内蒙古乌拉特中旗乌兰地区石炭纪花岗闪长岩年代学及地球化学研究

GEOCHRONOLOGY AND GEOCHEMISTRY OF GRANODIORITES FROM WULAN AREA OF URAD ZHONGQI,INNER MONGLIA

利用锆石SHRIMP U-Pb法对乌拉特中旗乌兰地区花岗闪长岩进行年龄测试,得到的两个花岗闪长岩样品中锆石的加权平均年龄分别为(322.1±3.4)Ma和(323.4±3.4)Ma,为早石炭世。岩石地球化学及同位素地质年代学研究显示该花岗闪长岩为具有埃达克岩性质的I型花岗岩类,属准铝质-过铝质高钾钙碱性系列;富集Rb,Ba,Sr等大离子亲石元素和Th,U,Nd,Zr等高场强元素;为轻稀土富集型,轻、重稀土高度分异,轻稀土发生明显的分馏作用,铕异常不明显。岩体形成于活动大陆边缘同碰撞构造环境,是残留洋壳部分熔融所形成的基性岩浆与由古老片麻岩基底部分熔融所形成的中酸性岩浆发生混合作用的产物。

Geochronology and petrogeochemistry of granodiorites from Wulan area in Urad Zhongqi are investigated,and its formation times,genesis and tectonic setting are discussed.The weighted ages of zircons dated by SHRIMP U-Pb method from two granodiorite samples are（322.1±3.4） Ma and（323.4±3.4） Ma respectively,indicating that the granodiorites were formed at Early Carboniferous Period.Petrogeochemical analysis shows that the granodiorites are of I-type granites with the characteristics of adakites,belonging to high-K calc-alkaline series,enriched in large ionic lithophile elements（LIL） of Rb,Ba and Sr and high field strength elements（HFS） of Th,U,Nd and Zr,with a LREE-enriched pattern without pronounced Eu anomaly.It is showed that both LREE and HREE are fractionated with LREE more pronounced.This kind of intrusions were formed in syn-collision tectonic setting along the active continental margins,derived from the mixings between underplating basaltic magma and intermediate-acid magma formed by partial melting of remanent oceanic crust and the old gneiss basement,respectively.