皖北沟后组页岩地球化学特征及其地质意义

Geochemical characteristics of the Gouhou Formation Shales and Its Geological Significances

沟后组在研究华北板块东南缘前寒武纪-寒武纪大地构造演化上具有重要意义。通过对沟后组页岩主微量元素地球化学的分析,取得了如下认识:Al2O3-Zr-TiO2和Zr/Sc-Th/Sc判别图解表明该套页岩中的碎屑物组分是火成岩没有再循环的特征,而是首次风化沉积的产物,因此其地球化学特征可以用于物源示踪。(SiO2/20)-(Na2O+K2O)-(MgO+TiO2+FeO*)、TiO2-Ni、Th-Hf-Co及Hf-La/Th图解及部分元素比值(如Co/Th、La/Sc及Zr/Sc)表明沟后组页岩的源区主要为中酸性火成岩。其CIA值较低(62),可能与钾交代有关,而较高的CIW值(89)表明其源区经历了中等-较高程度的风化。主微量元素一致表明其物源区具有活动性质。

Gouhou Formation is important for the study of the tectonic evolution of southeast margin of North China Craton during the period between Pre-Cambrian and Cambrian. Based on the major, as well as trace element geochemical studies of the shales from Gouhou Formation, the following understanding have been obtained. A1203- Zr-TiO2 and Zr/Sc-Th/Sc diagrams show that the shales were first order sediments of igneous rocks without recycling, and then their geochemical compositions can be used for provenance evaluation. Diagrams of （SiO2/20）- （Na20＋K20）-（MgO＋TiO2＋FeO）, TiOE-Ni, Th-Hf-Co and Hf-La/Th, as well as some ratios of elements （e.g. Co/Th, La/Sc and Zr/Sc）, suggest that intermediate to felsic igneous rocks constitute the source rocks in the provenance. The CIA values （62） of them are low, which might have been affected by K-metasomatism, whereas the high CIW values （89） suggest that the source area have undergone intensive weathering. Major oxides, as well as trace elements suggest that their provenance was located in the area with active signature.