四川广元上寺上二叠统硅质岩地球化学特征及成因分析  

GEOCHEMICAL CHARACTERISTICS AND PETROGENESIS OF SILICEOUS ROCKS FROM SHANGSI SECTION IN GUANGYUAN,SICHUAN PROVINCE

作　　者：方雪 周瑶琪[1] 姚旭[1] 刘美辰 加娜提古丽.吾斯曼 刘加召 

机构地区：[1]中国石油大学(华东)地球科学与技术学院,山东青岛266000 [2]山东省第八地质矿产勘查院,山东日照276800

出　　处：《矿物岩石》2017年第1期93-102,共10页Mineralogy and Petrology

基　　金：国家自然科学基金项目(编号:41272123)

摘　　要：四川广元上寺剖面广泛发育条带状、层状、团块状、结核状硅质岩。通过对上寺上二叠统硅质岩野外观察、取样,室内手标本观察及对其中的8块硅质岩样品进行元素地球化学的分析,对上寺上二叠统共8块硅质岩样品进行岩石学及地球化学特征研究,重点分析其成因。结果表明,硅质岩化学成分以SiO2为主,质量分数为73.05%~94.47%(平均87.1%),Fe,Mn含量较低,Al/(Al+Fe+Mn)值在0.54~0.70之间,平均值为0.63,在Al-Fe-Mn三角图解中,样品全部落在生物及非热液沉积区,MnO/TiO2值大部分小于0.5。硅质岩的大部分微量元素远远小于地壳克拉克值,V/(V+Ni)值均小于0.83,反映沉积环境为富氧;稀土元素总量较低,LREE/HREE平均值为5.84,δCe值变化范围0.20~1.30,为负异常且差异较大,δEu值变化范围1.01~4.10,较弱正异常,稀土元素北美页岩标准化曲线总体较平坦,略有右倾趋势。综合分析认为,硅质来源较复杂,生物来源为其主要来源,深部热水及火山作用为其次要来源,其中热液的注入与始于中二叠世的火山活动有关,硅质岩的形成以生物化学沉积为主,热水沉积为辅,硅质沉积环境为富氧的台盆相。The striped, layered, lump and nodular siliceous rocks occurred in the Upper Permian of Shangsi area in Guangyuan. Based on field observation, thin section identification and element geochemistry analysis,eight chert samples of the Upper Permian from the Shangsi cross section are studied so as to understand their lithological and geochemical characteristics. It shows that the silicon of cherts is primary microcrystalline quartz and chalcedony with small amounts of calcite and muscovite. Major element analysis indicates that SiO2 is the main chemical composition （73.05%-94.47%,87.1% ,on average）, while the contents of hydrothermal origin elements Fe, Mn content are low. Major element ratios Al/（Al＋Fe＋Mn） ranges from 0.54 to 0.70 （0.63, on average） ,with all samples falling in biological and non-hydrothermal deposition zone in Al-Fe-Mn discrimination diagram, with most of the ratios of MnO/TiO2 are less than 0.5. Most of the trace elements in silica rocks are much smaller than the Clark values of crust. The ratio V/（V＋Ni） is less than 0.83,indicating an oxygen-enriched sedimentary environment. ∑REE is relatively lower, LREE/HREE values is 5.84 on average. Ce values range from 0.2 to 1.30 with an overall negative anomaly. δEu values range from 1.01 to 4.10 with positive anomaly. REE patterns of siliceous rock are relatively flat with a slightly right trend. Comprehensive analysis reveals that the origin of these siliceous rocks are complicated,the siliceous organism is the primary source of silicon,the hydrotherm and volcanism is secondary source and the hydrothermal injection associated with volcanic activities begin in the Middle Permian. The formation of chert is mainly related to biochemical sedimentary and supplemented by hydrothermal sedimentary. It reveals that the sedimentary environment of the chert is oxygen--enriched platform-basin.

关 键 词：硅质岩 地球化学 成因 晚二叠世 上寺 

分 类 号：P588.244[天文地球—岩石学] P597.2[天文地球—地质学]