内蒙古乌拉特中旗海西期黑云母二长花岗岩锆石SHRIMPU-Pb年龄及其地质意义  

SHRIMP U-Pb Dating of the Zircon from the Hercynian Biotite Monzonitic Granites in Urad Zhongqi,Inner Mongolia,and Its Geological Significance

作　　者：王挽琼[1] 刘正宏[1] 王兴安[1] 张超[1] 范志伟[1] 时溢[1] 朱凯[1] 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《吉林大学学报（地球科学版）》2012年第6期1771-1782,共12页Journal of Jilin University：Earth Science Edition

基　　金：国家自然科学基金项目(90814006);内蒙古自治区地质勘查项目(NMKD2008-23)

摘　　要：对乌拉特中旗德尔斯地区黑云母二长花岗岩岩相学、锆石SHRIMP U-Pb年代学和岩石地球化学进行了研究,并讨论了岩石成因及研究区晚海西期构造演化。黑云母二长花岗岩发育两期:早期为中粗粒斑状黑云母二长花岗岩,晚期为中细粒黑云二长花岗岩。岩石中的锆石大部分具核-边结构:边部震荡环带发育,Th/U值为0.16～0.50,反映了岩浆成因;核部呈浑圆状,多数具岩浆环带,个别弱分带-无分带,Th/U值为0.06～0.44,表明核部大部分属岩浆型残留锆石,个别为变质型残留锆石。测年结果显示:边部锆石加权平均年龄为早、中二叠世((279±3)Ma、(266±3)Ma),代表黑云母二长花岗岩形成时代;核部残留锆石加权平均年龄为(1 972±63)Ma、(1 962±43)Ma,代表源岩的形成时代。岩石属于亚碱性系列,REE配分形式呈右倾型,LREE/HREE为5.86～22.81,明显亏损高场强元素Nb,富集大离子亲石元素Rb、Ba,显示活动大陆边缘火成岩的地球化学特征。黑云母二长花岗岩地球化学属性反映了早、中二叠世古亚洲洋向华北板块北缘的俯冲作用及古亚洲洋消亡的演化历史。Petrography,SHRIMP U-Pb chronology of the zircon and geochemistry of the Hercynian biotite monzonitic granites in Deersi area of Urad Zhongqi are studied to constrain the genesis of the rock and regional tectonic evolution in the study area.The emplacement of the biotite monzonitic granite in this area can be divided into two periods,the earlier is medium-coarse prophyritic biotite monzonitic granite and the latter is medium-fine grain biotite monzonitic granite.Most of zircons from biotite monzonitic granites show core-mantle ring structure,fine-scale oscillatory zoning and Th/U ratios of 0.16-0.50,implying their magmatic origin.Whereas most of cores of rouded zircons have fine-scale oscillatory zoning and Th/U ratios of 0.06-0.44,which indicates their magmatic genesis and residual zircons.While,there are some zircons with weak zoning or non-zoning,indicating their metamorphic genesis.The weighted mean ages of the edge of zircons from the biotite monzonitic granites indicate that the granite formed in the Early-Middle Permian（（279±3） Ma and（266±3） Ma）,but some results of residual zircons are（1 972±63） Ma,（1 962±43） Ma,implying the formation time of source rock.The biotite monzonitic granites belong to sub-alkaline series.Their rare earth elements（REE） patterns are right diping with LREE/HREE ratios range from 5.86 to 22.81.The biotite monzonitic granites are depleted in high field strength element Nb,and enriched in large ion lithophile elements Rb and Ba.These characters are similar to the igneous rocks from active continental margin setting.Taken all together,geochemical character of the Early-Middle Permian biotite monzonitic granites reflects the tectonic evolution including the subduction of the paleo-Asian oceanic plate beneath the North China craton and the dying out of paleo-Asian Ocean.

关 键 词：I型花岗岩 早、中二叠世 地球化学 活动大陆边缘 乌拉特中旗 

分 类 号：P588.12[天文地球—岩石学]