cambrian System in Western Hubei Province

作　　者：盛贤才[1] 肖传桃[2] 梁西文[1] 刘漪[1] 甘玉青[1] Sheng Xiancai;Xiao Chuantao;Liang Xiwen;Liu Yi;Gan Yuqing(Research Institute of Exploration and Development,Jianghan Oilfield Company,SINOPEC,Wuhan 430223,Hubei;School of Geosciences,Yangtze University,Wuhan 430100,Hubei)

机构地区：[1]中国石化江汉油田分公司勘探开发研究院,湖北武汉430223 [2]长江大学地球科学学院,湖北武汉430100

出　　处：《长江大学学报（自然科学版）》2020年第4期1-8,I0001,共9页Journal of Yangtze University(Natural Science Edition)

基　　金：国家科技重大专项“中扬子地区海相层系油气成藏条件及勘探评价”(2017ZX05005-003-008);国家自然科学基金项目“中扬子台地早奥陶世微生物岩及其控制因素研究”(41572322)。

摘　　要：为探讨鄂西地区震旦纪寒武纪之交的沉积转换机制,对鄂西长阳黄家坪、鹤峰白果坪岩家河组底部层状硅质岩通过主微量(含稀土)元素测试开展成因分析。按元素地球化学特征将硅质岩分为2类:Ⅰ类硅质岩具有相对较高SiO2质量分数(平均96.75%),较低的Al2O3质量分数(平均0.13%)与TiO2质量分数(小于0.01%),Al/(Al+Fe+Mn)在0.36~0.88之间,氧化物双变量图解落入生物成因硅质岩区;富集亲下地壳和地幔元素Ni、Co、Ag、V和热水沉积敏感元素Sb、As、Ba、U等;稀土总质量分数较低,重稀土富集,具有Ce轻度负异常(平均0.74)和Eu正异常(平均1.56),经北美页岩标准化后稀土元素配分曲线表现为左倾,应为受热水作用影响的生物成因硅质岩;Ⅱ类硅质岩具有相对较低的SiO2质量分数(平均85.77%),较高的Al2O3质量分数(平均4.06%)与TiO2质量分数(平均0.20%),Al/(Al+Fe+Mn)在0.63~0.95之间,氧化物双变量图解更接近火山成因硅质岩区;富集亲下地壳和地幔元素Cr、Ni、Co、Ag、V和热水沉积敏感元素Sb、As、Ba、U等;稀土元素质量分数相对较高,具有Ce轻度负异常(平均0.76)和Eu轻度负异常(平均0.85),经北美页岩标准化后稀土元素配分曲线变化平缓,应为受火山作用影响的硅质岩。结合前人报道鄂西地区寒武纪初岩家河组、牛蹄塘组下部火山作用、热水沉积的相关记录,认为层状硅质岩的形成主体应为早寒武世初期兴凯运动在鄂西地区的构造响应,兴凯运动对鄂西地区沉积转换、烃源岩形成有重要的控制作用。In order to explore the sedimentary transformation mechanism at the turn of Sinian to Cambrian in western Hubei province,the genetic analysis of the layered siliceous rocks at the bottom of Yanjiahe Formation in Huangjiaping of Changyang and Baiguoping of Hefeng were carried out by means of the main trace elements test(containing rare earth elements).Based on the elemental geochemical characteristics,the siliceous rocks can be divided into two types:TypeⅠsiliceous rocks and TypeⅡsiliceous rocks.TypeⅠsiliceous rocks have relatively high mass fraction of SiO 2(the average value is 96.75%)and low mass fraction of Al 2O 3(the average value is 0.13%)and TiO 2(the average value is less than 0.01%),with the value of Al/(Al+Fe+Mn)between 0.36 and 0.88.Their oxide bivariate diagram falls into the biogenic siliceous rock zone;Besides,TypeⅠsiliceous rocks are rich in the upper crust and mantle elements(such as Ni、Co、Ag、V)and hydrothermal sedimentary sensitive elements(such as Sb、As、Ba、U).The total mass fraction of rare earth is low,while the heavy rare earth is enriched;Ce is slightly negative anomaly(the average value is 0.74),while Eu is positive anomaly(the average value is 1.56)After the standardization by North American shale,the distribution curve of rare earth elements is left-leaning,indicating that TypeⅠshould be biogenic siliceous rocks affected by hydrothermal sedimentation.TypeⅡsiliceous rocks have relatively low mass fraction of SiO 2(the average value is 85.77%)and high mass fraction of Al 2O 3(the average value is 4.06%)and TiO 2(the average value is 0.20%),with the Al/(Al+Fe+Mn)value between 0.63 and 0.95.Their oxide bivariate diagram is closer to the volcanogenic siliceous rock zone.Moreover,TypeⅡsiliceous rocks are rich in the upper crust and mantle elements(such as Cr、Ni、Co、Ag、V)and hydrothermal sedimentary sensitive elements(such as Sb、As、Ba、U).The mass fraction of rare earth elements is relatively high,with Ce slightly negative anomaly(the average value is 0.76)an

关 键 词：元素地球化学特征 硅质岩成因 岩家河组 寒武系 鄂西地区 

分 类 号：P618.13[天文地球—矿床学]