内蒙古东乌旗晚古生代闪长岩、二长花岗岩年代学特征及岩石成因  

Chronology and petrogenesis of the diorite and monzonitic granite in Dong Ujimqin Banner, Inner Mongolia

作　　者：李敏[1] 李敏[1] 程银行[1] 任邦方[1] 李艳锋[1] 张天福 

机构地区：[1]天津地质矿产研究所,天津300170

出　　处：《中国地质》2016年第2期380-394,共15页Geology in China

基　　金：中国地质调查局项目"内蒙古1:5万奥尤特等六幅区调(1212011220446)"和"内蒙古1:5哈珠等四幅区调(12120114064601)"联合资助~~

摘　　要：为了解晚古生代西伯利亚板块南缘增生造山过程中的岩浆活动特征及其对贺根山洋盆闭合时间的制约,对东乌旗巴彦都兰闪长岩、二长花岗岩岩相学、锆石U-Pb年代学、锆石Hf同位素和岩石地球化学进行了研究,并讨论了岩石成因和构造环境。闪长岩、二长花岗岩锆石U-Pb同位素年龄依次为（319.8±0.9）Ma、（300.8±1.7）Ma,分别侵位于晚石炭世、早二叠世地层。闪长岩以正的锆石εHf（t）（13.5-17.1）为特征,具有年轻的锆石地壳模式年龄（tDMc）（335-466 Ma）,明显富集Rb、K等大离子亲石元素（LILE）,亏损Ba、Sr,相对亏损Ta、Nb和Ti等高场强元素（HFSE）,为洋壳俯冲阶段,地幔楔混入并与年轻洋壳部分熔融形成。二长花岗岩以高钾、富碱、弱过铝质为特征,富集部分大离子亲石元素（LREE、Rb、K等）;Zr弱负异常、Hf弱正异常,亏损Sr、Nb、Ta、P、Ti,显示后造山花岗岩特征。二长花岗岩形成于伸展构造环境,是贺根山洋盆闭合后后造山阶段的产物,为洋壳俯冲形成的先成地壳部分熔融而成。In order to understand the characteristics of magma activities in the southern part of Siberian plate and their influence on the closing time of Hegenshan Ocean during Late Palaeozoic, the authors studied petrography, zircon U-Pb chronology, zircon Hfisotope and geochemistry of the diorite and monzonitic granite to constrain the genesis and tectonic setting of the rock in Bayan Dulan of Dong Ujimqin Banner, Inner Mongolia. The zircon U-Pb dating results show that the diorite was formed at 319.8±0.9 Ma（Late Carboniferous）, and the monzonitic granite was formed at 300.8±1.7 Ma（Early Permian）. The εHf（t） values and the crust model ages（tDMc） of diorite are14.6-17.1 Ma and 335-466 Ma respectively. The Bayan Dulan diorite is enriched in such LILE as Rb and Kand depleted in Ba, Sr, Ta、Nb and Ti. The formation of diorite resulted from partial melting of juvenile oceanic crust mixed with mantle wedge during the subduction of the oceanic crust from Middle-Ordovician to Early-Carboniferous. The monzonitic granite is enriched in K and alkali, suggesting the weak peraluminous feature. The monzonitic granite is also enriched in some LILE and LREE, Rb and K with weak negative Zr anomaly and weak positive Hf anomaly, and depleted in Sr, Nb, Ta, P and Ti, suggesting characteristics of post- orogenic granite. The monzonitic granite was produced in an extension environment,and was formed by post-orogenic evolution after closing of Hegenshan Ocean.In addition, the formation of the rock was caused by partial melting of juvenile continental crust resulting from subducted oceanic crust.

关 键 词：晚古生代 地球化学 锆石U-Pb年龄 锆石HF同位素 岩石成因 

分 类 号：P597.3[天文地球—地球化学] P595[天文地球—地质学]