兰坪盆地及邻区岩浆岩的微量元素地球化学研究

摘要

采用中子活化分析方法系统研究了云南省兰坪盆地内永平卓潘、云龙皂角场及邻区二 龙山、剑川、甸南、马登、北衙、老君山等岩体的稀土元素及微量元素组成，探讨了岩浆岩 系的稀土元素特征、成岩物质来源、成岩方式、构造环境。该区岩浆岩系的稀土元素地球化 学特征表现为：(1）稀土元素组成特征相似，配分型式为轻稀土富集向右倾型；(2）(La/Yb )n较高，轻重稀土元素分异明显；(3）Eu负异常不明显，无Ce负异常或略显正Ce异常。该 区岩 浆岩系的微量元素以富集Rb,Ba,Sr,Th,U;而亏损Ta为特征。稀土元素、微量元素结合同 位素地球化学研究表明，该区岩浆岩系成岩物质主要来源于富集地幔并有地壳混染，成岩方 式以地幔部分熔融为主，成岩环境为大陆裂谷。%Using NAA method, the authors studied REE and trace el ements geochemistry of the ma gmatic rock series from Yongping Zhuopan, Yunlong Zaojiaochang, Erlongshan, Dian nan, Madeng, Beiya, and Laojunshan in Lanping basin and its neighboring regions. At the same time, the authors discussed REE geochemistry characteristics, diagenesis s tyle, tec tonic environment of the magmatic rock series. The results show: (1) REE pattern s of magmatic rock series are similar, and they are rich in LREE; (2) they have h igh La /Yb ratio, so the separation between HREE and LREE is significant; (3) Eu and Ce amormaly is not obvious. The magmatic rock series has high Rb, Ba, Sr, Th, U an d low Ta. Combining the studies of REE, Trace elements geochemistry with tha t of isotope geochemistry, the authors think that the diagenetic source mainly comes from enriched mantle and partly from the crust, the diagenetic process is batch partial melting, and the diagene tic environment is continental rifting.