内蒙古卫境地区查干哈达花岗岩体岩石地球化学特征及成因

Petrochemical Characteristics and Genesis of Chaganhada Granites in Weijing Area,Inner Mongolia

查干哈达花岗岩体位于华北板块北缘,是我国重要的有色金属矿集区。针对查干哈达花岗岩体开展岩相学、锆石U-Pb定年和岩石地球化学等研究,探讨岩体成因及其地质意义。结果表明:查干哈达花岗岩成岩年龄为147.9±1.5 Ma,在由弱过铝质花岗岩向强过铝质花岗岩演化过程中,显示了由碱性、镁质向碱钙性、铁质演化的特征,属于A型花岗岩,岩体同时显示K、Rb、Zr、Hf、Th和LREE的相对富集,Ba、P、Ti、Nb、Ta和HREE的相对亏损,在成岩过程中经历较强的分异演化。查干哈达岩体εHf(t)=1.1~5.0,TDMc=870~1122 Ma,具有高的εHf(t)值以及低的TDMc值,表明其主要来源于新生地壳物质部分熔融,同时有少量老的地壳物质再循环,查干哈达岩体形成于拉张伸展的构造环境,显示在晚侏罗世—早白垩世时期,研究区转入了板内伸展的环境。

Chaganhada granites which is located at the northern margin of North China Plate,is an important cluster area of nonferrous metal deposit in China.In this paper,the petrography,U-Pb geochronology and petrochemistry from Chaganhada granites were used to study the genesis of the pluton and its geological significance.The results showed Chaganhada granites formed at 147.9±1.5 Ma.In the process of evolution from weak peraluminous granite to strong peraluminous granite,they were of the evolution characteristics from alkaline,magnesian to alkali-calcium,iron of Atype granite,Which is enriched in K,Rb,Zr,HF,Th and LREE,depleted in Ba,P,Ti,Nb,Ta and HREE.The granite experienced a strong differential evolution in the diagenetic process.εHf(t)of Chaganhada granites ranges from 1.1~5.0,and TDMc range from 870~1122 Ma.That showed they came from partial melting of new crustal materials and fromed a few old crustal materials through recycling.Chaganhada granites were formed in an tension extensional structural environment,which means that the study area turned into an intraplate extensional environment during Late Jurassic-Early Cretaceous.