焦作地区太原组中硅质岩的矿物学特征和成因分析

Genesis analysis and mineralogical characteristics of siliceous rocks in Taiyuan formation,Jiaozuo area

华北板块太原组生物碎屑泥晶灰岩中夹有大量黑色层状、似层状、团块状和条带状的硅质岩,对其成因尚有较大争议。为了探讨其成因,选择焦作地区太原组硅质岩为研究对象,通过采集不同层位和形态的硅质岩样品,采用岩石薄片观察、电镜扫描、能谱分析、XRD分析、差热分析等方法,对太原组硅质岩的矿物成分及其成因进行了研究。结果表明:太原组硅质岩的矿物成分主要为蛋白石,并普遍含有玉燧、微晶石英和方解石,在底部层状硅质岩中还见有大量的叶腊石;硅质岩中的硅质矿物是SiO2对方解石的交代作用形成的,方解石是未被硅质完全交代的残留矿物,叶腊石是由体系外部提供的活性Si与岩浆岩碎屑水解提供的活性Al在微裂隙中经过合成作用形成的。研究结果为华北板块太原组硅质岩的成因提供了矿物学方面的约束条件。

Bioclastic limestones in Taiyuan formation of North China plate contains a large number of layered, lay-like, handed and clumped black siliceous rocks. Currently, there have great controversies on the genesis of them. In this paper, the siliceous rocks in Taiyuan tormation in Jiaozuo area were selected as samples. By mac- roscopic observation and collecting siliceous rocks samples of different layers and forms, the mineral compo- nents in the siliceous rocks in the Taiyuan tormation were analyzed. Thin rock sections, scanning electron mi- croscopy, energy spectrum analysis, X diffraction analysis and differential thermal analysis were used tor data a- nalysis. The result showed that main minerals of the siliceous rocks of Taiyuan formation were opal with chal- cedony, microcrystalline quartz and calcite. Meanwhile, a large number of pyrophyllite was found in the bottom layered siliceous rocks. Siliceous minerals in siliceous rocks were formed by the replacement of SiO2 to the cal- cite. The calcite was the remaining mineral of incompletely replacement of siliceous minerals. The pyrophillite was formed in the microfractures by the synthesis of active Si provided outside the system and active A1 provid- ed by hydrolysis of the magmatic rock fragments.