北京延庆北部地区后城组火山岩岩石化学特征与成因探讨  

A Discussion on Petrochemical Feature and Origin of the Volcanic Rocks of Houcheng Formation in Northern Part of Yanqing County, Beijing

作　　者：汪洋[1] 姬广义[2] 

机构地区：[1]中国科学院广州地球化学研究所 [2]北京市地质研究所,北京100011

出　　处：《北京地质》2004年第1期16-25,共10页Beijing Geology

基　　金：国家自然科学基金项目 (编号码 40 10 40 0 3 ) ;中国博士后科学基金;中国科学院王宽诚博士后工作奖励基金;中国地质调查局地质调查项目 (K1. 4 1 2 )联合资助

摘　　要：根据TAS图解 ,北京延庆北部地区后城组火山属于玄武粗安岩 +流纹岩 (和粗面岩 )的双峰式组合。该套火山岩不属于典型的钾玄岩系列 ,在基性岩和中性岩中总体上以碱性系列和向碱性系列过渡的高钾钙碱性系列、钾玄岩系列为主 ,流纹岩类属于富钾质的拉斑系列。该套火山岩轻稀土元素明显富集。玄武粗安岩类岩石没有负铕异常或负铕异常不明显 ,而流纹岩存在明显的负铕异常。延庆北部地区后城组火山岩形成于燕山运动早期或中期阶段的造山变形事件趋于结束时的后碰撞构造环境中。According to the total alkaline vs. silica (TAS)diagram, the volcanic rocks of the Houcheng Formation exposed in the northern part of Yangqing County, Beijing Municipality, belong to the basaltic trachyandesite and rhyolite(+trachyte) bimodal association. These Volcanic rocks cannot be classified as typical shoshonite series. The mafic and intermediate rocks of them belong to the K-rich alkaline series and the high-K calc-allkaline or shpshonite series with some feature of allkaline series. Meanwhile, the rhyolite belongs to K-rich tholeiitic series. The volcanic rocks exhibit enrichment of light rare earth elements(LREE), and small or no negative Eu anomaly in basaltic trachyandesite, but significant negative Eu anomaly in rhyolite. These volcanic rocks erupted in tectonic setting of post-collision during the late stage of early or middle Yanshanian deformation episode.

关 键 词：火山岩 岩石化学特征 后城组 延庆北部 北京 

分 类 号：P585.3[天文地球—岩石学]