阿尔泰造山带南缘昆格依特岩体LA-ICP-MS锆石U-Pb年代学、岩石成因及其地质意义

摘要

The Kungeyite plutons,outcropped in Qingeli River in Qinghe County of southern margin of Altay orogenic belt are mainly hornblende biotite tonalite,which were determined for LA-ICP-MS zircon U-Pb ages. The result shows that the zircon 206Pb/238U weighted average age is (403.4 ±7.4)Ma (MSWD=1.07),indi-cating the plutons were formed at Early Devonian.The SiO2 contents range from 52.39% to 71.89% and σfrom 0.68 to 1.53,A/CNK from 0.76 to 1.06,indicating that the plutons are mid-K calc-alkaline,metalumi-nous-weakly peraluminous rocks.In addition,the plutons are enrichment in LILE (Cs,Rb,Th,U )and LREE,obvious negative anomaly in HFSE (Nb,Ta,Hf,Ti),HREE and Eu (δEu =0.56 -0.86),thus resembling granitoid rocks formed in island-arc.Combined with the data of southern margin of Altay,the Kunge-yite plutons were generated by partial melting of the lower crust underplayed by mafic magma of the mantle in a continental arc setting of active continental margin,and occurred magma mixing and differentiation.%昆格依特岩体出露于阿尔泰造山带南缘青河县大青格里河昆格依特一带，主要为角闪黑云英云闪长岩。LA-ICP-MS锆石U-Pb定年结果显示，锆石的206 Pb/238 U年龄加权平均值为（403.4±7.4）Ma，表明该岩体形成于早泥盆世。岩体的SiO2含量介于52.39％～71.89％之间，里特曼指数为0.68～1.53，A/CNK值为0.76～1.06，属中钾、钙碱性、准铝质-弱过铝质岩石。具有富集Cs、Rb、Th、U等大离子亲石元素和轻稀土元素，相对亏损Nb、Ta、Hf、Ti等高场强元素和重稀土元素，弱的负Eu异常（δEu＝0.56～0.86）的岛弧岩浆岩特征。结合区域地质资料，认为阿尔泰造山带南缘早泥盆世昆格依特岩体形成于活动大陆边缘的陆缘弧构造环境，是古亚洲洋俯冲过程中幔源的基性岩浆底侵下地壳使之熔融，并发生了岩浆混合和分异作用的产物。