地球化学方法在硅质岩成因与构造背景研究中的进展及问题

硅质岩由于受后期风化作用及成岩作用影响较弱,其地球化学特征常被用来讨论硅质岩成因和形成构造背景。本文分析了硅质岩的成因以及形成于不同构造背景下硅质岩的主元素、痕量元素、稀土元素、Si同位素和Sr-Nd同位素组成特征。在总结硅质岩成因与构造背景研究方法和进展的同时,指出元素地球化学行为的错误理解和硅化作用过程中SiO_2稀释剂作用的影响是造成利用地球化学方法判别硅质岩成因和构造背景时产生多解性的主要原因。而对硅质岩成岩机理的再认识表明:硅质岩成岩过程中,SiO_2对主元素和稀土元素起稀释剂的作用;TiO_2、Al_2O_3、MgO、K_2O作为陆源组分,受成岩作用的影响比Fe_2O_3、MnO、CaO、Na_2O、P_2O_5弱;成岩作用对页岩或泥岩主元素的影响强于硅质岩;硅质岩的稀土元素含量除受沉积环境的控制外,还受硅化程度的影响。

Progress and problems in the geochemical study on chert genesis for interpretation of tectonic background

Silicolite is often used to discuss its genesis and tectonic setting duo to its immobility during the diagenesis and resistant to erosion.In the paper,the origin and major,trace,rare earth elements,Si and Sr-Nd isotopic compositions of cherts from different depositional environments are summarized.The progress and problems in the research of the origin and tectonic setting of cherts and some factors which caused its original multiple solution interpretation are also discussed.Diagenetic process study indicates that the SiO2 acts as a diluent of the major elements and REEs during the depositional processes.As terrigenous materials of TiO2,Al2O3,MgO and K2O,the influence from the diagenetic silicification is weaker than that of Fe2O3,MnO,CaO,Na2O and P2O5.It reveals that the influence from the diagenetic silicification for shale or mudstone is stronger than that for chert,and its REEs are controlled not only by the deposition environments but also by the degree of the diagenetic silicification.