北祁连山寒武─奥陶纪硅质岩岩石化学特征及形成环境

通过对北祁连地区寒武－奥陶纪硅质岩岩石化学特征研究，揭示硅质岩在成分上具有明显差异，这种差异是由于其生成构造环境不同而形成的。一般形成于大洋中脊的硅质岩在岩石化学成分上富于Ｆｅ＿２Ｏ＿３和ＭｎＯ，而Ａｌ＿２Ｏ＿３含量最低。形成于近弧环境的硅质岩在成分上相对富含ＦｅＯ＋ＭｇＯ＋ＣａＯ，而Ａｌ＿２Ｏ＿３较洋脊的稍高．但不及形成于深海盆地的硅质岩。富含Ａｌ＿２Ｏ＿３而贫Ｆｅ＿２Ｏ＿３、ＭｎＯ、ＦｅＯ、ＭｇＯ和ＣａＯ的硅质岩形成于近陆的深海或半深海盆地或初始洋盆的盆缘地带。由此可见，硅质岩岩石化学成分具有明显的指相意义。然而，研究表明，硅质岩中ＳｉＯ＿２含量的高低并不具有指相意义。

CHARACTERISTICS OF PETROCHEMICAL COMPONENTS OF CHERTS FROM THE NORTH QILIAN CAMBRIAN-ORDOVICIAN SEQUENCES AND THEIR SEDIMENTARY ENVIRONMENTS

The study of chens from the north Qilian Cambrian-Ordovician sequences reveals obvious differences in their petrochemical components, which are caused by their environments.Generally, the chert formed in a midoceanic ridge area is rich in Fe_2O_3 and MnO, but very poor in Al_2O_3; and formed nearby an island arc area, the chert has relativelly high content of FeO, MgO and CaO, but the content of Al_2O_3 is relatively little higher than that formed in the mid-oceanic ridge area and lower than that formed in an abyssal basin. Some chents,which are generated in an abyssal basin near a continent or on a margin of an embryonic ocean basin, have high content of Al_2O_3 and very low content of Fe_2O_3, MnO, FeO,MgO and CaO. Thus, petrochemical components of chens have some significance of indicating facies.In addition, the study has also shown that whether content of SiO_2 in chens is high or low has no any significance of indicating facies.