柴达木盆地北缘锲墨格山含绿柱石花岗伟晶岩特征及构造意义

Characteristics and Tectonic Significance of Beryl-bearing Pegmatites in Qiemoge Mountain, Northern Margin of Qaidam Basin

宗务隆构造带是近年来发现的重要的锂铍成矿带,锲墨格山地区隶属宗务隆构造带东段。本次通过对宗务隆构造带锲墨格山地区含绿柱石花岗伟晶岩岩石学、地球化学及年代学研究,结果显示,含绿柱石花岗伟晶岩脉以高硅、钙碱质和高分异以及低铁、镁、钙和钛为特征,属强过铝质花岗伟晶岩。微量元素特征上,样品明显富集Rb、Nb、Ta等元素,而亏损Zr、Hf、Th、Ce、Y、Yb等元素;且稀土元素总量较低,具轻稀土元素富集,轻重稀土元素分馏明显,Ce呈负异常,Eu为正异常特征,显示出岩浆演化晚期高度分异特性。锆石U-Pb年龄显示,绿柱石花岗伟晶岩锆石结晶年龄为229.5±1.3 Ma。综合研究显示,花岗伟晶岩主要形成于中‒晚三叠世,是宗务隆地区构造体制由挤压转换为伸展背景下,造山过程处于相对稳定阶段的产物。

The Zongwulong structural belt is an important lithium beryllium metallogenic belt discovered in recent years.The Qiemoge Mountain area belongs to the eastern section of the Zongwulong structural belt.In this study,we carried out a detailed study on petrology,geochemistry and chronology of the beryl-bearing granite pegmatites in the Qiemoge Mountain area of the Zongwulong structural belt.The results show that the beryl-bearing granite pegmatite veins in the study area are characterized by high silicon,calc-alkali,high heterogeneous and low iron,magnesium,calcium and titanium,and belong to strong peraluminous granite pegmatite.The granite pegmatites are obviously enriched in Rb,Nb,and Ta,while depleted in Zr,Hf,Th,Ce,Y,and Yb.In addition,the total amount of rare earth elements is low,which is characterized by light rare earth element enrichment,obvious fractionation of light and heavy rare earth elements,negative Ce anomalies and positive Eu anomalies.The above signatures of the granite pegmatites show that the magma is highly differentiated.The beryl-bearing granite pegmatites have zircon U-Pb age of 229.5±1.3 Ma.Our results show that the granite pegmatites in the Qiemoge Mountain area in the eastern section of the Zongwulong structural belt were mainly formed in the Middle-Late Triassic,under a compression to extension transitional tectonic background.