摘要
山西吕梁地区出露的紫金山岩体为我国著名的碱性岩体之一。为了探讨紫金山碱性岩体的物质来源及地质意义,对该岩体主要岩石进行了岩相学及岩石地球化学研究。结果表明紫金山岩体各期次岩石具有低硅、富碱、高钾的特点,属钾质碱性岩石;岩石轻重稀土元素分馏较强烈,具有轻稀土相对富集、重稀土相对亏损、无明显Eu异常的特征;微量元素总体表现为大离子亲石元素(Rb、Ba、K、Sr等)明显富集、高场强元素(Th、Nb、Ta、La、Ce、Nd、P、Ti等)亏损的特征。紫金山岩体岩浆来源较深,与富集地幔关系密切,岩浆演化机制以部分熔融作用为主且存在陆壳物质混染。结合山西境内多处同时期的碱性、偏碱性岩体特征,推断华北中部早白垩世碱性岩浆活动与古太平洋板块俯冲背景下华北克拉通破坏作用关系密切。
The Zijinshan rocks in Lvliang area of Shanxi Province,are one of the famous alkaline plutons in China.The petrography and petrogeochemistry of the main rocks of the rock mass were studied to explore the material source and geological significance of Zijinshan alkaline rock mass.The results show that Zijinshan rocks of all stages show characters of low silicon,rich alkali and high potassium,which indicates zijinshan rocks belong to potassium alkaline rocks.These rocks demonstrate a high degree of fractionation and are characterized by the richness of LREE and the poorness of HREE,without obvious Eu anomaly.The trace element pattern exhibits the enrichment of large ion lithophile elements,such as Rb,Ba,K and Sr,and relative depletion of high field strength elements,such as Th,Nb,Ta,La,Ce,Nd,P and Ti.The magma of Zijinshan rocks comes from a deeper source and is closely related to the enriched mantle.The mechanism of magma evolution is mainly partial melting and it may be inter-contamination of continental crust materials.Combined with the characteristics of alkaline and partial alkaline rocks of same age in many places in Shanxi,the authors deduce that the alkaline magma activity in the middle of North China during the Early Cretaceous is closely to the destruction of North China Craton under the background of the subduction of Pacific plate.
作者
郭喜运
GUO Xiyun(Shanxi Mineral Resources Survey and Monitoring Center, Taiyuan 030024, China)
出处
《中国地质调查》
2020年第5期66-76,共11页
Geological Survey of China
基金
山西省矿业权价款地质勘查基金“紫金山测区1∶5万(蔡家会幅、贺家会幅、白文幅、兔坂幅、紫金山幅、城庄幅)区域地质矿产调查(编号:200832)”
山西省地质勘查基金“山西省临县紫金山碱性岩-碳酸岩铌、稀土及放射性矿床调查(编号:201758)”项目联合资助。
关键词
碱性岩
华北克拉通
早白垩世
岩石圈减薄
山西
紫金山
alkaline rocks
North China Craton
Early Cretaceous
lithospheric thinning
Shanxi
Zijinshan
