冀北地区中三叠世火山岩地层三家北沟组的建立

Establishment of Sanjiabeigou Formation in Middle Triassic Volcanic Rocks in Northern Hebei

在详细的野外和岩相学研究的基础上,对冀北地区中三叠世火山岩进行研究,划分了6个火山喷发韵律,发现其岩石组合以玄武安山岩、安山岩、玄武粗安岩、粗安岩、英安岩、流纹岩与火山碎屑岩不等厚互层为特征。火山岩的岩石系列,中下部以钙碱性为特征,上部以钙碱性、碱性为特征。岩石地球化学特征显示火山岩属于钙碱性系列和碱性系列,轻稀土富集,Eu具弱的负异常,具有壳幔混源岩浆的特征,富集Ba、K、La、Nd、Zr、Sm元素,亏损U、Nb、Sr、P、Hf元素,显示其具有岩浆弧带岩浆岩的性质,构造判别图解显示中下部的钙碱性火山岩形成于中三叠世早中期后碰撞阶段的挤压造山构造环境,上部的钙碱性、碱性火山岩形成于中三叠世晚期后造山阶段的过渡构造环境。

On the basis of detailed field and petrographic studies,the Middle Triassic volcanic rocks in northern Hebei are studied,and six volcanic eruptive rhymes are classified.It is found that its rock assemblage is characterized by basaltic andesite,andesite,basalt trachyandesite,trachyandesite,dacite,rhyolite and pyroclastic rocks with different thicknesses from volcanic clastic rocks.The middle and lower part of volcanic rock association is characterized by calc-alkaline series,while the upper part is characterized by calc-alkaline series and alkaline series.The geochemical characteristics of the rocks show that the volcanic rocks belong to calc-alkaline series and alkaline series,are enriched in LREE,with weak negative anomaly in Eu,and have the characteristics of crust-mantle mixed magma.The volcanic rocks are enriched in Ba,K,La,Nd,Zr,Sm and depleted in U,Nb,Sr,P,Hf,indicating that they have the characteristics of magmatic arc zone magmatic rocks.