赤峰四家子盆地张家口组火山岩成因研究

根据最近几年开展的1∶5万区域地质调查获得的新资料,确认了内蒙古四家子盆地晚侏罗世张家口组的存在,并将张家口旋回火山岩划分为三个亚旋回.火山岩岩性为流纹岩类、粗面岩类和粗安岩类.对该地区火山岩的主量元素和微量元素进行了高精度分析测试,结果显示:火山岩具有高SiO2,Al2O3,K2O,Na2O含量和低MgO,TiO2含量的特征;里特曼指数σ(1.19~4.87)均值为2.47,属高钾钙碱性岩石系列.火山岩富集大离子亲石元素K,Rb,Sr,Zr,Ba,Pb,Li等,相容元素Ti,Co,Ni,Cr,V亏损.火山岩稀土总量较高,稀土配分模式呈右倾型,轻稀土分馏作用高于重稀土的分馏作用,总体显示弱负铕...

Study on Genesis of Volcanic Rocks from Zhangjiakou Formation in Sijiazi Basin of Chifeng

According to the data obtained from 1∶50 000 regional geological survey carried out during recent years,the authors confirm the existence of the Zhangjiakou formation of Late Jurassic in the Sijiazi basin,Inner Mongolia.The Zhangjiakou formation can be divided into three subcycles,i.e.,rhyolites,trachyte and trachyandesites.High-precise analysis of the major and trace elements shows that the volcanic rocks are characterized by relatively high SiO2,Al2O3,K2O and Na2O,and comparatively low MgO and TiO2 components.Rittmann index σ(in the range of 1.19 to 4.87) has the average value of 2.47,indicating that the rocks belong to high potassium calcium alkaline rock series.The volcanic rocks are obviously enriched in incompatible elements(K,Rb,Sr,Zr,Ba,Pb and Li),and depleted in compatible elements(Ti,Co,Ni,Cr and V).The REE content in the volcanic rocks is high.The distribution pattern is the right-incline.There is a slight low Eu and Ce negative abnormality.The REE characteristics show that the volcanic rocks were generated in the intraplate orogenic belt.The results of the comprehensive study on genesis and tectonic environment indicate that the volcanic rocks were mainly formed by the crust materials in a continental intraplate setting due to partial melting.