西南天山马达尔地区硅质岩地球化学特征及其沉积环境  

Geochemistry of cherts from Madaer area in Southwest Tianshan Mountains:Implications for deposition environments

作　　者：康健丽[1] 张招崇[1] 董书云[1] 马乐天[1] 张舒[1] 张东阳[1] 黄河[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石矿物学杂志》2010年第1期79-89,共11页Acta Petrologica et Mineralogica

基　　金：国家科技支撑计划资助项目(2007BAB25B05);111计划资助项目(B07011)

摘　　要：西南天山马达尔地区乌帕塔尔坎群硅质岩与玄武岩以逆冲断层接触产出,但其时代缺乏依据。本次研究的硅质岩中含有放射虫,经鉴定时代为D3—C1。11件硅质岩样品的SiO2含量为88.80%～93.28%,Al2O3含量为2.02%～3.72%,其中只有4件样品为纯硅质岩(SiO2的含量为91.0%～99.8%),所有样品的SiO2/Al2O3值(23.84～46.11)远低于纯硅质岩(SiO2/Al2O3=80～1400),表明其含有较高比例的陆源泥质沉积物。Al/(Al+Fe+Mn)=0.57～0.72,Ce/Ce*=0.90～1.21,显示出生物沉积硅质岩的特点。此外,其Al2O3/(Al2O3+Fe2O3)=0.64～0.77,V含量为10.92×10-6～26.70×10-6,Cu含量为2.15×10-6～34.10×10-6,Ti/V=25.53～44.93,∑REE为30.78×10-6～59.26×10-6,平均值为45.46×10-6,(La/Yb)N=0.88～1.33,平均值为1.09,(La/Ce)N=0.81～1.12,介于洋盆沉积物和大陆边缘沉积物之间,反映其沉积环境为接近陆源的深水-半深水的沉积环境。Ceanom值均大于-0.1,为-0.06～0.08,并且出现Eu的负异常,推测岩石沉积时水体贫氧。结合区域地质特征推测,乌帕塔尔坎群硅质岩形成于南天山洋盆闭合期的小洋盆。The Wupataerkan Group is characterized by cherts in contact with basalts through a thrust fault in Madaer area, Southwest Tianshan Mountains. However, definite evidence on the age of the group is absent. Based on the radiolarians picked up from the cherts, the authors hold that they were formed in Late Devonian to Early Carboniferous. Eleven chert samples have the SiO2 and Al2O3 content ranging respectively from 88.80% to 93.28% and from 2.02% to 3.72%. Four samples could be classified as pure cherts, which have SiO2 content of 91.0%～99.8%. However, all samples have much lower SiO2/Al2O3 ratios than the pure cherts （80～1400）. These values suggest that the cherts contain high ratios of continental margin materials in the sources. The Al/（Al＋Fe＋Mn） ratios of 0.57～0.72 and Ce/Ce＊ ratios of 0.90～1.21 suggest that these cherts are genetically biological sediments. Moreover, the Al2O3/（Al2O3＋Fe2O3） ratios are between 0.64 and 0.77, 10.92×10^-6～26.7×10^-6 for V, and 2.15×10^-6～34.10×10^-6 for Cu. The Ti/V ratios vary from 25.53 to 44.93. The cherts have a total REE concentration of 30.78×10^-6～59.26×10^-6, averaging 45.46×10^-6. The （La/Ce）N ratios range from 0.81 to 1.12, between the typical ocean basin and the continental margin. In 100 Fe2O3/SiO2 versus 100 Al2O3/SiO2, Fe2O3/（100-SiO2） versus Al2O3/（100-SiO2）, Fe2O3/TiO2 versus Al2O3/（Al2O3＋Fe2O3） and （La/Ce）N versus Al2O3/（Al2O3＋Fe2O3） diagrams, the samples fall into the area of continental margin. All these geochemical characteristics suggest that the cherts were formed in a continental margin setting. The Ceanom values range from -0.06 to 0.08. The characteristics of Ceanom〉-0.1 and significant negative Eu anomalies indicate that the sea water was in an anoxic environment during the deposition. In combination with regional geological setting, it could be inferred that the cherts of the Wupataerkan Group were formed in a small ocean basin, probably at the stage of closing of the South Tianshan o

关 键 词：放射虫硅质岩 地球化学 成因 沉积环境 西南天山 

分 类 号：P588.23[天文地球—岩石学] P512.2[天文地球—地质学]